Image forming apparatus

Abstract

To effectively remove back-accumulated toner accumulated on the back face of a cleaning blade to prevent the occurrence of a lateral streak image even when executing a job to form a high printing rate image and a job to form a large number of images.SOLUTION: An image forming apparatus 100 has: an image carrier 7; transfer means 9; a cleaning blade 82; a driving unit 22 that can rotate the image carrier 7 in a normal rotation direction and a reverse rotation direction; and a control unit 120 that can control the driving unit 22 to perform a normal rotation operation and a reverse rotation operation of the image carrier. The control unit 120 can perform control to continuously execute multiple times a reverse-normal rotation sequence of performing the reverse rotation operation and subsequently performing the normal rotation operation after the end of a job, and subsequently stop the image carrier 7, and when continuously executing the reverse-normal rotation sequence multiple times, performs control so that the amount of movement of the image carrier 7 in the normal rotation operation after the reverse rotation operation becomes larger than the amount of movement of the image carrier 7 in the next reverse rotation operation.SELECTED DRAWING: Figure 9

Description

Technical Field

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

Background Art

[0002] In an image forming apparatus using an electrophotographic method or the like, after transferring a toner image from an image carrier such as a photoreceptor or an intermediate transfer body to a transfer body, a blade cleaning method is widely adopted to remove the toner remaining on the surface of the image carrier (transfer residual toner) with a cleaning blade. The cleaning blade is a plate-like member formed of an elastic material such as urethane rubber, and is arranged to contact the surface of the image carrier so as to be in a counter direction with respect to the moving direction of the surface of the image carrier during image formation. Regarding the positional relationship of the contact portion between the image carrier and the cleaning blade, "upstream" and "downstream" mean "upstream" and "downstream" with respect to the moving direction of the surface of the image carrier during image formation. Further, the rotation in the rotation direction of the image carrier during image formation is called "forward rotation", and the rotation in the reverse direction is called "reverse rotation".

[0003] In the blade cleaning method, recovered toner containing foreign substances such as transfer residual toner and paper dust accumulates on the upstream side of the cleaning nip, which is the contact portion (nip portion) between the image carrier and the cleaning blade. When image formation is repeated, foreign substances such as paper dust contained in the accumulated recovered toner may be sandwiched in the cleaning nip. Therefore, after image formation is completed and the forward rotation operation of the image carrier is completed, a method of removing foreign substances such as paper dust sandwiched in the cleaning nip by performing a reverse rotation operation of the image carrier is known (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Incidentally, when the cleaning blade scrapes off residual toner from the image carrier, a small amount of toner may slip through the cleaning nip and wrap around to the back of the cleaning blade due to minute vibrations of the cleaning blade. Here, this toner is called "backside toner." As image formation is repeated, backside toner accumulates on the surface of the cleaning blade facing the image carrier downstream of the cleaning nip (here, also simply called the "backside surface of the cleaning blade"). When the backside toner accumulated on the backside surface of the cleaning blade adheres to the image carrier and is transferred to the recording material, it can cause a streaky image defect, which is a horizontal streak image that runs in a direction approximately perpendicular to the transport direction of the recording material (the longitudinal direction of the cleaning blade).

[0006] By performing the reverse rotation motion of the image carrier as described above, the tip of the cleaning blade is pulled by the image carrier, changing its orientation, and the toner accumulated on the back surface of the cleaning blade is pressed against the image carrier and ejected onto the image carrier. Therefore, it is considered effective to perform the reverse rotation motion of the image carrier after the completion of image formation in order to suppress the occurrence of lateral streaks in images caused by the toner accumulated on the back surface of the cleaning blade inadvertently adhering to the image formation area on the image carrier during image formation.

[0007] However, especially when performing jobs that produce high-print-rate images or jobs with a large number of images to be formed, the amount of toner that accumulates on the back surface of the cleaning blade increases. In such cases, a single reverse rotation may not be enough to discharge the toner onto the image carrier. This undischarged toner may then cause lateral streaks to continuously appear in subsequent image formation.

[0008] To address these challenges, one possible approach is to repeatedly rotate the image carrier in the reverse and forward directions to adequately expel the toner accumulated on the back surface of the cleaning blade. However, simply repeating the reverse and forward rotation of the image carrier multiple times may cause the expelled toner to re-adhere to the back surface of the cleaning blade, potentially leading to unintentional adhesion to the image carrier during subsequent image formation.

[0009] Therefore, the objective of the present invention is to effectively remove back-flow toner accumulated on the back surface of the cleaning blade and suppress the occurrence of horizontal streaks, even when performing jobs that form high-print-rate images or jobs that form a large number of images. [Means for solving the problem]

[0010] The above objective is achieved by the image forming apparatus according to the present invention. In summary, according to one aspect of the present invention, a rotatable image carrier that carries a toner image on its surface and a transfer unit that transfers the toner image from the image carrier, which rotates in the forward rotation direction, to a transfer target. component The device comprises: a cleaning blade that contacts the surface of the image carrier to form a contact portion and removes toner from the surface of the image carrier as it rotates in the forward direction; a drive unit capable of rotating the image carrier in the forward direction and in the reverse direction; and a control unit capable of controlling the drive unit to perform a forward rotation operation, which is the rotation of the image carrier in the forward direction, and a reverse rotation operation, which is the rotation of the image carrier in the reverse direction, and the control unit, at the end of a job in which a toner image is transferred from the image carrier to the transfer target, A series of actions, The forward rotation operation is performed after the reverse rotation operation. Action Execute multiple times A mode is available in which a series of operations are performed, and after the series of operations are performed, the image carrier is stopped. And, The series of operations includes a first reverse rotation operation which is the first reverse rotation operation performed in the series of operations, a first forward rotation operation which is the next forward rotation operation performed after the first reverse rotation operation, a second reverse rotation operation which is the last reverse rotation operation performed in the series of operations, and a second forward rotation operation which is the next forward rotation operation performed after the second reverse rotation operation. When the position of the image carrier that was located at the contact portion at the end of the first reverse rotation operation is defined as the first position, the control unit controls the drive unit so that the first position does not return to the contact portion from the end of the first forward rotation operation until the end of the second forward rotation operation, and controls the drive unit so that the amount of movement of the image carrier in the second forward rotation operation is smaller than the amount of movement of the image carrier in the second reverse rotation operation. Image forming apparatus characterized by is provided . According to another aspect of the present invention, the present invention comprises: a rotatable image carrier that carries a toner image on its surface; a transfer member in a transfer unit that transfers a toner image from the image carrier, which rotates in the forward direction, to a transfer target; a cleaning blade that contacts the surface of the image carrier to form a contact portion and removes toner from the surface of the image carrier, which rotates in the forward direction; a drive unit capable of rotating the image carrier in the forward direction and in the reverse direction opposite to the forward direction; and a control unit capable of controlling the drive unit to perform a forward rotation operation, which is a rotation operation of the image carrier in the forward direction, and a reverse rotation operation, which is a rotation operation of the image carrier in the reverse direction, wherein the control unit can execute a mode in which, at the end of a job of transferring a toner image from the image carrier to the transfer target, a series of operations in which the reverse rotation operation is performed followed by the forward rotation operation is performed multiple times, and after the series of operations is performed the image carrier is stopped. The provided image forming apparatus is characterized in that the series of operations includes a first reverse rotation operation which is the first reverse rotation operation performed in the series of operations, a first forward rotation operation which is the next forward rotation operation performed after the first reverse rotation operation, a second reverse rotation operation which is the last reverse rotation operation performed in the series of operations, and a second forward rotation operation which is the next forward rotation operation performed after the second reverse rotation operation, and the control unit controls the drive unit such that the first amount of movement, which is the sum of the amounts of movement of the image carrier in the forward rotation operation performed after the first reverse rotation operation in the series of operations, is greater than the second amount of movement, which is the sum of the amounts of movement of the image carrier in the reverse rotation operation performed after the first reverse rotation operation in the series of operations, and the amount of movement of the image carrier in the second forward rotation operation is smaller than the amount of movement of the image carrier in the second reverse rotation operation. [Effects of the Invention]

[0011] According to the present invention, even when a job for forming a high print rate image or a job with a large number of image formation sheets is executed, the reverse toner deposited on the back surface of the cleaning blade can be effectively removed to suppress the occurrence of horizontal streak images.

Brief Description of the Drawings

[0012] [Figure 1] It 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 schematic diagram for explaining the movement of the reverse toner. [Figure 4] It is a schematic block diagram showing the control mode of the image forming apparatus. [Figure 5] It is a flowchart showing the procedure of a job. [Figure 6] It is a flowchart showing the procedure for setting the reverse forward rotation control parameters. <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​Figure 1 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 laser beam printer employing an intermediate transfer method that is capable of forming full-color images using an electrophotographic method.

[0015] The image forming apparatus 100 has a plurality of image forming stations, namely the first, second, third, and fourth image forming units PY, PM, PC, and PK. The first, second, third, and fourth image forming units PY, PM, PC, and PK are arranged linearly in this order along the direction of movement of the surface of the intermediate transfer belt 7 during image formation, which will be described later. The first, second, third, and fourth image forming units PY, PM, PC, and PK each form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In addition, elements having the same or corresponding functions or configurations provided in relation to each image forming unit PY, PM, PC, and PK may be described collectively by omitting the Y, M, C, and K at the end of the symbols indicating that they are elements for one of the colors.

[0016] The image forming unit P has a photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor) serving as the first image carrier. The photosensitive drum 1 is rotated in the direction of arrow R1 (clockwise) in Figure 1 by a drum drive unit 21 (Figure 4) which serves as a driving means. The drum drive unit 21 is composed of a drum drive motor as a drive source, a drive transmission member, and the like. The following devices are arranged in order around the photosensitive drum 1. First, a charging roller 2, which is a roller-type charging member serving as a charging means, is arranged. Next, an exposure device (laser scanner) 3 is arranged as an exposure means. Next, a developing device 4 is arranged as a developing means. Next, a primary transfer roller 5, which is a roller-type primary transfer member serving as a primary transfer means, is arranged. Next, a drum cleaning device 6 is arranged as a photoreceptor cleaning means.

