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] This invention relates to image forming apparatus such as photocopiers, printers, and facsimile machines that use electrophotographic or electrostatic recording methods. [Background technology]

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

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

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-128613 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] An electrostatic cleaning belt cleaning device has a conductive, rotatable, brush-shaped cleaning member called a fur brush (conductive fur brush roller). This fur brush is in contact with the intermediate transfer belt to a certain extent.

[0006] Furthermore, as fur brushes are used more frequently, the bristles tend to flatten (permanently deform), causing their outer diameter to decrease. When the outer diameter of a fur brush decreases, it becomes difficult to ensure sufficient penetration into the intermediate transfer belt, making proper cleaning of the intermediate transfer belt difficult. Therefore, when the outer diameter of a fur brush becomes smaller than the acceptable range, it reaches the end of its lifespan and may require replacement.

[0007] According to the inventors' research, the flattening of the fur brush bristles (thinning of the outer diameter of the fur brush) is particularly noticeable when low-image-ratio images with a large amount of white space are formed. Furthermore, it is even more noticeable when the image forming apparatus has the following configuration. In other words, a product configuration in which only the parts and units necessary for single-color image formation are retained from the parts and units of a multi-color image forming apparatus is sometimes adopted for purposes such as high-mix low-volume production and improvement of development efficiency. In this case, compared to a multi-color image forming apparatus, a single-color image forming apparatus has less residual toner on the intermediate transfer belt sent to the belt cleaning device. Therefore, in a single-color image forming apparatus with such a configuration, the flattening of the fur brush bristles tends to occur more easily when low-image-ratio images are formed.

[0008] Therefore, the objective of the present invention is to suppress the flattening of the bristles of the brush used to clean the intermediate transfer belt. [Means for solving the problem]

[0009] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises a rotatable image carrier for carrying a toner image, an image forming means for forming a toner image on the image carrier, a rotatable intermediate transfer belt onto which the toner image is transferred from the image carrier, a primary transfer member for transferring the toner image from the image carrier to the intermediate transfer belt in a primary transfer section, a primary transfer power supply for applying a primary transfer bias to the primary transfer member, a secondary transfer member for forming a secondary transfer section for transferring the toner image from the intermediate transfer belt to a recording material, a brush for forming a cleaning section by contacting the intermediate transfer belt downstream of the secondary transfer section and upstream of the primary transfer section in the rotational direction of the intermediate transfer belt and removing toner from the intermediate transfer belt, and a cleaning bias for applying a cleaning bias to the cleaning section to recover toner from the intermediate transfer belt to the brush. The image forming apparatus comprises a power supply and a control unit capable of controlling the image forming means and the primary transfer power supply, wherein the control unit can control the execution of a predetermined operation in which a predetermined toner image is formed in an area on the image carrier where a toner image to be transferred to a recording material is not formed, and transfers at least a portion of the toner of the predetermined toner image to the intermediate transfer belt to reach the cleaning unit, and the control unit controls the primary transfer bias applied to the primary transfer member while the predetermined toner image formed on the image carrier is passing through the primary transfer unit to be a bias with the same polarity as the primary transfer bias when transferring the toner image to be transferred to the recording material from the image carrier to the intermediate transfer belt, and with an absolute value smaller than the primary transfer bias, or to 0V. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress the flattening of the bristles of the brush used to clean the intermediate transfer belt. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of an image forming apparatus. [Figure 2]It is a schematic cross-sectional view near the belt cleaning device. [Figure 3] It is a block diagram showing a schematic control configuration of an image forming apparatus. [Figure 4] It is a graph showing an example of the relationship between the usage amount of the fur brush and the change in the outer diameter. [Figure 5] It is a schematic diagram for explaining the movement of toner in the primary transfer unit during normal image formation. [Figure 6] It is a schematic diagram for explaining the movement of toner in the primary transfer unit during the conventional ejection operation. [Figure 7] It is a schematic diagram for explaining the movement of toner in the primary transfer unit during the ejection operation in the embodiment. [Figure 8] It is a graph showing an example of the relationship between the primary transfer current and the primary transfer efficiency. [Figure 9] It is a flowchart for explaining the outline of the job control procedure. [Figure 10] It is a flowchart for explaining another example of the job control procedure. [Figure 11] It is a schematic diagram for explaining the movement of toner in the primary transfer unit during the fusing suppression operation of another embodiment. [Figure 12] It is a schematic cross-sectional view of an image forming apparatus of another embodiment.

Embodiments for Carrying Out the Invention

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

[0013] [Example 1] 1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of the present embodiment is a printer (monochrome printer) adopting an intermediate transfer system that can form a black single-color image using an electrophotographic method.

[0014] Here, the image forming apparatus of this embodiment is a monochrome image forming apparatus 100, which is constructed by retaining only the parts and units necessary for monochrome image formation from the parts and units of the multicolor image forming apparatus 100' shown in Figure 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 composed of 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. constitute an image forming means that forms a toner image on the photosensitive drum 1.

[0015] The photosensitive drum 1, a rotatable drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor) that carries the toner image, is driven to rotate 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 with a predetermined polarity (negative polarity in this embodiment) by a charging device 2, which is a charging means. During the charging process, 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 based on image information by an exposure device (laser beam scanner) 3, which is an exposure means, and an electrostatic image (electrostatic latent image) corresponding to the desired image information is formed on the photosensitive drum 1. The exposure device 3 outputs on / off modulated laser light according to image information input from an image reading unit or an external device such as a computer, and scans and exposes the charged surface on the photosensitive drum 1.

[0016] The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by a developing device 4, which is a developing means, when toner is supplied as a developer, and a toner image is formed on the photosensitive drum 1. In this embodiment, the developing device 4 uses a two-component developer comprising toner (non-magnetic toner particles) and a 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 made of a non-magnetic hollow cylindrical member as a developer carrier (developing member). The developing sleeve 412 is rotationally driven by a drive motor (not shown) as a driving means. A magnetic roller is arranged inside the developing sleeve 412 (hollow part). The developing container 411 is also provided with a regulating member (not shown) that regulates the amount of developer carried in the developing sleeve 412, and a transporting member (not shown) that transports the developer in the developing container 411 while stirring it. The developer, supported on the developing sleeve 412 by the magnetic force of the magnetic roller, is transported to the part opposite the photosensitive drum 1 (developing section) after its amount is regulated by a regulating member as the developing sleeve 412 rotates. The developer on the developing sleeve 412 transported to the developing section is raised by the magnetic force of the magnetic roller to form a magnetic brush (magnetic bristles), which is 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, which is a superposition of a DC voltage (DC component) and an AC voltage (AC component), is applied to the developing sleeve 412 as the developing bias. As a result, in accordance with the electrostatic image on the photosensitive drum 1, toner moves from the magnetic brush on the developing sleeve 412 to the photosensitive drum 1, and a toner image is formed on the photosensitive drum 1. Toner is supplied to the developing container 411 as needed from a replenishment container (not shown). In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposure area (image area) on the photosensitive drum 1, where the absolute value of the potential has decreased after being uniformly charged and then exposed based on image information (reverse development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0017] Opposite the photosensitive drum 1 is an intermediate transfer belt 6, which is composed of an endless belt and serves as an intermediate transfer body. The intermediate transfer belt 6 is positioned so as to be able to contact the surface of the photosensitive drum 1. The intermediate transfer belt 6 is stretched over a plurality of tension rollers, the first to sixth tension rollers 21 to 26, and is taut with a predetermined tension. In this embodiment, the first tension roller 21 is a secondary transfer opposing roller (secondary transfer internal 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, on which the toner image is primary transferred from each photosensitive drum 1, 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. Furthermore, the sixth tension roller 26 is a pre-secondary transfer roller that forms the secondary transfer surface of the intermediate transfer belt 6, which enters the secondary transfer section N2 described later. The intermediate transfer belt 6 is driven by the rotational drive of the drive roller 22, and rotates (moves in a circular motion) at a peripheral speed of 150 to 470 mm / sec in the direction of arrow R2 (clockwise direction) in the figure. Note that "~" in the numerical range means that the values ​​before and after it are included. On the inner circumferential surface (back surface) side of the intermediate transfer belt 6, a primary transfer roller 5, which is a roller-type primary transfer member as a primary transfer means, is arranged corresponding to the photosensitive drum 1. The primary transfer roller 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 6, forming a primary transfer section (primary transfer nip section, primary transfer position) N1 where the photosensitive drum 1 and the intermediate transfer belt 6 come into contact. The tension rollers other than the second tension roller 22 and the primary transfer roller 5 rotate in conjunction with the rotation of the intermediate transfer belt 6.

