Image forming apparatus

Abstract

To suppress falling of bristles of a brush for cleaning an intermediate transfer belt.SOLUTION: The image forming apparatus 100 includes an image carrier 1, image forming units 2, 3, and 4, an intermediate transfer belt 6, a primary transfer member 5, a primary transfer power source E1, a secondary transfer member 9, a brush 122 that forms a cleaning portion CL1 to remove toner from the intermediate transfer belt 6, a cleaning power source E3, and a control unit 50. The control unit 50 can perform a predetermined operation to form a predetermined toner image in a non-image forming area on the image carrier 1. In the above-described predetermined operation, the controller 50 effects control so that the primary transfer bias applied to the primary transfer member 5 while the predetermined toner image formed on the image bearing member 1 passes through the primary transfer portion N1 is a bias which has the same polarity as that of the primary transfer bias when the toner image to be transferred onto the recording material P is transferred from the image bearing member 1 onto the intermediary transfer belt 6 and which is smaller in absolute value than the primary transfer bias.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine that uses an electrophotographic or electrostatic recording method. [Background technology]

[0002] Conventionally, some image forming apparatuses using electrophotography or the like employ an intermediate transfer method in which a toner image formed on an image carrier is primarily transferred onto an intermediate transfer body, and then secondarily transferred onto a recording material such as paper. An intermediate transfer belt, which is an endless belt, is widely used as the intermediate transfer body.

[0003] The toner remaining on the intermediate transfer belt after the secondary transfer process (secondary transfer residual toner) and other deposits are removed and collected from the intermediate transfer belt by a belt cleaning device. One such belt cleaning device is an electrostatic cleaning type belt cleaning device that electrostatically collects the toner on the intermediate transfer belt using a fur brush (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-128613 Summary of the Invention [Problem to be solved by the invention]

[0005] The electrostatic cleaning type belt cleaning device has a fur brush (conductive fur brush roller) which is a rotatable, conductive brush-like cleaning member. This fur brush is brought into contact with the intermediate transfer belt with a certain penetration amount.

[0006] As the fur brush is used more, the fibers tend to collapse (permanently deform), causing the outer diameter to shrink. When the outer diameter of the fur brush becomes smaller, it is no longer possible to ensure sufficient penetration into the intermediate transfer belt, making it difficult to properly clean the intermediate transfer belt. Therefore, when the outer diameter of the fur brush becomes smaller than the allowable range, it reaches the end of its life and may need to be replaced.

[0007] According to the inventors' research, fur brush bristle collapse (thinning of the outer diameter of the fur brush) is more pronounced when an image with a low image ratio and a large amount of white background is formed. Furthermore, this is even more pronounced when the image forming apparatus is configured as follows: Specifically, a monochromatic image forming apparatus is constructed by retaining only the components and units necessary for monochromatic image formation from among the components and units of a multicolor image forming apparatus, which is sometimes adopted for the purposes of high-mix, low-volume production and improving development efficiency. In this case, the monochromatic image forming apparatus leaves less residual toner on the intermediate transfer belt sent to the belt cleaning device than a multicolor image forming apparatus. Therefore, when an image with a low image ratio is formed in a monochromatic image forming apparatus with such a configuration, fur brush bristle collapse tends to occur more easily.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to prevent the bristles of the brush that cleans the intermediate transfer belt from falling over. [Means for solving the problem]

[0009] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus including a rotatable image carrier that carries a toner image, an image forming means that forms a toner image on the image carrier, a rotatable intermediate transfer belt to which the toner image is transferred from the image carrier, a primary transfer member that transfers the toner image from the image carrier to the intermediate transfer belt at a primary transfer portion, a primary transfer power source that applies a primary transfer bias to the primary transfer member, a secondary transfer member that forms a secondary transfer portion that transfers the toner image from the intermediate transfer belt to a recording material, a brush that forms a cleaning portion that contacts the intermediate transfer belt downstream of the secondary transfer portion and upstream of the primary transfer portion in the rotation direction of the intermediate transfer belt and removes toner from the intermediate transfer belt, and a cleaning bias that applies a cleaning bias to the cleaning portion to collect toner from the intermediate transfer belt to the brush. and a control unit capable of controlling the image forming means and the primary transfer power supply, wherein the control unit is capable of performing a predetermined operation of forming a predetermined toner image in an area on the image carrier where a toner image to be transferred to a recording material is not formed, and transferring at least a portion of the toner of the predetermined toner image to the intermediate transfer belt and causing it to reach the cleaning unit, and wherein the control unit controls, in the predetermined operation, a primary transfer bias applied to the primary transfer member while the predetermined toner image formed on the image carrier passes through the primary transfer unit to be a bias of the same polarity as the primary transfer bias when the toner image to be transferred to the recording material is transferred from the image carrier to the intermediate transfer belt but with a smaller absolute value than the primary transfer bias, or to be 0V. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent the bristles of the brush that cleans the intermediate transfer belt from falling over. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2]FIG. 2 is a schematic cross-sectional view of the vicinity of a belt cleaning device. [Figure 3] FIG. 2 is a block diagram showing a schematic control configuration of the image forming apparatus. [Figure 4] FIG. 10 is a graph showing an example of the relationship between the amount of use of the fur brush and the change in outer diameter. [Figure 5] FIG. 2 is a schematic diagram for explaining the movement of toner in a primary transfer portion during normal image formation. [Figure 6] 10A and 10B are schematic diagrams for explaining the movement of toner in a primary transfer portion during a conventional toner discharging operation. [Figure 7] 10A and 10B are schematic diagrams for explaining the movement of toner in the primary transfer portion during the toner discharging operation in the embodiment. [Figure 8] FIG. 10 is a graph showing an example of the relationship between a primary transfer current and a primary transfer efficiency. [Figure 9] FIG. 10 is a flowchart for explaining an outline of a job control procedure. [Figure 10] FIG. 10 is a flowchart illustrating another example of a job control procedure. [Figure 11] 10A and 10B are schematic diagrams for explaining the movement of toner in the primary transfer portion during the fusion suppression operation in another embodiment. [Figure 12] FIG. 10 is a schematic cross-sectional view of an image forming apparatus according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0013] [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 of this embodiment. The image forming apparatus 100 of this embodiment is a printer (monochrome printer) that employs an intermediate transfer method and is capable of forming a black monochrome image using an electrophotographic method.

[0014] Here, the image forming apparatus of this embodiment is a monochrome image forming apparatus 100 configured by leaving only the components and units necessary for monochrome image formation out of the components and units of the multicolor image forming apparatus 100' shown in FIG. 12 . The image forming apparatus 100 of this embodiment has an image forming unit (station) 10 that forms a black (K) image. In this embodiment, the image forming unit 10 is configured by a photosensitive drum 1, a charging device 2, an exposure device 3, a developing device 4, a primary transfer roller 5, a drum cleaning device 11, etc., which will be described later. In this embodiment, the charging device 2, the exposure device 3, the developing device 4, etc., configure an image forming means that forms a toner image on the photosensitive drum 1.

[0015] The photosensitive drum 1, a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as an image carrier for carrying a toner image, is rotated at a predetermined peripheral speed in the direction of arrow R1 (counterclockwise) in the figure. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charging device 2 serving as a charging means. During charging, a predetermined charging bias (charging voltage) is applied to the charging device 2 by a charging power supply (not shown). The charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device (laser beam scanner) 3 serving as an exposure means based on image information, forming an electrostatic image (electrostatic latent image) on the photosensitive drum 1 in accordance with the desired image information. The exposure device 3 outputs a laser beam that is on / off modulated in accordance with image information input from an image reader or external device such as a computer, to scan and expose the charged surface of the photosensitive drum 1.

[0016] The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4 as a developing means, which supplies toner as a developer, and forms a toner image on the photosensitive drum 1. In this embodiment, the developing device 4 uses a two-component developer containing toner (non-magnetic toner particles) and carrier (magnetic carrier particles) as the developer. The developing device 4 has a developing container 411 that contains the developer, and a developing sleeve 412 that is a non-magnetic hollow cylindrical member that serves as a developer carrier (developing member). The developing sleeve 412 is rotated by a driving motor (not shown) that serves as a driving means. A magnetic roller is disposed inside (hollow portion of) the developing sleeve 412. The developing container 411 also has a regulating member (not shown) that regulates the amount of developer carried by the developing sleeve 412, a conveying member (not shown) that conveys the developer in the developing container 411 while stirring it, and the like. The developer carried on the developing sleeve 412 by the magnetic force of the magnet roller is regulated in amount by a regulating member as the developing sleeve 412 rotates, and then transported to a portion (developing portion) facing the photosensitive drum 1. The developer on the developing sleeve 412 transported to the developing portion stands up due to the magnetic force of the magnet roller to form magnetic brushes (magnetic brushes), which are brought into contact with or close to the surface of the photosensitive drum 1. During development, a predetermined developing bias (developing voltage) is applied to the developing sleeve 412 by a developing power supply (not shown). In this embodiment, an oscillating voltage in which a direct current voltage (DC component) and an alternating current voltage (AC component) are superimposed is applied to the developing sleeve 412 as the developing bias. As a result, toner moves from the magnetic brush on the developing sleeve 412 to the photosensitive drum 1 in accordance with the electrostatic image on the photosensitive drum 1, and a toner image is formed on the photosensitive drum 1. The developing container 411 is appropriately replenished with toner from a supply container (not shown). In this embodiment, toner charged with the same polarity (negative in this embodiment) as the charge polarity of the photosensitive drum 1 adheres to the exposed area (image area) on the photosensitive drum 1, where the absolute value of the potential has been reduced by being exposed based on image information after being uniformly charged (reverse development method). In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative.

[0017] Opposing the photosensitive drum 1 is an intermediate transfer belt 6, which is an endless belt serving as an intermediate transfer body. The intermediate transfer belt 6 is arranged so as to be able to contact the surface of the photosensitive drum 1. The intermediate transfer belt 6 is stretched over first to sixth tension rollers 21 to 26, which serve as multiple tension rollers, and tensioned with a predetermined tension. In this embodiment, the first tension roller 21 is a secondary transfer opposing roller (secondary transfer inner roller) that functions as an opposing member (opposing electrode) of the secondary transfer roller 9, which will be described later. The second tension roller 22 is a drive roller for the intermediate transfer belt 6. The third and fourth tension rollers 23 and 24 are first and second auxiliary rollers that form the primary transfer surface of the intermediate transfer belt 6 onto which the toner images from each photosensitive drum 1 are primarily transferred, as will be described later. The fifth tension roller 25 is a tension roller configured to control the tension of the intermediate transfer belt 6 to be approximately constant. The sixth tension roller 26 is a pre-secondary transfer roller that forms the secondary transfer surface of the intermediate transfer belt 6 that enters the secondary transfer portion N2, which will be described later. The intermediate transfer belt 6 receives a driving force as the drive roller 22 is driven to rotate, and rotates (circularly moves) in the direction of arrow R2 (clockwise) in the figure at a peripheral speed of 150 to 470 mm / sec. Regarding numerical ranges, "to" indicates that the preceding and following numerical values ​​are included. A primary transfer roller 5, a roller-type primary transfer member serving as primary transfer means, is disposed on the inner peripheral surface (back surface) of the intermediate transfer belt 6, corresponding to the photosensitive drum 1. The primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 6, forming a primary transfer portion (primary transfer nip portion, primary transfer position) N1 where the photosensitive drum 1 and the intermediate transfer belt 6 come into contact with each other. The tension rollers other than the second tension roller 22 and the primary transfer roller 5 are rotated in accordance with the rotation of the intermediate transfer belt 6.