[0017] Furthermore, the image forming apparatus 100 has an intermediate transfer belt 7, which is a rotatable intermediate transfer body composed of an endless belt as a second image carrier, facing all of the photosensitive drums 1. The intermediate transfer belt 7 is stretched over a plurality of support rollers (tension rollers), namely drive rollers 71, a first auxiliary roller 72, a second auxiliary roller 73, and a tension roller 74, and is taut with a predetermined tension. The intermediate transfer belt 7 rotates (circumvents) in the direction of arrow R2 (counterclockwise) in Figure 1, as the drive force is transmitted when the drive rollers 71 are rotationally driven by a belt drive unit 22 (Figure 4) which serves as a driving means. The belt drive unit 22 is composed of a belt drive motor as a drive source, a drive transmission member, etc. The drive roller 71 also serves as a secondary transfer opposing roller, which is an opposing member (opposing electrode) of the secondary transfer roller 9 described later. The first and second auxiliary rollers 72 and 73 form a substantially horizontal image transfer surface of the intermediate transfer belt 7. The tension roller 74 applies a predetermined tension to the intermediate transfer belt 7. On the inner circumferential surface (back side) of the intermediate transfer belt 7, the primary transfer rollers 5Y, 5M, 5C, and 5K are positioned opposite each of the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. The primary transfer rollers 5 are pressed toward the photosensitive drum 1 and come into contact with the photosensitive drum 1 via the intermediate transfer belt 7, forming a primary transfer section (primary transfer nip) T1 where the intermediate transfer belt 7 and the photosensitive drum 1 come into contact. The support rollers 72-74, other than the drive roller 71, and each of the primary transfer rollers 5 rotate in conjunction with the rotation of the intermediate transfer belt 7. In addition, on the outer circumferential surface (front side) of the intermediate transfer belt 7, a secondary transfer roller 9, which is a roller-type secondary transfer member serving as a secondary transfer means, is positioned opposite the drive roller 71. The secondary transfer roller 9 is pressed toward the drive roller 71, which also serves as the secondary transfer opposing roller, and contacts the drive roller 71 via the intermediate transfer belt 7, forming a secondary transfer section (secondary transfer nip) T2 where the intermediate transfer belt 7 and the secondary transfer roller 9 are in contact. The secondary transfer roller 9 may rotate in conjunction with the rotation of the intermediate transfer belt 7, or it may be rotationally driven independently of the intermediate transfer belt 7. In addition, a belt cleaning device 8, which serves as an intermediate transfer body cleaning means, is positioned on the outer circumferential surface side of the intermediate transfer belt 7, opposite the tension roller 74.

[0018] Here, the intermediate transfer belt 7 is widely used to be made from rubber or resin material. In this embodiment, the intermediate transfer belt 7 is made from PEEK (polyether ether ketone), a resin material, and is molded into an endless single-layer structure. In this embodiment, the intermediate transfer belt 7 has carbon black dispersed in the resin material base, and for example, has a surface resistivity of 1 × 10⁻⁶ 12 [Ω / □], volume resistivity is 1 × 10⁻⁶ 9 The electrical resistance is adjusted to [Ω·cm]. In addition, a lubricant is applied to the surface of the intermediate transfer belt 7 to reduce initial surface friction resistance. Commonly used lubricants include quinine and zinc stearate. In this embodiment, zinc stearate was applied to the surface of the intermediate transfer belt 7 as a lubricant. By applying a mixture of powdered zinc stearate and a volatile solvent (HEF in this embodiment) in a predetermined ratio, zinc stearate can be efficiently and uniformly applied to the surface of the intermediate transfer belt 7.

[0019] Furthermore, the image forming apparatus 100 includes a feeding unit 15 as a means for feeding the recording material S, and a fixing device 10 as a fixing means for fixing a toner image onto the recording material S.

[0020] During image formation, the photosensitive drum 1 is driven to rotate, and the surface of the rotating photosensitive drum 1 is charged substantially uniformly to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by the charging roller 2. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging roller 2 from a charging power supply (not shown) which serves as a charging voltage application means (charging voltage application unit). With respect to the direction of movement of the surface of the photosensitive drum 1 during image formation, minute gaps are formed between the photosensitive drum 1 and the charging roller 2 on the upstream and downstream sides of the contact area between the photosensitive drum 1 and the charging roller 2. The charging roller 2 then charges the surface of the photosensitive drum 1 by discharge generated in at least one of these upstream and downstream gaps.

[0021] The surface of the electrostatically charged photosensitive drum 1 is scanned and exposed by an exposure device 3 with laser light based on image information, forming an electrostatic latent image (electrostatic image) on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by a developing device 4 when toner is supplied as a developer, forming a toner image (toner image, developer image) on the photosensitive drum 1. The developing device 4 has a developing roller 41 as a developer carrier that carries toner and transports it to the part opposite the photosensitive drum 1. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 41 from a developing power supply (not shown) as a developing voltage application means (developing voltage application unit). In this embodiment, an oscillating voltage, which is a superposition of a DC voltage and an AC voltage, is applied to the developing roller 41 as the developing voltage. In this embodiment, the toner image is formed by image exposure and inversion development. In other words, toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 1, where the absolute value of the potential has decreased due to exposure after being charged almost uniformly. In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0022] The toner image formed on the photosensitive drum 1 is transferred (primary transfer) to the rotating intermediate transfer belt 7, which is the transfer target, in the primary transfer section T1 by the action of the primary transfer roller 5. During primary transfer, a predetermined primary transfer voltage (primary transfer bias), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 5 from a primary transfer power supply (not shown) which is a primary transfer voltage application means (primary transfer voltage application section). For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are transferred onto the intermediate transfer belt 7 in such a way that they are superimposed in each primary transfer section T1.

[0023] The toner image formed on the intermediate transfer belt 7 is transferred (secondary transfer) in the secondary transfer section T2 to the recording material S, which is being transported between the intermediate transfer belt 7 and the secondary transfer roller 9, by the action of the secondary transfer roller 9. During secondary transfer, a predetermined secondary transfer voltage (secondary transfer bias), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 9 from the secondary transfer power supply 31 (Figure 4), which serves as a secondary transfer voltage application means (secondary transfer voltage application unit). In this embodiment, the drive roller 71 is electrically grounded. The recording material (transfer material, recording medium, sheet) S is fed from the feeding unit 15 and supplied to the secondary transfer section T2. ​​The feeding unit 15 is composed of a cassette 12, a feeding roller (pickup roller) 13, a transport roller 14, etc. Note that while ordinary paper, synthetic resin sheets, envelopes, etc., can be used as the recording material S, in this embodiment, the recording material S will be described as ordinary paper. The recording material S is stored in a cassette 12, which is a storage unit. The cassette 12 is detachably located at the bottom of the main body 110 of the image forming apparatus 100. The recording material S is separated one sheet at a time from the cassette 12 by a feeding roller 13, which is a feeding member. The recording material S sent out from the cassette 12 is transported to a pair of registration rollers 16 by a pair of transport rollers 14, which is a transport member. This recording material S is then transported to the secondary transfer unit T2 by the registration rollers 16, in timing with the toner image on the intermediate transfer belt 7.

[0024] The recording material S on which the toner image has been secondarily transferred is transported to the fuser unit 10. The fuser unit 10 is composed of a fuser roller (heating roller) 10a as a fuser member and a pressure roller 10b as a pressure member that presses against the fuser roller. The fuser unit 10 heats and pressurizes the recording material S carrying the unfixed toner image to fix (melt and solidify) the toner image onto the recording material S. The temperature of the fuser unit 10 is determined based on the detection result of an ambient temperature sensor (not shown) and the setting of the paper type (type of recording material S). Generally, if the process speed is the same, the lower the ambient temperature and the larger the basis weight of the set paper type, the higher the temperature of the fuser unit 10 will be set. In this embodiment, plain paper 1, plain paper 2, plain paper 3, etc. can be set as the paper type. For example, the basis weights of these plain paper 1, plain paper 2, and plain paper 3 are 64 to 75 g / m², respectively. 2 76-90g / m 2 91-105 g / m 2 The set temperatures for the fixing device 10 are 190°C, 200°C, and 210°C, respectively, at an ambient temperature of 23°C. After passing through the fixing device 10, the recording material S is discharged (output) to an output tray 11 located outside the main body 110 of the image forming apparatus 100.

[0025] Furthermore, the surface of the photosensitive drum 1 after the primary transfer process is cleaned by a drum cleaning device 6. The drum cleaning device 6 uses a cleaning blade (not shown) positioned in contact with the photosensitive drum 1 to scrape off and remove deposits such as residual toner from the primary transfer from the surface of the rotating photosensitive drum 1, and collect them in a collection container. In addition, the surface of the intermediate transfer belt 7 after the secondary transfer process is cleaned by a belt cleaning device 8. The belt cleaning device 8 uses a cleaning blade 82 positioned in contact with the intermediate transfer belt 7 to scrape off and remove deposits such as residual toner from the secondary transfer from the surface of the rotating intermediate transfer belt 7, and collect them in a collection container. The belt cleaning device 8 will be described in more detail later.

[0026] With this, the series of image formation processes is completed. The consumed toner is then replenished from the toner bottle 16 to the developing device 4.

[0027] 2. Belt cleaning device Next, the belt cleaning device 8 in this embodiment will be described further. Figure 2 is a schematic cross-sectional view of the vicinity of the belt cleaning device 8 in this embodiment (a cross-sectional view approximately perpendicular to the rotation axis direction of the support roller of the intermediate transfer belt 7).

[0028] The belt cleaning device 8 has a recovery container (casing) 81 having an opening 81a on the side of the intermediate transfer belt 7. A cleaning blade 82 is attached to the recovery container 81 via a support member 83, facing the opening 81a. The cleaning blade 82 is a plate-shaped member of a predetermined thickness, having a predetermined length in the longitudinal direction and a predetermined length in the short direction perpendicular to this longitudinal direction, which are arranged along a direction substantially perpendicular to the direction of movement of the surface of the intermediate transfer belt 7 (the width direction of the intermediate transfer belt 7). In this embodiment, the cleaning blade 82 is made of urethane rubber as an elastic material. One end (base end) of the cleaning blade 82 in the short direction is fixed to the support member 83, and this support member 83 is fixed to the recovery container 81. The outer edge portion 82a of the tip of the other end (free end) of the cleaning blade 82 in the short direction is in contact with the surface of the intermediate transfer belt 7 such that it is in a counter-direction with respect to the direction of movement of the surface of the intermediate transfer belt 7 during image formation. In other words, the cleaning blade 82 is in contact with the surface of the intermediate transfer belt 7 with its free end facing upstream in the direction of movement of the surface of the intermediate transfer belt 7 during image formation. The contact point between the cleaning blade 82 and the intermediate transfer belt 7 is the cleaning nip (cleaning section) Q.

[0029] Furthermore, a scrape sheet 84 is attached to the recovery container 81 as a contact member, facing the opening 81a upstream of the cleaning blade 82 with respect to the direction of movement of the surface of the intermediate transfer belt 7 during image formation. The scrape sheet 84 is a sheet-like member of a predetermined thickness, having a predetermined length in the longitudinal direction and a predetermined length in the short direction perpendicular to this longitudinal direction, which are arranged along a direction substantially perpendicular to the direction of movement of the surface of the intermediate transfer belt 7. In this embodiment, the scrape sheet 84 is made of a flexible plastic sheet. One end (base end) of the scrape sheet 84 in the short direction is fixed and supported by the recovery container 81. The tip of the other end (free end) of the scrape sheet 84 in the short direction is in contact with the intermediate transfer belt 7. The tip of the scrape sheet 84 on the free end side is facing downstream in the direction of movement of the surface of the intermediate transfer belt 7 during image formation and is in contact with the intermediate transfer belt 7. The scrape sheet 84 causes the toner scraped off by the cleaning blade 82 to fall into the collection container 81, and also prevents the toner from flowing back towards the intermediate transfer belt 7.