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

[0019] On the outer circumferential surface of the intermediate transfer belt 6, a secondary transfer roller (secondary transfer outer roller) 9, which is a roller-type secondary transfer member serving as a secondary transfer means, is positioned opposite the secondary transfer opposing roller 21. The secondary transfer roller 9 is pressed toward the secondary transfer opposing roller 21 via the intermediate transfer belt 6, forming a secondary transfer section (secondary transfer nip, secondary transfer position) N2 where the intermediate transfer belt 6 and the secondary transfer roller 9 come into contact (directly contact or grip the recording material P). As described above, the toner image formed on the intermediate transfer belt 6 is transferred (secondary transfer) in the secondary transfer section N2 to the recording material P, which is being transported while being gripped between the intermediate transfer belt 6 and the secondary transfer roller 9, 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 section (not shown), such as a feeding cassette. The recording material P is fed one sheet at a time from the recording material storage section by a feeding member (not shown), such as a feeding roller, which is driven based on a feeding start signal. The recording material P is then transported to the secondary transfer section N2 by a register roller 8, which acts as a transport member. The register 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 OHP sheet, etc. In this embodiment, an inner roller corresponding to the secondary transfer opposing roller 21 may be used as the secondary transfer member, and a voltage with the opposite polarity (same polarity as the normal charging polarity of the toner) to the voltage applied to the secondary transfer roller 9 in this embodiment may be applied to it. In this case, an outer roller corresponding to the secondary transfer roller 9 in this embodiment may be used as the opposing member and electrically grounded.

[0020] In this embodiment, the secondary transfer roller 9 is composed of a core metal (base material) and an elastic layer formed of ion-conductive foamed rubber on the outer circumference of the core metal. In this embodiment, the outer diameter of the secondary transfer roller 9 is 20 to 25 mm. In this embodiment, the electrical resistance of the secondary transfer roller 9 is 1 × 10⁻¹⁶ when measured by applying a voltage of 2 kV in an N / N environment (23°C, 50% RH). 5 ~1 × 10 8The value is Ω. In this embodiment, the secondary transfer opposing roller 21 is composed of a core metal (base material) and an elastic layer made of electronically conductive rubber on the outer circumference of the core metal. In this embodiment, the outer diameter of the secondary transfer opposing roller 21 is 20 to 22 mm. In this embodiment, the electrical resistance 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 The value is Ω. During secondary transfer, a secondary transfer bias (secondary transfer voltage), which is a constant voltage controlled DC voltage with the opposite polarity to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the secondary transfer roller 9 by the secondary transfer power supply (high voltage power supply) E2. This supplies a secondary transfer current to the secondary transfer section N2. During secondary transfer, a constant voltage controlled secondary transfer bias of, for example, +1 to +7kV is applied to the secondary transfer roller 9, and a secondary transfer current of +40 to +120μA flows. In this embodiment, the secondary transfer opposing roller 21 is electrically grounded (connected to ground).

[0021] The recording material P onto which the toner image has been transferred is separated from the intermediate transfer belt 6 and transported by the pre-fixing transport device 20 to the fixing device 30, which serves as the fixing means. The pre-fixing transport device 20 has a rotatable endless belt body made of rubber material such as EPDM, with a width of 100-110 mm and a thickness of 1-3 mm, located in the center of a direction approximately perpendicular to the transport direction of the recording material P, and the recording material P is placed on top of this belt for transport. The belt body has holes with a diameter of 3-7 mm, and air is drawn in from the inside of the belt body. This increases the load-bearing force of the recording material P on the belt body, stabilizing the transport of the recording material P. The fixing device 30 uses a fixing rotating body pair to heat and pressurize the recording material P carrying the unfixed toner image, thereby fixing (melting and solidifying) the toner image onto the recording material P. The recording material P with the fixed toner image is discharged (output) to the outside of the main body of the image forming apparatus 100.

[0022] Furthermore, toner that remains on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 during the primary transfer (primary transfer residue toner) is removed from the photosensitive drum 1 and recovered by the drum cleaning device 11, which serves as a photoreceptor cleaning means. In this embodiment, the drum cleaning device 11 includes a cleaning container 111 and a cleaning blade 112 as a cleaning member. The cleaning blade 112 is made of a rubber plate-shaped member having a predetermined length in the longitudinal direction, which is arranged substantially parallel to the rotation axis direction of the photosensitive drum 1, and a predetermined thickness in the short direction, which is substantially perpendicular to the longitudinal direction. The cleaning blade 112 is in contact with the photosensitive drum 1 in a counter-direction with respect to the rotation direction of the photosensitive drum 1 (the direction in which the free end faces upstream in the rotation direction). The drum cleaning device 11 cleans the surface of the photosensitive drum 1 by blocking (scraping off) the primary transfer residue toner on the photosensitive drum 1 with the cleaning blade 112 as the photosensitive drum 1 rotates, and recovering it in the cleaning container 111. The cleaned photosensitive drum 1 is used repeatedly for image formation.

[0023] Furthermore, any deposits such as toner that remains on the intermediate transfer belt 6 without being transferred to the recording material P during secondary transfer (secondary transfer residue toner) are removed and recovered from the intermediate transfer belt 6 by the belt cleaning device 12, which serves 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 recovering the secondary transfer residue toner on the intermediate transfer belt 6. The cleaned intermediate transfer belt 6 is then repeatedly used for image formation. Details of the belt cleaning device 12 will be described later.

[0024] 2. Intermediate Transfer Form In this embodiment, the intermediate transfer belt 6 is composed of a base layer (a layer forming the inner circumferential surface), an elastic layer (intermediate layer), and a surface layer (a layer forming the outer circumferential surface). The base layer is made of a material containing an appropriate amount of carbon black as an antistatic agent in a resin such as polyimide or polycarbonate, or various types of rubber, and has a thickness of 0.05 to 0.15 mm. The elastic layer is made of a material containing an appropriate amount of an ion conductive agent in a rubber such as chloroprene rubber (CR rubber), urethane rubber, or silicone rubber, 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 example, the volume resistivity of the intermediate transfer belt 6 is 5 × 10 8 ~1 × 10 14 The hardness is Ω·cm (23℃, 50%RH). The hardness of the intermediate transfer belt 6 is 60~85° on the MD1 hardness scale (23℃, 50%RH). The static friction coefficient of the intermediate transfer belt 6 is 0.15~0.6 (23℃, 50%RH, HEIDON type94i).

[0026] 3. Electrostatic cleaning device Figure 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 positioned downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 in the rotational direction of the intermediate transfer belt 6, and in particular, opposite the drive roller 22 via the intermediate transfer belt 6. In this embodiment, the belt cleaning device 12 is composed of an electrostatic cleaning device that electrostatically recovers toner on the intermediate transfer belt 6, and in particular, an electrostatic brush cleaning device using a conductive fur brush roller.

[0027] In this embodiment, the belt cleaning device 12 has a housing 121 disposed in the vicinity of 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 as the first and second cleaning members are provided. Also, first and second recovery rollers 124 and 125 as the first and second recovery members are provided. Further, first and second blades 126 and 127 as the first and second scraping members are provided.