[0018] The toner image formed on the photosensitive drum 1 as described above is transferred (primary transfer) onto the rotating intermediate transfer belt 6 at the primary transfer portion N1 by the action of the primary transfer roller 5. During the primary transfer, a primary transfer bias (primary transfer voltage), which is a constant-voltage controlled DC voltage of polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the primary transfer roller 5 by a primary transfer power supply (high-voltage power supply) E1. This supplies a primary transfer current to the primary transfer portion N1. During the primary transfer, a constant-voltage controlled primary transfer bias of, for example, +1500 to +2500 V is applied to the primary transfer roller 5, and a primary transfer current of +50 to +80 μA flows. In this embodiment, the primary transfer bias is applied to the primary transfer roller 5 in synchronization with the toner image being transported to the primary transfer portion N1. In this embodiment, the primary transfer roller 5 is configured to have a core metal (substrate) and an elastic layer formed of ion-conductive foam rubber on the outer periphery of the core metal. In this embodiment, the outer diameter of the primary transfer roller 5 is 15 to 20 mm. In addition, in this embodiment, the electrical resistance value of the primary transfer roller 5 is 1×10 when measured by applying a voltage of 2 kV in an N / N environment (23°C, 50% RH). 5 ~1×10 8 It is Ω.

[0019] A secondary transfer roller (secondary transfer outer roller) 9, which is a roller-type secondary transfer member serving as secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 6 at a position facing the secondary transfer opposing roller 21. The secondary transfer roller 9 is pressed against the secondary transfer opposing roller 21 via the intermediate transfer belt 6, forming a secondary transfer portion (secondary transfer nip, secondary transfer position) N2 where the intermediate transfer belt 6 and the secondary transfer roller 9 come into contact (direct contact or sandwich the recording material P). The toner image formed on the intermediate transfer belt 6 as described above is transferred (secondarily transferred) onto the recording material P being sandwiched and conveyed between the intermediate transfer belt 6 and the secondary transfer roller 9 at the secondary transfer portion N2 by the action of the secondary transfer roller 9. The recording material (transfer material, recording medium, sheet) P is stored in a recording material storage portion (not shown) such as a feeding cassette. A feeding member (not shown), such as a feeding roller, is driven based on a feeding start signal to feed the recording material P one sheet at a time from a recording material storage section. The recording material P is then transported to the secondary transfer section N2 by a registration roller 8, which serves as a transport member. The registration roller 8 is controlled to transport the recording material P to the secondary transfer section N2 in synchronization with the timing at which the leading edge of the toner image on the intermediate transfer belt 6 reaches the secondary transfer section N2. The recording material P is typically paper, but may also be synthetic paper, a resin sheet (film) such as an overhead projector sheet, or the like. Note that an inner roller corresponding to the secondary transfer opposing roller 21 in this embodiment may be used as a secondary transfer member, and a voltage of the opposite polarity (the same polarity as the normal charging polarity of the toner) to that applied to the secondary transfer roller 9 in this embodiment may be applied to the inner roller. In this case, an outer roller corresponding to the secondary transfer roller 9 in this embodiment may be used as an opposing member and electrically grounded.

[0020] In this embodiment, the secondary transfer roller 9 is configured to have a core metal (substrate) and an elastic layer formed of ion-conductive foam rubber on the outer periphery of the core metal. In this embodiment, the outer diameter of the secondary transfer roller 9 is 20 to 25 mm. In addition, in this embodiment, the electrical resistance value of the secondary transfer roller 9 is 1×10 when measured by applying a voltage of 2 kV in an N / N environment (23°C, 50% RH). 5 ~1×10 8Ω. In this embodiment, the secondary transfer opposing roller 21 is configured to have a core (substrate) and an elastic layer formed of electronically conductive rubber on the outer periphery of the core. In this embodiment, the outer diameter of the secondary transfer opposing roller 21 is 20 to 22 mm. In this embodiment, the electrical resistance value of the secondary transfer opposing roller 21 is 1×10 when measured by applying a voltage of 50 V in an N / N environment (23°C, 50% RH). 5 ~1×10 8 Ω. During the secondary transfer, a secondary transfer bias (secondary transfer voltage), which is a constant-voltage controlled DC voltage of polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the secondary transfer roller 9 by a secondary transfer power supply (high-voltage power supply) E2. This causes a secondary transfer current to be supplied to the secondary transfer section N2. During the secondary transfer, a constant-voltage controlled secondary transfer bias of, for example, +1 to +7 kV is applied to the secondary transfer roller 9, and a secondary transfer current of +40 to +120 μA flows. In this embodiment, the secondary transfer opposing roller 21 is electrically grounded (connected to ground).

[0021] The recording material P with the transferred toner image is separated from the intermediate transfer belt 6 and conveyed by a pre-fixing conveying device 20 to a fixing device 30 (a fixing unit). The pre-fixing conveying device 20 has a rotatable endless belt member, 100-110 mm wide and 1-3 mm thick, made of a rubber material such as EPDM, at its center in a direction substantially perpendicular to the conveyance direction of the recording material P. The belt member has holes with a diameter of 3-7 mm that allow air to be sucked from the inside of the belt member. This increases the belt member's ability to support the recording material P and stabilizes the conveyance of the recording material P. The fixing device 30 applies heat and pressure to the recording material P bearing the unfixed toner image using a pair of fixing rotors, thereby fixing (melting and adhering) the toner image to the recording material P. The recording material P with the fixed toner image is then discharged (output) from the main body of the image forming apparatus 100.

[0022] Furthermore, toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 during the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 1 and collected by a drum cleaning device 11 serving as a photosensitive body cleaning means. In this embodiment, the drum cleaning device 11 includes a cleaning container 111 and a cleaning blade 112 serving as a cleaning member. The cleaning blade 112 is configured as a rubber plate-like member having a predetermined length and a predetermined thickness in both a longitudinal direction disposed substantially parallel to the rotational axis direction of the photosensitive drum 1 and a lateral direction substantially perpendicular to the longitudinal direction. The cleaning blade 112 is brought into contact with the photosensitive drum 1 in a counter direction to the rotational direction of the photosensitive drum 1 (the free end faces upstream in the rotational direction). The drum cleaning device 11 cleans the surface of the photosensitive drum 1 by using the cleaning blade 112 to intercept (scrape off) the primary transfer residual toner on the photosensitive drum 1 as the photosensitive drum 1 rotates and collecting it in the cleaning container 111. The cleaned photosensitive drum 1 is reused for image formation.

[0023] Furthermore, deposits such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 6 without being transferred to the recording material P during the secondary transfer are removed and collected from the intermediate transfer belt 6 by a belt cleaning device 12 serving as an intermediate transfer body cleaning means. In this embodiment, the belt cleaning device 12 cleans the surface of the intermediate transfer belt 6 by electrostatically collecting the secondary transfer residual toner on the intermediate transfer belt 6. The cleaned intermediate transfer belt 6 is reused for image formation. Details of the belt cleaning device 12 will be described later.

[0024] 2. Intermediate transfer body In this embodiment, the intermediate transfer belt 6 is composed of a base layer (layer forming the inner peripheral surface), an elastic layer (intermediate layer), and a surface layer (layer forming the outer peripheral surface). 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, and has a thickness of 0.05 to 0.15 mm. The elastic layer is made of a material such as a rubber such as chloroprene rubber (CR rubber), urethane rubber, or silicone rubber containing an appropriate amount of an ion conductive agent, and has a thickness of 0.1 to 0.500 mm. The surface layer is made of a resin such as urethane resin or fluororesin, and has a thickness of 0.0002 to 0.020 mm.

[0025] In this embodiment, the volume resistivity of the intermediate transfer belt 6 is 5×10 8 ~1×10 14 The intermediate transfer belt 6 has a static friction coefficient of 0.15 to 0.6 (23°C, 50% RH, HEIDON type 94i) and a hardness of 60 to 85° (MD1 hardness) of 23°C, 50% RH.

[0026] 3. Electrostatic cleaning device 2 is a schematic enlarged cross-sectional view of the vicinity of the belt cleaning device 12 in this embodiment. The belt cleaning device 12 is disposed downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1 in the rotation direction of the intermediate transfer belt 6, particularly at a position facing the drive roller 22 with the intermediate transfer belt 6 interposed therebetween. In this embodiment, the belt cleaning device 12 is configured as an electrostatic cleaning device that electrostatically collects toner on the intermediate transfer belt 6, particularly an electrostatic brush cleaning device using a conductive fur brush roller.

[0027] In this embodiment, the belt cleaning device 12 has a housing 121 arranged near the intermediate transfer belt 6. The following members are provided inside the housing 121. First, first and second fur brushes (cleaning brushes) 122 and 123 are provided as first and second cleaning members. Also, first and second collection rollers 124 and 125 are provided as first and second collection members. Also, first and second blades 126 and 127 are provided as first and second scraping members.

[0028] The first and second fur brushes 122 and 123 are made up of conductive fur brush rollers, which are conductive, rotatable brush-shaped cleaning members. The brush fibers of the first and second fur brushes 122 and 123 have an electrical resistance of 3×10 5 ~1×10 13 The first and second fur brushes 122 and 123 are made of carbon-dispersed nylon fibers, acrylic fibers, or polyester fibers with a fiber thickness of 2 to 15 denier and a fiber resistance of Ω / cm. 2The fur brushes are implanted on a metal roller as a base material at a ratio of 1.0 to 5 mm. The length of the brush fibers is, for example, approximately 3 to 5 mm. The first and second fur brushes 122 and 123 are positioned with a penetration depth of approximately 1.0 to 2.0 mm relative to the intermediate transfer belt 6. This penetration depth can be represented by the length of the brush fibers minus the distance (shortest distance) between the base material of the fur brush (such as a metal roller) and the object of contact. The first and second fur brushes 122 and 123 are driven to rotate in the direction of arrow R3 (clockwise) in the figure by a drive motor (not shown) as a driving means at a peripheral speed that is 20 to 80% of the peripheral speed of the intermediate transfer belt 6. The peripheral speed of the fur brush is represented by the peripheral speed at the outer diameter when the brush fibers are not deformed by an external force. That is, the first and second fur brushes 122 and 123 rotate at the contact portion with the intermediate transfer belt 6 so as to move in the opposite direction to the movement direction of the intermediate transfer belt 6, thereby rubbing the surface of the intermediate transfer belt 6. In this embodiment, the first and second fur brushes 122 and 123 are brought into contact with the drive roller 22, which functions as an opposing member, via the intermediate transfer belt 6. The drive roller 22 is electrically grounded. The first and second fur brushes 122 and 123 are arranged such that their rotation axes are substantially parallel to a direction (herein also referred to as the "width direction") substantially perpendicular to the movement direction of the surface of the intermediate transfer belt 6. The length of the first and second fur brushes 122 and 123 in the rotation axis direction is longer than the maximum image formation width on the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 6. The contact area between the first fur brush 122 and the intermediate transfer belt 6 is a first cleaning section (first cleaning position) CL1 where the first fur brush 122 collects toner from the intermediate transfer belt 6. The contact area between the second fur brush 123 and the intermediate transfer belt 6 is a second cleaning section (second cleaning position) CL2 where the second fur brush 123 collects toner from the intermediate transfer belt 6. The first and second cleaning sections CL1 and CL2 are located downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 in the rotation direction of the intermediate transfer belt 6.In this embodiment, in the rotation direction of the intermediate transfer belt 6, the first cleaning unit CL1 is located upstream of the second cleaning unit CL2.