[0030] Furthermore, a transport screw 85 is positioned inside the collection container 81 as a transport member for transporting the toner collected in the collection container 81. The transport screw 85 transports the toner collected in the collection container 81 in a direction substantially perpendicular to the direction of movement of the surface of the intermediate transfer belt 7, and discharges it from the collection container 81 toward a toner recovery box (not shown) separately provided in the image forming apparatus 100.

[0031] 3. Developer In this embodiment, the developing device 4 develops the electrostatic latent image on the photosensitive drum 1 using a two-component developer, which is a mixture of a carrier (magnetic) and a toner (non-magnetic). In this embodiment, a developer was used in which the carrier and toner were mixed in a weight ratio of 91:9 (toner concentration: 9%). In this embodiment, the initial total weight of the developer contained in the developing device 4 was 208g.

[0032] In this embodiment, ferrite particles coated with silicone resin were used as the carrier. This carrier had a saturation magnetization of 24 [Am] for an applied magnetic field of 240 [kA / m]. 2 The value is [ / kg]. Furthermore, this carrier has a resistivity of 1 × 10⁻¹⁰ at an electric field strength of 3000 [V / cm]. 7 [Ω·cm] ~ 1 × 10 8 The pressure is [Ω·cm]. Furthermore, this carrier has a weight-average particle size of 50 μm.

[0033] The toner contains a binder resin, a colorant, and a charge control agent. In this embodiment, a styrene-acrylic resin is used as the binder resin. However, resins such as styrene, polyester, and polyethylene can also be used as the binder resin. As the colorant, one type of pigment or dye may be used alone, or multiple types may be used in combination. The charge control agent may contain a charge control agent for reinforcement as needed. Examples of charge control agents for reinforcement include nigrosine-based dyes and triphenylmethane-based dyes.

[0034] Furthermore, the toner contains wax. The wax is included in the toner to improve release properties and adhesion from the fixing material during fixing. Paraffin wax, carnauba wax, polyolefin, etc., can be used as the wax. The wax is used by kneading and dispersing it in the binder resin. In this example, the toner used was a resin obtained by kneading and dispersing a binder resin, a colorant, a charge control agent, and wax, and then grinding it with a mechanical grinder. The melting point of the wax used in this example is 100°C or lower.

[0035] Furthermore, the toner contains external additives. Examples of external additives include inorganic oxide fine particles such as amorphous silica that has been hydrophobically treated, and titanium compounds such as titanium dioxide. By adding these fine particles to the toner, the powder fluidity and charge level of the toner can be adjusted. The particle size of the external additive particles is preferably 1 nm or more and 100 nm or less. In this example, titanium dioxide with an average particle size of 50 nm was added to the toner at a weight ratio of 0.5 wt%, and amorphous silica with average particle sizes of 2 nm and 100 nm were added to the toner at weight ratios of 0.5 wt% and 1.0 wt%, respectively.

[0036] When the particle size of the toner with the above configuration was measured using the Sysmex FPIA-3000 powder particle size image analyzer, the weight-average particle size was found to be 6.6 μm.

[0037] 4. Image showing horizontal streaks caused by toner on the back of the cleaning blade. Next, we will explain the lateral streaks caused by the toner flowing behind the cleaning blade 82. Figure 3 is a schematic diagram illustrating the movement of the toner flowing behind the cleaning blade 82 (a cross-sectional view approximately perpendicular to the rotation axis direction of the support roller of the intermediate transfer belt 7). Here, the rotation of the intermediate transfer belt 7 in the direction of normal image formation (arrow R2 direction in Figure 3) is called "forward rotation," and that direction is called the "forward rotation direction." Similarly, the rotation of the intermediate transfer belt 7 in the opposite direction to the normal image formation rotation (arrow R3 direction in Figure 3) is called "reverse rotation," and that direction is called the "reverse rotation direction." The same applies to the rotation of the photosensitive drum 1. Also, here, "upstream" and "downstream" in relation to the positional relationship with respect to the cleaning nip Q refer to "upstream" and "downstream" with respect to the forward rotation direction of the intermediate transfer belt 7. In other words, the upstream side of the cleaning nip Q with respect to the rotation direction in which it strikes the cleaning blade 82 in the counter direction is also simply called the "upstream side of the cleaning nip Q." Furthermore, the downstream side of the cleaning nip Q in the rotational direction that strikes the cleaning blade 82 in the counter-direction is also simply called the "downstream side of the cleaning nip Q."

[0038] First, during secondary transfer, most of the toner on the intermediate transfer belt 7 is transferred onto the recording material S. However, some toner that was not transferred (secondary transfer residue toner) remains on the intermediate transfer belt 7 after secondary transfer. This secondary transfer residue toner is transported to the belt cleaning device 8 and scraped off the intermediate transfer belt 7 by the cleaning blade 82. The toner scraped off the intermediate transfer belt 7 is collected in the collection container 81. The toner collected in the collection container 81 is transported by the transport screw 85, discharged from the collection container 81, and transported to a toner collection box (not shown).

[0039] When the cleaning blade 82 scrapes off the secondary transfer residue from the intermediate transfer belt 7, a small amount of toner may seep to the back of the cleaning blade 82 through the gaps created by the minute vibrations of the intermediate transfer belt 7 and the cleaning blade 82. Here, this toner is referred to as "backside toner Ta". As image formation continues, as shown in Figure 3(a), the backside toner Ta accumulates on the surface of the cleaning blade 82 that faces the intermediate transfer belt 7 downstream of the cleaning nip Q ("the back surface of the cleaning blade 82"). In other words, when the intermediate transfer belt 7 is rotating in the forward direction, the outer edge portion 82a of the tip of the cleaning blade 82 is bent as it is pushed downstream by the intermediate transfer belt 7. The backside toner Ta adheres to and accumulates on the back surface of the cleaning blade 82, surrounded by this bent portion. Furthermore, when the toner Ta accumulated on the back surface of the cleaning blade 82 adheres to the intermediate transfer belt 7 and is transferred to the recording material S, there is a possibility that a streaky image, which is a streaky image defect along a direction approximately perpendicular to the transport direction of the recording material S, may occur.

[0040] Furthermore, recovered toner containing foreign matter such as secondary transfer residue and paper dust accumulates upstream of the cleaning nip Q. As image formation continues, foreign matter such as paper dust and wax components contained in the accumulated recovered toner may enter and become trapped in the cleaning nip Q. When this trapped foreign matter deforms the cleaning blade 82 by pushing it up locally, toner may slip through the deformed area, resulting in cleaning failure.

[0041] To remove foreign matter such as paper dust and wax components trapped in the cleaning nip Q, it is effective to rotate the intermediate transfer belt 7 in the reverse direction. When the intermediate transfer belt 7 is rotated in the reverse direction, as shown in Figure 3(b), foreign matter such as paper dust and wax components trapped in the cleaning nip Q are released from the cleaning nip Q. On the other hand, as shown in Figure 3(b), when the intermediate transfer belt 7 is rotated in the reverse direction, the tip of the cleaning blade 82 is pulled upstream by the intermediate transfer belt 7 and deformed. As a result, the back-side toner Ta that was attached to the back surface of the cleaning blade 82 is pressed against the intermediate transfer belt 7 and adheres to the intermediate transfer belt 7.

[0042] Furthermore, if the intermediate transfer belt 7 is stopped and left unattended after the reverse rotation operation, a different load than during normal image formation will be applied to the cleaning blade 82. This may cause cleaning failure due to deformation of the cleaning blade 82. In addition, if the photosensitive drum 1 is reversed in conjunction with the reverse rotation operation of the intermediate transfer belt 7, if it is stopped and left unattended after the reverse rotation operation, a different load than during normal image formation will be applied to the charging roller 2. This may cause charging failure due to deformation of the charging roller 2. Therefore, as shown in Figure 3(c), after the reverse rotation operation of the intermediate transfer belt 7, the intermediate transfer belt 7 is rotated forward before being stopped. At this time, as shown in Figure 3(c), some of the back-circulating toner Ta that adhered to the intermediate transfer belt 7 during the reverse rotation operation is carried away by the forward rotation of the intermediate transfer belt 7 and discharged onto the intermediate transfer belt 7. Here, the back-circulating toner Ta discharged from the back surface of the cleaning blade 82 onto the intermediate transfer belt 7 by this mechanism is also referred to as "discharged toner Tb". Therefore, in order to suppress the occurrence of horizontal streaks caused by the back-circulating toner Ta accumulated on the back surface of the cleaning blade 82 inadvertently adhering to the image-forming area on the intermediate transfer belt 7 during image formation, it is considered effective to reverse the rotation of the intermediate transfer belt 7 after the completion of image formation.

[0043] However, especially when performing jobs that form high-print-rate images or jobs with a large number of image formations, the amount of back-flow toner Ta that accumulates on the back surface of the cleaning blade 82 increases. In such cases, the amount of back-flow toner Ta discharged onto the intermediate transfer belt 7 may be insufficient with just one reverse rotation and one forward rotation as described above. As a result, the undischarged back-flow toner Ta may cause the continuous generation of horizontal streaks in subsequent image formation.

[0044] To address these challenges, one possible approach is to repeatedly deform the tip of the cleaning blade 82 as described above, and to repeatedly rotate the intermediate transfer belt 7 in the reverse and forward directions to sufficiently discharge the backside toner Ta accumulated on the back surface of the cleaning blade 82. However, simply repeating the reverse and forward rotation of the intermediate transfer belt 7 multiple times may cause the discharged backside toner Ta to re-adhere to the back surface of the cleaning blade 82, potentially leading to unintentional adhesion to the intermediate transfer belt 7 during subsequent image formation.