[0028] The first and second fur brushes 122 and 123 are composed of conductive fur brush rollers which are rotatable brush-shaped cleaning members having conductivity. The brush fibers of the first and second fur brushes 122 and 123 have an electrical resistance value of the yarn of 3×10 5 ~1×10 13 Ω / cm, and are composed of carbon-dispersed nylon fibers, acrylic fibers or polyester fibers with a fiber thickness of 2 to 15 denier. And the first and second fur brushes 122 and 123 have these brush fibers with a tufting density of 50,000 to 500,000 per inch 2The brushes are constructed by implanting bristles onto a metal roller, which serves as the base material, in a specific ratio. The length of the brush fibers is, for example, about 3 to 5 mm. The first and second fur brushes 122 and 123 are positioned to maintain an insertion depth of approximately 1.0 to 2.0 mm into the intermediate transfer belt 6. This insertion depth can be represented by the length of the brush fibers minus the distance (shortest distance) between the base material (metal roller, etc.) of the fur brush and the object it contacts. The first and second fur brushes 122 and 123 are rotated in the direction of arrow R3 (clockwise) in the figure at a peripheral speed of 20 to 80% of the peripheral speed of the intermediate transfer belt 6 by a drive motor (not shown) as a driving means. 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 external force. In other words, the first and second fur brushes 122 and 123 rotate in a direction opposite to the direction of movement of the intermediate transfer belt 6 at the point of contact with the intermediate transfer belt 6, and rub against the surface of the intermediate transfer belt 6. In this embodiment, the first and second fur brushes 122 and 123 are in contact with a drive roller 22 that functions as an opposing member via the intermediate transfer belt 6. The drive roller 22 is electrically grounded. The rotational axis directions of the first and second fur brushes 122 and 123 are arranged to be approximately parallel to the direction (here also called the "width direction") which is approximately perpendicular to the direction of movement of the surface of the intermediate transfer belt 6. The length of the rotational axis directions of the first and second fur brushes 122 and 123 is longer than the maximum image forming width on the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 6. The contact point between the first fur brush 122 and the intermediate transfer belt 6 is the first cleaning section (first cleaning position) CL1, where toner is recovered from the intermediate transfer belt 6 by the first fur brush 122. The contact point between the second fur brush 123 and the intermediate transfer belt 6 is the second cleaning section (second cleaning position) CL2, where toner is recovered from the intermediate transfer belt 6 by the second fur brush 123. 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 rotational direction of the intermediate transfer belt 6.Furthermore, in this embodiment, the first cleaning section CL1 is located upstream of the second cleaning section CL2 in the rotational direction of the intermediate transfer belt 6.

[0029] The first and second recovery rollers 124 and 125 are composed of rotatable metal rollers (made of aluminum in this embodiment). The first and second recovery rollers 124 and 125 are positioned to maintain an insertion depth of approximately 1.5 to 2.5 mm relative to the first and second fur brushes 122 and 123. The first and second recovery rollers 124 and 125 are rotated by a drive motor (not shown) as a driving means in the direction of arrow R4 in the figure (counterclockwise) at a peripheral speed equivalent to that of the first and second fur brushes 122 and 123. In other words, the first and second recovery rollers 124 and 125 rotate so as to move in the same direction as the movement of the first and second fur brushes 122 and 123 at the contact point with the first and second fur brushes 122 and 123. The first and second recovery rollers 124 and 125 are positioned so that their rotational axis directions are approximately parallel to the width direction of the intermediate transfer belt 6. The lengths of the first and second recovery 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 positioned in contact with the first and second recovery rollers 124 and 125. The first and second blades 126 and 127 are made 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 the longitudinal direction which is approximately parallel to the rotation axis direction of the first and second recovery rollers 124 and 125, and a predetermined thickness in the short direction which is approximately perpendicular to the longitudinal direction. The thickness of the first and second blades 126 and 127 is 1.6 to 2.2 mm, and the hardness is 70 to 78° on the IRHD hardness scale (23°C, 50% RH). Furthermore, the first and second blades 126 and 127 are positioned to penetrate the first and second recovery rollers 124 and 125 by 0.5 to 2.0 mm. The first and second blades 126 and 127 are in contact with the first and second recovery rollers 124 and 125 in a counter-direction (the direction in which the free ends face upstream in the direction of rotation) with respect to the rotational direction of the first and second recovery rollers 124 and 125. The longitudinal length of the first and second blades 126 and 127 is equal to the length of the first and second recovery rollers 124 and 125 in the direction of the rotational axis.

[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 rotational direction of the intermediate transfer belt 6. In this embodiment, a constant-current controlled negative DC voltage is applied to the first recovery roller 124 by a first cleaning power supply (high-voltage power supply) E3, which is a DC power supply. As a result, a constant-current controlled negative DC voltage is applied to the first fur brush 122 via the first recovery roller 124. In this embodiment, a first cleaning bias is applied so that a first cleaning current of -60 to -73 μA flows from the first cleaning power supply E3 to the first fur brush 122 (i.e., the first cleaning section CL1) via the first recovery roller 124. In this embodiment, the first cleaning current is set to -60 to -73 μA, but this is not limited to this.

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

[0033] When a cleaning bias is applied to the first and second fur brushes 122 and 123, a cleaning electric field suitable for recovering toner from 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 residue 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. The first fur brush 122 is coated with positively charged toner, which is the opposite polarity to the normal charging polarity of the secondary transfer residue toner on the intermediate transfer belt 6. The second fur brush 123 is coated with negatively charged toner, which is the normal charging polarity of the secondary transfer residue toner on the intermediate transfer belt 6. Furthermore, this toner is transferred from the first and second fur brushes 122 and 123 to the first and second recovery rollers 124 and 125 by the electric field formed between the first and second recovery rollers 124 and 125 and the first and second fur brushes 122 and 123. The toner transferred to the first and second recovery rollers 124 and 125 is then scraped off from the first and second recovery rollers 124 and 125 by the first and second blades 126 and 127. The toner scraped off from the first and second recovery rollers 124 and 125 is contained within the housing 121. The toner contained within the housing 121 is transported, for example, by a transport member (such as a screw) 128 provided within the housing 121 and discharged from the housing 121. Furthermore, this toner is transported toward a recovery container (not shown) provided within the main body of the image forming apparatus 100 or the like.

[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 opposing rollers may be provided independently for each of the first and second fur brushes 122 and 123.

[0035] Furthermore, in this embodiment, a voltage is applied to the first and second recovery rollers 124 and 125, but the method of supplying the cleaning current is not limited to this. For example, rollers facing each of the first and second fur brushes 122 and 123 may be independently provided via 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 can be used as opposing members and electrically grounded via the first and second recovery rollers 124 and 125. In this case, a voltage with the opposite polarity to the voltage applied to the first and second recovery 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 in the same manner as in this embodiment. Alternatively, a configuration in which a voltage is applied directly to the first and second fur brushes 122 and 123 (or directly electrically grounded) may also be used.

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

[0037] The image forming apparatus 100 has a control unit 50 as a control means. The control unit 50 is composed of a CPU 51 as an arithmetic control means (arithmetic processing unit) which is the central element that performs arithmetic processing, a memory (storage medium) such as RAM 52 and ROM 53 as a storage means (storage unit), and an input / output circuit (not shown) as an input / output means (input / output unit) that exchanges signals with external devices of the control unit 50. The RAM 52, which is a rewritable memory, stores information input to the control unit 50, detected information, calculation results, etc., and the ROM 53 stores the control program, a pre-determined data table, etc. The CPU 51 and the memories such as RAM 52 and ROM 53 can transfer and read data from each other.

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

[0039] The control unit 50 comprehensively controls each part of the image forming apparatus 100 to execute image forming operations based on instructions from the operation unit of the image forming apparatus 100, image data from the image reading unit, or image forming signals (image information, control commands) from an external device. The control unit 50 also controls each part of the image forming apparatus 100 to execute the operation of supplying toner to the first and second fur brushes 122 and 123, which will be described later.

[0040] Here, the primary transfer power supply E1 is connected to, or incorporates, a voltage detection circuit as a voltage detection means (voltage detection unit) for detecting its output voltage and a current detection circuit 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 and a negative bias. In other words, 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 when not forming an image, set a target voltage so that a preset target current flows, and output a bias with 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 when not forming an image and detecting the current flowing or the applied voltage at that time.

[0041] Similarly, in this embodiment, the secondary transfer power supply E2 is connected to, or incorporates, a voltage detection circuit as a voltage detection means (voltage detection unit) for detecting its output voltage and a current detection circuit 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 output a positive bias and a negative bias. In other words, in this embodiment, the secondary transfer power supply E2 has a positive bias output unit and a negative bias output unit. In addition, 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 when not forming an image, set a target voltage so that a preset target current flows, and output a bias with 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 when not forming an image and detecting the current flowing or the applied voltage at that time.

[0042] The image forming apparatus 100 also has 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 image reading unit or an external device such as a personal computer. The image processing unit 60 also outputs a pulse signal with 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 apparatus 3 based on this pulse signal. As a result, the exposure apparatus 3 irradiates the photosensitive drum 1 with laser light and forms an electrostatic image on the photosensitive drum 1. The image processing unit 60 also has a video count unit 61. The video count unit 61 integrates the levels (0 to 255 levels) of each pixel of the image data for one image plane. This integrated image data value is called the "video count value". Alternatively, the video count value can be obtained from the signal controlling the laser light-emitting element of the exposure apparatus 3 instead of the video count unit 61. In this embodiment, as will be described later, the video count value is used by the control unit 50 to acquire information regarding the image ratio.