[0029] The first and second collection rollers 124, 125 are rotatable rollers (metal rollers) made of metal (aluminum in this embodiment). The first and second collection rollers 124, 125 are disposed with a penetration amount of approximately 1.5 to 2.5 mm relative to the first and second fur brushes 122, 123. The first and second collection rollers 124, 125 are driven to rotate in the direction of arrow R4 (counterclockwise) in the figure at the same peripheral speed as the first and second fur brushes 122, 123 by a drive motor (not shown) serving as a driving means. In other words, the first and second collection rollers 124, 125 rotate so as to move in the same direction as the first and second fur brushes 122, 123 at their contact portions. The first and second collection rollers 124 and 125 are disposed so that their rotational axes are substantially parallel to the width direction of the intermediate transfer belt 6. The lengths of the first and second collection rollers 124 and 125 in the rotational axis direction are equal to the lengths of the first and second fur brushes 122 and 123 in the rotational axis direction.

[0030] The first and second blades 126 and 127 are disposed in contact with the first and second collection rollers 124 and 125. The first and second blades 126 and 127 are formed of a rubber material such as urethane rubber as an elastic member. The first and second blades 126 and 127 are plate-shaped members having a predetermined length in both a longitudinal direction, which is disposed substantially parallel to the rotational axis direction of the first and second collection rollers 124 and 125, and a lateral direction, which is substantially perpendicular to the longitudinal direction, and having a predetermined thickness. The thickness of the first and second blades 126 and 127 is 1.6 to 2.2 mm, and their hardness is 70 to 78° (IRHD hardness) (23°C, 50% RH). The first and second blades 126 and 127 are disposed with a penetration depth of 0.5 to 2.0 mm relative to the first and second collection rollers 124 and 125. The first and second blades 126, 127 are brought into contact with the first and second collection rollers 124, 125 in a counter direction (a direction in which the free ends face upstream in the rotation direction) relative to the rotation direction of the first and second collection rollers 124, 125. The longitudinal lengths of the first and second blades 126, 127 are equal to the lengths of the first and second collection rollers 124, 125 in the rotation axis direction.

[0031] In this embodiment, a first cleaning bias (first cleaning voltage) of negative polarity, which is the same polarity as the normal charging polarity of the toner, is applied to the first fur brush 122 located upstream in the rotation direction of the intermediate transfer belt 6. In this embodiment, a constant current controlled negative DC voltage is applied to the first collection roller 124 by a first cleaning power supply (high voltage power supply) E3, which is a DC power supply. As a result, the constant current controlled negative DC voltage is applied to the first fur brush 122 via the first collection roller 124. In this embodiment, a first cleaning bias is applied from the first cleaning power supply E3 via the first collection roller 124 so that a first cleaning current of −60 to −73 μA flows to the first fur brush 122 (i.e., the first cleaning unit CL1). In this embodiment, the first cleaning current is −60 to −73 μA, but this is not limited to this.

[0032] Meanwhile, in this embodiment, a second cleaning bias (second cleaning voltage) of positive polarity, which is opposite to the normal charging polarity of the toner, is applied to the second fur brush 123 located downstream in the rotation direction of the intermediate transfer belt 6. In this embodiment, a constant-current-controlled positive DC voltage is applied to the second collection roller 125 by a second cleaning power supply (high-voltage power supply) E4, which is a DC power supply. As a result, the constant-current-controlled positive DC voltage is applied to the second fur brush 123 via the second collection roller 125. In this embodiment, the second cleaning bias is applied from the second cleaning power supply E4 via the second collection roller 125 so that a second cleaning current of +20 to +73 μA flows to the second fur brush 123 (i.e., the second cleaning unit CL2). In this embodiment, the second cleaning current is +20 to +73 μA, but this is not limited to this.

[0033] By applying a cleaning bias to the first and second fur brushes 122 and 123, a cleaning electric field suitable for collecting toner on the intermediate transfer belt 6 is formed between the first and second fur brushes 122 and 123 and the intermediate transfer belt 6. As a result, the secondary transfer residual toner on the intermediate transfer belt 6 is electrostatically attracted to the first and second fur brushes 122 and 123 and removed from the intermediate transfer belt 6. Of the secondary transfer residual toner on the intermediate transfer belt 6, toner charged with a positive polarity, which is opposite to the normal charge polarity, adheres to the first fur brush 122. Furthermore, of the secondary transfer residual toner on the intermediate transfer belt 6, toner charged with a negative polarity, which is the normal charge polarity, adheres to the second fur brush 123. Furthermore, this toner is transferred from the first and second fur brushes 122 and 123 to the first and second collection rollers 124 and 125 due to an electric field formed between the first and second collection rollers 124 and 125 and the first and second fur brushes 122 and 123. Furthermore, the toner transferred to the first and second collection rollers 124 and 125 is scraped off the first and second collection rollers 124 and 125 by the first and second blades 126 and 127. The toner scraped off the first and second collection rollers 124 and 125 is contained in the housing 121. The toner contained in the housing 121 is transported by, for example, a transport member (such as a screw) 128 provided in the housing 121 and discharged from the housing 121. Furthermore, this toner is transported toward a collection container (not shown) provided in the main body of the image forming apparatus 100.

[0034] In this embodiment, the drive roller 22 is used as a common opposing roller for the first and second fur brushes 122 and 123, but the first and second fur brushes 122 and 123 may each be provided with an independent opposing roller.

[0035] In this embodiment, a voltage is applied to the first and second collection rollers 124 and 125, but the method of supplying the cleaning current is not limited to this. For example, rollers may be provided independently facing the first and second fur brushes 122 and 123 across the intermediate transfer belt 6, and a voltage may be applied to these rollers. In this case, the first and second fur brushes 122 and 123 may be used as opposing members and electrically grounded via the first and second collection rollers 124 and 125. In this case, a voltage of the opposite polarity to the voltage applied to the first and second collection rollers 124 and 125 in this embodiment may be applied to each roller facing the first and second fur brushes 122 and 123. This also allows cleaning of the intermediate transfer belt 6 to be performed in a manner similar to that of this embodiment. Alternatively, a voltage may be applied directly to the first and second fur brushes 122 and 123 (or they may be electrically grounded directly).

[0036] 4. Control Configuration FIG. 3 is a block diagram showing a schematic control configuration of the image forming apparatus 100 of this embodiment.

[0037] The image forming apparatus 100 has a control unit 50 as a control means. The control unit 50 is configured to include a CPU 51 as an arithmetic control means (arithmetic processing unit) that is a central element for performing arithmetic processing, memories (storage media) such as RAM 52 and ROM 53 as storage means (storage units), and an input / output circuit (not shown) as input / output means (input / output unit) for sending and receiving signals to and from devices external to the control unit 50. 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 the RAM 52 and ROM 53 can transfer and read data to and from each other.

[0038] The control unit 50 is connected to an operation unit (not shown) and an image reading unit (not shown) of the image forming apparatus 100, and external devices (not shown) such as a personal computer. Although not shown, the control unit 50 is also connected to various components of the image forming apparatus 100 that execute the image formation process described above. For example, the control unit 50 is connected to a primary transfer power supply E1, a secondary transfer power supply E2, and first and second cleaning power supplies E3 and E4. The control unit 50 is also connected to a sheet number counter 70, which counts the number of sheets of recording material P on which images have been formed and output from the image forming apparatus 100 (the number of sheets on which images have been formed). In this embodiment, the control unit 50 is also connected to a parts counter 80, which stores information about the usage history of parts. In this embodiment, the parts counter 80 is configured as a counting unit that counts the number of sheets on which images have been formed since the primary transfer roller 5 was first used (when it was new), as an index value correlated with the usage amount of the primary transfer roller 5 as a part. The index value correlated with the usage of the primary transfer roller 5 is not limited to the number of images formed, but any value correlated with the usage, such as the number of rotations or rotation time, can be used.

[0039] The control unit 50 comprehensively controls each unit of the image forming apparatus 100 to perform an image forming 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 information, control commands) from an external device. The control unit 50 also controls each unit of the image forming apparatus 100 to perform an operation of supplying toner to first and second fur brushes 122 and 123, which will be described later.

[0040] The primary transfer power supply E1 is connected to or incorporates a voltage detection circuit serving as a voltage detection means (voltage detection unit) for detecting its output voltage and a current detection circuit serving as a current detection means (current detection unit) for detecting its output current. In this embodiment, the primary transfer power supply E1 is configured to output a positive bias (positive bias) and a negative bias (negative bias). That is, in this embodiment, the primary transfer power supply E1 has a positive bias output unit and a negative bias output unit. In this embodiment, the image forming apparatus 100 is configured to acquire information (voltage-current characteristics) regarding the electrical resistance of the primary transfer unit N1 during non-image formation, set a target voltage so that a predetermined target current flows, and output a bias under constant voltage control. Information (voltage-current characteristics) regarding the electrical resistance of the primary transfer unit N1 can be acquired, for example, by supplying multiple test voltages or test currents to the primary transfer unit N1 during non-image formation and detecting the current flowing or the voltage applied.

[0041] Similarly, in this embodiment, the secondary transfer power supply E2 is connected to or incorporates a voltage detection circuit serving as a voltage detection means (voltage detection unit) for detecting its output voltage and a current detection circuit serving as a current detection means (current detection unit) for detecting its output current. Furthermore, in this embodiment, the secondary transfer power supply E2 is configured to be able to output a positive bias (positive bias) and a negative bias (negative bias). That is, in this embodiment, the secondary transfer power supply E2 has a positive bias output unit and a negative bias output unit. Furthermore, in this embodiment, the image forming apparatus 100 is configured to acquire information (voltage-current characteristics) regarding the electrical resistance of the secondary transfer unit N2 during non-image formation, set a target voltage so that a predetermined target current flows, and output a bias under constant voltage control. Information (voltage-current characteristics) regarding the electrical resistance of the secondary transfer unit N2 can be acquired, for example, by supplying multiple test voltages or test currents to the secondary transfer unit N2 during non-image formation and detecting the current flowing or the voltage applied at that time.

