Image forming apparatus

Abstract

To prevent the occurrence of an image defect in a subsequent image caused by toner in an untransferred toner image on an intermediate transfer body occurring due to switching of an automatic feeder.SOLUTION: When an automatic feeder switching is performed, when a position of a leading end in a conveyance direction of an untransferred toner image on an intermediate transfer body is defined as an untransferred toner image leading end, and a position of a leading end in the conveyance direction of an image forming area on an image carrier on which the first toner image after resumption of image formation may be formed is defined as a post-resumption image leading end, a control unit performs control of resuming image formation so that after the untransferred toner image leading end passes through a primary transfer unit first, the post-resumption image leading end reaches the primary transfer unit first.SELECTED DRAWING: Figure 10

Description

[Technical Field]

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

[0002] Conventionally, some image forming apparatuses, such as electrophotographic copying machines, employ an intermediate transfer system. In such image forming apparatuses, a toner image formed on an image carrier is primarily transferred to an intermediate transfer member at a primary transfer unit, and then this toner image is secondarily transferred to a recording material, such as paper, at a secondary transfer unit. A photosensitive drum, which is a drum-shaped photosensitive member (electrophotographic photosensitive member), is often used as the image carrier. An endless intermediate transfer belt is often used as the intermediate transfer member. The recording material is housed in, for example, a cassette serving as a feeding unit and fed from the cassette toward the secondary transfer unit. Toner remaining on the intermediate transfer belt without being transferred to the recording material at the secondary transfer unit (transfer residual toner) is cleaned by a belt cleaning device. Belt cleaning devices often employ a blade cleaning system equipped with a cleaning blade made of a plate-shaped elastic material as a cleaning member. The cleaning blade is made of a rubber material, such as urethane rubber, and is brought into contact with the surface of the intermediate transfer belt in a direction counter to the direction of movement of the intermediate transfer belt surface.

[0003] In such image forming apparatuses, it may be detected that a cassette is out of recording material (herein referred to as "out of paper") during continuous image formation, in which images are formed on multiple recording materials. In such cases, the image forming apparatus may be equipped with a function that automatically switches the recording material feed source to another cassette containing the same type of recording material to continue continuous image formation (herein referred to as "automatic feed unit switching"). Furthermore, for purposes such as improving productivity, intermediate transfer type image forming apparatuses may be configured to start image formation (specifically, formation of an electrostatic latent image on a photosensitive drum by exposure) prior to the start of recording material feeding. In this case, when the paper out state is detected, image formation on the next recording material has already begun. Therefore, in this case, the toner image (herein referred to as "untransferred toner image") that has already been transferred to the intermediate transfer belt when image formation was already underway when the paper out state was detected is cleaned by a belt cleaning device, and image formation of the same page as the untransferred toner image is resumed.

[0004] Patent Document 1 proposes that when switching automatic feeding units, image formation is resumed before the secondary transfer member to which toner adheres as an untransferred toner image passes through the secondary transfer unit is cleaned. This makes it possible to transfer a toner image of the same page as the untransferred toner image to the recording material fed from the switched cassette immediately after cleaning of the secondary transfer member is completed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-152884 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the untransferred toner image has a large amount of toner on the intermediate transfer belt and contains a large amount of toner with high fluidity. Therefore, when the untransferred toner image is transported to the cleaning nip, which is the contact point between the cleaning blade and the intermediate transfer belt, the toner may slip through the cleaning blade (also referred to as "slip-through" here). The toner that slips through the cleaning blade is transferred to the recording material after switching to the automatic feed unit, causing a defective image (slipped-through image).

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to prevent the occurrence of image defects in subsequent images due to toner remaining in an untransferred toner image on an intermediate transfer body caused by switching of an automatic feed unit. [Means for solving the problem]

[0008] The above object is achieved by an image forming apparatus according to the present invention. In summary, according to one aspect of the present invention, the image forming apparatus includes an image forming unit including a rotatable image carrier and performing image formation by forming a toner image on the image carrier, a rotatable intermediate transfer member to which the toner image is primarily transferred from the image carrier at a primary transfer unit, a secondary transfer member forming a secondary transfer unit that secondarily transfers the toner image from the intermediate transfer member to a recording material, a cleaning device that removes toner on the intermediate transfer member downstream of the secondary transfer unit and upstream of the primary transfer unit in the movement direction of the intermediate transfer member, the cleaning device having a cleaning blade that abuts on the surface of the intermediate transfer member along the width direction of the intermediate transfer member, a first feed unit and a second feed unit that feed the recording material toward the secondary transfer unit, and a control that changes the recording material feed source from the first feed unit to the second feed unit when it is detected that the recording material is not present in the first feed unit after the image formation has started. and a control unit that controls the resumption of the image formation, which forms a toner image to be secondarily transferred onto the recording material fed from the second feeding unit, when the feeding source of the recording material is changed from the first feeding unit to the second feeding unit, when a toner image that passes through the secondary transfer unit without being transferred onto the recording material before the recording material fed from the second feeding unit reaches the secondary transfer unit is defined as an untransferred toner image, the position of the leading edge of the untransferred toner image on the intermediate transfer body in the transport direction is defined as the leading edge of the untransferred toner image, and the position of the leading edge of the image forming area on the image carrier on which a first toner image can be formed after the image formation is resumed is defined as the leading edge of the image after resumption. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent the occurrence of image defects in subsequent images due to toner of an untransferred toner image on an intermediate transfer body that occurs due to switching of an automatic feed unit. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic cross-sectional view of an image forming unit. [Figure 3] FIG. 2 is a schematic diagram illustrating an outline of a control configuration of the image forming apparatus. [Figure 4] FIG. 2 is a schematic cross-sectional view showing a belt cleaning device. [Figure 5] 5A and 5B are schematic cross-sectional views for explaining the contact conditions of the cleaning blade. [Figure 6] FIG. 10 is a flowchart for explaining an outline of control in a comparative example. [Figure 7] FIG. 10 is a timing chart for explaining an example of the operation of the comparative example. [Figure 8] FIG. 10 is a schematic diagram for explaining toner slip-through. [Figure 9] FIG. 10 is a schematic diagram for explaining the leading edge of an untransferred toner image. [Figure 10] FIG. 2 is a flowchart for explaining an outline of control in the embodiment. [Figure 11] FIG. 4 is a timing chart for explaining an example of the operation of the embodiment. [Figure 12] FIG. 10 is a schematic cross-sectional view showing another example of a belt cleaning device. [Figure 13] FIG. 4 is a schematic cross-sectional view for explaining the swing angle of the cleaning blade. [Figure 14] FIG. 10 is a timing chart illustrating an example of a voltage at a secondary transfer portion when an untransferred toner image passes through. [Figure 15] FIG. 10 is a timing chart illustrating an example of a voltage at a secondary transfer portion when an untransferred toner image passes through. DETAILED DESCRIPTION OF THE INVENTION

[0011] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0012] [Example 1] 1. Overall configuration and operation of the image forming apparatus FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 is a tandem laser beam printer employing an intermediate transfer method, capable of forming full-color images using electrophotography. The image forming apparatus 100 forms an image on a sheet-like recording material S in response to an image signal (image information) received from an external device such as a personal computer. Because the image forming apparatus 100 primarily uses paper as the recording material S, the recording material S is sometimes referred to as paper, but the recording material S is not limited to paper. The recording material S may also be made of materials other than paper or materials containing materials other than paper, such as synthetic paper or film made primarily of a synthetic resin, or special paper such as metal-coated paper.

[0013] Image forming apparatus 100 has four image forming stations PY, PM, PC, and PK that form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The four image forming stations PY, PM, PC, and PK are linearly arranged in this order along the direction of movement (conveyance direction, advancement direction, running direction) of the surface of intermediate transfer belt 7, which will be described later. Note that elements having the same or corresponding functions or configurations provided for each color may be described collectively by omitting the Y, M, C, or K suffixes to the reference numerals indicating that the element is for one of the colors. Figure 2 is a schematic cross-sectional view of image forming station P. In this embodiment, the image forming unit P is configured to include photosensitive drums 1 (1Y, 1M, 1C, 1K), charging rollers 2 (2Y, 2M, 2C, 2K), exposure devices 3 (3Y, 3M, 3C, 3K), developing devices 4 (4Y, 4M, 4C, 4K), drum cleaning devices 6 (6Y, 6M, 6C, 6K), etc., which will be described later.

[0014] The photosensitive drum 1, a rotatable drum-type (cylindrical) electrophotographic photosensitive member (photoconductor) serving as an image carrier, is driven to rotate at a predetermined peripheral speed (surface movement speed) in the direction of arrow R1 (clockwise) in the figure. The photosensitive drum 1 is driven to rotate by a driving force transmitted from a drum drive motor D1 (FIG. 3) serving as a driving means. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charging roller 2, a roller-type charging member serving as a charging means. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source E1 (FIG. 3) serving as a charging voltage application means (application unit). In this embodiment, an oscillating voltage composed of a superimposed DC voltage and an AC voltage is applied to the charging roller 2 as the charging voltage. Note that, in the direction of rotation of the photosensitive drum 1, minute gaps are formed between the photosensitive drum 1 and the charging roller 2 on the upstream and downstream sides of the contact point between the photosensitive drum 1 and the charging roller 2. The charging roller 2 charges the surface of the photosensitive drum 1 by discharging generated in at least one of the gaps on the upstream side and the downstream side.