[0045] Therefore, in this embodiment, based on the amount of back-side toner Ta expected from the number of images formed in the job, the intermediate transfer belt 7 is rotated in reverse and forward multiple times after the completion of image formation. Here, the set of the reverse rotation of the intermediate transfer belt 7 followed by the forward rotation of the intermediate transfer belt 7 is called a "reverse-forward rotation sequence". One reverse-forward rotation sequence consists of one reverse rotation and one forward rotation. For example, executing a reverse-forward rotation sequence three times means rotating the intermediate transfer belt 7 in the order of 1st reverse rotation, 1st forward rotation, 2nd reverse rotation, 2nd forward rotation, 3rd reverse rotation, and 3rd forward rotation. Here, the control that executes this reverse-forward rotation sequence a single time or multiple times consecutively at a single execution timing is called "reverse-forward rotation control". The execution timing at which this reverse-forward rotation control is executed is after the completion of image formation (more specifically, after the completion of the post-rotation process of the job) in this embodiment, but it may also be during the inter-paper process (see Embodiment 2). In this embodiment, when the reverse-forward rotation sequence is executed multiple times in succession, the intermediate transfer belt 7 is moved by a greater amount (forward rotation distance) in the forward rotation operation following the reverse rotation operation than the amount (reverse rotation distance) of the intermediate transfer belt 7 in the next reverse rotation operation. By doing so, it is possible to prevent the back-flow toner Ta that has been discharged from returning to the cleaning blade nip Q and adhering again to the back surface of the cleaning blade 82. Thus, in this embodiment, by executing the reverse-forward rotation sequence multiple times, the back-flow toner Ta accumulated on the back surface of the cleaning blade 82 is effectively discharged, and the back-flow toner Ta that has been discharged is prevented from adhering again to the back surface of the cleaning blade 82. As a result, even when performing jobs that form high-print-rate images or jobs with a large number of image formations, the back-flow toner Ta accumulated on the back surface of the cleaning blade 82 can be effectively removed, and the occurrence of horizontal streaks can be suppressed. The reverse-forward rotation control in this embodiment will be explained in more detail below.

[0046] Although not shown in Figure 3, in this embodiment, when the intermediate transfer belt 7 is rotating in the forward direction, the photosensitive drum 1 also rotates in sync with it in the forward direction (in the direction of arrow R1 in Figure 1). Conversely, when the intermediate transfer belt 7 is rotating in the reverse direction, the photosensitive drum 1 also rotates in sync with it in the reverse direction (in the opposite direction to arrow R1 in Figure 1). This is to suppress wear on the intermediate transfer belt 7 and the photosensitive drum 1 due to friction between them.

[0047] 5. Effective ejection of toner from the back of the print. Next, I will describe the experiment conducted to verify the settings for effective ejection of back-circulating toner Ta.

[0048] First, a job was performed to continuously form a predetermined image with a print density (image duty cycle, image ratio) of 5% on one side of a predetermined number of A4-sized recording materials S. Then, after the post-rotation process of that job was completed, a reverse-forward rotation sequence was performed a predetermined number of times. After the completion of each experiment, it was checked whether the back-rotated toner Ta accumulated on the back surface of the cleaning blade 82 was discharged and removed onto the intermediate transfer belt 7 by the reverse-forward rotation sequence (whether there was any remaining back-rotated toner Ta). The results are shown in Table 1.

[0049] [Table 1]

[0050] When the number of images to be formed in a job was small, the amount of toner Ta on the back of the print was eliminated by executing a reverse-forward rotation sequence once after the completion of the post-rotation process of the job. However, when the number of images to be formed in a job was large, such as 50 images or more, there was still some toner Ta remaining on the back of the print even after executing a reverse-forward rotation sequence once after the completion of the post-rotation process of the job.

[0051] On the other hand, by executing the reverse-forward rotation sequence five times after the completion of the job's post-rotation process, the amount of back-side toner Ta was depleted even when the number of image-forming sheets for the job was as high as 200. As mentioned above, executing the reverse-forward rotation sequence five times means rotating the intermediate transfer belt 7 in the following order: 1st reverse rotation, 1st forward rotation, 2nd reverse rotation, 2nd forward rotation, 3rd reverse rotation, 3rd forward rotation, 4th reverse rotation, 4th forward rotation, 5th reverse rotation, 5th forward rotation, and finally completing the reverse-forward rotation sequence. When the reverse-forward rotation sequence was executed three times after the completion of the job's post-rotation process, the result was somewhere between the case of one execution and the case of five executions.

[0052] Thus, it can be seen that the amount of back-side toner Ta accumulated increases with a large number of images to be formed in a job. Furthermore, when the print density of the images to be formed is high, the amount of back-side toner Ta accumulated also tends to increase. In addition, it can be seen that increasing the number of reverse and forward rotation sequences performed in the post-rotation process of the job makes it easier to discharge the back-side toner Ta accumulated on the back surface of the cleaning blade 82.

[0053] 6. Control Modes Figure 4 is a schematic block diagram showing the control configuration of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 is equipped with a control unit 120. The control unit 120 includes a CPU 121 as an arithmetic processing means, which is the central element for performing arithmetic processing; a memory (storage element) 122 such as ROM or RAM as a storage means; and an input / output unit (not shown) that controls the exchange of signals between the control unit 120 and elements connected to it. Sensor detection results, calculation results, etc. are stored in the RAM, and control programs, pre-determined data tables, etc. are stored in the ROM (including rewritable ones).

[0054] The control unit 120 is a control means capable of comprehensively controlling the operation of the image forming apparatus 100. Various parts of the image forming apparatus 100 are connected to the control unit 120. For example, the control unit 120 is connected to various drive units such as the drum drive unit 21 and the belt drive unit 22, various power supplies such as the secondary transfer power supply 31, an exposure device 3 (not shown), an operation unit 130, etc. The control unit 120 can perform image forming and reverse / forward rotation control by controlling the operation of the various drive units (ON / OFF and rotation direction), the operation of the various power supplies (ON / OFF and output value), the operation of the exposure device 3 (ON / OFF and exposure amount), and the timing of these operations. The image forming apparatus 100 may be provided with or connected to an image reading device that reads an image from a document and supplies image information to the image forming unit, and the image forming apparatus 100 may be capable of operating as a copier.

[0055] Here, the image forming apparatus 100 is capable of executing a job (print job), which is a series of operations that form an image on one or more recording materials S, initiated by a single start instruction. The start instruction is input to the control unit 120 from an external device such as a personal computer connected to the image forming apparatus 100 or from the operation unit 130. A job generally consists of an image forming process (printing process), a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials S, and a post-rotation process. The image forming process is the period during which the electrostatic latent image is actually formed on the photosensitive drum 1, the electrostatic latent image is developed (toner image formation), the toner image is primary transferred, the toner image is secondary transferred, and the toner image is fixed. The term "image forming time" refers to this period. More specifically, the timing of image forming time differs depending on the position where these processes—electrostatic latent image formation, toner image formation, primary transfer of the toner image, secondary transfer of the toner image, and toner image fixing—are performed. The pre-rotation process is the period during which preparatory operations are performed before the image forming process. The inter-paper process (inter-image process) is the period between recording materials S when the image forming process is performed continuously on multiple recording materials S (continuous image forming). The post-rotation process is the period during which the tidying operations (preparation operations) after the image forming process are performed. Non-image forming time refers to the period other than the image forming time, and includes the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation process, which is the preparation operation when the image forming apparatus 100 is powered on or when it returns from sleep mode. In this embodiment, the image forming apparatus 100 can perform reverse forward rotation control during non-image forming time.

[0056] 7. Reverse / Forward Rotation Control Figure 5 is a flowchart illustrating the procedure of a job including reverse and forward rotation control in this embodiment. In this embodiment, the control (calculation, decision) according to this flowchart is performed by a control unit 120 provided in the image forming apparatus 100.

[0057] When the control unit 120 acquires job information (including various setting information such as start instructions, image information, and the number of images to be formed), it first adds the number of images to be formed for the job to the image count storage unit N, which stores the cumulative number of images to be formed since the last execution of reverse and forward rotation control (S101). For example, if the control unit 120 executes a job of continuous image formation with 40 images to be formed, it adds 40 to the image count storage unit N. In this embodiment, the image count storage unit N is configured as a storage area provided in the memory 122. The image count storage unit N may store the cumulative number of images to be formed as a value converted to, for example, the number of recording materials S of a predetermined size. In this embodiment, the initial value of the number of images to be formed stored in the image count storage unit N is set to 0. In this embodiment, since at least one reverse and forward rotation sequence is executed after the completion of the post-rotation process of the job (see S105), the cumulative number of images to be formed stored in the image count storage unit N is equal to the value of the number of images to be formed for the job. However, in configurations where the reverse-forward rotation sequence is not executed even once, the cumulative number of images stored in the image count storage unit N will be the sum of the number of images formed for jobs executed before the current job and the number of images formed for the current job. Also, for simplicity, the image count information stored in the image count storage unit N is sometimes referred to as the number of images formed N. Next, the control unit 120 executes a predetermined pre-rotation step (S102) and performs image formation for a predetermined number of images for the job (S103). After that, the control unit 120 executes a predetermined post-rotation step (S104).

[0058] Then, after the post-rotation process is completed, the control unit 120 sets 1 to the count storage unit REV, which stores the number of times the reverse-forward rotation sequence has been executed (S105). In this embodiment, the count storage unit REV is configured as a storage area provided in the memory 122. For simplicity, the count information stored in the count storage unit REV is sometimes referred to as the reverse-forward rotation sequence execution count REV. In this embodiment, since the reverse-forward rotation sequence is to be executed at least once after the post-rotation process of the job is completed, the control unit 120 sets 1 to the count storage unit REV in S105. However, if the configuration is such that the reverse-forward rotation sequence may not be executed even once, the value set to the count storage unit REV in S105 may be 0. Next, the control unit 120 sets the reverse-forward rotation control parameters in order to execute the reverse-forward rotation control (S106). Figure 6 is a flowchart showing the procedure for setting the reverse-forward rotation control parameters executed in S106 of Figure 5.

[0059] The procedure for setting the reverse and forward rotation control parameters will be explained using Figure 6. First, the control unit 120 sets 100 msec in the reverse rotation time storage unit RT, which stores the reverse rotation time that defines the reverse rotation distance (S201). In this embodiment, the reverse rotation time storage unit RT is configured as a storage area provided in the memory 122. For simplicity, the time information stored in the reverse rotation time storage unit RT is sometimes referred to as the reverse rotation time RT. Next, the control unit 120 sets 80 msec in the forward rotation time storage unit FT, which stores the forward rotation time that defines the forward rotation distance (S202). In this embodiment, the forward rotation time storage unit FT is configured as a storage area provided in the memory 122. For simplicity, the time information stored in the forward rotation time storage unit FT is sometimes referred to as the forward rotation time FT. Next, the control unit 120 determines whether the number of integrated image formations stored in the number of images storage unit N is greater than a predetermined threshold (S203). In other words, in this embodiment, the number of times the reverse-forward rotation sequence is executed is made variable according to the number of accumulated images formed since the last execution of reverse-forward rotation control. Here, a decision is made as to whether or not to change the number of times the reverse-forward rotation sequence is executed. In this embodiment, the threshold for the number of accumulated images formed is set to 20. This threshold can be any value. For example, when executing a continuous image formation job with 40 images formed as described above, the number of accumulated images stored in the image count storage unit N is 40, so the control unit 120 will determine "Yes" in S203. For example, if the threshold for the number of accumulated images formed is set to 0, the reverse-forward rotation sequence will be executed multiple times regardless of the number of accumulated images formed. If the control unit 120 determines "Yes" in S203, it resets the number of times the reverse-forward rotation sequence is executed (S204). In this embodiment, if the number of integrated image formations is greater than 20, the control unit 120 sets the count memory unit REV to 3 in S204 to execute at least three reverse-forward rotation sequences. On the other hand, if the control unit 120 determines "No" in S203, it terminates the setting of the reverse-forward rotation control parameters (S209).