[0042] The image forming apparatus 100 also includes an image processing unit (video controller) 60. The image processing unit 60 generates image data for forming an image in the image forming apparatus 100 based on image information input from an external device such as an image reader or a personal computer. The image processing unit 60 also outputs a pulse signal having a pulse width corresponding to the level of the image data (image signal). The control unit 50 drives the laser light-emitting element of the exposure device 3 based on this pulse signal. As a result, the exposure device 3 irradiates the photosensitive drum 1 with laser light to form an electrostatic image on the photosensitive drum 1. The image processing unit 60 also includes a video counting unit 61. The video counting unit 61 integrates the image data levels (levels 0 to 255) for each pixel of the image data for one image. This integrated image data value is referred to as a "video count value." Note that instead of using the video counting unit 61, the video count value can also be calculated from a signal controlling the laser light-emitting element of the exposure device 3. In this embodiment, as described below, the video count value is used by the control unit 50 to obtain information regarding the image ratio.

[0043] The image forming apparatus 100 executes a job (printing operation), which is a series of operations that starts with a single start command and forms and outputs an image on one or more recording materials P. A job generally includes an image forming process, a pre-rotation process, a sheet-to-sheet process when forming images on multiple recording materials P, and a post-rotation process. The image forming process is a period during which electrostatic image formation, toner image formation, and primary and secondary transfer of the toner image are performed for the image that will actually be formed and output on the recording materials P. This period is referred to as the image formation time. More specifically, the timing of the image formation process differs depending on the positions where the electrostatic image formation, toner image formation, and primary and secondary transfer of the toner image are performed. The pre-rotation process is a period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image forming process. The sheet-to-sheet process is a period corresponding to the interval between recording materials P when image formation is performed continuously on multiple recording materials P (continuous image formation). The post-rotation process is a period during which a tidying up operation (preparatory operation) is performed after the image forming process. Non-image formation refers to periods other than image formation, and includes the above-mentioned pre-rotation process, paper interval process, post-rotation process, and also the pre-multi-rotation process, which is a preparatory operation when the image forming device 100 is turned on or when it returns from a sleep state.

[0044] 5.Fur brush bristles falling down Next, we will explain fur brush bristle collapse, which is a phenomenon in which the bristle tips of the first and second fur brushes 122 and 123 collapse. When describing the first and second fur brushes 122 and 123 without making any particular distinction, they will each be simply referred to as a "fur brush." ​​Similarly, when describing the first and second collection rollers 122 and 123 without making any particular distinction, they will each be simply referred to as a "collection roller."

[0045] The fur brushes 122 and 123 are pressed against the intermediate transfer belt 6 and the collection rollers 126 and 127. As a result, the brush fibers of the fur brushes 122 and 123 flutter as they rotate, causing the bristles to lay flat. As a result, the fur brushes 122 and 123 tend to collapse (permanently deform) as they are used, causing the outer diameter to decrease. The outer diameter of the fur brush is represented by the diameter of the circumscribed circle when the brush fibers are not deformed by external force.

[0046] This phenomenon becomes more pronounced when an image with a small image ratio, i.e., a low image ratio, is formed. This will be explained below. Here, the image ratio is also referred to as "image duty." Here, an image with a low image ratio is also referred to as "low-duty image," and an image with a high image ratio is also referred to as "high-duty image." As will be described later, the specific image ratios of images that are low-duty images and high-duty images are set appropriately. Details of the image ratio will be described later.

[0047] FIG. 4 is a graph showing an example of the relationship between the amount of use of the fur brushes 122 and 124 and the change in outer diameter. In FIG. 4, the horizontal axis represents the number of images formed as an index value for the amount of use of the fur brushes 122 and 123, and the vertical axis represents the outer diameter of the fur brushes 122 and 123. (a) in FIG. 4 shows the above relationship when a durability test was conducted in which low-duty images with thin vertical lines and an image ratio of 2% were continuously formed. (b) in FIG. 4 shows the above relationship when a durability test was conducted in which high-duty images with a full solid black image ratio of 100% were continuously formed. In both cases, the durability test was started with an initial (new) outer diameter of the fur brushes 122 and 123 of 18 mm, and the penetration depth of the fur brushes 122 and 123 into the intermediate transfer belt 6 of 2 mm.

[0048] As shown in (a) of Figure 4, when low-duty images were formed, the outer diameter of the fur brushes 122 and 123 was reduced to 16 mm after 1,000,000 sheets. This caused cleaning defects due to the secondary transfer residual toner on the intermediate transfer belt 6 slipping through the fur brushes 122 and 123 (hereinafter simply referred to as "slip-through"). On the other hand, as shown in (b) of Figure 4, when high-duty images were formed, no slip-through occurred up to 2,000,000 sheets.

[0049] This is thought to be due to the following reason: When forming a high-duty image with a relatively large amount of secondary-transfer residual toner, toner is supplied sufficiently to the fur brushes 122 and 123. In this case, the presence of toner at the base of the fur brushes 122 and 123 suppresses the collapse of the fur brushes 122 and 123, and thus suppresses a decrease in the outer diameter of the fur brushes 122 and 123. On the other hand, when forming a low-duty image with a relatively small amount of secondary-transfer residual toner, almost no toner is supplied to the fur brushes 122 and 123. In this case, the collapse of the fur brushes 122 and 123 is promoted, and a decrease in the outer diameter of the fur brushes 122 and 123 is promoted.

[0050] 6. Prevents fur brush hair from falling over <Summary> As described above, the reduction in the outer diameter of the fur brushes 122, 123 is accelerated when toner is not sufficiently supplied to the fur brushes 122, 123. Therefore, in order to prevent the bristles of the fur brushes 122, 123 from collapsing, it is effective to supply toner to the fur brushes 122, 123.

[0051] Here, when a low-duty image is formed, there is a possibility that a malfunction may occur in a device other than the electrostatic cleaning device, namely, the developing device 4. When an image with a low image ratio is formed, and the toner in the developing device 4 continues to be insufficiently consumed, the developability of the developing device 4 may deteriorate. In other words, when an image with a low image ratio is continuously formed, the toner in the developing device 4 may deteriorate. When such a situation occurs, one method is to form a predetermined toner image on the photosensitive drum 1, and then eject (forcefully consume) the toner from the developing device 4 onto the photosensitive drum 1, thereby increasing the proportion of fresh toner in the developing device 4 and maintaining image quality.

[0052] In this way, in order to maintain developability, when a low-duty image is formed, the image forming apparatus 100 performs an operation of forming a predetermined toner image and consuming toner. Here, this operation is also referred to as a "discharge operation."

[0053] In this embodiment, the toner of the toner image formed by this discharging operation is supplied to the fur brushes 122 and 123 .

[0054] <Discharge action> The toner discharging operation will be further described. The toner discharging operation is performed during non-image formation. In the toner discharging operation, a predetermined toner image is formed in a non-image formation area on the photosensitive drum 1 other than the image formation area (the area where a toner image can be transferred to the recording material P and output), and the toner is discharged (forcibly consumed) from the developing device 4 to the photosensitive drum 1. In this embodiment, the toner image formed on the photosensitive drum 1 during the toner discharging operation is formed through the charging process, exposure process, and development process of the photosensitive drum 1, as in normal image formation. This toner image is preferably formed at a relatively high density level over substantially the entire image formation area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1 in order to minimize downtime (time during which an image cannot be output) due to the toner discharging operation. In this embodiment, this toner image is a solid image (also referred to here as a "toner band") that covers substantially the entire image formation area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1 (a direction substantially perpendicular to the surface movement direction).

[0055] When images with a low image ratio are continuously formed, the proportion of toner transferred from the developing device 4 to the photosensitive drum 1 is low, resulting in a small amount of toner being replenished to the developing device 4. This results in prolonged agitation by the conveying members within the developing device 4 and friction as the toner passes through the regulating member. As a result, for example, external additives in the toner may peel off from the toner matrix or become embedded in the surface of the toner matrix, degrading the toner's fluidity and charging performance and resulting in a decline in image quality. Examples of image quality that may be affected by toner degradation include fogging, toner scattering, and graininess. The "image ratio" refers to the ratio of the area covered by toner to the area of ​​the maximum image formation area (area where a toner image can be formed). It is 100% for a solid image and 0% for no image (solid white image).

[0056] The progress of toner deterioration differs depending on the image ratio of the image to be formed (the lower the image ratio, the greater the proportion of deteriorated toner). The progress of toner deterioration also differs depending on the configuration of image forming apparatus 100 and the characteristics of the toner. It is possible to determine in advance by experimentation or the like that image quality may deteriorate if image formation is not performed with an image ratio above a certain level (i.e., a video count value above a certain level). In other words, it is possible to determine in advance by experimentation or the like the image ratio (i.e., a video count value that serves as the threshold) at which deterioration of image quality occurs.

[0057] As a specific method for determining whether or not to perform the toner discharging operation and executing the toner discharging operation, any known method can be used. Here, an outline of an example of control of the toner discharging operation will be described. In this embodiment, the control unit 50 determines whether or not to perform the toner discharging operation based on a video count value acquired from the video count unit 61 of the image processing unit 60. When a job is started, the control unit 50 acquires a video count value V from the video count unit 61 for each image formation (formation of an image transferred to one side of one sheet of recording material P). The control unit 50 also acquires a toner deterioration threshold value Vt that is preset and stored in the ROM 53. Here, the "toner deterioration threshold value Vt" is a video count value corresponding to the minimum amount of toner consumption required to prevent degradation of image quality due to toner deterioration. The toner deterioration threshold value Vt is set to, for example, "2." The control unit 50 calculates the difference between the video count value V and the toner deterioration threshold value Vt (=Vt-V) and determines whether "Vt-V" is positive or negative. If the control unit 50 determines that "Vt-V" is negative, it adds 0 to the toner deterioration integrated value X and stores the result in the RAM 52. A negative "Vt-V" indicates a state in which the image ratio is high and toner deterioration is unlikely to progress. On the other hand, if the control unit 50 determines that "Vt-V" is positive, it adds "Vt-V" to the toner deterioration integrated value X and stores the result in the RAM 52. A positive "Vt-V" indicates a state in which the image ratio is low and toner deterioration is likely to progress. Here, the "toner deterioration integrated value X" is an index representing the current state of toner deterioration and is the integrated value of the video count value calculated using "Vt-V." Next, the control unit 50 calculates the difference (=AX) between the toner deterioration integrated value X, which is calculated and updated for each image formation, and the toner discharge execution threshold A, which is preset and stored in the ROM 53. Here, the "discharge execution threshold A" is a predetermined value that can be set arbitrarily. The smaller the toner discharge threshold A, the more frequently the toner discharge operation is performed even for continuous image formation with the same image ratio. If the toner discharge threshold A is set too high, it takes a long time for toner deterioration to progress before the toner discharge operation is performed.The discharge execution threshold A can be set to, for example, approximately the same as the video count value of a full-page solid image (image with 100% image ratio) on one side of an A4- to A3-sized sheet of paper, e.g., "512." The control unit 50 then determines whether "AX" is positive or negative, and continues image formation if it determines that "AX" is positive. A positive "AX" indicates that toner deterioration has not progressed to the point where a discharge operation should be performed at that time. On the other hand, if the control unit 50 determines that "AX" is negative, it decides to perform the discharge operation. A negative "AX" indicates that toner deterioration has progressed to the point where a discharge operation should be performed at that time. The discharge operation can be performed, for example, during the inter-sheet process when image formation for a job is in progress, or during the post-rotation process when image formation for a job has ended. However, this is not limited to this, and the discharge operation can be performed at any time during non-image formation. Furthermore, if the control unit 50 performs the discharge operation, it resets the toner deterioration integrated value X to its initial value (here, "0").