[0015] The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure device (laser scanner) 3 serving as an exposure means, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. The exposure device 3 irradiates the surface of the photosensitive drum 1 with laser light based on an image signal, and forms an electrostatic latent image on the photosensitive drum 1. Note that the exposure device 3 may be configured as a single unit that exposes the four photosensitive drums 1Y, 1M, 1C, and 1K.

[0016] The toner image formed on the photosensitive drum 1 is developed (visualized) by a developing device 4 serving as a developing means, which supplies toner and forms a toner image (toner image, developer image) on the photosensitive drum 1. In this embodiment, the developing device 4 uses a two-component developer, which is a mixture of carrier (magnetic carrier particles) and toner (non-magnetic toner particles) (details of the developer will be described later). The developing device 4 includes a developing sleeve 41 serving as a developer carrier (developing member) and a developing container 42 that contains the developer. The developing sleeve 41 carries the developer and transports it to a developing section that faces the photosensitive drum 1, where the toner adheres to the photosensitive drum 1 in accordance with the electrostatic latent image on the photosensitive drum 1. During development, the developing sleeve 41 is rotated by a driving force transmitted from, for example, a drum drive motor D1. During development, a predetermined developing voltage (developing bias) is applied to the developing sleeve 41 by a developing power source E2 serving as a developing voltage applying means (applying section). In this embodiment, an oscillating voltage in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 41 as a developing voltage. In this embodiment, a toner image is formed by image area exposure and reversal development. That is, toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 1, where the absolute value of the potential is reduced by exposure after being substantially uniformly charged. In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative. In addition, the amount of toner consumed during development is replenished to the developing devices 4Y, 4M, 4C, and 4K from toner bottles 16Y, 16M, 16C, and 16K, which serve as replenishment containers.

[0017] An intermediate transfer belt 7, which is an endless belt serving as an intermediate transfer body, is disposed facing the four photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 7 is stretched over and tensioned by a predetermined tension around a plurality of support rollers (tension rollers) including a drive roller 71, a downstream auxiliary roller 72, an upstream auxiliary roller 73, and a tension roller 74. The drive roller 71 is driven to rotate by a driving force transmitted from a belt drive motor D2 (FIG. 3) serving as a driving means. The intermediate transfer belt 7 receives a driving force transmitted by the rotation of the drive roller 71, and rotates (moves orbitally) in the direction of arrow R2 (counterclockwise) in the figure at a peripheral speed substantially equal to that of the photosensitive drum 1. The peripheral speed (surface movement speed) of the photosensitive drum 1 and the intermediate transfer belt 7 corresponds to the process speed of the image forming apparatus 100. The downstream auxiliary roller 72 and the upstream auxiliary roller 73 form an image transfer surface (a plane onto which a toner image is primarily transferred) of the intermediate transfer belt 7, which is disposed substantially horizontally. A tension roller 74 applies a predetermined tension to the intermediate transfer belt 7. Primary transfer rollers 5Y, 5M, 5C, and 5K, which are roller-type primary transfer members serving as primary transfer means, are disposed on the inner circumferential surface (back surface) of the intermediate transfer belt 7, corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. The primary transfer rollers 5Y, 5M, 5C, and 5K are pressed against the photosensitive drums 1 and contact the photosensitive drums 1 via the intermediate transfer belt 7, forming a primary transfer portion (primary transfer nip portion) N1, which is the contact portion between the photosensitive drums 1 and the intermediate transfer belt 7. The primary transfer portion N1 is a position where a toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 7. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 7 at the primary transfer portion N1 by the action of the primary transfer rollers 5. During primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage of opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 5 by a primary transfer power supply E3 (FIG. 3) serving as a primary transfer voltage application means (application unit). For example, when a full-color image is formed, toner images of each color, yellow, magenta, cyan, and black, formed on each photosensitive drum 1 are transferred sequentially onto the intermediate transfer belt 7 so as to be superimposed at each primary transfer unit N1.

[0018] Here, rubber materials and resin materials are widely used as materials for the intermediate transfer belt 7. In this embodiment, a belt (film) formed in an endless shape with a single layer structure, made of PEEK (polyether ether ketone), a resin material, was used as the intermediate transfer belt 7. The intermediate transfer belt 7 has a resin base material in which, for example, carbon black is dispersed as a conductive agent, and has a surface resistivity of, for example, 1×10 12 [Ω / □], volume resistivity is 1×10 9 The electrical resistance is adjusted to [Ω·cm]. A lubricant is applied to the surface of the intermediate transfer belt 7 to reduce the initial (new) surface friction resistance (mainly the friction resistance against the cleaning blade 82, which will be described later). Kyna and zinc stearate are widely used lubricants. In this embodiment, zinc stearate was used as the lubricant. Zinc stearate can be applied to the surface of the intermediate transfer belt 7 as follows: Powdered zinc stearate is mixed with a volatile solvent (HEF in this embodiment) at a predetermined ratio, and the mixture is applied. This allows the lubricant to be applied efficiently and uniformly to the surface of the intermediate transfer belt 7.

[0019] A secondary transfer roller (secondary transfer outer roller) 9, a roller-shaped secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface (surface) of the intermediate transfer belt 7, facing the drive roller 71, which functions as a secondary transfer opposing roller (secondary transfer inner roller). The secondary transfer roller 9 is pressed against the drive roller 71 and contacts the drive roller 71 via the intermediate transfer belt 7, forming a secondary transfer portion (secondary transfer nip portion) N2, which is the contact portion between the intermediate transfer belt 7 and the secondary transfer roller 9. At the secondary transfer portion N2, the toner image formed on the intermediate transfer belt 7 is transferred (secondarily transferred) onto the recording material S, which is being conveyed while being sandwiched between the intermediate transfer belt 7 and the secondary transfer roller 9, by the action of the secondary transfer roller 9. During the secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 9 by a secondary transfer power source E4 ( FIG. 3 ) serving as a secondary transfer voltage application means (application unit). In this embodiment, the drive roller 71 is electrically grounded (connected to ground potential). A recording material (transfer material, paper, sheet) S such as paper is fed from a feeding device (paper feeder) 20 serving as a feeding means and supplied to the secondary transfer unit N2. The feeding device 20 includes cassettes 12 (first cassette 12A, second cassette 12B) serving as a recording material storage unit serving as a feeding unit, paper feed rollers (pickup rollers) 13 (first paper feed roller 13A, second paper feed roller 13B) serving as feeding members, and a pair of conveying rollers 14 (first conveying roller pair 14A, second conveying roller pair 14B) serving as conveying members. The recording material S stored in the first cassette 12A is sent out from the first cassette 12A by the first paper feed roller 13A, conveyed by the first conveying roller pair 14A, and conveyed to a pair of registration rollers 16 serving as a synchronous conveying member. Similarly, the recording material S stored in the second cassette 12B is sent out from the second cassette 12B by the second paper feed roller 13B, and is then conveyed by the second conveying roller pair 14B to the registration roller pair 16. The recording material S conveyed to the registration roller pair 16 is conveyed to the secondary transfer portion T2 by the registration roller pair 16 in synchronization with the toner image on the intermediate transfer belt 7.Although, for example, plain paper, synthetic resin sheets, envelopes, etc. are used as the recording material S, in this embodiment, the recording material S will be described as plain paper. The first and second cassettes 12A and 12B are removably disposed at the bottom of the apparatus body 101 of the image forming apparatus 100. The recording materials S stored in the first and second cassettes 12A and 12B are selectively fed one sheet at a time from the first cassette 12A or the second cassette 12B by the first paper feed roller 13A or the second paper feed roller 13B.

[0020] The recording material S onto which the toner image has been secondarily transferred is conveyed to a fixing device 10 serving as a fixing means. The fixing device 10 has a fixing film 10a serving as a fixing member (fixing rotor) with a heat source provided on its inner circumferential surface, and a pressure roller 10b serving as a pressure member (pressure rotor). The fixing device 10 heats and presses the recording material S onto which the toner image has been transferred in a fixing section (fixing nip section) where the fixing film 10a and the pressure roller 10b contact each other, thereby fixing (melting and adhering) the toner image onto the recording material S. The temperature of the fixing device 10 is determined based on the detection results of an environmental temperature sensor (not shown) and the type of recording material S. Generally, for the same process speed, the lower the environmental temperature and the greater the basis weight of the set recording material S (paper), the higher the temperature of the fixing device 10 is set. The types of recording material S include, for example, plain paper 1, plain paper 2, and plain paper 3, each with a basis weight of 64 to 75 g / m. 2 , 76~90g / m 2 , 91~105g / m 2 In addition, when referring to a numerical range, "to" means that the numerical values ​​before and after it are included. The temperatures of the fixing device 10 set for plain paper 1, plain paper 2, and plain paper 3 are 190°C, 200°C, and 210°C, respectively, at an ambient temperature of 23°C. The recording material S on which the toner image has been fixed is discharged (output) by a pair of discharge rollers 11, which serves as a discharge and conveyance member, onto a discharge tray 30 provided on the outside (top surface) of the device main body 101 of the image forming apparatus 100.

[0021] Toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed (cleaned) and collected from the photosensitive drum 1 by a drum cleaning device 6 serving as a photosensitive body cleaning means. The drum cleaning device 6 has a collection container 61 that stores toner, and a cleaning blade 62 that serves as a cleaning member disposed in contact with the photosensitive drum 1. The drum cleaning device 6 uses the cleaning blade 62 to scrape the primary transfer residual toner from the surface of the rotating photosensitive drum 1 and collects it in the collection container 61.