[0043] The image forming apparatus 100 executes a job (print operation), which is a series of operations that form and output an image on one or more recording materials P, initiated by a single start instruction. A job generally includes an image forming process, a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials P, and a post-rotation process. The image forming process is the period during which the electrostatic image, toner image, and primary or secondary transfer of the toner image are formed and output on the recording materials P are performed, and this period is referred to as the image forming time. More specifically, the timing of the image forming time differs depending on the position where each of these processes—electrostatic image formation, toner image formation, and primary or secondary transfer of the toner image—is performed. The pre-rotation process is the period during which preparatory operations are performed before the image forming process, from when the start instruction is input until the image is actually formed. The paper-to-paper process is the period corresponding to the space between recording materials P when image forming is performed continuously on multiple recording materials P (continuous image forming). The post-rotation process is the period during which cleanup operations (preparatory operations) are performed after the image forming process. Non-image forming periods refer to periods other than image forming periods, and include the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation processes which are preparatory operations when the image forming apparatus 100 is powered on or when it returns from sleep mode.

[0044] 5. Fur brush bristles flattened Next, we will explain the phenomenon of the bristles of the first and second fur brushes 122 and 123 falling over. When explaining the first and second fur brushes 122 and 123 without making a particular distinction, they will each simply be referred to as "fur brushes." Similarly, when explaining the first and second retrieval rollers 122 and 123 without making a particular distinction, they will each simply be referred to as "retrieval rollers."

[0045] The fur brushes 122 and 123 are pressed against the intermediate transfer belt 6 and the recovery 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 lie flat. Consequently, as the amount of use of the fur brushes 122 and 123 increases, the bristles tend to flatten (permanently deform), and the outer diameter tends 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 aspect ratio, i.e., a low aspect ratio image, is formed. This will be explained below. Here, the aspect ratio will also be referred to as "image duty." Furthermore, here, an image with a low aspect ratio will be referred to as a "low-duty image," and an image with a high aspect ratio will be referred to as a "high-duty image." As will be discussed later, the specific aspect ratios of images designated as low-duty or high-duty are set as appropriate. Details regarding aspect ratios will be discussed later.

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

[0048] As shown in Figure 4(a), when a low-duty image was formed, the outer diameter of the fur brushes 122 and 123 decreased to 16 mm after 1000 k sheets. This sometimes resulted in cleaning problems due to residual toner from the secondary transfer on the intermediate transfer belt 6 passing through the fur brushes 122 and 123 (also simply referred to as "passing through"). On the other hand, as shown in Figure 4(b), when a high-duty image was formed, no pass-through occurred up to 2000 k sheets.

[0049] This is thought to be due to the following reasons: When forming a high-duty image with a relatively large amount of secondary transfer toner residue, sufficient toner is supplied 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 bristles of the fur brushes 122 and 123, thereby suppressing 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 toner residue, almost no toner is supplied to the fur brushes 122 and 123. In this case, the collapse of the bristles 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. Preventing the bristles of the fur brush from becoming flattened. <Overview> As described above, the decrease in the outer diameter of the fur brushes 122 and 123 is accelerated when the fur brushes 122 and 123 are not sufficiently supplied with toner. Therefore, supplying toner to the fur brushes 122 and 123 is effective in suppressing the collapse of the bristles of the fur brushes 122 and 123.

[0051] Here, in the case of low-duty images, the developing unit 4 is another component that may malfunction when a low-duty image is formed, in addition to the electrostatic cleaning device. If the developing unit 4 continues to be in a state where toner is not consumed sufficiently due to the formation of low-image-ratio images, its developing performance may deteriorate. In other words, if the formation of low-image-ratio images continues, the toner in the developing unit 4 may deteriorate. Therefore, in such a situation, there is a method to maintain image quality by forming a predetermined toner image on the photosensitive drum 1 and ejecting (forcibly consuming) toner from the developing unit 4 to the photosensitive drum 1, thereby increasing the proportion of fresh toner in the developing unit 4.

[0052] Thus, in order to maintain developability, the image forming apparatus 100 performs an operation to form a predetermined toner image and consume toner when a low-duty image is formed. Here, this operation is also called the "ejection operation".

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

[0054] <Spit-out action> The ejection operation will be explained further. The ejection operation is performed when no image is being formed. In the ejection operation, a predetermined toner image is formed in the non-image-forming area of ​​the photosensitive drum 1, excluding the image-forming area (the area where a toner image can be formed and output on the recording material P), and toner is ejected (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 ejection operation is formed through the charging, exposure, and development processes of the photosensitive drum 1, as in normal image formation. To minimize downtime (time when an image cannot be output) due to the ejection operation, it is preferable that this toner image be formed at a relatively high density level over substantially the entire image-forming area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, this toner image is a solid image (here also called a "toner band") that covers substantially the entire image-forming area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1 (a direction substantially perpendicular to the direction of surface movement).

[0055] When low-image ratio images are formed continuously, the proportion of toner transferred from the developing unit 4 to the photosensitive drum 1 is small, resulting in insufficient toner supply to the developing unit 4. Consequently, the toner is subjected to prolonged agitation by the transport members within the developing unit 4 and friction when passing through the regulating members. As a result, for example, the toner's external additives may peel off from the toner matrix or become embedded on the surface of the toner matrix, worsening the toner's fluidity and charging performance, and potentially degrading image quality. Image quality degradation due to toner deterioration can include fogging, toner scattering, and graininess. "Image ratio" refers to the ratio of the area to which toner adheres to the area of ​​the maximum image formation area (the area where a toner image can be formed). For solid images, it is 100%, and for no image (solid white image), it is 0%.

[0056] The rate of toner degradation varies depending on the aspect ratio of the formed image (the lower the aspect ratio, the greater the proportion of degraded toner). Furthermore, the rate of toner degradation also differs depending on the configuration of the image forming apparatus 100 and the characteristics of the toner. It is possible to determine in advance, through experiments, that image quality may deteriorate if image formation is not performed at an aspect ratio above a certain level (i.e., above a certain video count value). In other words, the threshold aspect ratio (i.e., the threshold video count value) at which image quality deterioration occurs can be determined in advance through experiments.

[0057] As a specific method for determining whether or not to perform an ejection operation and then executing the ejection operation, any known method can be used. Here, an outline of an example of ejection operation control is described. In this embodiment, the control unit 50 determines whether or not to perform an ejection operation based on the video count value obtained from the video count unit 61 of the image processing unit 60. When the job starts, the control unit 50 obtains 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 recording material P). The control unit 50 also obtains a toner degradation threshold Vt that is set in advance and stored in the ROM 53. Here, the "toner degradation threshold Vt" is a video count value corresponding to the minimum amount of toner consumption required to prevent a decrease in image quality due to toner degradation. The toner degradation threshold Vt is set to, for example, "2". The control unit 50 calculates the difference between the video count value V and the toner degradation threshold 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 degradation cumulative value X and stores it in the RAM 52. A negative "Vt-V" indicates a high image ratio and that toner degradation is less likely to progress. On the other hand, if the control unit 50 determines that "Vt-V" is positive, it adds "Vt-V" to the toner degradation cumulative value X and stores it in the RAM 52. A positive "Vt-V" indicates a low image ratio and that toner degradation is more likely to progress. Here, the "toner degradation cumulative value X" is an indicator representing the current toner degradation state and is the cumulative value of the video count value calculated by "Vt-V". Next, the control unit 50 calculates the difference (=AX) between the toner degradation cumulative value X, which is calculated and updated for each image formed, and the ejection execution threshold A, which is pre-set and stored in the ROM 53. Here, the "ejection execution threshold A" is a predetermined value that can be set arbitrarily. The smaller the ejection threshold A, the more frequently the ejection operation will be performed, even for the formation of consecutive images with the same image ratio. If the setting of the ejection threshold A is too high, the time it takes for toner degradation to progress before the ejection operation is performed will be longer.The ejection threshold A can be set to approximately the same value as the video count of a full-page solid image (100% image ratio) on one side of an A4 to A3 size paper, for example, to "512". The control unit 50 then determines whether "AX" is positive or negative, and if it determines that "AX" is positive, it continues image formation. If "AX" is positive, it indicates that toner degradation has not progressed to the point where ejection should be performed at that time. On the other hand, if the control unit 50 determines that "AX" is negative, it decides to perform ejection. If "AX" is negative, it indicates that toner degradation has progressed to the point where ejection should be performed at that time. Ejection can be performed, for example, in the inter-paper process if image formation of the job is in progress, or in the post-rotation process if image formation of the job is completed. However, it is not limited to this, and ejection can be performed at any time when image formation is not in progress. Also, if the control unit 50 performs ejection, it resets the toner degradation cumulative value X to its initial value (in this case, "0").