[0060] After S204, the control unit 120 stores the recalculated average print rate from the previous execution of reverse and forward rotation control in the print rate storage unit D, which stores the average print rate from the previous execution of reverse and forward rotation control (S205). In this embodiment, the print rate storage unit D is configured as a storage area provided in memory 122. For simplicity, the print rate information stored in the print rate storage unit D is sometimes referred to as the average print rate D. In other words, in S205, the control unit 120 reads the print rate stored in the print rate storage unit D and recalculates the average print rate from the previous execution of reverse and forward rotation control based on the print rate of each image formed in the currently executing job. The print rate is generally expressed as the percentage of the image area when the entire image formation area (the area in which a toner image can be formed) is an image at the highest density level (full solid). In this embodiment, the initial value of the average print rate stored in the print rate storage unit D is set to 0. For example, if the average print rate is 5%, the control unit 120 sets 5% in the print rate storage unit D. Next, the control unit 120 determines whether the average print rate stored in the print rate storage unit D is greater than a predetermined threshold (S206). In other words, in this embodiment, the number of times the reverse forward rotation sequence is executed is varied according to the average print rate since the last execution of the reverse forward rotation control. Here, a decision is made as to whether or not to change the number of times the reverse forward rotation sequence is executed. In this embodiment, the threshold for the average print rate is set to 20%. Note that this threshold may be any value. For example, if the average print rate is 5%, the control unit 120 will determine "No" in S206. If the average print rate is greater than 20%, the control unit 120 will determine "Yes" in S206. If the control unit 120 determines "Yes" in S206, it adds 3 to the number of times the reverse forward rotation sequence is executed stored in the count storage unit REV (S207). On the other hand, if the control unit 120 determines "No" in S206, it proceeds to processing S208 without adding to the number of executions of the reverse and forward rotation sequence.

[0061] Then, after S206 and S207, the control unit 120 resets the forward rotation time set in S202 to 180 msec (S208). This is because, in response to the determination in S203 to execute the reverse forward rotation sequence multiple times, the forward rotation time (forward rotation distance) is made longer than the reverse rotation time (reverse rotation distance). In other words, this prevents the reverse toner Ta discharged onto the intermediate transfer belt 7 by the reverse rotation operation from returning to the cleaning nip Q. After that, the control unit 120 finishes setting the reverse forward rotation control parameters (S209).

[0062] Next, the control unit 120 returns to the procedure in Figure 5 and performs reverse forward rotation control (S107). Figure 7 is a flowchart showing the procedure for reverse forward rotation control performed in S107 of Figure 5.

[0063] The procedure for reverse and forward rotation control will be explained using Figure 7. First, the control unit 120 determines whether or not to execute the reverse and forward rotation sequence by checking whether the value of the number of executions of the reverse and forward rotation sequence stored in the count storage unit REV is greater than 0 (S301). In this embodiment, since the reverse and forward rotation sequence is to be executed at least once after the completion of the post-rotation process of the job (see S105), the control unit 120 will determine "Yes" in S301. Next, the control unit 120 executes the reverse rotation operation (S302). Here, the reverse rotation operation is performed for the time (distance) stored in the reverse rotation time storage unit RT. In this embodiment, the reverse rotation time is 100 msec. Next, the control unit 120 executes the forward rotation operation (S303). Here, the forward rotation operation is performed for the time (distance) stored in the forward rotation time storage unit FT. In this embodiment, the forward rotation time for forward rotation operations, excluding the last forward rotation operation when the reverse-forward rotation sequence is executed multiple times (or the forward rotation operation when the reverse-forward rotation sequence is executed once), is 180 msec. Thus, in this embodiment, during the repetition of the reverse-forward rotation sequence, the relationship RT < forward rotation time FT holds when executing reverse-forward rotation sequences other than the last reverse-forward rotation sequence. Therefore, the reverse rotation time RT < forward rotation time FT is prevented from being discharged onto the intermediate transfer belt 7 and returning to the cleaning nip Q. The forward rotation time for the last forward rotation operation when the reverse-forward rotation sequence is executed multiple times (or the forward rotation operation when the reverse-forward rotation sequence is executed once) will be described later.

[0064] Next, the control unit 120 subtracts 1 from the number of executions of the reverse forward rotation sequence stored in the count storage unit REV (S304). Next, the control unit 120 subtracts 1 from the value of the number of executions of the reverse forward rotation sequence stored in the count storage unit REV. 0The control unit 120 determines whether the value of the number of executions of the reverse-forward rotation sequence stored in the count storage unit REV is 0 or not, based on whether it is greater than or equal to (S305). If the control unit 120 determines "Yes" in S305, it determines whether the value of the number of executions of the reverse-forward rotation sequence stored in the count storage unit REV is 1 or not, and determines whether the next repetition of the reverse-forward rotation sequence is the last (S306). If the control unit 120 determines "Yes" in S306, it sets the reverse rotation time storage unit RT to 100 msec (S307) and the forward rotation time storage unit FT to 80 msec (S308). Thus, in this embodiment, in the repetition of the reverse-forward rotation sequence, when the last reverse-forward rotation sequence is executed, the relationship is reverse rotation time RT > forward rotation time FT. The same applies when the reverse-forward rotation sequence is executed only once. By setting it in this way, it is possible to prevent the intermediate transfer belt 7 from stopping with foreign matter such as paper dust and wax components that were trapped in the cleaning nip Q and removed from the cleaning nip Q by the reverse rotation operation returning to the cleaning nip Q. In other words, if foreign matter such as paper dust and wax removed from the cleaning nip Q returns to the cleaning nip Q and is blocked by the cleaning blade 82, and the intermediate transfer belt 7 is stopped, traces of the accumulation of that foreign matter may remain on the surface of the intermediate transfer belt 7. These accumulation traces may have an effect on subsequent image formation, such as causing image unevenness. Therefore, as described above, in the last forward rotation operation when the reverse forward rotation sequence is executed multiple times (or the forward rotation operation when the reverse forward rotation sequence is executed once), it is preferable to move the intermediate transfer belt 7 by a smaller amount (forward rotation distance) than the amount of movement of the intermediate transfer belt 7 in the previous reverse rotation operation (reverse rotation distance).

[0065] Then, if the control unit 120 determines "NO" in S305, the value of the number of executions of the reverse-forward rotation sequence stored in the count storage unit REV is 0, so it resets the value of the number of sheets storage unit N to 0 (S309), resets the value of the print rate storage unit D to 0 (S310), and terminates the reverse-forward rotation control (repetition of the reverse-forward rotation sequence).

[0066] The pre-rotation and post-rotation processes of the job refer to control sequences that include starting and stopping the drive of the photosensitive drum 1, developing device 4, and intermediate transfer belt 7, and starting and stopping the application of high pressure to the charging roller 2, developing roller 41, primary transfer roller 5, and secondary transfer roller 9. In this embodiment, the specific control sequences for the pre-rotation and post-rotation processes are arbitrary, and known sequences can be appropriately adopted, for example.

[0067] Figure 9 will be used to further explain the movement of the back-rotating toner Ta (discharged toner Tb) in the reverse-forward rotation control according to this embodiment. Figure 9 is a schematic diagram (a cross-sectional view approximately perpendicular to the rotation axis direction of the support roller of the intermediate transfer belt 7) to explain how the discharged toner Tb, which is the back-rotating toner Ta discharged onto the intermediate transfer belt 7, moves during reverse-forward rotation control. Figure 9 shows an example where the reverse-forward rotation sequence is executed three times. Here, the area on the intermediate transfer belt 7 where the discharged toner Tb is attached is also simply called the "discharge area Tb". More specifically, this discharge area Tb is the area on the intermediate transfer belt 7 that was at the cleaning nip Q after one reverse rotation operation and before the next forward rotation operation in the reverse-forward rotation control.

[0068] Figure 9(a) shows the state after the first reverse rotation and the subsequent first forward rotation have been completed. The back-rotating toner Ta accumulated on the back surface of the cleaning blade 82 is pressed against and adheres to the intermediate transfer belt 7 by the first reverse rotation (dashed arrow). Subsequently, this back-rotating toner Ta is discharged onto the intermediate transfer belt 7 and transported by the first forward rotation (solid arrow). Here, the distance of the first reverse rotation is assumed to be 32 mm, and the distance of the first forward rotation is assumed to be 50 mm. Figure 9(b) shows the state after the second reverse rotation has been completed. Here, the distance of the second reverse rotation is assumed to be 32 mm. Since the relationship is second reverse rotation distance < first forward rotation distance, the discharge section Tb (Tb1) from the first reverse rotation does not return to the cleaning nip Q by the second reverse rotation. Figure 9(c) shows the state after the second forward rotation has been completed. Here, the distance of the second forward rotation is assumed to be 112 mm. The toner Ta that was not completely ejected during the first reverse rotation is ejected onto the intermediate transfer belt 7 and transported. On the intermediate transfer belt 7, there is an ejection section Tb (Tb1) from the first reverse rotation on the downstream side with respect to the forward rotation direction of the intermediate transfer belt 7, and an ejection section Tb (Tb2) from the second reverse rotation on the upstream side with respect to the forward rotation direction of the intermediate transfer belt 7. Figure 9(d) shows the state at the end of the third reverse rotation and the subsequent third forward rotation. Here, the distance of the third reverse rotation is assumed to be 32 mm, and the distance of the third forward rotation is assumed to be 24 mm. In the illustrated example, since the toner that was almost completely ejected during the two reverse-forward rotation sequences is the toner that was almost completely ejected during the third reverse-forward rotation sequence, almost no toner Ta is ejected during the third reverse-forward rotation sequence. Also, since the distance of the second reverse rotation > the distance of the third forward rotation, the intermediate transfer belt 7 will not stop with foreign matter such as paper dust that has been removed from the cleaning nip Q by the time of the third reverse rotation returning to the cleaning nip Q. In the example shown in Figure 9, the second forward rotation distance is made longer than the first forward rotation distance in order to set the position of the discharge section Tb (Tb1, Tb2) at the end of the third forward rotation operation to the position described in Example 3.

[0069] In other words, when the reverse-forward rotation sequence is performed n times (any integer greater than or equal to 0, but here an integer greater than or equal to 2), and the reverse rotation is performed k times (0 to n-1), the forward rotation distance of the kth rotation is greater than the reverse rotation distance of the (k+1)th rotation. Also, in this embodiment, the forward rotation distance of the nth rotation is smaller than the reverse rotation distance of the (n-1)th rotation.