[0022] Furthermore, a belt cleaning device 8 serving as intermediate transfer cleaning means is disposed on the outer peripheral surface side of the intermediate transfer belt 7, at a position facing the tension roller 74. Adherents such as toner remaining on the intermediate transfer belt 7 after the secondary transfer (secondary transfer residual toner) are removed (cleaned) and collected from the intermediate transfer belt 7 by the belt cleaning device 8. Details of the belt cleaning device 8 will be described later.

[0023] The first and second paper feed rollers 13A and 13B are each driven to rotate by a driving force transmitted from a paper feed motor D3 (FIG. 3) serving as a driving means. The first and second conveyance roller pairs 14A and 14B, the registration roller pair 16, and the paper discharge roller pair 11 are each driven to rotate by a driving force transmitted from a conveyance motor D4 (FIG. 3) serving as a driving means. The image forming apparatus 100 also includes a paper presence sensor 21 (first paper presence sensor 21A, second paper presence sensor 21B) serving as a recording material presence / absence detection means, paper feed sensors (first paper feed sensor 22A, second paper feed sensor 22B) serving as a recording material feed detection means, and a paper discharge sensor 31 serving as a recording material discharge detection means. The first and second paper feed sensors 22A and 22B detect whether feeding of the recording material S from the first and second cassettes 12A and 12B has been completed, respectively. Furthermore, when paper feeding from first and second cassettes 12A and 12B is completed, first and second paper presence sensors 21A and 21B detect the presence or absence of recording material S in first and second cassettes 12A and 12B, respectively. Furthermore, paper discharge sensor 31 detects whether recording material S has been discharged to the outside (outside the machine) of apparatus main body 101 of image forming apparatus 100. Paper presence sensor 21 (first and second paper presence sensors 21A and 21B), paper feed sensor 22 (first and second paper feed sensors 22A and 22B), and paper discharge sensor 31 are configured, for example, with optical sensors equipped with a light-emitting section and a light-receiving section.

[0024] 2. Control Configuration 3 is a block diagram showing an outline of the control configuration of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 has an engine controller 110 and a video controller 120. The video controller 120 processes an image signal input from an external device (not shown) such as a personal computer and sends the processed image signal to the engine controller 110. The engine controller 110 controls the operation of the image forming apparatus 100, such as an image forming operation, based on the image signal input from the video controller 120.

[0025] The engine controller 110 includes a CPU 111 as a control unit (arithmetic processing unit), a memory 112 as a storage unit, and an input / output unit (not shown) for inputting and outputting information to and from devices external to the engine controller 110. The memory 112 includes storage media such as a ROM and a RAM. The ROM stores control programs, such as programs for executing image forming operations, in advance. The RAM stores information input to the engine controller 110, detected information, and calculation results. The engine controller 110 is connected to various components of the image forming apparatus 100. For example, the engine controller 110 is connected to various power sources, such as a charging power source E1, a developing power source E2, a primary transfer power source E3, and a secondary transfer power source E4. The engine controller 110 is also connected to various drive units, such as a drum drive motor D1, a belt drive motor D2, a paper feed motor D3, and a conveyance motor D4. Furthermore, various sensors such as a paper presence sensor 21 (first and second paper presence sensors 21A and 21B), a paper feed sensor 22 (first and second paper feed sensors 22A and 22B), and a paper discharge sensor 31 are connected to the engine controller 110. Signals indicating the detection results of the various sensors are input to the engine controller 110. The CPU 111 controls the operation of each part of the image forming apparatus 100 and causes the image forming apparatus 100 to perform various operations such as an image forming operation.

[0026] Although not shown in the drawings, in this embodiment, the charging power supply E1, the developing power supply E2, and the primary transfer power supply E3 are provided independently for each image forming station P. The drum drive motor D1 may be provided independently for each photosensitive drum 1, or may be shared by all or some of the photosensitive drums 1. The paper feed motor D3 may be provided independently for each paper feed roller 13A, 13B, or may be shared by all or some of the paper feed rollers 13A, 13B. The transport motor D4 may be provided independently for each of the transport roller pairs 14A, 14B, the registration roller pair 16, and the paper discharge roller pair 11, or may be shared by all or some of them.

[0027] The image forming apparatus 100 executes a job (print job), which is a series of operations that starts with a single start command and forms and outputs an image on one or multiple recording materials S. A job generally includes an image formation process, a pre-rotation process, a sheet spacing process, and a post-rotation process. The image formation process is a period during which electrostatic image formation (exposure), toner image formation (development), and toner image transfer of the image that will actually be formed and output on the recording material S are performed. This period is referred to as the image formation time. More specifically, the timing of the image formation process differs depending on the position where each of the electrostatic image formation, toner image formation, and toner image transfer processes is performed. The pre-rotation process is a period during which preparatory operations are performed before the image formation process, from when a start command is input until the actual start of image formation. The sheet spacing process is a period corresponding to the interval between recording materials S when image formation is performed continuously on multiple recording materials S (continuous image formation). The post-rotation process is a period during which tidying up operations (preparatory operations) are performed after the image formation process. Non-image formation refers to periods other than image formation, and includes the above-mentioned pre-rotation process, paper interval process, post-rotation process, and also the pre-multi-rotation process, which is a preparatory operation when the image forming device 100 is turned on or when it returns from a sleep state.

[0028] 3. Belt cleaning device 4 is a schematic cross-sectional view showing the belt cleaning device 8 in this embodiment. Fig. 4 shows a cross section in the width direction of the intermediate transfer belt 7 (a direction substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 7), i.e., substantially perpendicular to the direction of the rotation axis of the support rollers (tension roller 74, etc.) of the intermediate transfer belt 7.

[0029] The belt cleaning device 8 is disposed on the outer peripheral surface side of the intermediate transfer belt 7, downstream of the secondary transfer portion N2 and upstream of the primary transfer portion N1 (the most upstream primary transfer portion N1Y) in the rotation direction of the intermediate transfer belt 7. In this embodiment, the belt cleaning device 8 is disposed opposite the tension roller 74 across the intermediate transfer belt 7.

[0030] The belt cleaning device 8 has a collection container (casing) 81 with an opening 81a on the side of the intermediate transfer belt 7. The belt cleaning device 8 also has a cleaning blade 82 as a cleaning member, positioned at the opening 81a of the collection container 81. The cleaning blade 82 is attached to the collection container 81 via a support member 83.

[0031] The cleaning blade 82 is a plate-like member having a predetermined thickness and a predetermined length in both a longitudinal direction disposed substantially parallel to the width direction of the intermediate transfer belt 7 and a lateral direction substantially perpendicular to the longitudinal direction. In this embodiment, the cleaning blade 82 is formed of urethane rubber (polyurethane) as an elastic material. The cleaning blade 82 has a fixed end, which is one end in the lateral direction, fixed to a support member 83. In this embodiment, the support member 83 is fixed to a collection container 81. An edge portion 82a on the outer side (the intermediate transfer belt 7 side) of the tip of the free end, which is the other end in the lateral direction, of the cleaning blade 82 is brought into contact with the surface of the intermediate transfer belt 7. The tip of the free end of the cleaning blade 82 is brought into contact with the surface of the intermediate transfer belt 7 so that it faces upstream in the direction of movement of the surface of the intermediate transfer belt 7 during image formation, i.e., in the counter direction to the direction of movement of the surface of the intermediate transfer belt 7. The cleaning blade 82 is pressed against the tension roller 74 via the intermediate transfer belt 7. The contact area between the cleaning blade 82 and the intermediate transfer belt 7 is a cleaning nip area (cleaning area) Q. The belt cleaning device 8 uses the cleaning blade 82 to scrape off adhering matter such as secondary transfer residual toner from the surface of the rotating intermediate transfer belt 7 and collects the adhering matter in a collection container 81.

[0032] The belt cleaning device 8 also includes a collecting sheet 84 located upstream of the cleaning blade 82 in the moving direction of the surface of the intermediate transfer belt 7 and at the opening 81 of the collection container 81. The collecting sheet 84 is attached to the collection container 81. The collecting sheet 84 is a sheet-like member having a predetermined thickness and a predetermined length in both a longitudinal direction substantially parallel to a direction substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 7 and a lateral direction substantially perpendicular to the longitudinal direction. In this embodiment, the collecting sheet 84 is formed of a flexible plastic sheet. A fixed end, which is one end in the lateral direction of the collecting sheet 84, is fixed to the collection container 81. The tip of the free end, which is the other end in the lateral direction of the collecting sheet 84, is in contact with the intermediate transfer belt 7. The tip of the free end of the collecting sheet 84 is in contact with the intermediate transfer belt 7 so that it faces downstream in the moving direction of the surface of the intermediate transfer belt 7 during image formation. The scouring sheet 84 drops the toner scraped off from the surface of the intermediate transfer belt 7 by the cleaning blade 82 into the collection container 81, and also prevents the toner from flowing back from the collection container 81 to the intermediate transfer belt 7.

[0033] The belt cleaning device 8 also has a conveying screw 85 as a toner conveying member in the collection container 81. The conveying screw 85 conveys the toner collected in the collection container 81 along the longitudinal direction of the collection container 81 (the width direction of the intermediate transfer belt 7, the longitudinal direction of the cleaning blade 82) and discharges the toner from a discharge port (not shown) provided in the collection container 81. The toner discharged from the collection container 82 is conveyed to a collected toner box (not shown) arranged in the image forming apparatus 100 through a conveying path (not shown) provided in the image forming apparatus 100.

[0034] 4. Cleaning blade contact conditions The contact conditions of the cleaning blade 82 with the intermediate transfer belt 7 in this embodiment will be further described.