[0058] In the toner discharging operation, for example, a toner image (toner band) with a toner amount corresponding to a video count value equal to the toner discharging execution threshold A is formed on the photosensitive drum 1, and the developing device 4 can discharge toner onto the photosensitive drum 1. As described above, in this embodiment, this toner band is formed through the charging process, the exposure process, and the development process of the photosensitive drum 1, and is a solid image covering substantially the entire image forming area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. Furthermore, when the toner discharging operation is performed in the inter-sheet process, the necessary amount of toner can be discharged by performing the toner discharging operation between multiple sheets. In this case, for example, the number of image formation sheets (number of inter-sheet intervals) required to discharge the necessary amount of toner can be calculated, the number of image formation sheets can be counted each time the toner discharging operation is performed, and the execution of the inter-sheet discharge operation can be terminated when the necessary number of image formation sheets (number of inter-sheet intervals) is reached. However, this is not limited to this, and the toner discharging operation may be performed by extending the inter-sheet distance (period) to discharge the necessary amount of toner.

[0059] <Toner movement in the primary transfer area> Next, the movement of the toner at the primary transfer portion N1 when a toner image is formed on the photosensitive drum 1 will be described.

[0060] FIG. 5 is a schematic diagram illustrating the movement of toner at the primary transfer portion N1 during normal image formation in this embodiment. FIG. 5(a) shows the state in which the toner image T formed on the photosensitive drum 1 by the developing device 4 enters the primary transfer portion N1. During normal image formation, as the toner image T passes through the primary transfer portion N1, a positive bias is applied to the primary transfer roller 5 by the primary transfer power supply E1. As a result, as the toner image T passes through the primary transfer portion N1, the toner image T is transferred onto the intermediate transfer belt 6. Note that the positive bias is a bias with a polarity opposite to the normal charging polarity of the toner. FIG. 5(b) shows the state after the toner image T has passed through the primary transfer portion N1. As the toner image T on the photosensitive drum 1 passes through the primary transfer portion N1, it separates into toner BT on the intermediate transfer belt 6 and toner DT on the photosensitive drum 1. The toner BT on the intermediate transfer belt 6 is transferred onto the recording material P at the secondary transfer portion N2. Toner remaining on the intermediate transfer belt 6 without being transferred to the recording material P is collected by a belt cleaning device 12. During normal image formation, a primary transfer bias of 1500 to 2500 V, which is appropriate so that the amount of toner BT on the intermediate transfer belt 6 is greater than the amount of toner DT on the photosensitive drum 1, is applied to the primary transfer roller 5, and a primary transfer current of 50 to 80 μA flows. In this embodiment, as described above, the primary transfer bias is constant-voltage controlled at a target voltage set so that a target current flows. However, this is not limited to this, and the primary transfer bias may also be constant-current controlled at a target current. The toner DT on the photosensitive drum 1 is collected by a drum cleaning device 11.

[0061] FIG. 6 is a schematic diagram illustrating the movement of toner at the primary transfer portion N1 during a conventional toner discharging operation. FIG. 6(a) shows the toner band T' formed on the photosensitive drum 1 by the developing device 4 entering the primary transfer portion N1. Conventionally, during the toner discharging operation, as the toner band T' passes through the primary transfer portion N1, a negative bias is applied to the primary transfer roller 5 by the primary transfer power supply E1 to prevent the toner band T' from being transferred onto the intermediate transfer belt 6. The negative bias is a bias (reverse bias) with the same polarity as the normal charging polarity of the toner. FIG. 6(b) shows the state after the toner band T' has passed through the primary transfer portion N1. As shown in FIG. 6(b), during the conventional toner discharging operation, after the toner band T' passes through the primary transfer portion N1, there is a large amount of toner DT' on the photosensitive drum 1 and a small amount of toner BT' on the intermediate transfer belt 6.

[0062] In contrast, FIG. 7 is a schematic diagram illustrating the movement of toner at the primary transfer portion N1 during the toner discharging operation in this embodiment. FIG. 7(a) shows the state when the toner band T' formed on the photosensitive drum 1 by the developing device 4 enters the primary transfer portion N1. In this embodiment, when the toner band T' passes through the primary transfer portion N1 during the toner discharging operation, a positive bias is applied to the primary transfer roller 5 by the primary transfer power supply E1. However, this positive bias is set to have a smaller absolute value than the positive bias during normal image formation shown in FIG. 7. If the positive bias is set so that a primary transfer current of 70 μA flows during normal image formation, the positive bias is set so that a primary transfer current of, for example, 10 μA flows during the toner discharging operation. FIG. 7(b) shows the state after the toner band T' has passed the primary transfer portion N1. As a result of applying a positive bias (herein also referred to as a "weak positive bias") with a smaller absolute value than that used during normal image formation as described above, the toner DT' on the photosensitive drum 1 and the toner BT' on the intermediate transfer belt 6 become equal in amount, as shown in FIG. 7(b). The toner DT' on the photosensitive drum 1 is collected by the drum cleaning device 11. Meanwhile, the toner BT' on the intermediate transfer belt 6 is passed through the secondary transfer portion N2 and sent to the belt cleaning device 12, where it is collected by the belt cleaning device 12. This supplies the toner to the fur brushes 122 and 123. In this embodiment, a negative bias is applied to the secondary transfer roller 9 when the toner BT' on the intermediate transfer belt 6 passes through the secondary transfer portion N2 so that the toner BT' on the intermediate transfer belt 6 can sufficiently pass through the secondary transfer portion N2. However, this is not limited thereto. If the image forming apparatus 100 has a mechanism for separating the secondary transfer roller 9 from the intermediate transfer belt 6, the secondary transfer roller 9 may be separated from the intermediate transfer belt 6 when the toner BT' passes through the secondary transfer portion N2. In addition, the weak positive bias is a bias that has the same polarity as the bias during normal image formation but a smaller absolute value when compared under substantially the same other conditions (such as the same environment and the same usage history of the primary transfer roller).Typically, when a toner band is formed in the inter-paper process as in this embodiment, the primary transfer bias when the toner band passes through the primary transfer section N1 is compared with the primary transfer bias when at least one of the image forming area preceding or following the toner band passes through the primary transfer section N1.

[0063] FIG. 8 is a graph showing an example of the relationship between the primary transfer current and the primary transfer efficiency. The primary transfer efficiency indicates the percentage (by weight) of toner on the photosensitive drum 1 that can be transferred to the intermediate transfer belt 6. (a) in FIG. 8 shows the above relationship when a new primary transfer roller 5 is used, and (b) in FIG. 8 shows the above relationship when a primary transfer roller 5 that has been used to form 1,000,000 images is used. When a new primary transfer roller 5 is used, the primary transfer efficiency is 40% when the primary transfer current is set to 15 μA. In this case, 40% of the toner amount in the toner band is supplied to the fur brushes 122 and 123, and the remaining 60% is supplied to the cleaning blade 112. If the toner concentration on the intermediate transfer belt 6 is too high (too much toner), the toner may not be able to be collected by the fur brushes 122 and 123 and may slip through them. In this case, this may affect images formed thereafter, or may require the intermediate transfer belt 6 to be further rotated to collect the toner on the intermediate transfer belt 6. However, in the configuration of this embodiment, if the amount of toner in the toner band is reduced to 40%, the toner can be collected by the fur brushes 122, 123 without slipping through the fur brushes 122, 123. Note that the primary transfer efficiency that allows sufficient toner to be supplied to the fur brushes 122, 123 while sufficiently preventing toner from slipping through the fur brushes 122, 123 is not limited to 40%. This primary transfer efficiency can be, for example, approximately 20 to 80%, preferably approximately 30 to 70%, and typically approximately 40 to 60%.

[0064] Furthermore, as can be seen from (b) in FIG. 8, when the cumulative usage of the primary transfer roller 5 increases, the primary transfer efficiency may decrease compared to when the primary transfer roller 5 was new, even if the same positive bias is applied to the primary transfer roller 5. In this case, setting the primary transfer current to 20 μA results in a primary transfer efficiency of 40%. Thus, by considering information about the usage history of the primary transfer roller 5, it may be possible to more appropriately set the primary transfer efficiency when supplying toner to the fur brushes 122 and 123. Typically, the primary transfer bias is set so that the primary transfer current when supplying toner to the fur brushes 122 and 123 is larger when the usage of the primary transfer roller 5 is a second usage amount greater than the first usage amount, compared to when the usage amount is a first usage amount. In other words, the primary transfer bias is typically set so that the primary transfer current (absolute value of the primary transfer bias) when supplying toner to the fur brushes 122 and 123 is larger when the usage amount of the primary transfer roller 5 is a second usage amount greater than the first usage amount, compared to when the usage amount is a first usage amount. It should be noted that, depending on the configuration and characteristics of the primary transfer roller 5, the accuracy of control of the primary transfer efficiency required from the viewpoint of suppressing hair fall of the fur brushes 122 and 123, etc., it is not essential to change the primary transfer current in accordance with information regarding the usage history of the primary transfer roller 5.

[0065] Furthermore, the setting of the primary transfer efficiency when toner is supplied to the fur brushes 122 and 123 may be changed depending on the image ratio of the image formed before toner is supplied to the fur brushes 122 and 123. For example, when the image ratio setting for a low-duty image (specifically, the aforementioned toner deterioration threshold Vt) is higher than the aforementioned 2%, such as 4%, the amount of toner supplied to the fur brushes 122 and 123 can be reduced from the aforementioned amount. In this case, for example, the primary transfer current may be set to 10 μA, at which the primary transfer efficiency drops to 30%. Typically, when the image ratio for a low-duty image is a second image ratio higher than the first image ratio, the primary transfer bias is set so that the primary transfer efficiency when toner is supplied to the fur brushes 122 and 123 is lower than when the image ratio is a first image ratio. In other words, typically, the primary transfer bias is set so that the primary transfer current (absolute value of the primary transfer bias) when toner is supplied to the fur brushes 122 and 123 is lower when the second image ratio is higher than the first image ratio than when the image ratio is a first image ratio.

[0066] As mentioned above, the toner band can be formed, for example, between sheets of paper while a job is being executed. Then, the number of times toner bands are formed between sheets of paper can be determined depending on how many low-duty images have been formed. For example, if 100 low-duty images have been formed, a setting can be made such that a toner band is formed between sheets of paper while the next 100 sheets of image formation are being executed.