[0070] Thus, in this embodiment, the image forming apparatus 100 includes a rotatable image carrier 7 that carries a toner image on its surface, a transfer means 9 that transfers the toner image from the image carrier 7 rotating in the forward rotation direction to the transfer target S in the transfer unit T2, a cleaning blade 82 that contacts the surface of the image carrier 7 to form a contact portion Q and removes toner from the surface of the image carrier 7 rotating in the forward rotation direction, a drive unit 22 that can rotate the image carrier 7 in the forward rotation direction and in the reverse rotation direction which is opposite to the forward rotation direction, and a forward rotation operation which is the rotation operation of the image carrier 7 and the image carrier 7 The system includes a control unit 120 capable of controlling the drive unit 22 to perform a reverse rotation operation, which is a rotation operation in the reverse direction. The control unit 120 can control the system to stop the image carrier 7 after executing a reverse-forward rotation sequence multiple times in a row, which consists of a reverse rotation operation followed by a forward rotation operation, when the job of transferring a toner image from the image carrier 7 to the transfer target S is completed. When the reverse-forward rotation sequence is executed multiple times in a row, the control unit 120 controls the system so that the amount of movement of the image carrier 7 in the forward rotation operation following the reverse rotation operation is greater than the amount of movement of the image carrier 7 in the next reverse rotation operation. In this embodiment, when the reverse-forward rotation sequence is executed multiple times in a row, the control unit 120 controls the system so that the amount of movement of the image carrier 7 in the last forward rotation operation is less than the amount of movement of the image carrier 7 in the reverse rotation operation immediately preceding it. In this embodiment, the control unit 120 can also change the number of times the reverse-forward rotation sequence is executed at the end of the current job based on the number of integrated images formed after the previous reverse-forward rotation sequence was executed. Furthermore, the control unit 120 can change the number of times the reverse-forward rotation sequence is executed at the end of the current job based on the average print rate after the previous reverse-forward rotation sequence was executed.

[0071] As described above, according to this embodiment, even when performing jobs that form high-printability images or jobs that form a large number of images, the back-flow toner Ta accumulated on the back surface of the cleaning blade 82 can be effectively discharged. Furthermore, according to this embodiment, it is possible to prevent the back-flow toner Ta that has been discharged from adhering again to the back surface of the cleaning blade 82. Therefore, according to this embodiment, even when performing jobs that form high-printability images or jobs that form a large number of images, the back-flow toner Ta accumulated on the back surface of the cleaning blade 82 can be effectively removed, thereby suppressing the occurrence of horizontal streaks.

[0072] [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 in the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as those in Embodiment 1, and detailed descriptions are omitted.

[0073] 1. Overview of this embodiment In this embodiment, the image forming apparatus 100 is capable of performing reverse and forward rotation control by interrupt control during the inter-paper process of the job. In other words, when using recording material S that generates a relatively large amount of foreign matter such as paper dust, when executing a job with a large number of images, foreign matter such as paper dust may become significantly trapped in the cleaning nip Q midway through the job. As a result, toner may slip through the cleaning blade 82, leading to cleaning failures.

[0074] Table 2 shows the results of checking for the presence or absence of foreign matter such as paper dust (whether or not toner has leaked through) caught in the cleaning nip Q after the completion of each experiment, when the same experiment as the one that yielded the results in Table 1 in Example 1 was performed using recording material S, which generates a relatively large amount of foreign matter such as paper dust.

[0075] [Table 2]

[0076] When the number of image formation frames for a job is large, it can be found that even after performing a reverse rotation sequence five times after the completion of the post-rotation process of the job, it may not be possible to sufficiently remove foreign matter such as paper dust trapped in the cleaning nip Q.

[0077] Therefore, in this embodiment, reverse and forward rotation control can be executed by interrupt control during the inter-paper process of the job, based on the number of images formed in the job. Furthermore, when reverse and forward rotation control is executed during the inter-paper process of the job, it is possible to change the method to reduce the number of executions of the reverse and forward rotation sequence in the reverse and forward rotation control executed after the completion of the post-rotation process of the job.

[0078] 2. Control of this embodiment Figure 8 is a flowchart showing the procedure of a job including reverse and forward rotation control in this embodiment. In this embodiment, the control (calculation, decision) according to this flowchart is performed by a control unit 120 provided in the image forming apparatus 100. Note that the reverse and forward rotation control itself is the same as that described in Embodiment 1, so a detailed explanation will be omitted as appropriate.

[0079] When the control unit 120 acquires job information, it first acquires information on the number of images to be formed for the job and stores it in the image count storage unit N (S401). In this embodiment, the image count storage unit N stores the number of images to be formed for the job. For example, when executing a job of continuous image formation with 40 images to be formed, 40 images are stored in the image count storage unit N. Next, the control unit 120 executes a predetermined pre-rotation process (S402). Next, the control unit 120 determines whether the number of images to be formed for the job N is 21 or more (S403). For example, if the number of images to be formed for the job is 40, the control unit 120 will determine "Yes" in S403. If the control unit 120 determines "No" in S403, it executes the image formation of the predetermined number of images for the job, and after the completion of the post-rotation process of the job, it executes a reverse forward rotation sequence once to terminate the job (S404).

[0080] If the control unit 120 determines "Yes" in S403, it determines whether the cleaning stability enhancement mode is set (S405). Here, the cleaning stability enhancement mode is a mode that makes it possible to suppress cleaning defects caused by toner passing through the cleaning blade 82, even when using recording material S which generates a relatively large amount of foreign matter such as paper dust. Specifically, in this embodiment, when the cleaning stability enhancement mode is set, it becomes possible to perform reverse and forward rotation control by interrupt control in the inter-paper process according to the number of images to be formed in the job. The cleaning stability enhancement mode can be set by an operator such as a user or service person from the UI display screen of the operation unit 130 (Figure 4) provided on the image forming apparatus 100, or from an external device such as a personal computer connected to the image forming apparatus 100. When the cleaning stability enhancement mode is set, the control unit 120 stores information indicating this in the memory 122. If the control unit 120 determines "No" in S405, it performs image formation for a predetermined number of images for the job, and after the completion of the post-rotation process of the job, it performs the reverse forward rotation sequence three times to terminate the job (S407).

[0081] If the control unit 120 determines "Yes" in S405, it determines whether the number of images N for the job is 101 or more (S406). For example, if the number of images for the job is 75, the control unit 120 will determine "No" in S406. If the control unit 120 determines "No" in S406, it performs the image formation of the predetermined number of images for the job, and after the completion of the post-rotation process of the job, it performs the reverse and forward rotation sequence three times to terminate the job (S407).

[0082] If the control unit 120 determines "Yes" in S406, it executes reverse forward rotation control via interrupt control during the inter-paper process after 100 image formation (the inter-paper process between the 100th and 101st image) (S408). Specifically in this embodiment, at this time it enters the same operation as the post-rotation process, and after the completion of this operation it executes the reverse forward rotation sequence three times. After that, the control unit 120 obtains the remaining number of image formations N (=N-100) for the job and updates and stores (overwrites) the number storage unit N (S409). Then the control unit 120 S 4 Returning to step 02, the same operation as the previous rotation process is performed again. For example, if the number of images to be formed in the job is 110 and the cleaning stability enhancement mode is set, then in S408, reverse forward rotation control is performed, and the number of remaining images to be formed in the job, which is updated in S409, will be 10. In this case, the control unit 120 will determine "No" in the next step, S403. Therefore, in this case, the control unit 120 will continue to form images for the remaining number of images, and after the completion of the post-rotation process of the job, it will execute the reverse forward rotation sequence only once to finish the job (S404).

[0083] In this embodiment, when reverse-forward rotation control is executed by interrupt control during the inter-paper process, the reverse-forward rotation sequence is executed three times. In this case, foreign matter such as paper dust trapped in the cleaning nip Q is removed, and the back-side toner Ta accumulated on the back surface of the cleaning blade 82 is also effectively discharged. Therefore, if the number of remaining image formation sheets is sufficiently small, the system is controlled to prevent excessive execution of the reverse-forward rotation sequence after the completion of the post-rotation process of the job. This prevents the time until the intermediate transfer belt 7 stops after the completion of image formation from becoming excessively long.

[0084] Thus, in this embodiment, the control unit 120 can control the execution of the reverse-forward rotation sequence multiple times consecutively during the period (between sheets of paper) between the transfer of one toner image and the transfer of the next toner image in a job that transfers multiple toner images from the image carrier 7 to the transfer target S. Furthermore, in this embodiment, the control unit 120 can change the number of times the reverse-forward rotation sequence is executed at the end of the job based on whether or not the reverse-forward rotation sequence was executed during the above period (between sheets of paper) of the job.

[0085] As described above, according to this embodiment, foreign matter such as paper dust trapped in the cleaning nip Q during job execution can be removed in the inter-paper process, and back-side toner Ta accumulated on the back surface of the cleaning blade 82 can be effectively discharged while suppressing an increase in downtime (period during which an image cannot be formed).

[0086] [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 in the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as those in Embodiment 1, and detailed descriptions are omitted.

[0087] 1. Overview of this embodiment In the mechanism described in Example 1, the discharged toner Tb, which is the back-circumference toner Ta discharged onto the intermediate transfer belt 7 from the back surface of the cleaning blade 82, is transported on the intermediate transfer belt 7. Depending on the position of the discharge portion Tb (the area on the intermediate transfer belt 7 to which the discharged toner Tb is attached) on the intermediate transfer belt 7 in the rotation direction (circumferential direction) of the intermediate transfer belt 7 when the intermediate transfer belt 7 stops at the end of the job, the discharged toner Tb may be transported to the secondary transfer portion T2 in the pre-rotation process of the next job, transferred to the recording material S, fixed, and result in the occurrence of horizontal streaks. This phenomenon can be avoided by allowing the intermediate transfer belt 7 to rotate idle for a sufficient amount of time (distance) in the pre-rotation process of the next job. However, in order to minimize the FCOT (First Copy Time), it is desirable to minimize the time (distance) that the intermediate transfer belt 7 rotates before the first recording material S in the next job reaches the secondary transfer portion T2. Additionally, it is conceivable to add a cleaning component for cleaning the ejected toner Tb, but this could lead to increased complexity and size of the device configuration.

[0088] 2. Control of this embodiment In this embodiment, before the recording material S reaches the secondary transfer section T2 during the next image formation, the intermediate transfer belt 7 is rotated and then stopped so that the ejection section Tb on the intermediate transfer belt 7 passes through the secondary transfer section T2 and reaches a position that is more than one rotational distance from the secondary transfer section T2 to the secondary transfer roller 9. By ensuring that the ejection section Tb passes through the secondary transfer section T2 before the recording material S reaches the secondary transfer section T2, it is possible to suppress the transfer of ejected toner Tb to the recording material S and the occurrence of horizontal streaks. Furthermore, by ensuring that the ejection section Tb moves more than one rotational distance from the secondary transfer section T2 to the secondary transfer roller 9 before the recording material S reaches the secondary transfer section T2, even if the ejected toner Tb is transferred to the secondary transfer roller 9, it is possible to return the toner to the intermediate transfer belt 7 before the recording material S reaches the secondary transfer section T2. ​​This makes it possible to suppress the occurrence of toner stains (horizontal streaks) on the non-image surface of the recording material S.