[0035] In this embodiment, the rubber hardness (JIS-A hardness) of the cleaning blade 82 is set to 65 to 75°. The set angle θ1 of the cleaning blade 82 is set to 12 to 18°. The penetration amount δ of the cleaning blade 82 into the intermediate transfer belt 7 is set to 0.3 to 1.2 mm. By setting the rubber hardness, set angle θ1, and penetration amount δ as described above, the contact pressure (static pressure) of the cleaning blade 82 against the intermediate transfer belt 7 is set to 18 gf / cm or less, and preferably 15 gf / cm or less. From the viewpoint of sufficiently cleaning residual toner after secondary transfer, the contact pressure (static pressure) of the cleaning blade 82 against the intermediate transfer belt 7 is set to 5 gf / cm or more, and preferably 10 gf / cm or more.

[0036] The cleaning blade 82 may be configured so that the rubber hardness of the entire cleaning blade 82 is within the above-mentioned range, or may be configured so that the portion that contacts the intermediate transfer belt 7 has a hardened layer whose rubber hardness is within the above-mentioned range. The hardened layer may be a layer provided on the surface of the cleaning blade 82, or, from the viewpoint of improving durability, may be a layer obtained by processing a portion of the substrate (main body) of the cleaning blade 82. When polyurethane is used as the substrate of the cleaning blade 82, the hardened layer can be formed as follows. That is, the portion of the cleaning blade 82 that contacts the intermediate transfer belt 7 is immersed in an isocyanate compound for a certain period of time. Then, the polyurethane contained in the substrate of the cleaning blade 82 is reacted with the isocyanate compound to form the reacted portion as a hardened layer.

[0037] The set angle θ1 and the penetration amount δ are defined as follows. FIG. 5 is a schematic cross-sectional view of the vicinity of the cleaning blade 82, assuming that the tip of the cleaning blade 82 penetrates into the intermediate transfer belt 7 (tension roller 74) without deformation. FIG. 5 shows a cross section approximately perpendicular to the width direction of the intermediate transfer belt 7 (the longitudinal direction of the cleaning blade 82). In FIG. 5, the point where the tip surface of the cleaning blade 82 intersects with the intermediate transfer belt 7 is defined as intersection F. The tangent to the intermediate transfer belt 7 at intersection F is defined as tangent L1. The angle between tangent L1 and the surface of the cleaning blade 82 facing the intermediate transfer belt 7 is defined as set angle θ1. In FIG. 5, the straight line that is parallel to tangent L1 and passes through the edge portion 82a of the tip of the cleaning blade 82 is defined as straight line L2. At this time, the distance (shortest distance) between the tangent line L1 and the straight line L2, that is, the distance from the tangent line L1 to the edge portion 82a at the tip of the free end portion 31e of the cleaning blade 82, is defined as the penetration amount δ.

[0038] Furthermore, the cleaning blade 82 is brought into contact with the opposing member with the set angle θ1 and penetration amount δ set as desired conditions, and the pressure with which the opposing member is pressed by the cleaning blade 82 is measured with a pressure sensor (for example, manufactured by MISUMI Co., Ltd.), and this value is taken as the contact pressure (static pressure). The contact pressure (static pressure) of the cleaning blade 82 against the intermediate transfer belt 7 is expressed as a contact load (gf) per unit length (1 cm) in the longitudinal direction of the cleaning blade 82.

[0039] In this embodiment, in a configuration in which the cleaning blade 82 is fixed (fixed system), the contact pressure (static pressure) of the cleaning blade 82 against the intermediate transfer belt 7 is set relatively low due to the contact conditions described above. This increases the dynamic friction coefficient at the contact portion between the cleaning blade 82 and the intermediate transfer belt 7, making it less likely that blade squeal (generation of abnormal noise) will occur when the frictional force between the cleaning blade 82 and the intermediate transfer belt 7 increases. The dynamic friction coefficient at the contact portion between the cleaning blade 82 and the intermediate transfer belt 7 can increase due to continued image formation at a low print rate, an increase in the cumulative amount of use of the intermediate transfer belt 7, and the like.

[0040] However, this configuration makes it easier for toner in untransferred toner images to slip through when the automatic feeder switching described below is performed. In other words, in a fixed system, if the contact pressure (static pressure) is set to 18 gf / cm or less, it becomes difficult to ensure sufficient dynamic pressure when the dynamic friction coefficient at the contact point between the cleaning blade 82 and the intermediate transfer belt 7 decreases due to the presence of toner in the untransferred toner image. This makes it easier for toner in the untransferred toner image to slip through. Here, dynamic pressure refers to the pressure applied by the cleaning blade 82 to the intermediate transfer belt 7 when the surface of the intermediate transfer belt 7 moves. As will be described in detail later, the frictional force generated when the surface of the intermediate transfer belt 7 moves causes the tip of the cleaning blade 82 to deform so as to be caught in the direction of movement of the surface of the intermediate transfer belt 7. Dynamic pressure refers to the pressure applied to the tip of the cleaning blade 82 when this deformation occurs. As the dynamic friction coefficient at the contact point between the cleaning blade 82 and the intermediate transfer belt 7 increases, the frictional force also increases, resulting in greater deformation of the tip of the cleaning blade 82 and an increase in dynamic pressure.

[0041] 5. Developer In this embodiment, the developing device 4 develops the electrostatic image on the photosensitive drum 1 using a two-component developer, which is a mixture of carrier (magnetic carrier particles) and toner (non-magnetic toner particles). In this embodiment, a developer in which the carrier and toner are mixed at a weight ratio of 91:9 (toner concentration: 9%) is used. In this embodiment, the total weight of the initial developer contained in the developing device 4 is 208 g.

[0042] In this example, ferrite particles coated with silicone resin were used as the carrier. In this example, the saturation magnetization of the carrier with respect to an applied magnetic field of 240 kA / m was 24 [Am 2 / kg]. In this example, the specific resistance of the carrier at an electric field strength of 3000 [V / cm] is 1×10 7 [Ω·cm]~1×10 8 In this example, the weight average particle diameter of the carrier is 50 μm.

[0043] The toner is composed of materials containing at least 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-based resins, polyester-based resins, and polyethylene resins can also be used as the binder resin. As the colorant, various pigments and dyes can be used alone or in combination. As the charge control agent, a material containing a charge control agent to reinforce charge control can be used as needed. As the charge control agent to reinforce charge control, nigrosine dyes, triphenylmethane dyes, etc. can be used.

[0044] The toner may also contain wax. The wax is contained for the purpose of improving the releasability from the fixing member during fixing and the fixing property. Examples of wax that can be used include paraffin wax, carnauba wax, and polyolefin. The wax is used by mixing and dispersing it in a binder resin. In this example, the toner material used was a resin in which a binder resin, a colorant, a charge control agent, and wax were mixed and dispersed, and then pulverized using a mechanical pulverizer. The melting point of the wax used in this example was 100°C or less.

[0045] Furthermore, external additives are added to the toner. Examples of external additives include hydrophobically treated amorphous silica, titanium oxide, and titanium compounds. Typical examples of external additives include inorganic oxide particles. Adding external additives to the toner can adjust the toner's fluidity and charge amount. The particle size (average particle size) of the external additive particles is preferably 1 nm or more and 100 nm or less. In this example, titanium oxide with an average particle size of 50 nm, amorphous silica with an average particle size of 2 nm, and amorphous silica with an average particle size of 100 nm were added to the toner base particles. The amounts (weight ratios) of the external additives added to the toner base particles were 0.5 wt% for titanium oxide with an average particle size of 50 nm, 0.5 wt% for amorphous silica with an average particle size of 2 nm, and 1.0 wt% for amorphous silica with an average particle size of 100 nm.

[0046] The toner having the above-mentioned composition had a weight average particle size of 6.6 μm when measured using a powder particle size image analyzer FPIA-3000 manufactured by Sysmex Corporation.

[0047] 6. Operation when out of paper is detected in the comparative example Next, the operation when a paper out state is detected during continuous image formation in a comparative example will be described. The image forming apparatus of the comparative example is essentially the same in basic configuration and operation as the image forming apparatus of this embodiment, except for the timing at which image formation resumes when the automatic feed unit is switched. Furthermore, in the image forming apparatus of the comparative example, elements having the same or corresponding functions or configurations as those of the image forming apparatus of this embodiment will be described using the same reference numerals as those of this embodiment.

[0048] The image forming apparatus 100 in this embodiment and the comparative example is provided with an automatic feed unit switching function, and is configured so that image formation starts prior to the feeding operation of the recording material S. Furthermore, the image forming apparatus 100 in this embodiment and the comparative example is configured so that the intermediate transfer belt 7 and the secondary transfer roller 9 cannot be separated from each other.

[0049] 6 is a flowchart for explaining an outline of the operation when paper out is detected during continuous image formation in a comparative example. Here, the overall flow of the operation when image forming apparatus 100 executes a job of continuous image formation will be explained. Details such as the timing at which image formation is resumed when automatic feed unit switching is performed will be described later.

[0050] When job information is input to the image forming apparatus 100 from an external device, the CPU 111 starts image formation based on an image signal (S101). The job information includes an instruction to start the job, information related to operation settings such as information specifying the type of recording material S (the cassette 12 containing a predetermined type of recording material S), and the image signal. The CPU 111 controls the image formation to start for each page before the recording material S is fed from the cassette 12. Then, every time the paper feed sensor 22 detects the completion of feeding one sheet of recording material S, the CPU 111 determines whether or not a paper out state has been detected based on the detection result of the paper presence / absence sensor 21 (S102). For example, when the recording material S is fed from the first cassette 12A, every time the first paper feed sensor 22 detects the completion of paper feeding, the first paper presence / absence sensor 21A determines whether or not a paper out state has been detected in the first cassette 12. For example, when the paper feed sensor 22 detects the passage of the leading edge of the recording material S in the transport direction, and then detects the passage of the trailing edge of the recording material S in the transport direction, the paper feed can be considered to be complete.