[0058] In the ejection operation, for example, a toner image (toner band) corresponding to a video count value equivalent to the ejection execution threshold A is formed on the photosensitive drum 1, and toner can be ejected from the developing device 4 to the photosensitive drum 1. As described above, in this embodiment, this toner band is formed through the charging process, exposure process, and developing process of the photosensitive drum 1, and is a solid image covering almost the entire image formation area on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. Furthermore, when the ejection operation is performed in the inter-paper process, the required amount of toner can be ejected by performing the ejection operation between multiple sheets of paper. In this case, for example, the number of image formation sheets (number of sheets) required to eject the required amount of toner can be determined, the number of image formation sheets can be counted each time the ejection operation is performed, and the execution of the inter-paper ejection operation can be terminated when the required number of image formation sheets (number of sheets) is reached. However, it is not limited to this, and the ejection operation may be performed by extending the inter-paper distance (duration) to eject the required amount of toner.

[0059] <Toner movement in the primary transfer section> Next, we will explain the movement of toner in the primary transfer section N1 when a toner image is formed on the photosensitive drum 1.

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

[0061] Figure 6 is a schematic diagram illustrating the movement of toner in the primary transfer section N1 during a conventional ejection operation. Figure 6(a) shows how the toner strip T' formed on the photosensitive drum 1 by the developing device 4 enters the primary transfer section N1. Conventionally, during the ejection operation, when the toner strip T' passes through the primary transfer section N1, a negative bias is applied to the primary transfer roller 5 by the primary transfer power supply E1 to prevent the toner strip T' from being transferred onto the intermediate transfer belt 6 as much as possible. The negative bias is a bias (reverse bias) with the same polarity as the normal charge polarity of the toner. Figure 6(b) shows the state after the toner strip T' has passed through the primary transfer section N1. As shown in Figure 6(b), conventionally, during the ejection operation, after the toner strip T' has passed through the primary transfer section 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, Figure 7 is a schematic diagram illustrating the movement of toner in the primary transfer section N1 during the ejection operation of this embodiment. Figure 7(a) shows the toner strip T' formed on the photosensitive drum 1 by the developing device 4 as it enters the primary transfer section N1. In this embodiment, during the ejection operation, a positive bias is applied to the primary transfer roller 5 by the primary transfer power supply E1 as the toner strip T' passes through the primary transfer section N1. However, this positive bias is set to have a smaller absolute value than the positive bias during normal image formation shown in Figure 7. If the positive bias is set so that a primary transfer current of 70 μA flows during normal image formation, then during the ejection operation, the positive bias is set so that a primary transfer current of, for example, 10 μA flows. Figure 7(b) shows the state after the toner strip T' has passed through the primary transfer section N1. As described above, by applying a positive bias (also referred to here as a "weak positive bias") with a smaller absolute value than during normal image formation, the amount of toner DT' on the photosensitive drum 1 and the amount of toner BT' on the intermediate transfer belt 6 become equal, as shown in Figure 7(b). The toner DT' on the photosensitive drum 1 is recovered by the drum cleaning device 11. On the other hand, the toner BT' on the intermediate transfer belt 6 is passed through the secondary transfer section N2 and sent to the belt cleaning device 12, where it is recovered. This supplies 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' passes through the secondary transfer section N2, so that the toner BT' on the intermediate transfer belt 6 can pass through the secondary transfer section N2 sufficiently. However, this is not limited to this, and if the image forming apparatus 100 has a mechanism to separate 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 section N2. Furthermore, a weakly positive bias is a bias with the same polarity as the bias during normal image formation and a smaller absolute value when compared under substantially the same other conditions (same environment, same primary transfer roller usage history, etc.).Typically, when forming a toner strip in an inter-paper process as in this embodiment, one can compare the primary transfer bias when the toner strip is passing through the primary transfer section N1 with the primary transfer bias when at least one of the image forming region preceding or following the toner strip is passing through the primary transfer section N1.

[0063] Figure 8 is a graph illustrating an example of the relationship between primary transfer current and primary transfer efficiency. Primary transfer efficiency indicates what percentage (by weight) of toner on the photosensitive drum 1 can be transferred to the intermediate transfer belt 6. Figure 8(a) shows the above relationship when a new primary transfer roller 5 is used, and Figure 8(b) shows the above relationship when a primary transfer roller 5 that has been used for 1000k image formation is used. When a new primary transfer roller 5 is used, setting the primary transfer current to 15μA results in a primary transfer efficiency of 40%. 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% of the toner is supplied to the cleaning blade 112. If the toner density on the intermediate transfer belt 6 is too high (too much toner), the fur brushes 122 and 123 may not be able to collect all of the toner, and some may pass through the fur brushes 122 and 123. In that case, it may affect the image formed thereafter, or it may become necessary to rotate the intermediate transfer belt 6 further to collect the toner on the intermediate transfer belt 6. However, in the configuration of this embodiment, once the amount of toner in the toner strip is reduced to 40%, that toner can be collected by the fur brushes 122 and 123 without passing through them. Note that the primary transfer efficiency that allows sufficient toner to be supplied to the fur brushes 122 and 123 while sufficiently suppressing the toner from passing through the fur brushes 122 and 123 is not limited to 40%. This primary transfer efficiency can be, for example, around 20-80%, preferably around 30-70%, and typically around 40-60%.

[0064] Furthermore, as can be seen from (b) in Figure 8, if the cumulative usage of the primary transfer roller 5 increases, the primary transfer efficiency may decrease compared to when the primary transfer roller 5 is 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 regarding the usage history of the primary transfer roller 5, it may be possible to set the primary transfer efficiency when supplying toner to the fur brushes 122 and 123 more appropriately. Typically, the primary transfer bias is set so that the primary transfer current when supplying toner to the fur brushes 122 and 123 is greater when the usage amount of the primary transfer roller 5 is a second amount greater than the first amount, compared to when the usage amount is a first amount. In other words, typically, the primary transfer bias is 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 greater when the usage amount is a second amount greater than the first amount, compared to when the usage amount is a first amount. Furthermore, depending on the configuration and characteristics of the primary transfer roller 5, and the required precision in controlling the primary transfer efficiency from the standpoint of suppressing the collapse of the fur brushes 122 and 123, it is not essential to change the primary transfer current according to the usage history information of the primary transfer roller 5.

[0065] Furthermore, the primary transfer efficiency setting when supplying toner to the fur brushes 122 and 123 may be changed depending on the image ratio of the image formed before supplying toner to the fur brushes 122 and 123. For example, if the setting of the image ratio for a low-duty image (specifically, the toner degradation threshold Vt mentioned above) 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, which drops the primary transfer efficiency to 30%. Typically, the primary transfer bias is set such that the primary transfer efficiency when supplying toner to the fur brushes 122 and 123 is lower when the image ratio for a low-duty image is a second image ratio higher than the first image ratio compared to the first image ratio. In other words, typically, the primary transfer bias is set such that the primary transfer current (absolute value of the primary transfer bias) when supplying toner to the fur brushes 122 and 123 is lower when the image ratio for a low-duty image is a second image ratio higher than the first image ratio compared to the first image ratio.

[0066] Furthermore, as mentioned above, toner strips can be formed, for example, between sheets of paper while a job is running. The number of times toner strips are formed between sheets of paper can be determined by how many low-duty images have been formed. For example, if 100 low-duty images have been formed, the system can be set to form toner strips between sheets of paper while the next 100 images are being formed.

[0067] Furthermore, it can be advantageous to control the primary transfer current to be approximately constant regardless of the environment during the operation of supplying toner to the fur brushes 122 and 123. In other words, according to the inventors' studies, the bristles of the fur brushes 122 and 123 tend to collapse in high-temperature and high-humidity environments. Therefore, in high-temperature and high-humidity environments, it is desirable to supply more toner to the fur brushes 122 and 123 than in low-temperature and low-humidity environments or normal temperature and normal humidity environments. On the other hand, in high-temperature and high-humidity environments, the amount of charge on the toner on the photosensitive drum 1 decreases, so the value of the primary transfer current required to transfer the same amount of toner from the photosensitive drum 1 to the intermediate transfer belt 6 is small. Therefore, if approximately the same primary transfer current is supplied to the primary transfer section N1 when the toner strip passes through the primary transfer section N1, more toner will be transferred to the intermediate transfer belt 6 in a high-temperature and high-humidity environment than in a low-temperature and low-humidity environment or normal temperature and normal humidity environment. In this way, by simple control such as controlling the primary transfer current to be approximately constant 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 suppresses the collapse of the fur brushes 122 and 123, which is likely to occur in a high-temperature, high-humidity environment. The high-temperature, high-humidity environment is, for example, 30°C, 70%RH; the low-temperature, low-humidity environment is, for example, 23°C, 10%RH; and the normal temperature, normal humidity environment is, for example, 23°C, 50%RH. The environment may also be at least one of the temperature or humidity inside or outside the image forming apparatus 100. The image forming apparatus 100 usually has an environmental sensor (temperature sensor, humidity sensor, temperature and humidity sensor, etc.) 90 (Figure 3) as an environmental sensing means for detecting the environment, such as for controlling process conditions. 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 ambient temperature and humidity detected by, for example, an environmental sensor (which may also be the absolute amount of moisture determined from the temperature and humidity).