[0089] In reverse-forward rotation control, if the reverse-forward rotation sequence is executed multiple times, it is sufficient that at least the ejection part Tb from the first reverse rotation operation moves to the position described above before the recording material S reaches the secondary transfer part T during the next image formation. This is because, in reverse-forward rotation control at one execution timing, the most back-facing toner Ta adheres to the ejection part Tb from the first reverse rotation operation. However, it is preferable that at least the ejection part Tb from multiple reverse rotation operations, including the ejection part Tb from the first reverse rotation operation, moves to the position described above before the recording material S reaches the secondary transfer part T2 during the next image formation. As explained in Example 1, the amount of back-facing toner Ta ejected by the last reverse rotation operation may be sufficiently small. In such cases, it is preferable that the ejection parts Tb from the first reverse rotation operation to the ejection part Tb from the reverse rotation operation immediately preceding the last reverse rotation operation move to the position described above before the recording material S reaches the secondary transfer part T2 during the next image formation. Typically, all reverse rotational movements can be used to ensure that the ejection section Tb moves to the position described above before the recording material S reaches the secondary transfer section T2 during the next image formation.

[0090] Furthermore, it is preferable that the position reached by the ejection section Tb (at least the ejection section Tb from the initial reverse rotation) before the recording material S reaches the secondary transfer section T2 during the next image formation is a position between passing the secondary transfer section T2 and first reaching the cleaning nip Q. The ejected toner Tb is then removed from the intermediate transfer belt 7 by the belt cleaning device 8. Although not limited to this, typically the position reached is a distance of 5 rotations or less, preferably 3 rotations or less, from the secondary transfer section T2 to the secondary transfer roller 9. This minimizes the time (distance) during which the intermediate transfer belt 7 rotates before the recording material S reaches the secondary transfer section T2 during the next image formation.

[0091] Furthermore, the ejection section Tb (at least the ejection section Tb resulting from the initial reverse rotation) may be moved to the position described above before the intermediate transfer belt 7 is stopped at the end of the job in which the reverse rotation control was performed, or it may be done in the preceding rotation process of the next job. In other words, the ejection section Tb may pass through the secondary transfer section T2 before the intermediate transfer belt 7 is stopped at the end of the job in which the reverse rotation control was performed, or it may pass through the secondary transfer section T2 in the preceding rotation process before the first recording material S of the next job reaches the secondary transfer section T2.

[0092] The movement of the ejection unit Tb in this embodiment described above will be further explained using Figure 10. Figure 10 is a schematic diagram (a cross-sectional view approximately perpendicular to the rotation axis direction of the support roller of the intermediate transfer belt 7) to illustrate how the ejection toner Tb moves. For simplicity, here we will use the case where the reverse and forward rotation sequence is executed once as an example.

[0093] First, the back-flow toner Ta accumulated on the back surface of the cleaning blade 82 is pressed against and adheres to the intermediate transfer belt 7 during the reverse rotation operation after image formation is complete (dashed arrow). Then, during the forward rotation operation (solid arrow), this back-flow toner Ta is carried along by the forward rotation of the intermediate transfer belt 7 and discharged onto the intermediate transfer belt 7 and transported. As described above, before the recording material S reaches the secondary transfer section T2 during the next image formation, the intermediate transfer belt 7 is rotated and then stopped so that the discharge section Tb on the intermediate transfer belt 7 has passed the secondary transfer section T2 and moved a distance of more than one rotation of the secondary transfer roller 9 from the secondary transfer section T2.

[0094] In the illustrated example, the reverse rotation distance is assumed to be 32 mm, and the forward rotation distance is assumed to be 24 mm. The distance from the cleaning nip Q to the secondary transfer section T2 is assumed to be 396.5 mm. At the end of the reverse forward rotation operation (the end of the last forward rotation operation), the discharge section Tb is located 24 mm downstream from the cleaning nip Q in the forward rotation direction of the intermediate transfer belt 7. The upper tolerance limit for the circumference of one rotation of the secondary transfer roller 9 is assumed to be 62.8 mm. In this case, before the recording material S reaches the secondary transfer section T2 during the next image formation, the discharge section Tb on the intermediate transfer belt 7 should move by a distance equal to the distance from the discharge section Tb, which is 24 mm downstream of the cleaning nip Q in the forward rotation direction of the intermediate transfer belt 7, to the secondary transfer section T2 (=396.5 mm - 24 mm = 372.5 mm), plus the upper limit of the tolerance of the circumference of the secondary transfer roller 9 (=62.8 mm).

[0095] As mentioned above, when performing multiple reverse-forward rotation sequences in reverse-forward rotation control, the intermediate transfer belt 7 should be rotated and then stopped so that at least the ejection section Tb from the first reverse rotation operation moves by the aforementioned distance before the recording material S reaches the secondary transfer section T2 during the next image formation. For example, in the example explained using Figure 9, the positions of the ejection sections Tb (Tb1, Tb2) from the first and second reverse rotation operations at the end of the last forward rotation operation (third forward rotation operation) should be set so that the ejection sections Tb from the first and second reverse rotation operations move to the aforementioned positions before the recording material S reaches the secondary transfer section T2 during the next image formation. Typically, these ejection sections Tb (Tb1, Tb2) from the first and second reverse rotation operations pass through the secondary transfer section T2 in the pre-rotation process of the next job. For example, as shown in the example in Figure 9, if we want to shorten the distance of the third forward rotation, we can adjust the position of the discharge section Tb (Tb1, Tb2) at the end of the third forward rotation by lengthening the distance of the second forward rotation.

[0096] Furthermore, when the ejection section Tb (at least the ejection section Tb due to the initial reverse rotation) passes through the secondary transfer section T2, it is preferable to form an electric field (an electric field in the opposite direction to that during secondary transfer) in the secondary transfer section T2 that biases the toner, which is charged with the correct charge polarity, from the secondary transfer roller 9 side to the intermediate transfer belt 7 side. Specifically, in the configuration of this embodiment, it is preferable to apply a voltage to the secondary transfer roller 9 that has the same polarity as the correct charge polarity of the toner (opposite polarity to that during secondary transfer) when the ejection section Tb passes through the secondary transfer section T2. ​​This makes it possible to suppress the transfer of ejected toner Tb to the secondary transfer roller 9. The voltage may be applied starting before the ejection section Tb reaches the secondary transfer section T2 and continued until the ejection section Tb has finished passing through the secondary transfer section T2. ​​However, it is also possible to configure the system so that no voltage is applied to the secondary transfer section T2 when the ejection section Tb passes through the secondary transfer section T2. In this case as well, after the ejection section Tb passes through the secondary transfer section T2, but before the recording material S reaches the secondary transfer section T2, the ejection toner Tb (which is often hardly charged) that has been transferred to the secondary transfer roller 9 can be returned to the intermediate transfer belt 7 and reduced.

[0097] Furthermore, after the ejection section Tb (at least the ejection section Tb from the initial reverse rotation) has passed through the secondary transfer section T2, and before the recording material S reaches the secondary transfer section T2, the secondary transfer roller 9 may be cleaned. The cleaning of the secondary transfer roller 9 can be performed by forming an electric field in the secondary transfer section T2 that biases toner charged with the correct charge polarity from the secondary transfer roller 9 side towards the intermediate transfer belt 7 side (an electric field in the opposite direction to that during secondary transfer), or by forming an electric field that biases toner charged with the correct charge polarity from the secondary transfer roller 9 side towards the intermediate transfer belt 7 side (an electric field in the opposite direction to that during secondary transfer), and an electric field that biases toner charged with the opposite charge polarity from the secondary transfer roller 9 side towards the intermediate transfer belt 7 side (an electric field in the same direction as during secondary transfer). In this embodiment, the cleaning of the secondary transfer roller 9 can be performed by applying a voltage to the secondary transfer roller 9 that has the same polarity as the normal charge polarity of the toner (opposite polarity to that used during secondary transfer), or by applying a voltage that has the same polarity as the normal charge polarity of the toner (opposite polarity to that used during secondary transfer) and a voltage that has the opposite polarity to the normal charge polarity of the toner (same polarity as that used during secondary transfer). The voltages of each polarity may be applied alternately multiple times. Although not limited to this, it is preferable that the voltage of each polarity be applied for a time equivalent to at least one rotation of the secondary transfer roller 9 (typically three rotations or less). This allows the toner, which is charged with the opposite polarity to the applied voltage, to be effectively returned from the secondary transfer roller 9 to the intermediate transfer belt 7. For example, as described above, if a voltage of the same polarity as the normal charging polarity of the toner (opposite polarity to that during secondary transfer) is applied to the secondary transfer roller 9 when the ejection unit Tb passes through the secondary transfer unit T2, the application of this voltage can be continued for the duration of one rotation of the secondary transfer roller 9 after the ejection unit Tb has passed through the secondary transfer unit T2, and then a voltage of the opposite polarity to the normal charging polarity of the toner (same polarity as during secondary transfer) can be applied for the duration of one rotation of the secondary transfer roller 9. Cleaning of the secondary transfer roller 9 can be performed after the completion of the post-rotation process of the job (after the completion of reverse / forward rotation control) and before the intermediate transfer belt 7 stops, or at least one of the pre-rotation processes of the job.

[0098] In this embodiment, a secondary transfer voltage with the same polarity as the normal charging polarity of the toner is applied to the inner roller corresponding to the drive roller 71, and the outer roller corresponding to the secondary transfer roller 9 is electrically grounded. In this embodiment, the following procedure is necessary: ​​That is, a voltage with the opposite polarity to the voltage applied to the secondary transfer roller 9 when the discharge section Tb passes through the secondary transfer section T2, or when the secondary transfer roller 9 is being cleaned, should be applied to the inner roller.

[0099] Figure 11 will be used to further explain an example of the voltage applied to the secondary transfer roller 9 before and after the ejection section Tb passes through the secondary transfer section T2. ​​Figure 11 is a timing chart diagram that shows a schematic of the voltage changes applied to the secondary transfer roller 9 before and after the ejection section Tb passes through the secondary transfer section T2. ​​Here, as explained using Figure 9, we will take the case where the reverse forward rotation sequence is executed three times in reverse forward rotation control as an example. In this case, the ejection section Tb due to the first and second reverse rotation operations will move to the position described above before the recording material P reaches the secondary transfer section T2 during the next image formation. In addition, the ejection sections Tb (Tb1, Tb2) due to the first and second reverse rotation operations will pass through the secondary transfer section T2 in the pre-rotation process of the next job.