[0051] If the CPU 111 determines in S102 that no paper has been detected, it suspends image formation for the job (S103). Then, the CPU 111 determines whether recording material S is present in another cassette 12 that accommodates the type of recording material S specified in the job (S104). For example, if the first and second cassettes 12A and 12B accommodate the same type of recording material S and it is detected that no paper is present in the first cassette 12A, the second paper presence / absence sensor 21B detects whether recording material S is present in the second cassette 12B. In other words, for example, if recording material S is being fed from the first cassette 12A and it is detected that no paper is present in the first cassette 12A, it is detected whether there is another cassette 12 that accommodates the same type of recording material S as the first cassette 12A.

[0052] If the CPU 111 determines in S104 that another cassette 12 contains recording material S, it controls the cassette 12 from which the recording material S is fed to be switched to the other cassette 12 (S105). Here, when the paper-out state is detected in S102, image formation on the next recording material S has already begun. Therefore, the toner image transferred to the intermediate transfer belt 7, which has already started when the paper-out state is detected in S102, reaches the secondary transfer portion N2 before the recording material S reaches the secondary transfer portion N2. A portion of the toner in the toner image (untransferred toner image) that is not transferred to the recording material S at the secondary transfer portion N2 adheres to the surface of the secondary transfer roller 9, contaminating the secondary transfer roller 9. This contamination of the secondary transfer roller 9 causes contamination of the back side of the recording material S during subsequent image formation. Therefore, the CPU 111 controls the secondary transfer roller 9 to be cleaned (S106). In this example, the CPU 111 generates an electric field in the secondary transfer portion N2 to clean the secondary transfer roller 9. For example, CPU 111 controls the application of a voltage (herein also referred to as a "cleaning voltage") of the opposite polarity to that used during secondary transfer (i.e., negative polarity, which is the same polarity as the normal charging polarity of the toner) to secondary transfer roller 9. By applying the cleaning voltage to secondary transfer roller 9 in this manner, toner adhering to secondary transfer roller 9 can be moved (returned) to intermediate transfer belt 7. Toner of the untransferred toner image on intermediate transfer belt 7 and toner moved from secondary transfer roller 9 to intermediate transfer belt 7 by cleaning secondary transfer roller 9 are removed from intermediate transfer belt 7 and collected by belt cleaning device 8.

[0053] Then, the CPU 111 resumes image formation for the job from the same page as the untransferred toner image (S107). The CPU 111 determines whether or not all images for the job have been output (S108), and if they have been output, ends the job (S109), or if they have not been output, continues the job (S110) and returns to the process of S102.

[0054] If the CPU 111 determines in S102 that no paper is present, the process proceeds to S108. If the CPU 111 determines in S104 that no recording material S is present in another cassette 12, the CPU 111 controls the display unit provided in the image forming apparatus 100 or the display unit of an external device to notify the user that no recording material S is present (S111), and ends (interrupts) the job (S109).

[0055] FIG. 7 is a timing chart illustrating an example of operation when a paper out condition is detected during continuous image formation in a comparative example. FIG. 7 illustrates an example in which one sheet of recording material S is stored in the first cassette 12A, and multiple sheets of the same type of recording material S as the first cassette 12A are stored in the second cassette 12B. The recording material S is first fed from the first cassette 12A, and three pages of images are output in single-sided printing. FIG. 7 also shows the drive timing of the first and second paper feed rollers 13A and 13B, the image formation (exposure) timing, the voltage application timing of the primary transfer unit, and the voltage application timing (and polarity) of the secondary transfer unit over time. The operation of each unit according to this timing chart is controlled by the CPU 111. Here, the image of each page is formed using toner of at least one color over substantially the entire image formation area (the area where a toner image can be formed). The leading and trailing ends of the toner image and the image forming area refer to the leading and trailing ends in the transport direction (the direction of movement of the surface of the photosensitive drum 1 or the intermediate transfer belt 7), respectively. Also, the image forming area on the intermediate transfer belt 7 where an untransferred toner image can be carried is called the "untransferred toner image area."

[0056] First, image formation (exposure) of the first page begins (T1). After image formation of the first page begins, the first paper feed roller 13A is driven to start feeding the first sheet of recording material S from the first cassette 12A (T2). When feeding of the first sheet of recording material S is completed, the first paper presence / absence sensor 21A detects that there is no paper (T4). However, prior to this, image formation of the second page has already started (T3). The toner image of the first page is primarily transferred to the intermediate transfer belt 7 and then secondarily transferred to the first sheet of recording material S (T6-T7). Meanwhile, the toner image of the second page is primarily transferred to the intermediate transfer belt 7 and then reaches the secondary transfer portion N2, but at this time the recording material S has not yet been transported to the secondary transfer portion N2. Therefore, this toner image (untransferred toner image) passes through the secondary transfer portion N2 while still carried on the intermediate transfer belt 7 without being secondarily transferred to the recording material S. In this example, when the untransferred toner image area passes through the secondary transfer portion N2, the voltage applied to the secondary transfer roller 9 is turned OFF (0 V) (T8 to T10) so that the toner of the untransferred toner image does not adhere to the secondary transfer roller 9 as much as possible. After that, cleaning of the secondary transfer roller 9 is performed (T10 to T15). Specifically, a cleaning voltage (for example, -300 V) of the same polarity as the normal charging polarity of the toner is applied to the secondary transfer roller 9.

[0057] Meanwhile, after the image formation (exposure) of the second page is completed (T5), the image formation of the job is interrupted. Then, after waiting for a predetermined time corresponding to the time required for cleaning the secondary transfer roller 9, re-image formation (exposure) of the second page, which is the same as the untransferred toner image, is started (T9). After the re-image formation of the second page has started, the second paper feed roller 13B is driven to start feeding the recording material S (the first sheet after switching, the second sheet of the job) from the second cassette 12B after the automatic feed unit switching (T12). The toner image of the second page resulting from the re-image formation is primarily transferred to the intermediate transfer belt 7 (T11 to T14), and then secondarily transferred to the recording material S (T15 to T16). Thus, when the automatic feed unit switching is performed, the period from when the recording material S before the switching passes through the secondary transfer unit N2 until when the recording material S after the switching reaches the secondary transfer unit N2 is longer than the normal sheet interval. In other words, when the automatic feeding section is switched, the distance traveled by the surface of the intermediate transfer belt 7 from when the recording material S before the switch passes through the secondary transfer section N2 until when the recording material S after the switch reaches the secondary transfer section N2 becomes larger than the normal paper spacing.

[0058] Since the second cassette 12B contains a plurality of recording materials S, the toner image of the third page is secondarily transferred onto the recording material S transported from the second cassette 12B with the normal paper spacing therebetween.

[0059] In the comparative example, when automatic feed unit switching is performed, image formation is resumed as quickly as possible by performing secondary transfer immediately after cleaning of the secondary transfer roller 9. Therefore, the leading edge of the untransferred toner image area on the intermediate transfer belt 7 that has passed through the secondary transfer unit N2 overlaps with the image formation area to which the toner image after image formation is resumed can be primarily transferred before the intermediate transfer belt 7 reaches the secondary transfer unit N2. In other words, the leading edge of the untransferred toner image on the intermediate transfer belt 7 that has passed through the secondary transfer unit N2 can overlap with the image formation area to which the toner image after image formation is resumed can be primarily transferred before the intermediate transfer belt 7 reaches the secondary transfer unit N2. In the illustrated example, the leading edge of the untransferred toner image area on the intermediate transfer belt 7 that has passed through the secondary transfer unit N2 overlaps with the image formation area to which the toner image of the first page (the second page of the job) after image formation is resumed can be primarily transferred before the intermediate transfer belt 7 reaches the secondary transfer unit N2. In other words, image formation is resumed so that the image forming area on the intermediate transfer belt 7 after image formation is resumed reaches the secondary transfer portion N2 before the untransferred toner image area on the intermediate transfer belt 7 that has passed the secondary transfer portion N2 next reaches the secondary transfer portion N2. Note that depending on the time required for cleaning the secondary transfer roller 9, the leading edge of the untransferred toner image area on the intermediate transfer belt 7 may overlap with the image forming area onto which the toner images of the second and subsequent pages after image formation is resumed may be primarily transferred.

[0060] 7. Toner slippage of untransferred toner images Next, the slip-through of toner from an untransferred toner image will be described. Figure 8 is a schematic cross-sectional view of the vicinity of the cleaning nip portion Q. Figure 8 shows a cross section approximately perpendicular to the width direction of the intermediate transfer belt 7 (the longitudinal direction of the cleaning blade 82).

[0061] An untransferred toner image on the intermediate transfer belt 7 that is generated by switching the automatic feed unit is transported by the intermediate transfer belt 7 and cleaned by the cleaning blade 82 of the belt cleaning device 8. Because the untransferred toner image is not transferred to the recording material S at the secondary transfer unit N2, the amount of toner carried on the intermediate transfer belt 7 (weight of toner per unit area) is greater than that of normal secondary transfer residual toner. When an untransferred toner image with a large amount of toner carried on the intermediate transfer belt 7 enters the cleaning nip Q, there is a possibility that toner may slip through.