[0067] Furthermore, it may be advantageous to control the primary transfer current to a substantially constant level regardless of the operating environment for supplying toner to the fur brushes 122 and 123. Specifically, according to the inventors' investigations, the fur brushes 122 and 123 tend to collapse more easily in a high-temperature, high-humidity environment. Therefore, it is desirable to supply more toner to the fur brushes 122 and 123 in a high-temperature, high-humidity environment than in a low-temperature, low-humidity environment or a room-temperature, normal-humidity environment. Meanwhile, in a high-temperature, high-humidity environment, the charge amount of the toner on the photosensitive drum 1 decreases, so the primary transfer current required to transfer the same amount of toner from the photosensitive drum 1 to the intermediate transfer belt 6 is smaller. Therefore, if substantially the same primary transfer current is supplied to the primary transfer portion N1 when the toner band passes through the primary transfer portion N1, more toner is transferred to the intermediate transfer belt 6 in a high-temperature, high-humidity environment than in a low-temperature, low-humidity environment or a room-temperature, normal-humidity environment. In this way, by simply controlling the primary transfer current to a substantially constant level regardless of the environment, more toner can be supplied to the fur brushes 122 and 123 in a high-temperature, high-humidity environment than in a low-temperature, low-humidity environment or a normal-temperature, normal-humidity environment. This effectively prevents the fur brushes 122 and 123 from collapsing, which is likely to occur in a high-temperature, high-humidity environment. The high-temperature, high-humidity environment may be, for example, a 30°C, 70% RH environment; the low-temperature, low-humidity environment may be, for example, a 23°C, 10% RH environment; and the normal-temperature, normal-humidity environment may be, for example, a 23°C, 50% RH environment. The environment may be at least one of the temperature and humidity inside or outside the image forming apparatus 100. The image forming apparatus 100 typically has an environmental sensor (such as a temperature sensor, humidity sensor, or temperature and humidity sensor) 90 (FIG. 3) as an environmental detection unit for detecting the environment to control process conditions, etc. Therefore, the control unit 50 can control the primary transfer current during the operation of supplying toner to the fur brushes 122 and 123 to be approximately constant, regardless of the environmental temperature and humidity (which may be the absolute moisture content determined from the temperature and humidity) detected, for example, by an environmental sensor.

[0068] <Control procedure> Next, the procedure for controlling a job including the operation of supplying toner to the fur brushes 122 and 123 in this embodiment will be described. FIG. 9 is a flowchart showing an outline of this control procedure. Here, an example is taken of a case where a discharging operation is performed in the inter-sheet step during execution of a job, and toner of the toner band formed by the discharging operation is supplied to the fur brushes 122 and 123. However, as mentioned above, the timing for executing the operation of supplying toner to the fur brushes 122 and 123 is not limited to the inter-sheet step. Also, as will be described later, the toner supplied to the fur brushes 122 and 123 is not limited to the toner of the toner band formed by the discharging operation.

[0069] When the control unit 50 starts image formation for a job (S101), it acquires image duty information for the image from the image processing unit 60 and stores the acquired information in the RAM 52 (S102). Next, the control unit 50 determines whether or not to execute the toner discharging operation (supply of toner to the fur brushes 122 and 123) based on the acquired image duty information (S103). If the control unit 50 determines not to execute the toner discharging operation in S103 (No in S103), it proceeds to processing in S107. If the control unit 50 determines to execute the toner discharging operation in S103 (Yes in S103), it calculates the amount of toner to be discharged in the toner discharging operation based on the acquired image duty information (S104). Specifically, the processing in S103 and S104 can be executed according to an example of the control of the toner discharging operation described above.

[0070] Next, the control unit 50 sets the primary transfer current for the toner discharging operation (S105). In this embodiment, information indicating the relationship between the usage history of the primary transfer roller 5 and the primary transfer current setting that achieves a predetermined primary transfer efficiency is preset as a table or the like and stored in ROM 53. The control unit 50 sets the primary transfer current based on the information indicating the usage history of the primary transfer roller 5 obtained from the parts counter 80 and the information indicating the above relationship stored in ROM 53. Next, the control unit 50 forms a toner band on the photosensitive drum 1 in the sheet-to-sheet interval process, applies a primary transfer bias so that the primary transfer current set in S105 flows, and controls the toner of the toner band to be sent to the fur brushes 122 and 123 (S106). Also, in S106, the control unit 50 controls the sheet number counter 70 to count the number of image formation sheets each time the toner discharging operation is performed until the required amount of toner has been discharged. Next, the control unit 50 determines whether formation of all images for the job has been completed (S107). If the control unit 50 determines in S107 that image formation has not ended (No in S107), it returns to the process of S101 and performs subsequent image formation. If the control unit 50 determines in S107 that image formation has ended (Yes in S107), it ends the job.

[0071] Here, in a durability test in which a low-duty image with an image duty of 2% was formed, similar to that shown in FIG. 4, toner in the toner band was supplied to the fur brushes 122 and 123 according to this embodiment. As described above, when toner in the toner band was not supplied to the fur brushes 122 and 123, slippage occurred after 1000k sheets. In contrast, when toner in the toner band was supplied to the fur brushes 122 and 123, the decrease in the outer diameter of the fur brushes 122 and 123 slowed, similar to when a high-duty image with an image duty of 100% was formed. As a result, slippage was sufficiently suppressed up to 2000k sheets.

[0072] As described above, in this embodiment, the image forming apparatus 100 includes a rotatable image carrier (photosensitive drum) 1 that carries a toner image, image forming means (such as a charging device 2, an exposure device 3, and a developing device 4) that form a toner image on the image carrier 1, a rotatable intermediate transfer belt 6 to which the toner image is transferred from the image carrier 1, a primary transfer member (primary transfer roller) 5 that transfers the toner image from the image carrier 1 to the intermediate transfer belt 6 at a primary transfer portion N1, a primary transfer power source E1 that applies a primary transfer bias to the primary transfer member 5, and a secondary transfer member (secondary transfer roller) 9 that forms a secondary transfer portion N2 that transfers the toner image from the intermediate transfer belt 6 to a recording material P. The intermediate transfer belt 6 includes a brush (e.g., a first fur brush) 122 that contacts the intermediate transfer belt 6 downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1 in the rotation direction of the intermediate transfer belt 6 to form a cleaning portion (e.g., a first cleaning portion) CL1 and removes toner from the intermediate transfer belt 6, a cleaning power supply (e.g., a first cleaning power supply) E3 that applies a cleaning bias to the cleaning portion CL1 to recover toner from the intermediate transfer belt 6 to the brush 122, and a control unit 50 that can control the image forming means (charging device 2, exposure device 3, developing device 4, etc.) and the primary transfer power supply E1. In this embodiment, the control unit 50 can be controlled to form a predetermined toner image (toner band) in an area on the image carrier where a toner image to be transferred to the recording material P is not formed, and to perform a predetermined operation (discharge operation) to transfer at least a portion of the toner of the predetermined toner image to the intermediate transfer belt 6 and make it reach the cleaning unit CL1, and in the predetermined operation, the control unit 50 controls the primary transfer bias applied to the primary transfer member 5 while the predetermined toner image formed on the image carrier 1 is passing through the primary transfer unit N1 to be a bias of the same polarity as the primary transfer bias when transferring the toner image to be transferred to the recording material P from the image carrier 1 to the intermediate transfer belt 6, but with a smaller absolute value than the primary transfer bias.

[0073] In this embodiment, during execution of a continuous image formation job in which images are formed continuously on a plurality of recording materials P, the control unit 50 controls the formation of the predetermined toner image in an area (sheet gap) between an image forming area where a toner image to be transferred to a preceding recording material P can be formed and an image forming area where a toner image to be transferred to a next recording material P can be formed. Furthermore, the control unit 50 can control not to execute the predetermined operation when a job in which an image having a first image ratio is formed on a predetermined number of recording materials P is executed, and to execute the predetermined operation when a job in which an image having a second image ratio lower than the first image ratio is formed on the predetermined number of recording materials P is executed. Furthermore, the control unit 50 can change the primary transfer bias applied to the primary transfer member 5 while the predetermined toner image formed on the image carrier 1 passes through the primary transfer portion N1 during the predetermined operation, based on information about the usage history of the primary transfer member 5. In this case, the control unit 50 can control the absolute value of the primary transfer bias applied to the primary transfer member 5 while the predetermined toner image formed on the image carrier 1 passes through the primary transfer unit N1 in the predetermined operation to be larger when the usage amount of the primary transfer member 5 since it was new, as indicated by the usage history information, is a second usage amount greater than the first usage amount. In this embodiment, the image forming apparatus 100 has only one image forming unit 10 including the image carrier 1, image forming means (such as the charging device 2, exposure device 3, and developing device 4), and the primary transfer member 5. In this embodiment, the predetermined toner image is a solid image formed over substantially the entire image formation area in a direction substantially perpendicular to the movement direction of the surface of the image carrier 1. In this embodiment, the brush 122 is a rotatable brush roller. In addition, the image forming apparatus 100 may have an environment detection means (environmental sensor) 90 that detects the environment, which is at least one of the temperature and humidity inside or outside the image forming apparatus 100, and the control unit 50 may be configured to control the value of the current that flows when a primary transfer bias is applied to the primary transfer member 5 while the specified toner image formed on the image carrier 1 passes through the primary transfer section N1 during the specified operation, so that the value is approximately constant regardless of the environment detected by the environment detection means.

[0074] As described above, this embodiment can prevent the fur brushes 122 and 123 that clean the intermediate transfer belt 6 from falling over. That is, when low-duty images are formed, a toner band is formed between the sheets, depending on the number of sheets, for example, to prevent the outer diameter of the fur brushes 122 and 123 from decreasing, thereby extending the life of the belt cleaning device 12 (the fur brushes 122 and 123). In this embodiment, the toner in the toner band formed by the spit operation is used as the toner supplied to the fur brushes 122 and 123, thereby efficiently preventing the fur brushes 122 and 123 from falling over. Furthermore, in this embodiment, a weak positive bias is used as the primary transfer bias when the toner band is primarily transferred to the intermediate transfer belt 6, thereby preventing toner from slipping through the fur brushes 122 and 123 due to excessive toner being supplied to them.

[0075] [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.

[0076] In the first embodiment, the toner supplied to the fur brushes 122 and 123 is the toner of the toner band formed by the discharging operation.

[0077] On the other hand, when a low-duty image is formed, the drum cleaning device 11, in addition to the developing device 4, is another device other than the electrostatic cleaning device that may cause a malfunction.

[0078] The drum cleaning device 11 is able to properly clean the surface of the photosensitive drum 1 by having the toner (more specifically, the external additive in the toner) function as a lubricant at the contact area between the cleaning blade 112 and the photosensitive drum 1. When the toner (more specifically, the external additive in the toner) at the contact area between the cleaning blade 112 and the photosensitive drum 1 is depleted, the frictional force between the cleaning blade 112 and the photosensitive drum 1 increases, which can cause chattering or curling of the cleaning blade 112. Chattering is a phenomenon in which the cleaning blade 112 vibrates, and can cause abnormal noise and poor cleaning. Curling is a phenomenon in which the tip of the cleaning blade 112 curls up downstream in the direction of movement of the surface of the photosensitive drum 1, and can cause poor cleaning.