[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. Figure 9 is a flowchart illustrating the outline of this control procedure. Here, we take the example of a case where an ejection operation is performed in the inter-paper process during job execution, and the toner of the toner band formed by the ejection operation is supplied to the fur brushes 122 and 123. However, as mentioned above, the timing of the operation to supply toner to the fur brushes 122 and 123 is not limited to the inter-paper process. 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 ejection operation.

[0069] When the control unit 50 starts image formation for a job (S101), it obtains image duty information from the image processing unit 60 and stores the acquisition result in the RAM 52 (S102). Next, the control unit 50 determines whether or not to perform a ejection operation (supplying toner to the fur brushes 122 and 123) based on the acquisition result of the image duty information (S103). If the control unit 50 determines in S103 not to perform the ejection operation (No in S103), it proceeds to the process in S107. If the control unit 50 determines in S103 to perform the ejection operation (Yes in S103), it calculates the amount of toner to be ejected in the ejection operation based on the acquisition result of the image duty information (S104). The processes in S103 and S104 can be specifically performed according to the example of ejection operation control described above.

[0070] Next, the control unit 50 sets the primary transfer current during the ejection operation (S105). In this embodiment, information showing the relationship between the usage history of the primary transfer roller 5 and the setting of the primary transfer current that can obtain a predetermined primary transfer efficiency is pre-set as a table and stored in the ROM 53. The control unit 50 sets the primary transfer current based on the information showing the usage history of the primary transfer roller 5 obtained from the parts counter 80 and the information showing the above relationship stored in the ROM 53. Next, the control unit 50 forms a toner strip on the photosensitive drum 1 in the inter-paper process and applies a primary transfer bias so that the primary transfer current set in S105 flows, and controls the toner of the toner strip to be sent to the fur brushes 122 and 123 (S106). Also in S106, the control unit 50 controls the number of images formed using the sheet counter 70 each time the ejection operation is performed until the required amount of toner has been ejected. Next, the control unit 50 determines whether the formation of all images in the job has been completed (S107). If the control unit 50 determines in S107 that image formation is not yet complete (No in S107), it returns to the process in S101 to perform subsequent image formation. If the control unit 50 determines in S107 that image formation is complete (Yes in S107), it terminates the job.

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

[0072] Thus, in this embodiment, the image forming apparatus 100 includes a rotatable image carrier (photosensitive drum) 1 that carries a toner image, an image forming means (charging device 2, exposure device 3, developing device 4, etc.) that forms a toner image on the image carrier 1, a rotatable intermediate transfer belt 6 onto 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 in the primary transfer section N1, a primary transfer power supply 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 section N2 that transfers the toner image from the intermediate transfer belt 6 to the recording material P. The device includes a brush (e.g., a first fur brush) 122 that contacts the intermediate transfer belt 6 downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 in the rotational direction of the intermediate transfer belt 6 to form a cleaning section (e.g., a first cleaning section) CL1 and remove 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 section 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 perform a predetermined operation (discharge operation) in which a predetermined toner image (toner band) is formed in an area on the image carrier where a toner image to be transferred to the recording material P is not formed, and transfers at least a portion of the toner of the predetermined toner image to the intermediate transfer belt 6 to reach the cleaning unit CL1. 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 with 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, and with an absolute value smaller than the primary transfer bias.

[0073] In this embodiment, the control unit 50 controls the execution of a continuous image formation job in which images are formed consecutively on multiple recording materials P, to form the predetermined toner image in the region (between the sheets) between the image formation region where a toner image to be transferred to the preceding recording material P can be formed and the image formation region where a toner image to be transferred to the next recording material P can be formed. Furthermore, the control unit 50 can control the execution of the predetermined operation if a job is executed to form an image with a first image ratio on a predetermined number of recording materials P, and to execute the predetermined operation if a job is executed to form an image with a second image ratio lower than the first image ratio on a predetermined number of recording materials P. In addition, 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 is passing through the primary transfer section N1 in the predetermined operation, based on information regarding the usage history of the primary transfer member 5. In this case, the control unit 50 can control the system so that 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 is passing through the primary transfer unit N1 is larger when the amount of use of the primary transfer member 5 from new, as indicated by the usage history information, is a second amount greater than the first amount of use. Furthermore, the image forming apparatus 100 may have an environmental detection means (environmental sensor) 90 that detects the environment, which is at least one of the temperature or humidity inside or outside the image forming apparatus 100, and the control unit 50 may control the value of the current that flows when a primary transfer bias is 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, so that it is substantially constant regardless of the environment detected by the environmental detection means.

[0074] As explained above, this embodiment makes it possible to suppress the collapse of the bristles of the fur brushes 122 and 123 that clean the intermediate transfer belt 6. In other words, when a low-duty image is formed, a toner strip is formed between the sheets of paper according to the number of sheets, for example, thereby suppressing the decrease in the outer diameter of the fur brushes 122 and 123 and extending the lifespan of the belt cleaning device 12 (fur brushes 122 and 123). In this embodiment, by using the toner from the toner strip formed by the discharge operation as the toner supplied to the fur brushes 122 and 123, the collapse of the bristles of the fur brushes 122 and 123 can be efficiently suppressed. Furthermore, in this embodiment, by setting the primary transfer bias to a weakly positive bias when the toner strip is first transferred to the intermediate transfer belt 6, it is possible to suppress toner leakage caused by too much toner being supplied to the fur brushes 122 and 123.

[0075] [Example 2] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in 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 in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0076] In Example 1, it was explained that the toner used to supply to the fur brushes 122 and 123 is the toner from the toner strip formed by the ejection operation.

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

[0078] The drum cleaning device 11 can properly clean the surface of the photosensitive drum 1 by having toner (more specifically, toner additives) function as a lubricant at the contact point between the cleaning blade 112 and the photosensitive drum 1. When the toner (more specifically, toner additives) at the contact point 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 "peeling" of the cleaning blade 112. "Chattering" is a phenomenon in which the cleaning blade 112 vibrates, causing abnormal noise and poor cleaning. "Peeling" is a phenomenon in which the tip of the cleaning blade 112 peels back on the downstream side in the direction of movement of the surface of the photosensitive drum 1, causing poor cleaning.

[0079] Furthermore, if the toner (more specifically, its external additives) at the contact point between the cleaning blade 112 and the photosensitive drum 1 is depleted, a phenomenon called "toner fusion" may occur, in which the toner present near the contact point melts and adheres to the surface of the photosensitive drum 1. In other words, normally, a deposit of the toner's external additives (a blocking layer) is formed near the contact point, suppressing the toner from penetrating that area. As a result, the temperature rise of the toner is suppressed, and the occurrence of toner fusion is inhibited. However, if the blocking layer decreases, toner is more likely to penetrate the area near the contact point, which is heated by friction between the photosensitive drum 1 and the cleaning blade 112. Then, for example, in a high-temperature, high-humidity environment, toner fusion may occur, in which the toner that has penetrated the area near the contact point melts and adheres to the surface of the photosensitive drum 1.

[0080] Here, the toner in the toner strip formed by the ejection operation described in Example 1 is supplied to the contact area between the photosensitive drum 1 and the cleaning blade 112, thereby supplying a lubricant between them or forming a barrier layer.

[0081] In addition to the ejection operation, to suppress the increase in frictional force ("chatter" and "peeling") as described above, 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. This operation can be performed, similar to the ejection operation, when low-duty images are continuously formed. Here, this operation is also called the "lubrication operation." In addition to the ejection operation, to suppress the problem of toner melting and sticking to the photosensitive drum 1 ("toner fusion") as described above, 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. 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 called the "fusion suppression operation." The toner in the toner band formed by these "lubrication operation" and "fusion suppression operation" may be used as toner supplied to the fur brushes 122 and 123.