[0062] As shown in FIG. 8 , the cleaning blade 82 is in contact with the surface of the intermediate transfer belt 7 in a counter-direction relative to the moving direction of the surface of the intermediate transfer belt 7. The cleaning blade 82 is pressed against the tension roller 74 via the intermediate transfer belt 7. When the surface of the intermediate transfer belt 7 moves, the edge portion 82a at the tip of the cleaning blade 82 is deformed so as to be caught in the moving direction of the surface of the intermediate transfer belt 7 due to the frictional force between the cleaning blade 82 and the intermediate transfer belt 7. An external additive reservoir (hereinafter also referred to as a "blocking layer") containing external additives to be added to toner is formed near the edge portion 82a at the tip of the cleaning blade 82 (between the tip surface of the cleaning blade 82 and the surface of the intermediate transfer belt 7). This blocking layer prevents toner (recovered toner) on the intermediate transfer belt 7 from penetrating into the cleaning nip Q. In this way, the pressure of the cleaning blade 82 against the surface of the intermediate transfer belt 7 and the formation of the blocking layer prevent the recovered toner from penetrating into the cleaning nip Q. This allows the cleaning blade 82 to scrape the collected toner from the surface of the intermediate transfer belt 7, thereby cleaning the surface of the intermediate transfer belt 7.

[0063] However, when a toner image, such as an untransferred toner image, which has a large amount of toner on the intermediate transfer belt 7 and contains a large amount of highly fluid toner, is transported to the cleaning nip Q, toner slip-through may occur. This occurs because, when a large amount of highly fluid toner is transported, the toner that was blocked by the blocking layer circulates, pushing up the cleaning blade 82 and destroying the blocking layer. At this time, at each position in the longitudinal direction of the cleaning blade 82, when the leading edge of the untransferred toner image enters the cleaning nip Q, the toner lifts the cleaning blade 82, causing the toner to slip-through. Furthermore, for a one-page untransferred toner image, at each position in the longitudinal direction of the cleaning blade 82, after the leading edge of the untransferred toner image passes through the cleaning nip Q, the cleaning nip Q stabilizes, making toner slip-through less likely to occur.

[0064] As described above, in the comparative example, when the automatic feed unit is switched, the leading edge of the untransferred toner image area on the intermediate transfer belt 7 overlaps with the image forming area to which the toner image after image formation is resumed can be primarily transferred. In other words, the leading edge of the untransferred toner image on the intermediate transfer belt 7 can overlap with the image forming area to which the toner image after image formation is resumed can be primarily transferred. Therefore, in the comparative example, toner of the untransferred toner image that has slipped past the cleaning blade 82 is likely to be transferred to the recording material S after the automatic feed unit is switched, resulting in an image defect (slipped-through image). This is because the toner at the leading edge of the untransferred toner image that easily slips past the cleaning blade 82 can be transferred to the recording material S together with the toner image after image formation is resumed.

[0065] 8. Overview of Control in This Example Therefore, in this embodiment, the timing for resuming image formation when automatic feed unit switching is performed is set as follows. The leading edge of the untransferred toner image on the intermediate transfer belt 7 is defined as the "leading edge of the untransferred toner image." The leading edge of the image forming area on the photosensitive drum 1 where the first toner image will be formed after image formation is resumed is defined as the "leading edge of the image after resumption." Image formation is resumed so that the leading edge of the untransferred toner image first passes through the primary transfer unit N1, and then the leading edge of the image after resumption arrives at the primary transfer unit N1 first. Note that at multiple primary transfer units N1, primary transfer is performed so that toner images are superimposed on the same image forming area on the intermediate transfer belt 7. Therefore, if the above relationship holds for one primary transfer unit N1, the same relationship also holds for the other primary transfer units N1. In other words, image formation is resumed so that the image forming area on the intermediate transfer belt 7 corresponding to the leading edge of the image after resumption arrives at the secondary transfer unit N2 after the leading edge of the untransferred toner image that has passed through the secondary transfer unit N2 next arrives at the secondary transfer unit N2. In other words, after the leading edge of the untransferred toner image passes through the secondary transfer section N2 and the intermediate transfer belt 7 makes one revolution, the image forming area on the intermediate transfer belt 7 onto which the first toner image after image formation resumes can be primarily transferred reaches the secondary transfer section N2.

[0066] Here, the "leading edge of the untransferred toner image" will be further explained. The untransferred toner image area on the intermediate transfer belt 7 is divided into predetermined units along the longitudinal direction of the cleaning blade 82 (the width direction of the intermediate transfer belt 7), and each division is referred to as a "divided area." This predetermined unit is typically one pixel, but is not limited thereto. For example, the area may be divided into any number of divisions, for example, 2 to 50 (typically 5 to 20), each with a predetermined length (which may be multiple pixels) along the longitudinal direction of the cleaning blade 82 (the width direction of the intermediate transfer belt 7). In this case, the leading edge of the toner image in at least one divided area can be designated as the "leading edge of the untransferred toner image." In this way, by setting the timing for resuming image formation with the leading edge of the toner image in at least one divided area as the "leading edge of the untransferred toner image," the occurrence of slip-through images can be reduced compared to the comparative example. Furthermore, it is preferable to designate the leading edge of the toner image furthest from the leading edges of the toner images in each divided area as the "leading edge of the untransferred toner image." In this way, the occurrence of slip-through images can be more effectively suppressed by setting the timing for resuming image formation to be the "leading edge of the untransferred toner image" based on the leading edge of the toner image in each divided area that is the last to reach the cleaning nip portion Q. As described above, when the leading edge of the untransferred toner image enters the cleaning nip portion Q at each position in the longitudinal direction of the cleaning blade 82, the toner lifts the cleaning blade 82, causing the toner to slip through.

[0067] 9(a) and 9(b) are schematic diagrams of an untransferred toner image area on the intermediate transfer belt 7 and the untransferred toner image formed in that untransferred toner image area. In the illustrated example, the untransferred toner image area is divided into 12 divided areas in the longitudinal direction of the cleaning blade 82. The positions of each divided area are represented by H1 to H12. The position of the toner image in each divided area is represented by the position of each of the 15 divided areas in the transport direction of the intermediate transfer belt 7. The positions of each area in the transport direction of the intermediate transfer belt 7 are represented by V1 to V15. In FIGS. 9(a) and 9(b), the black dots indicate the positions (printed areas, image areas) where the toner image is formed. For example, as shown in FIG. 9(a), if a toner image is formed in the entire untransferred toner image area, the leading edge of the toner image is located at V1 in each of the divided areas H1 to H12. In this case, whether the leading edge of the toner image in at least one divided area is defined as the "leading edge of the untransferred toner image" as described above or the leading edge of the toner image at the rearmost side is defined as the "leading edge of the untransferred toner image," the leading edge of the untransferred toner image is at position V1. For example, if the letter "A" is formed in the untransferred toner image area as shown in FIG. 9(b), toner images are formed in divided areas H2 to H11, and some divided areas have different leading edge positions of the toner images. For example, in divided areas H6 and H7, the leading edge of the toner image is at position V3, and in divided areas H2 and H11, the leading edge of the toner image is at position V11. In this case, if the leading edge of the toner image in at least one divided area is defined as the "leading edge of the untransferred toner image" as described above, any one of positions V3, V5, V7, V9, and V11 can be defined as the leading edge of the untransferred toner image. On the other hand, if the leading edge of the toner image at the rearmost side is defined as the "leading edge of the untransferred toner image," the leading edge of the untransferred toner image is at position V3.

[0068] In the example shown in Figures 9(a) and 9(b), the untransferred toner image area is divided into 12 areas in the longitudinal direction of the cleaning blade 82 and 15 areas in the transport direction of the intermediate transfer belt 7. However, this is merely a schematic example. The number of divisions in both directions can be selected as desired. For example, if a 300 dpi image is to be formed, 300 dots are arranged per inch. In this case, the leading edge of the untransferred toner image can be determined based on the leading edge of the toner image in each of the approximately 25,000 divided areas (LTR size longitudinal feed or A4 size longitudinal feed) in the longitudinal direction of the cleaning blade 82. On the other hand, from the perspective of reducing memory usage and computational load, the leading edge of the untransferred toner image may be determined based on the leading edge of the toner image in each of the divided areas divided into several areas (e.g., 2 to 5) in the longitudinal direction of the cleaning blade 82. For example, the leading edge of the untransferred toner image can be determined based on the leading edges of the toner images in three divided areas: one end, the center, and the other end. Image defects such as slip-through images can become more noticeable when the image size exceeds a certain level. For example, the cleaning blade 82 can be divided in the longitudinal direction so that the width of each divided region in the longitudinal direction is about 5 mm to 50 mm, typically about 10 mm to 30 mm.

[0069] However, as a typical example, continuous image formation is performed to form images using at least one color of toner over almost the entire image forming area, and by observing the timing at which image formation resumes when the automatic feed unit is switched, it is possible to determine whether or not control according to this embodiment is being executed.

[0070] Furthermore, from the viewpoint of resuming image formation as quickly as possible when switching the automatic feed unit, it is preferable to set the timing for resuming image formation as follows. In other words, it is preferable to resume image formation so that the leading edge of the image after resumption reaches the primary transfer unit N1 first before the leading edge of the untransferred toner image that first passed through the primary transfer unit N1 next reaches the secondary transfer unit N2. In this case, it is more preferable that the leading edge of the image after resumption reaches the primary transfer unit N1 first before the trailing edge of the untransferred toner image area first reaches the primary transfer unit N1. However, depending on the position of the leading edge of the untransferred toner image, the leading edge of the image after resumption may also reach the primary transfer unit N1 after the trailing edge of the untransferred toner image area has passed the primary transfer unit N1.