[0079] Furthermore, when the toner (more specifically, the external additives) at the contact area between the cleaning blade 112 and the photosensitive drum 1 is depleted, a phenomenon known as "toner fusion" may occur, in which toner present near the contact area melts and adheres to the surface of the photosensitive drum 1. In other words, a deposit (blocking layer) of the external additives in the toner is normally formed near the contact area, preventing the toner from entering the area near the contact area. As a result, the temperature rise of the toner is suppressed, and toner fusion is prevented. However, when the blocking layer decreases, the toner is more likely to enter the area near the contact area, which is heated by the friction between the photosensitive drum 1 and the cleaning blade 112. Then, for example, in a high-temperature, high-humidity environment, the toner that has entered the area near the contact area may melt and adhere to the surface of the photosensitive drum 1, causing toner fusion.

[0080] Here, the toner of the toner band formed by the expulsion operation described in Example 1 can be supplied to the contact point between the photosensitive drum 1 and the cleaning blade 112, thereby serving to supply a lubricant between them or to form a blocking layer.

[0081] In addition to the expelling operation, a toner band can be formed on the photosensitive drum 1 to supply toner to the contact area between the photosensitive drum 1 and the cleaning blade 112 in order to suppress the increase in frictional force (chattering and curling) as described above. This operation, like the expelling operation, can be performed when low-duty images are continuously formed. Here, this operation is also referred to as a "lubrication operation." In addition to the expelling operation, a toner band can be formed on the photosensitive drum 1 to supply toner to the contact area between the photosensitive drum 1 and the cleaning blade 112 in order to suppress the problem of toner melting and adhering to the photosensitive drum 1 (toner fusion) as described above. This operation can be performed, for example, when low-duty images are continuously formed and the temperature of the photosensitive drum 1 rises. Here, this operation is also referred to as a "fusion suppression operation." The toner in the toner band formed by the "lubrication operation" and "fusion suppression operation" may be used as toner to be supplied to the fur brushes 122 and 123.

[0082] In this way, the toner in the toner band formed by the "discharge operation," "lubrication operation," and "fusing suppression operation," which serve to supply toner to the contact area between the photosensitive drum 1 and the cleaning blade 112, can be used as toner to be supplied to the fur brushes 122 and 123. This allows toner to be efficiently supplied to both the drum cleaning device 11 (cleaning blade 112) and the belt cleaning device 12 (fur brushes 122 and 123).

[0083] At this time, the amount of toner in the toner band is determined based on the amount of toner required for the cleaning blade 112 and the amount of toner required for the fur brushes 122 and 123, and the primary transfer efficiency can be set so that the required amount of toner can be supplied to each (Figure 7).

[0084] Next, an example of a job control procedure in this embodiment will be described using the flowchart in Fig. 10. Here, we will take as an example a case where the fusion suppression operation is performed in the inter-sheet process during job execution, and the toner of the toner band formed by the fusion suppression operation is supplied to the fur brushes 122 and 123.

[0085] When the control unit 50 starts image formation for a job (S201), it acquires image duty information for the image from the image processing unit 60 and stores the acquired information in the RAM 52 (S202). Next, the control unit 50 determines whether to execute the fusion suppression operation (supply of toner to the drum cleaning device 11 and the belt cleaning device 12) based on the acquired image duty information (S203). If the control unit 50 determines not to execute the fusion suppression operation in S203 (No in S203), it proceeds to processing in S207. If the control unit 50 determines to execute the fusion suppression operation in S203 (Yes in S203), it calculates the amount of toner required for the cleaning blade 112 and the amount of toner required for the fur brushes 122 and 123 based on the acquired image duty information (S204). The processing in S203 and S204 can be executed, for example, in accordance with the example of control of the toner discharge operation described in the first embodiment. For example, a threshold value can be set in advance to prevent toner fusion, thereby determining whether to perform the fusion suppression operation. Furthermore, a threshold value can be set in advance to prevent the fur brushes 122 and 123 from falling over, thereby determining whether to supply toner to the fur brushes 122 and 123 (here, the fusion suppression operation). For example, the fusion suppression operation can be performed when it is determined that at least one of these operations should be performed. Furthermore, as with the expulsion operation described in the first embodiment, the number of times a toner band is formed between sheets can be determined based on the number of low-duty images formed. The required amount of toner can be calculated in advance, for example, in relation to the conditions (such as the threshold value) for determining whether to perform the toner band. Here, an example is given in which toner for the toner band formed in the fusion suppression operation is supplied to both the drum cleaning device 11 and the belt cleaning device 12. However, the same applies when toner for the toner band formed in the expulsion operation or the lubrication operation is used.

[0086] Next, in order to ensure the necessary amount of toner for the fur brushes 122 and 123, the control unit 50 calculates the necessary primary transfer efficiency based on the relationship between the primary transfer efficiency and the primary transfer current (FIG. 8) stored in the ROM 53, and calculates the primary transfer current required to obtain that primary transfer efficiency (S205). At this time, as in the first embodiment, the primary transfer current can be set taking into consideration the usage history of the primary transfer roller 5. Next, the control unit 50 forms a toner band on the photosensitive drum 1 in the sheet-to-sheet interval process, applies a primary transfer bias so that the primary transfer current set in S205 flows, and controls the toner in the toner band to be sent to the cleaning blade 112 and the fur brushes 122 and 123 (S206). Also in S206, the control unit 50 controls the sheet counter 70 to count the number of image formation sheets until the necessary amount of toner is supplied. Next, the control unit 50 determines whether formation of all images for the job has been completed (S207). If the control unit 50 determines in S207 that image formation has not ended (No in S207), it returns to the process of S201 and performs subsequent image formation. If the control unit 50 determines in S207 that image formation has ended (Yes in S207), it ends the job.

[0087] As described above, the image forming apparatus 100 includes a cleaning member (cleaning blade) 112 that is disposed in contact with the image carrier 1 and removes toner from the image carrier 1, and in a predetermined operation (such as a fusion suppression operation) that causes the toner to reach the cleaning portion CL1 (i.e., the fur brush 122), at least a portion of the toner of a predetermined toner image (toner band) may reach the contact portion between the image carrier 1 and the cleaning member 112. The control unit 50 can control the primary transfer bias applied to the primary transfer member 5 while the predetermined toner image formed on the image carrier 1 passes through the primary transfer portion N1 in the predetermined operation, so that the ratio of the toner that reaches the cleaning portion CL1 (fur brush 122) to the toner that reaches the contact portion (i.e., the cleaning blade 112) is a predetermined ratio.

[0088] As described above, according to this embodiment, similar to the first embodiment, it is possible to prevent the fur brushes 122 and 123 that clean the intermediate transfer belt 6 from falling over. According to this embodiment, it is possible to efficiently supply toner to both the drum cleaning device 11 (cleaning blade 112) and the belt cleaning device 12 (fur brushes 122 and 123). Furthermore, in this embodiment, similar to the first embodiment, by using a weak positive primary transfer bias when the toner band is primarily transferred to the intermediate transfer belt 6, it is possible to prevent toner from slipping through due to too much toner being supplied to the fur brushes 122 and 123.

[0089] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, 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.

[0090] 11A and 11B are schematic diagrams illustrating the movement of toner at the primary transfer portion N1 during the operation of supplying toner to the fur brushes 122 and 123 of this embodiment. Fig. 11A shows the state when the toner band T' formed on the photosensitive drum 1 by the developing device 4 enters the primary transfer portion N1. Fig. 11B shows the state after the toner band T' has passed through the primary transfer portion N1.

[0091] In Examples 1 and 2, as shown in FIG. 7(a), when the toner band T' passes through the primary transfer portion N1, a weak positive bias is applied to the primary transfer roller 5 by the primary transfer power supply E1. In contrast, in this example, as shown in FIG. 11(a), the negative power supply (negative bias output portion) in FIG. 7(a) is changed to ground. In other words, in this example, when the toner band T' passes through the primary transfer portion N1, the primary transfer roller 5 is connected to ground (electrically earthed). This allows for cost reduction by eliminating the negative power supply.

[0092] In this embodiment, the image forming apparatus 100 is configured so that toner in the toner band T' is transferred to the intermediate transfer belt 6 by pressure transfer. The primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 6 by the force of a spring, which is a biasing member serving as a biasing means. The amount of toner transferred to the intermediate transfer belt 6 can be adjusted by adjusting the force of this spring. Increasing the force of this spring increases the amount of toner transferred to the intermediate transfer belt 6, and decreasing the force decreases it. In this embodiment, the force of this spring is adjusted (set) in advance so that the primary transfer efficiency is, for example, approximately 40%.

[0093] 11(b), in this embodiment as well, the toner DT' on the photosensitive drum 1 and the toner BT' on the intermediate transfer belt 6 are equal in amount. The toner DT' on the photosensitive drum 1 is then collected by the drum cleaning device 11. Meanwhile, the toner BT' on the intermediate transfer belt 6 is passed through the secondary transfer portion N2 and sent to the belt cleaning device 12, where it is collected by the belt cleaning device 12. As a result, the toner is supplied to the fur brushes 122 and 123.

[0094] Although the primary transfer roller 5 is connected to the ground in this embodiment, it may be connected to a positive power supply and its output may be set to 0 V. The configuration of this embodiment may be combined with either of the first and second embodiments.

[0095] Thus, in this embodiment, in a predetermined operation (such as a discharge operation) for causing toner to reach the cleaning section CL1 (i.e., the fur brush 122), the control section 50 controls the primary transfer bias (potential of the primary transfer member 5) applied to the primary transfer member 5 to be 0 V while the above-mentioned predetermined toner image formed on the image carrier 1 passes through the primary transfer section N1.

[0096] As described above, the configuration of this embodiment can also provide the same effects as those of the first and second embodiments.

[0097] [Example 4] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, 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.

[0098] In the first and second embodiments, a toner band is formed on the photosensitive drum 1 in the inter-sheet process, and the toner of this toner band is supplied to the fur brushes 122 and 123. However, toner may be supplied to the fur brushes 122 and 123 all at once, for example, periodically.

[0099] For example, the fixing device 30 may develop uneven gloss or gloss streaks in images due to changes in the surface shape of the fixing member caused by image formation. To address this issue, the image forming apparatus 100 may be configured to periodically perform a fixing refresh operation in which an abrasive member is pressed against the belt constituting the fixing member of the fixing device 30 to smooth the surface of the belt. During the fixing refresh operation, image formation is halted, and during this time, a toner band corresponding to the number of low-duty images can be collectively sent to the fur brushes 122 and 123. This allows the fur brushes 122 and 123 to receive an amount of toner equivalent to the amount supplied to the fur brushes 122 and 123 during the multiple inter-sheet processes in the first and second embodiments while image formation is halted.

[0100] In this case, too, the toner in the toner band can be supplied to both the drum cleaning device 11 (cleaning blade 112) and the belt cleaning device (fur brushes 122, 123) by applying a weak positive bias to the primary transfer roller 5. Alternatively, the toner in the toner band may be supplied to both the drum cleaning device 11 (cleaning blade 112) and the belt cleaning device (fur brushes 122, 123) by pressure transfer, as in the third embodiment.