[0100] First, during secondary transfer, a positive voltage is applied to the secondary transfer roller 9. Once secondary transfer is complete, the post-rotation process is executed (t1-t2). Then, reverse-forward rotation control is executed and the intermediate transfer belt 7 is stopped (t2-t3). For example, during the post-rotation process and reverse-forward rotation control, the application of voltage to the secondary transfer roller 9 is stopped. Then, when the next job starts, the pre-rotation process begins (t4). At this time, a negative voltage (opposite polarity to that during secondary transfer) is applied to the secondary transfer roller 9. Then, at t5 and t6, the discharge sections Tb1 and Tb2 from the first and second reverse rotation operations of the reverse-forward rotation control at the end of the previous job, respectively, pass through the secondary transfer section T2. ​​Then, from the time when the discharge section Tb2 from the second reverse rotation operation passes through the secondary transfer section T2 until the time equivalent to one rotation of the secondary transfer roller 9 has elapsed, the application of a negative voltage to the secondary transfer roller 9 continues (t6-t7). Subsequently, the voltage applied to the secondary transfer roller 9 is switched to a positive voltage (the same polarity as during secondary transfer), and this voltage is continued to be applied until the time required for one rotation of the secondary transfer roller 9 has elapsed (t7~t8). After that, the recording material S reaches the secondary transfer section T2 (t9), and secondary transfer is performed.

[0101] Thus, in this embodiment, the image forming apparatus 100 is an intermediate transfer body that transports a toner image, which has been primarily transferred from another image carrier 1, to a recording material S, which is the material to be transferred, in the transfer section T2. ​​The transfer means has a transfer roller 9 that contacts the image carrier 7 to form the transfer section T2. ​​When the reverse-forward rotation sequence is executed multiple times in succession, the control unit 120 controls the position of the image carrier Tb in the forward rotation direction of the image carrier 7, which was at the contact section Q after the reverse rotation operation and before the next forward rotation operation, to be at a position where, at the end of the last forward rotation operation, the position of the ejection section Tb in the forward rotation direction of the image carrier 7 due to at least the first reverse rotation operation is such that the ejection section Tb can pass through the transfer section T2 and move a distance of at least one rotation of the transfer roller 9 from the transfer section T2 before the recording material S reaches the transfer section T2 for the next transfer. In this embodiment, the control unit 120 controls the position of the ejection unit Tb after multiple reverse rotation operations, including the first reverse rotation operation, so that it is in the position described above. The ejection unit Tb after at least the first reverse rotation operation may pass through the transfer unit T2 before the first recording material S of the next job after a job in which the reverse rotation sequence is executed multiple times in succession reaches the transfer unit T2. Alternatively, the ejection unit Tb after at least the first reverse rotation operation may pass through the transfer unit T2 before the image carrier 7 stops at the end of a job in which the reverse forward rotation sequence is executed multiple times. The image forming apparatus 100 also has a power supply 31 that applies voltage to the transfer means 9 to form an electric field in the transfer unit T2. Furthermore, the control unit 120 can control the power supply 31 to form an electric field in the transfer unit T2 that is in the same direction as the transfer electric field for transfer, and an electric field in the opposite direction to the transfer electric field. The control unit 120 can control the transfer unit T2 to form an electric field in the transfer unit T2 that is in the opposite direction to the transfer electric field when the discharge unit Tb, which is generated by at least the first reverse rotation operation, passes through the transfer unit T2. In addition, the control unit 120 can control the transfer unit T2 to form an electric field in the transfer unit T2 that is in the opposite direction to the transfer electric field, or an electric field in the opposite direction to the transfer electric field and an electric field in the same direction as the transfer electric field, after the discharge unit Tb, which is generated by at least the first reverse rotation operation, has passed through the transfer unit T2.

[0102] As described above, this embodiment provides the same effects as in Embodiment 1, while minimizing the FCOT of the job following the job in which reverse rotation control was performed, and suppressing lateral streaks and toner staining on the non-image surface of the recording material S in the subsequent job.

[0103] In this embodiment, the position of the ejection unit Tb due to reverse and forward rotation control performed after the completion of the post-rotation process of the job has been described. However, even when reverse and forward rotation control is performed in the inter-paper process as described in Embodiment 2, the same effect can be obtained by setting the position of the ejection unit Tb at the end of the reverse and forward rotation control in the same manner as described above, in relation to the timing when the recording material S reaches the secondary transfer unit T2 during image formation following the inter-paper process.

[0104] [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.

[0105] In the above-described embodiment, an example of applying the present invention to an intermediate transfer cleaning means was explained. However, it can also be applied to, for example, a photoreceptor cleaning means, and the same effects as in the above-described embodiment can be obtained.

[0106] Furthermore, the image forming apparatus is not limited to a tandem type image forming apparatus, but may be an image forming apparatus of another type. Also, the image forming apparatus is not limited to an image forming apparatus capable of forming full-color images, but may be an image forming apparatus capable of forming only monochrome (black and white or monocolor) images. Furthermore, the image forming apparatus may be an image forming apparatus for various purposes, such as a printer, various printing machines, copiers, fax machines, or multifunction devices. [Explanation of symbols]

[0107] 1 Photosensitive drum 2 Charging rollers 3. Exposure apparatus 5. Primary transfer roller 7. Intermediate transfer belt 8. Belt cleaning device 9. Secondary transfer roller 82 Cleaning Blades T2 Secondary Transfer Section Ta back-side toner Tb Toner ejected (Toner ejected from the back of the card)

Claims

1. A rotatable image carrier that holds a toner image on its surface, The transfer section includes a transfer member that transfers a toner image from the image carrier, which rotates in the forward rotation direction, to the object to be transferred, A cleaning blade that contacts the surface of the image carrier to form a contact portion and removes toner from the surface of the image carrier as it rotates in the forward rotation direction, A drive unit capable of rotating the image carrier in the forward rotation direction and in the reverse rotation direction which is opposite to the forward rotation direction, A control unit capable of controlling the drive unit to perform a forward rotation operation, which is a rotational operation of the image carrier in the forward rotation direction, and a reverse rotation operation, which is a rotational operation of the image carrier in the reverse rotation direction. It has, The control unit is capable of executing a mode in which, at the end of a job in which a toner image is transferred from the image carrier to the transfer target, a series of operations is performed in which the reverse rotation operation is followed by the forward rotation operation multiple times, and after the series of operations is performed, the image carrier is stopped. The series of operations includes a first reverse rotation operation which is the first reverse rotation operation performed in the series of operations, a first forward rotation operation which is the next forward rotation operation performed after the first reverse rotation operation, a second reverse rotation operation which is the last reverse rotation operation performed in the series of operations, and a second forward rotation operation which is the next forward rotation operation performed after the second reverse rotation operation. The image forming apparatus is characterized in that, when the position of the image carrier that was located at the contact portion at the end of the first reverse rotation operation is taken as the first position, the control unit controls the drive unit so that the first position does not return to the contact portion from the end of the first forward rotation operation until the end of the second forward rotation operation, and controls the drive unit so that the amount of movement of the image carrier in the second forward rotation operation is smaller than the amount of movement of the image carrier in the second reverse rotation operation.

2. The image forming apparatus according to Claim 1, wherein the series of operations includes a third reverse rotation operation which is performed after the first forward rotation operation, and a third forward rotation operation which is performed after the third reverse rotation operation, and when the position of the image carrier that was located at the contact portion at the end of the third reverse rotation operation is set to the second position, the control unit controls the drive unit so that the second position does not return to the contact portion after it has moved by the third forward rotation operation until the second forward rotation operation is completed.

3. The image forming apparatus according to claim 1, characterized in that the control unit controls the drive unit such that the amount of movement of the image carrier in any of the reverse rotation operations performed after the first reverse rotation operation in the series of operations is smaller than the amount of movement of the image carrier in the forward rotation operation performed immediately before it.

4. The image forming apparatus according to claim 1, characterized in that the control unit is configured to execute the mode when the number of output sheets for the job is greater than a predetermined number.

5. The image forming apparatus according to claim 4, characterized in that, when the number of output images of the job is less than or equal to the predetermined number, the control unit stops the image carrier after performing the reverse rotation operation followed by the forward rotation operation once at the end of the job, and controls the drive unit such that the amount of movement of the image carrier in the forward rotation operation is less than the amount of movement of the image carrier in the reverse rotation operation.

6. A rotatable image carrier having a toner image on its surface, The transfer section includes a transfer member that transfers a toner image from the image carrier, which rotates in the forward rotation direction, to the object to be transferred, A cleaning blade that contacts the surface of the image carrier to form a contact portion and removes toner from the surface of the image carrier as it rotates in the forward rotation direction, A drive unit capable of rotating the image carrier in the forward rotation direction and in the reverse rotation direction which is opposite to the forward rotation direction, A control unit capable of controlling the drive unit to perform a forward rotation operation, which is a rotational operation of the image carrier in the forward rotation direction, and a reverse rotation operation, which is a rotational operation of the image carrier in the reverse rotation direction. It has, The control unit is capable of executing a mode in which, at the end of a job in which a toner image is transferred from the image carrier to the transfer target, a series of operations is performed in which the reverse rotation operation is followed by the forward rotation operation multiple times, and after the series of operations is performed, the image carrier is stopped. The series of operations includes a first reverse rotation operation which is the first reverse rotation operation performed in the series of operations, a first forward rotation operation which is the next forward rotation operation performed after the first reverse rotation operation, a second reverse rotation operation which is the last reverse rotation operation performed in the series of operations, and a second forward rotation operation which is the next forward rotation operation performed after the second reverse rotation operation. The control unit controls the drive unit such that the first amount of movement of the image carrier in the forward rotation operation performed after the first reverse rotation operation in the series of operations is greater than the second amount of movement of the image carrier in the reverse rotation operation performed after the first reverse rotation operation in the series of operations, and the amount of movement of the image carrier in the second forward rotation operation is less than the amount of movement of the image carrier in the second reverse rotation operation.

7. The image forming apparatus according to claim 6, characterized in that the control unit controls the drive unit such that the amount of movement of the image carrier in any of the reverse rotation operations performed after the first reverse rotation operation in the series of operations is smaller than the amount of movement of the image carrier in the forward rotation operation performed immediately before it.

8. The image forming apparatus according to claim 6, characterized in that the control unit is configured to execute the mode when the number of output sheets for the job is greater than a predetermined number.

9. The image forming apparatus according to claim 8, characterized in that, when the number of output sheets for the job is less than or equal to the predetermined number, the control unit stops the image carrier after performing the reverse rotation operation followed by the forward rotation operation once at the end of the job, and controls the drive unit such that the amount of movement of the image carrier in the forward rotation operation is less than the amount of movement of the image carrier in the reverse rotation operation.

Images