[0071] 9. Details of Control in this Example 10 is a flowchart for explaining an outline of the operation when paper out is detected during continuous image formation in this embodiment. Here, the overall flow of the operation when image forming apparatus 100 executes a continuous image formation job will be explained. Details such as the timing at which image formation is resumed when automatic feed unit switching is performed will be described later.

[0072] The processes of S201 to S206 in Fig. 10 are respectively the same as the processes of S101 to S106 in Fig. 6. Furthermore, the processes of S208 to S212 in Fig. 10 are respectively the same as the processes of S107 to S111 in Fig. 6. Descriptions of the processes in Fig. 10 that are the same as those in Fig. 6 will be omitted where appropriate.

[0073] In this embodiment, the CPU 111 controls to perform cleaning of the secondary transfer roller 9 (S206), and then waits for the resumption of image formation until the timing when the leading edge of the untransferred toner image after restart reaches the primary transfer portion N1 after the leading edge of the untransferred toner image has passed the primary transfer portion N1 (S207). The CPU 111 can determine (calculate) the timing when the leading edge of the untransferred toner image, the leading edge of the image after restart, or the trailing edge of the untransferred toner image area will reach or pass the primary transfer portion N1, based on the image signal input from the video controller 120 to the engine controller 110, the configurations (circumferential lengths) of the intermediate transfer belt 7 and the photosensitive drum 1, the circumferential speeds of the intermediate transfer belt 7 and the photosensitive drum 1, etc.

[0074] Fig. 11 is a timing chart for explaining an example of the operation when paper exhaustion is detected during continuous image formation in this embodiment. Fig. 11 shows an example of a job executed under the same conditions as Fig. 7. Fig. 11 also shows a schematic diagram of the time progression of the operation of each part, similar to Fig. 7. The operation of each part according to this timing chart is controlled by CPU 111. Here, it is assumed that the image of each page is formed with toner of at least one color over substantially the entire image forming area.

[0075] The operations from T1 to T8 in Fig. 11 are the same as the operations from T1 to T8 in Fig. 7. The explanation of the operations in Fig. 11 that are the same as those in Fig. 7 will be omitted as appropriate.

[0076] In this embodiment, as in the comparative example, the toner image of the second page is primarily transferred to the intermediate transfer belt 7 and then reaches the secondary transfer portion N2, but at this time the recording material S has not been conveyed to the secondary transfer portion N2. Therefore, in this embodiment, as in the comparative example, when the untransferred toner image area passes through the secondary transfer portion N2, the voltage applied to the secondary transfer roller 9 is turned OFF (0 V) so that the toner of the untransferred toner image does not adhere to the secondary transfer roller 9 as much as possible (T8 to T9). Thereafter, cleaning of the secondary transfer roller 9 is performed (T9 to T14). Specifically, a cleaning voltage having the same polarity as the normal charging polarity of the toner is applied to the secondary transfer roller 9.

[0077] Meanwhile, after image formation (exposure) of the second page is completed (T5), image formation of the job is interrupted. Then, after waiting for the timing (T12) when the leading edge of the image after resumption reaches the primary transfer unit N1 after the timing (T10) when the leading edge of the untransferred toner image passes the primary transfer unit N1, re-image formation (exposure) of the second page with the same untransferred toner image is started (T11). In the illustrated example, image formation is resumed so that the leading edge of the image after resumption reaches the primary transfer unit N1 at the timing (T12) before the trailing edge of the untransferred toner image area reaches the primary transfer unit N1 at the timing (T13). After re-image formation of the second page is started, the second paper feed roller 13B is driven to start feeding the recording material S (the first sheet after switching, the second sheet of the job) from the second cassette 12B after the automatic feed unit switching (T15). The toner image of the second page formed again is primarily transferred onto the intermediate transfer belt 7 (T12 to T16), and then secondarily transferred onto the recording material S (T17 to T18).

[0078] Since the second cassette 12B contains a plurality of recording materials S, the toner image of the third page is secondarily transferred onto the recording material S transported from the second cassette 12B with the normal paper spacing therebetween.

[0079] In this manner, in this embodiment, when automatic feed unit switching is performed, image formation is resumed so that the leading edge of the post-restart image reaches the primary transfer unit N1 after the leading edge of the untransferred toner image passes the primary transfer unit N1. In other words, after the leading edge of the untransferred toner image passes the secondary transfer unit N2 and the intermediate transfer belt 7 makes one idle rotation, the image formation area on the intermediate transfer belt 7 corresponding to the leading edge of the post-restart image reaches the secondary transfer unit N2. This makes it possible to prevent the occurrence of slip-through images caused by toner at the leading edge of the untransferred toner image, which tends to slip through the cleaning blade 82.

[0080] 10. Confirmation of effectiveness The occurrence of slip-through images was evaluated using the image forming apparatuses 100 of this example and the comparative example. In the test, 10 sheets of the same type of recording material S (for example, A4 size plain paper) were stored in each of the first and second cassettes 12A and 12B, and a job of continuous image formation of 20 sheets (20 pages) was executed. The test image on each page was formed with a single color (for example, black) toner over almost the entire image formation area. The job started by first feeding the recording material S from the first cassette 12A.

[0081] In both the present embodiment and the comparative example, the automatic feeder unit was switched when 10 sheets of recording material S were fed from the first cassette 12A. In the comparative example, a slip-through image occurred on the first sheet after the automatic feeder unit was switched, due to toner from the untransferred toner image slipping through. In contrast, in this embodiment, no slip-through image occurred on the first sheet after the automatic feeder unit was switched. In this embodiment, after the leading edge of the untransferred toner image passes the secondary transfer unit N2 and the intermediate transfer belt 7 rotates idly for one revolution, the image formation area on the intermediate transfer belt 7 corresponding to the leading edge of the image after restart reaches the secondary transfer unit N2. Therefore, before the first sheet of recording material S after the automatic feeder unit was switched reaches the secondary transfer unit N2, the toner from the leading edge of the untransferred toner image that slipped past the cleaning blade 82 passes through the secondary transfer unit N2. As a result, in this embodiment, the occurrence of a slip-through image due to toner from the untransferred toner image slipping through was successfully suppressed.

[0082] As described above, in this embodiment, the image forming apparatus 100 includes an image forming section P that includes a rotatable image carrier (photosensitive drum) 1 and that performs image formation to form a toner image on the image carrier 1, a rotatable intermediate transfer member (intermediate transfer belt) 7 to which the toner image is primarily transferred from the image carrier 1 at a primary transfer section N1, a secondary transfer member (secondary transfer roller) 9 that forms a secondary transfer section N2 that secondarily transfers the toner image from the intermediate transfer member 7 to a recording material S, and a cleaning device that removes toner on the intermediate transfer member downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 in the movement direction of the intermediate transfer member 7. The image forming apparatus includes a cleaning device 8 having a cleaning blade 82 that contacts the surface of the intermediate transfer body 7 along the width direction of the transfer body 7, a first feeding section 12A and a second feeding section 12B that feed the recording material S toward the secondary transfer section N2, and a control section (CPU) 111 that, when it is detected that the recording material S is not present in the first feeding section 12A after the image formation has started, controls to change the feeding source of the recording material S from the first feeding section 12A to the second feeding section 12B and controls to resume the image formation that forms a toner image that is secondarily transferred onto the recording material S fed from the second feeding section 12B. When the feeding source of the recording material S is changed from the first feeding unit 12A to the second feeding unit 12B, the toner image that passes through the secondary transfer unit N2 without being transferred to the recording material S before the recording material S fed from the second feeding unit 12B reaches the secondary transfer unit N2 is defined as an untransferred toner image, the leading edge of the untransferred toner image on the intermediate transfer body 7 in the transport direction is defined as the leading edge of the untransferred toner image, and the leading edge of the image forming area on the image carrier on which the first toner image is formed after the image formation is resumed is defined as the leading edge of the post-restart image. In this embodiment, the cleaning device 8 includes a container 81, a support member 83 fixed to the container 81, and a cleaning blade 82 fixed to the support member 83.In this embodiment, the cleaning blade 82 contacts the intermediate transfer body 7 in a counter-direction relative to the movement direction of the intermediate transfer body 7, and the rubber hardness of the cleaning blade 82 is set to 65 to 75°, the set angle θ1 of the cleaning blade 82 is set to 12 to 18°, and the penetration amount δ of the cleaning blade 82 into the intermediate transfer body 7 is set to 0.3 to 1.2 mm. Preferably, the control unit 111 controls the image formation to be resumed so that the leading edge of the image after resumption reaches the primary transfer unit N1 first before the leading edge of the untransferred toner image that first passed through the primary transfer unit N1 next reaches the secondary transfer unit N2. Furthermore, when the image formation area on the intermediate transfer body 7 where an untransferred toner image may exist is defined as the untransferred toner image area, the control unit 111 preferably controls the image formation to be resumed so that the leading edge of the image after resumption reaches the primary transfer unit N1 first before the trailing edge of the untransferred toner image area in the transport direction first reaches the primary transfer unit N1. Here, the leading edge of the untransferred toner image may be at least one of the leading edge positions of the toner images formed at any position in the width direction of the intermediate transfer body 7. Preferably, the leading edge of the untransferred toner image is the leading edge position of the toner image that is located furthest to the rear end in the transport direction among the leading edge positions of the toner images formed at any position in the width direction of the intermediate transfer body 7.