[0101] In this embodiment, the fixing refresh operation has been described as an example of the operation that the image forming apparatus 100 performs when image formation is stopped (when the image forming apparatus 100 is waiting for a job or when image formation for a job is interrupted), but the operation is not limited to this. Any operation that does not prevent the formation of a toner band and the supply of that toner to the fur brushes 122 and 123 can be performed when image formation is stopped (or interrupted) for any operation.

[0102] In this way, the control unit 50 can control the cleaning unit CL1 (i.e., the fur brush 122) to perform a predetermined operation to cause toner to reach the cleaning unit CL1 (i.e., the fur brush 122) during the period when the control unit 50 is waiting for an instruction to start a job to form an image on one or more recording materials P, or during the period when image formation for the job is interrupted.

[0103] [Example 5] Next, another embodiment of the present invention will be described. 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 the first embodiment will be assigned the same reference numerals as those of the first embodiment, and detailed descriptions thereof will be omitted.

[0104] 12 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 (color printer) that employs an intermediate transfer method and is capable of forming full-color images using an electrophotographic method.

[0105] Image forming apparatus 100' has four image forming units (stations) 10Y, 10M, 10C, and 10K that form images of the colors yellow (Y), magenta (M), cyan (C), and black (K), respectively. Elements in each of image forming units 10Y, 10M, 10C, and 10K that have the same or corresponding functions or configurations are designated by the suffix Y, M, C, or K to indicate that they are elements for any of the colors.

[0106] In this embodiment, for example, when a full-color image is formed, toner images of yellow, magenta, cyan, and black formed on the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially transferred so as to be superimposed on the intermediate transfer belt 6. In addition, in this embodiment, the belt cleaning device 12 is disposed downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1 (the most upstream primary transfer portion N1Y) in the rotation direction of the intermediate transfer belt 6, particularly at a position facing the drive roller 22 across the intermediate transfer belt 6.

[0107] As described above, the image forming apparatus 100 of the first embodiment is a monochrome printer configured by retaining only the components and units necessary for forming a monochrome black image from among the components and units of the image forming apparatus 100' of this embodiment. For example, the image forming apparatus 100 of the first embodiment has the components of the color image forming units 10Y, 10M, and 10C of the image forming apparatus 100' of this embodiment removed. However, the image forming apparatus 100 of the first embodiment and the image forming apparatus 100' of this embodiment have the same primary transfer position (primary transfer unit N1) and secondary transfer position (secondary transfer unit N2) for black in the device main body of the image forming apparatuses 100 and 100'.

[0108] As described above, in the relationship between such a multi-color image forming apparatus and a monochrome image forming apparatus, the monochrome image forming apparatus has less residual toner on the intermediate transfer belt 6 sent to the belt cleaning device 12 than the multi-color image forming apparatus. Therefore, in a monochrome image forming apparatus with such a configuration, when an image with a low image ratio is formed, the fur brush tends to collapse more easily. Therefore, the effects of the present invention are particularly pronounced in a monochrome image forming apparatus with such a configuration. However, the present invention can also be applied to a multi-color image forming apparatus such as the image forming apparatus 100' of this embodiment.

[0109] In this embodiment, the determination of whether to perform the discharging operation, lubrication operation, and fusion suppression operation described in the above embodiments may be performed for each of the image forming units 10Y, 10M, 10C, and 10K. When it is determined that at least one of these operations is necessary for at least one image forming unit, the operation can be performed for at least one (or all) of the image forming units, including that image forming unit. At that time, the toner of the toner band formed in at least one image forming unit can be supplied to the fur brushes 122 and 123 in the same manner as in the above embodiments. The determination of whether to perform the operation of supplying toner to the fur brushes 122 and 123 and the control of the operation of supplying toner to the fur brushes 122 and 123 are the same as those described in the above embodiments.

[0110] In this way, the image forming apparatus may have a plurality of image forming units 10 each having an image carrier 1, an image forming means (such as a charging device 2, an exposure device 3, and a developing device 4), and a primary transfer member 5, and may be configured such that a predetermined toner image (toner band) is formed on the image carrier 1 of at least one of the plurality of image forming units 10 in a predetermined operation of causing toner to reach the cleaning unit CL1 (i.e., the fur brush 122).

[0111] As explained above, the present invention can be applied to a multi-color image forming apparatus, and the same effects as those of the above-mentioned embodiment can be obtained.

[0112] [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.

[0113] In the above-described embodiment, the toner of a predetermined toner image formed during predetermined operations, such as the spit operation, lubrication operation, and fusion suppression operation, to prevent problems when a low-image-ratio image is formed on a device other than the fur brush is supplied to the fur brush. This effectively prevents the fur brush from falling over, as described above. However, if these operations result in a shortage of toner being supplied to the fur brush, a special operation may be performed to supply toner to the fur brush. In this case, a toner image (corresponding to the toner band in the above-described embodiment) with a density sufficient to prevent toner from slipping through the fur brush is formed on the photosensitive drum, and then transferred to the intermediate transfer belt by applying a primary transfer bias equivalent to that used during normal image formation. This toner image is preferably a halftone image with a density of 30 to 70% (typically 40 to 60%), assuming a solid image density of 100%.

[0114] In the above-described embodiment, the electrostatic cleaning device has two fur brushes, but the present invention is not limited to such a configuration. The number of fur brushes that the image forming apparatus has for electrostatically cleaning the intermediate transfer belt is not limited to two, but may be one, or three or more.

[0115] In the above-described embodiment, the toner image transferred to the intermediate transfer belt to supply toner to the fur brush was a band-shaped toner image that spanned the entire image forming area in the width direction of the intermediate transfer belt (the direction of the rotation axis of the photosensitive drum), but this is not limited to this. This toner image only needs to supply sufficient toner to the fur brush and sufficiently prevent the fur brush from falling over. This toner image may, for example, be a toner image that is narrower than the image forming area in the width direction of the intermediate transfer belt. This toner image may also be divided into multiple parts, for example, in at least one of the width direction of the intermediate transfer belt or the direction of movement of the surface of the intermediate transfer belt.

[0116] In addition, in the above-described embodiment, the brush that removes toner from the intermediate transfer belt is composed of a rotatable brush roller, but it may also be a brush (such as a deck brush) that is fixedly positioned with a certain amount of penetration into the intermediate transfer belt. [Explanation of symbols]

[0117] 1 Photosensitive drum 4. Developing device 5 Primary transfer roller 6 Intermediate transfer belt 11 Drum cleaning device 12 Belt cleaning device 112 Cleaning blade 122 First Fur Brush 123 Second Fur Brush

Claims

1. a rotatable image carrier that carries a toner image; an image forming means for forming a toner image on the image carrier; a rotatable intermediate transfer belt onto which a toner image is transferred from the image carrier; a primary transfer member that transfers a toner image from the image carrier to the intermediate transfer belt at a primary transfer portion; a primary transfer power supply that applies a primary transfer bias to the primary transfer member; a secondary transfer member forming a secondary transfer portion that transfers a toner image from the intermediate transfer belt to a recording material; a brush that contacts the intermediate transfer belt downstream of the secondary transfer unit and upstream of the primary transfer unit in the rotation direction of the intermediate transfer belt to form a cleaning unit and remove toner from the intermediate transfer belt; a cleaning power supply that applies a cleaning bias to the cleaning unit to collect toner from the intermediate transfer belt onto the brush; a control unit capable of controlling the image forming unit and the primary transfer power source; and the control unit is capable of performing a predetermined operation to form a predetermined toner image in an area on the image carrier where a toner image to be transferred to a recording material is not formed, and to transfer at least a portion of the toner of the predetermined toner image onto the intermediate transfer belt and have it reach the cleaning unit; an image forming apparatus characterized in that, in the specified operation, the control unit controls the primary transfer bias applied to the primary transfer member while the specified toner image formed on the image carrier passes through the primary transfer unit so that the primary transfer bias is a bias having the same polarity as the primary transfer bias used when transferring the toner image to be transferred onto the recording material from the image carrier to the intermediate transfer belt but with a smaller absolute value than the primary transfer bias, or is set to 0 V.

2. The image forming apparatus according to claim 1, characterized in that the control unit controls the formation of the specified toner image in an area between an image forming area where a toner image to be transferred to a preceding recording material can be formed and an image forming area where a toner image to be transferred to a next recording material can be formed during execution of a continuous image formation job in which images are formed continuously on multiple recording materials.

3. 2. The image forming apparatus according to claim 1, wherein the control unit controls the image forming apparatus to execute the predetermined operation during a period in which the control unit is waiting for an instruction to start a job for forming an image on one or more recording materials, or during a period in which image formation for the job is interrupted.

4. The image forming apparatus according to claim 1, characterized in that the control unit does not perform the specified operation when a job is executed to form an image having an image ratio of a first image ratio on a predetermined number of sheets of recording material, and controls to perform the specified operation when a job is executed to form an image having an image ratio of a second image ratio lower than the first image ratio on the predetermined number of sheets of recording material.

5. 2. The image forming apparatus according to claim 1, wherein the control unit changes the primary transfer bias applied to the primary transfer member while the specified toner image formed on the image carrier passes through the primary transfer unit during the specified operation based on information regarding the usage history of the primary transfer member.

6. 6. The image forming apparatus according to claim 5, wherein the control unit controls the absolute value of the primary transfer bias applied to the primary transfer member while the specified toner image formed on the image carrier passes through the primary transfer section in the specified operation to be larger when the usage amount of the primary transfer member since it was new, as indicated by the information on the usage history, is a second usage amount greater than the first usage amount, than when the information on the usage history indicates a first usage amount.

7. an environment detection unit for detecting at least one of the temperature and humidity inside or outside the image forming apparatus; The image forming apparatus according to claim 1, wherein the control unit controls the value of the current that flows when a primary transfer bias is applied to the primary transfer member while the specified toner image formed on the image carrier passes through the primary transfer unit during the specified operation so that the value is approximately constant regardless of the environment detected by the environmental detection means.

8. 2. The image forming apparatus according to claim 1, further comprising a cleaning member that is arranged to contact the image carrier and removes toner from the image carrier, and wherein during the specified operation, at least a portion of the toner of the specified toner image reaches the contact point between the image carrier and the cleaning member.

9. 9. The image forming apparatus according to claim 8, wherein the control unit controls the primary transfer bias applied to the primary transfer member while the specified toner image formed on the image carrier passes through the primary transfer unit in the specified operation so that the ratio of the toner of the specified toner image that reaches the cleaning unit and the toner that reaches the contact unit is a specified ratio.

10. 10. The image forming apparatus according to claim 1, further comprising only one image forming unit including the image carrier, the image forming means, and the primary transfer member.

11. 10. The image forming apparatus according to claim 1, further comprising a plurality of image forming units each including the image carrier, the image forming means, and the primary transfer member, wherein the predetermined toner image is formed on the image carrier of at least one of the image forming units among the plurality of image forming units during the predetermined operation.

12. 10. The image forming apparatus according to claim 1, wherein the predetermined toner image is a solid image formed over substantially the entire image forming area in a direction substantially perpendicular to the moving direction of the surface of the image carrier.

13. 10. The image forming apparatus according to claim 1, wherein the brush is a rotatable brush roller.

Images