[0082] In this way, the toner in the toner strip formed by the "ejection operation," "lubrication operation," and "fusion 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 supply to the fur brushes 122 and 123. This allows for efficient toner supply 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 strip can be determined according to 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 is supplied to each (Figure 7).

[0084] Next, an example of the job control procedure in this embodiment will be explained using the flowchart diagram in Figure 10. Here, we will take the example of a case in which a fusion suppression operation is performed in the inter-paper process during job execution, and the toner of the toner strip 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 obtains image duty information from the image processing unit 60 and stores the acquisition result in the RAM 52 (S202). Next, the control unit 50 determines whether or not to perform a fusion suppression operation (supplying toner to the drum cleaning device 11 and the belt cleaning device 12) based on the acquisition result of the image duty information (S203). If the control unit 50 determines in S203 not to perform the fusion suppression operation (No in S203), it proceeds to the process in S207. If the control unit 50 determines in S203 to perform the fusion suppression operation (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 acquisition result of the image duty information (S204). The processes in S203 and S204 can be performed, for example, in accordance with the example of controlling the ejection operation described in Embodiment 1. For example, a threshold can be set in advance from the perspective of suppressing toner fusion to determine whether to perform the fusion suppression operation. Also, a threshold can be set in advance from the perspective of suppressing the collapse of the fur brushes 122 and 123 to determine whether to supply toner to the fur brushes 122 and 123 (in this case, the fusion suppression operation). For example, the fusion suppression operation should be performed if it is determined that it should be performed in at least one of these cases. Furthermore, similar to the ejection operation described in Example 1, the number of times toner strips are formed between the paper can be determined by how many low-duty images are formed. The required amount of toner can be determined in advance in relation to the conditions for determining whether toner strip formation is necessary (such as the threshold mentioned above). Here, the example shows the case where the toner of the toner strip formed by the fusion suppression operation is supplied to both the drum cleaning device 11 and the belt cleaning device 12, but the same applies when using the toner of the toner strip formed by the ejection operation or the lubrication operation.

[0086] Next, in order to secure the necessary amount of toner for the fur brushes 122 and 123, the control unit 50 calculates the required primary transfer efficiency based on the relationship between primary transfer efficiency and primary transfer current stored in the ROM 53 (Figure 8), and calculates the primary transfer current required to obtain that primary transfer efficiency (S205). At this time, as in Example 1, the primary transfer current can be set while also considering the usage history of the primary transfer roller 5. Next, the control unit 50 forms a toner strip on the photosensitive drum 1 in the inter-paper process, applies a primary transfer bias so that the primary transfer current set in S205 flows, and controls the toner of the toner strip to be sent to the cleaning blade 112 and fur brushes 122 and 123 (S206). Also in S206, the control unit 50 controls the sheet counter 70 to count the number of images formed until the supply of the required amount of toner is finished. Next, the control unit 50 determines whether or not the formation of all images in the job has been completed (S207). If the control unit 50 determines in S207 that image formation is not yet complete (No in S207), it returns to the process in S201 to perform subsequent image formation. If the control unit 50 determines in S207 that image formation is complete (Yes in S207), it terminates the job.

[0087] Thus, the image forming apparatus 100 has a cleaning member (cleaning blade) 112 that is provided to contact the image carrier 1 and removes toner from the image carrier 1, and in a predetermined operation (such as a fusion suppression operation) that brings the toner to the cleaning section 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 is passing through the primary transfer section N1 in the predetermined operation, so that the ratio of the toner of the predetermined toner image that reaches the cleaning section CL1 (fur brush 122) and 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 Embodiment 1, it is possible to suppress the collapse of the bristles of the fur brushes 122 and 123 that clean the intermediate transfer belt 6. According to this embodiment, toner can be efficiently supplied to both the drum cleaning device 11 (cleaning blade 112) and the belt cleaning device 12 (fur brushes 122 and 123). In addition, in this embodiment, similar to Embodiment 1, by setting the primary transfer bias to a weakly positive bias when the toner strip is first transferred to the intermediate transfer belt 6, it is possible to suppress toner leakage caused by too much toner being supplied to the fur brushes 122 and 123.

[0089] [Example 3] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in 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 in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0090] Figure 11 is a schematic diagram illustrating the movement of toner in the primary transfer section N1 during the operation of supplying toner to the fur brushes 122 and 123 of this embodiment. Figure 11(a) shows the toner strip T' formed on the photosensitive drum 1 by the developing device 4 as it enters the primary transfer section N1. Figure 11(b) shows the state after the toner strip T' has passed through the primary transfer section N1.

[0091] In Examples 1 and 2, as shown in Figure 7(a), a weak positive bias was applied to the primary transfer roller 5 by the primary transfer power supply E1 when the toner strip T' passed through the primary transfer section N1. In contrast, in this embodiment, as shown in Figure 11(a), the location that was a negative power supply (negative bias output section) in Figure 7(a) has been changed to ground. In other words, in this embodiment, when the toner strip T' passes through the primary transfer section N1, the primary transfer roller 5 is connected to ground (electrically grounded). As a result, costs can be reduced because there is no negative power supply.

[0092] In this embodiment, the image forming apparatus 100 is configured to transfer the toner of the toner strip T' onto 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 acting as a biasing means. By adjusting the force of this spring, the amount of toner transferred to the intermediate transfer belt 6 can be adjusted. Increasing the force of this spring increases the amount of toner transferred to the intermediate transfer belt 6, while decreasing it decreases it. In this embodiment, for example, the force of this spring is pre-adjusted (set) so that the primary transfer efficiency is approximately 40%.

[0093] As a result, as shown in Figure 11(b), in this embodiment as well, the amount of toner DT' on the photosensitive drum 1 and the amount of toner BT' on the intermediate transfer belt 6 are equal. The toner DT' on the photosensitive drum 1 is recovered by the drum cleaning device 11. On the other hand, the toner BT' on the intermediate transfer belt 6 is passed through the secondary transfer section N2 and sent to the belt cleaning device 12, where it is recovered. This supplies toner to the fur brushes 122 and 123.

[0094] In this embodiment, the primary transfer roller 5 is connected to ground, but it may also be connected to a positive power supply and its output set to 0V. Furthermore, the configuration of this embodiment may be combined with either Embodiment 1 or Embodiment 2.

[0095] Thus, in this embodiment, the control unit 50 controls the primary transfer bias (potential of the primary transfer member 5) applied to the primary transfer member 5 to 0V during a predetermined operation (such as an ejection operation) that brings the toner to the cleaning unit CL1 (i.e., the fur brush 122), while the predetermined toner image formed on the image carrier 1 is passing through the primary transfer unit N1.

[0096] As described above, the same effects as in Examples 1 and 2 can be obtained with the configuration of this embodiment.

[0097] [Example 4] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in 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 in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0098] In Examples 1 and 2, a toner strip was formed on the photosensitive drum 1 during the inter-paper process, and the toner from this toner strip was supplied to the fur brushes 122 and 123. Alternatively, the toner could be supplied to the fur brushes 122 and 123 in batches, for example, periodically.

[0099] For example, the fixing device 30 may develop uneven gloss or streaks in the image due to changes in the surface shape of the fixing member caused by image formation. To counteract this, the image forming apparatus 100 may be configured to perform a fixing refresh operation in which an abrasive member is periodically pressed against the belt constituting the fixing member of the fixing device 30 to smooth the surface of the belt. Since image formation is stopped during the fixing refresh operation, during this time, for example, a toner strip with a toner amount corresponding to the number of low-duty images can be sent to the fur brushes 122 and 123 all at once. This makes it possible to supply the fur brushes 122 and 123 with an amount of toner equivalent to the amount supplied to the fur brushes 122 and 123 in multiple inter-paper processes in Examples 1 and 2 while image formation is stopped.

[0100] In this case as well, by applying a weakly positive bias to the primary transfer roller 5, the toner from the toner strip can be supplied to both the drum cleaning device 11 (cleaning blade 112) and the belt cleaning device (fur brushes 122, 123). Alternatively, as in Example 3, the toner from the toner strip 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.

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

[0102] In this way, the control unit 50 can be controlled to perform a predetermined operation to deliver toner to the cleaning unit CL1 (i.e., the fur brush 122) during the period when it 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, other embodiments 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 Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0104] Figure 12 is a schematic cross-sectional view of the image forming apparatus 100' of this embodiment. The image forming apparatus 100' of this embodiment is a tandem type printer (color printer) employing an intermediate transfer method that is capable of forming full-color images using an electrophotographic method.

[0105] The image forming apparatus 100' has four image forming units (stations) 10Y, 10M, 10C, and 10K, which form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Elements in each image forming unit 10Y, 10M, 10C, and 10K that have the same or corresponding function or configuration are denoted by the letters Y, M, C, and K at the end of their symbols to indicate that they are elements for one of the respective colors.

[0106] In this embodiment, for example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 1Y, 1M, 1C, and 1K are sequentially transferred onto the intermediate transfer belt 6 so as to be superimposed. In this embodiment, the belt cleaning device 12 is positioned downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 (the uppermost primary transfer section N1Y) in the rotational direction of the intermediate transfer belt 6, and in particular, it is positioned facing the drive roller 22 via the intermediate transfer belt 6.

[0107] As described above, the image forming apparatus 100 of Example 1 is a monochrome printer configured by retaining only the parts and units necessary for black monochrome image formation from the parts and units of the image forming apparatus 100' of this embodiment. For example, in the image forming apparatus 100 of Example 1, the elements of the color image forming sections 10Y, 10M, and 10C of the image forming apparatus 100' of this embodiment have been removed. However, the primary transfer position (primary transfer section N1) and secondary transfer position (secondary transfer section N2) for black in the main body of the image forming apparatus 100 and 100' of this embodiment are the same.

[0108] As mentioned above, in the relationship between such a multicolor image forming apparatus and a monocolor image forming apparatus, the monocolor image forming apparatus has less residual toner on the intermediate transfer belt 6 sent to the belt cleaning device 12 compared to the multicolor image forming apparatus. Therefore, in a monocolor image forming apparatus with such a configuration, when an image with a low image ratio is formed, the bristles of the fur brush tend to be more prone to flattening. Thus, the effects of the present invention are particularly pronounced in a monocolor image forming apparatus with such a configuration. However, the present invention can also be applied to a multicolor image forming apparatus such as the image forming apparatus 100' of this embodiment.

[0109] In this embodiment, the decision to perform the ejection operation, lubrication operation, and fusion suppression operation described in the above embodiment may be made for each image forming unit 10Y, 10M, 10C, and 10K. When it is determined that these operations are necessary in at least one image forming unit, the operations can be performed in at least one (or all) image forming units, including that unit. At that time, the toner of the toner strip 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 embodiment. The decision 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, will be described by reference to the above embodiment.

[0110] Thus, the image forming apparatus may have a plurality of image forming units 10 each equipped with an image carrier 1, image forming means (charging device 2, exposure device 3, developing device 4, etc.), and a primary transfer member 5, and in a predetermined operation to bring toner to the cleaning unit CL1 (i.e., the fur brush 122), a predetermined toner image (toner band) may be formed on the image carrier 1 of at least one of the plurality of image forming units 10.

[0111] As described above, the present invention can also be applied to multi-color image forming apparatuses, and the same effects as those in the above-described embodiments 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 embodiments described above.

[0113] In the above-described embodiment, toner for a predetermined toner image formed in predetermined operations such as ejection, lubrication, and fusion suppression operations, which are used to suppress problems that may occur when low-image-ratio images are formed on areas other than the fur brush, was supplied to the fur brush. As a result, as described above, the collapse of the fur brush bristles can be efficiently suppressed. However, if the amount of toner supplied to the fur brush becomes insufficient due to such operations, a special operation to supply toner to the fur brush may be performed. In this case, a toner image of a density sufficient to sufficiently suppress the toner from passing through the fur brush (corresponding to the toner band in the above-described embodiment) is formed on the photosensitive drum, and can be transferred to the intermediate transfer belt by applying a primary transfer bias equivalent to that during normal image formation. For example, this toner image is preferably a halftone image with a density of 30-70% when the density of a solid image is 100%, and is typically a halftone image with a density of 40-60%.

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

[0115] Furthermore, in the above-described embodiment, the toner image transferred to the intermediate transfer belt in order to supply toner to the fur brush was a band-shaped toner image that covered the entire image-forming region in the width direction of the intermediate transfer belt (the direction of the rotation axis of the photosensitive drum), but it is not limited to this. This toner image only needs to be able to supply sufficient toner to the fur brush and sufficiently suppress the collapse of the fur brush bristles. This toner image may, for example, be a toner image with a width narrower than the image-forming region in the width direction of the intermediate transfer belt. Also, this toner image may be divided into multiple parts in, for example, the width direction of the intermediate transfer belt or the direction of movement of the surface of the intermediate transfer belt.

[0116] Furthermore, in the above-described embodiment, the brush used to remove toner from the intermediate transfer belt was composed of a rotatable brush roller, but it may also be a brush (such as a deck brush) that is fixedly positioned on the intermediate transfer belt with a certain amount of penetration. [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 Blades 122 First fur brush 123 Second fur brush

Claims

1. A rotatable image carrier that holds a toner image, 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 the toner image from the image carrier to the intermediate transfer belt in the primary transfer section, A primary transfer power supply for applying a primary transfer bias to the primary transfer member, A secondary transfer member that forms a secondary transfer section for transferring 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 section and upstream of the primary transfer section in the rotational direction of the intermediate transfer belt to form a cleaning section and removes toner from the intermediate transfer belt, The cleaning unit is equipped with a cleaning power supply that applies a cleaning bias to the brush to recover toner from the intermediate transfer belt, The image forming means and the control unit capable of controlling the primary transfer power supply, It has, 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 the recording material is not formed, and to transfer at least a portion of the toner of the predetermined toner image to the intermediate transfer belt so that it reaches the cleaning unit. The image forming apparatus is characterized in that, in the predetermined operation, the control unit controls the primary transfer bias applied to the primary transfer member while the predetermined toner image formed on the image carrier is passing through the primary transfer section to be a bias with the same polarity as the primary transfer bias when transferring the toner image to be transferred to the recording material from the image carrier to the intermediate transfer belt, and having an absolute value smaller than the primary transfer bias, or to 0V.

2. The image forming apparatus according to claim 1, characterized in that the control unit controls the process to form the predetermined toner image in the region between the image forming region where a toner image to be transferred to the preceding recording material can be formed and the image forming region where a toner image to be transferred to the next recording material can be formed, during the execution of a continuous image forming job in which images are to be formed on a plurality of recording materials in succession.

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

4. The image forming apparatus according to claim 1, characterized in that the control unit does not perform the predetermined operation when it performs a job to form an image with a first image ratio on a predetermined number of recording materials, and performs the predetermined operation when it performs a job to form an image with a second image ratio lower than the first image ratio on a predetermined number of recording materials.

5. The image forming apparatus according to claim 1, characterized in that the control unit changes the primary transfer bias applied to the primary transfer member while the predetermined toner image formed on the image carrier in the predetermined operation is passing through the primary transfer section, based on information regarding the usage history of the primary transfer member.

6. The image forming apparatus according to claim 5, characterized in that the control unit controls the primary transfer bias applied to the primary transfer member during the predetermined operation while the predetermined toner image formed on the image carrier passes through the primary transfer section to be larger when the amount of use is a second amount which is greater than the first amount of use, as indicated by the information regarding the usage history.

7. The image forming apparatus has an environmental detection means for detecting the environment, which is at least one of the temperature or humidity inside or outside the apparatus. The image forming apparatus according to claim 1, characterized in that 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 predetermined toner image formed on the image carrier passes through the primary transfer section in the predetermined operation, so that it is substantially constant regardless of the environment detected by the environment detection means.

8. The image forming apparatus according to claim 1, comprising a cleaning member provided so as to contact the image carrier and for removing toner from the image carrier, wherein in the predetermined operation, at least a portion of the toner of the predetermined toner image reaches the contact portion between the image carrier and the cleaning member.

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

10. The image forming apparatus according to any one of claims 1 to 9, characterized in that it has only one image forming unit comprising the image carrier, the image forming means, and the primary transfer member.

11. The image forming apparatus according to any one of claims 1 to 9, wherein it has a plurality of image forming units each comprising the image carrier, the image forming means and the primary transfer member, and in the predetermined operation, the predetermined toner image is formed on the image carrier of at least one of the plurality of image forming units.

12. The image forming apparatus according to any one of claims 1 to 9, characterized in that the predetermined toner image is a solid image formed over substantially the entire area of ​​the image forming region in a direction substantially perpendicular to the direction of movement of the surface of the image carrier.

13. The image forming apparatus according to any one of claims 1 to 9, characterized in that the brush is a rotatable brush roller.

Images