[0083] As described above, according to this embodiment, it is possible to suppress the occurrence of image defects caused by toner passing through of an untransferred toner image due to switching of the automatic feed unit. According to this embodiment, it is possible to suppress the occurrence of image defects caused by toner passing through of an untransferred toner image even in a configuration in which the contact pressure of the cleaning blade 82 against the intermediate transfer belt 7 is set relatively low. In other words, it can be said that the control of the timing at which image formation resumes when switching of the automatic feed unit according to the present invention is particularly effective in a configuration in which the contact pressure of the cleaning blade 82 against the intermediate transfer belt 7 is set relatively low.

[0084] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0085] In this embodiment, the configuration of the belt cleaning device 8 is different from that in Embodiment 1. Fig. 12 is a schematic cross-sectional view showing the belt cleaning device 8 in this embodiment. Fig. 12 shows a cross section approximately perpendicular to the width direction of the intermediate transfer belt 7.

[0086] In this embodiment, the cleaning blade 82 is provided to the belt cleaning device 8 so as to be able to swing (rotate). That is, in this embodiment, swing support portions 83a are provided at both ends of the support member 83 in the longitudinal direction (the width direction of the intermediate transfer belt 7, the longitudinal direction of the cleaning blade 82). The swing support portions 83a at both ends of the support member 83 are swingably attached to the collection container 81 via swing shafts 86. The swing shaft 86 is disposed downstream of the cleaning nip portion Q in terms of the movement of the surface of the intermediate transfer belt 7. The swing shaft 86 is also disposed approximately parallel to the width direction of the intermediate transfer belt 7 (the longitudinal direction of the cleaning blade 82). This allows the support member 83 to rotate about the swing shaft 86, i.e., about a swing axis that is approximately parallel to the width direction of the intermediate transfer belt 7 (the longitudinal direction of the cleaning blade 82). This also allows the cleaning blade 82 fixed to the support member 83 to swing about the swing shaft 86 so that the edge portion 82a at the tip of the cleaning blade 82 moves toward and away from the intermediate transfer belt 7. The support member 83 is also pressed by a pressure spring 87, which is a biasing member serving as a biasing means, so that the edge portion 82a at the tip of the cleaning blade 82 rotates in a direction toward the intermediate transfer belt 7. In this embodiment, the pressure spring 87 is configured as a compression coil spring. This causes the cleaning blade 82 to be pressed toward the tension roller 74 via the intermediate transfer belt 7.

[0087] The configuration in which the cleaning blade 82 can oscillate (oscillation system) is such that the edge portion 82a at the tip of the cleaning blade 82 can move in a direction away from the intermediate transfer belt 7, and therefore, it can be said that this configuration is prone to toner slipping through. In particular, in this embodiment, the oscillation shaft 86 is disposed in a position where, when the intermediate transfer belt 7 rotates, the frictional force between the cleaning blade 82 and the intermediate transfer belt 7 acts to rotate the cleaning blade 82 in a direction away from the intermediate transfer belt 7. The arrangement of this oscillation shaft 86 will be further explained using FIG. 13 .

[0088] 13(a) and 13(b) are schematic cross-sectional views of the vicinity of the cleaning nip portion Q for explaining the arrangement of the swing shaft 86. Figures 13(a) and 13(b) each show a cross section substantially perpendicular to the width direction of the intermediate transfer belt 7.

[0089] In Figures 13(a) and (b), the point of contact between the edge portion 82a at the tip of the cleaning blade 82 and the surface of the intermediate transfer belt 7 is called point of contact G, the tangent to the intermediate transfer belt 7 at point of contact G is called tangent line L3, the straight line passing through point of contact G and the oscillation axis (oscillation center) 86 is called line L4, and the angle between tangent line L3 and line L4 based on point of contact G is called oscillation angle θ2.

[0090] In this case, as shown in FIG. 13A, the swing angle θ2 is defined as a positive angle when the line L4 is located on the cleaning blade 82 side relative to the tangent line L3 with respect to the contact point G. In a configuration in which the swing shaft 86 is disposed in this manner, when the intermediate transfer belt 7 rotates, the frictional force between the cleaning blade 82 and the intermediate transfer belt 7 acts to rotate the cleaning blade 82 in a direction toward the intermediate transfer belt 7. Therefore, in this configuration, the frictional force between the cleaning blade 82 and the intermediate transfer belt 7 tends to increase when the intermediate transfer belt 7 rotates. Therefore, in this configuration, the dynamic friction coefficient at the contact point between the cleaning blade 82 and the intermediate transfer belt 7 increases. When the frictional force between the cleaning blade 82 and the intermediate transfer belt 7 increases, blade squeal (generation of abnormal noise) is likely to occur. The dynamic friction coefficient at the contact point between the cleaning blade 82 and the intermediate transfer belt 7 may increase due to, for example, continued image formation at a low print rate or an increase in the cumulative usage of the intermediate transfer belt 7.

[0091] On the other hand, as shown in FIG. 13(b), when the line L4 is on the intermediate transfer belt 7 side with respect to the tangent line L3 with respect to the contact point G as the reference point, the oscillation angle θ2 is set to a negative (-) angle. In a configuration in which the oscillation shaft 86 is arranged in this manner, when the intermediate transfer belt 7 rotates, the frictional force between the cleaning blade 82 and the intermediate transfer belt 7 acts to rotate the cleaning blade 82 in a direction away from the intermediate transfer belt 7. Therefore, in this configuration, it is possible to prevent the frictional force between the cleaning blade 82 and the intermediate transfer belt 7 from increasing when the intermediate transfer belt 7 rotates. Therefore, with this configuration, it is possible to make it less likely for blade noise to occur than with the configuration in FIG. 13(b).

[0092] In this embodiment, as shown in FIG. 11 , the swing shaft 86 is positioned so that the swing angle θ2 is a negative angle. Therefore, in this embodiment, blade squeal is less likely to occur. However, in a configuration in which the swing angle θ2 is a negative angle, the dynamic pressure of the cleaning blade 82 against the intermediate transfer belt 7 when the intermediate transfer belt 7 rotates is more likely to be lower than in a configuration in which the swing angle θ2 is a positive angle. Therefore, in a configuration in which the swing angle θ2 is a negative angle, toner from the untransferred toner image is more likely to slip through when the automatic feed unit is switched than in a configuration in which the swing angle θ2 is a positive angle.

[0093] Therefore, in this embodiment, when the automatic feed unit is switched, the timing at which image formation is resumed is controlled according to the present invention, as in embodiment 1. This makes it possible to suppress the occurrence of slip-through images caused by the toner of an untransferred toner image slipping through.

[0094] Thus, in this embodiment, the cleaning device 8 has a container 81, a support member 83 attached to the container 81 so as to be swingable around a swing axis 86, and a cleaning blade 82 fixed to the support member 83 and swingable so as to move toward and away from the intermediate transfer body 7 around the swing axis 86 as the support member 83 swings. In addition, in this embodiment, the cleaning blade 82 contacts the intermediate transfer body 7 in a counter direction to the movement direction of the intermediate transfer body 7, and the oscillation shaft 86 is positioned downstream of the contact point between the cleaning blade 82 and the intermediate transfer body 7 in the movement direction of the intermediate transfer body 7. In a cross section approximately perpendicular to the width direction of the intermediate transfer body 7, when the contact point between the cleaning blade 82 and the intermediate transfer body 7 is defined as contact point G, the tangent to the intermediate transfer body 7 at contact point G is defined as tangent line L3, the straight line passing through contact point G and the oscillation shaft 86 is defined as line L4, and the angle between tangent line L3 and line L4 based on contact point G is defined as oscillation angle θ2, the oscillation angle θ2 is set so that line L4 is on the intermediate transfer body side with respect to tangent line L3.

[0095] As described above, according to this embodiment, similar to the first embodiment, it is possible to suppress the occurrence of image defects caused by toner passing through of an untransferred toner image due to switching of the automatic feed unit. According to this embodiment, it is possible to suppress the occurrence of image defects caused by toner passing through of an untransferred toner image even in a configuration in which the cleaning blade 82 is swingable, particularly in a configuration in which the swing angle θ2 is a negative angle. In other words, it can be said that the control of the timing at which image formation resumes when switching of the automatic feed unit according to the present invention is particularly effective in a configuration in which the cleaning blade 82 is swingable, particularly in a configuration in which the swing angle θ2 is a negative angle.

[0096] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0097] In this embodiment, a description will be given of modified examples relating to the control of the voltage applied to the secondary transfer unit N2 when an untransferred toner image generated by switching the automatic feed unit passes through the secondary transfer unit N2 or when cleaning the secondary transfer roller 9. Here, each modified example will be described as being applied to the image forming apparatus 100 having the configuration of the first embodiment, but it may also be applied to the image forming apparatus 100 having the configuration of the second embodiment.

[0098] <Variation 1> In the first embodiment, when an untransferred toner image generated by switching the automatic feed unit passes through the secondary transfer unit N2 for the first time, the voltage applied to the secondary transfer roller 9 is set to OFF (0 V). The control in the first embodiment makes it possible to prevent the occurrence of a slip-through image due to the toner at the leading edge of the untransferred toner image, which is prone to slip-through. However, there is a possibility that some of the toner at the leading edge of this untransferred toner image will adhere to the secondary transfer roller 9 the next time it reaches the secondary transfer unit N2, causing contamination of the secondary transfer roller 9. This contamination of the secondary transfer roller 9 will cause contamination of the back side of the recording material S. The "leading edge of the untransferred toner image" is as described in the first embodiment.

[0099] Therefore, in this modified example, a voltage (also referred to here as a "tip voltage") of the same polarity as that during secondary transfer (i.e., positive polarity, which is the same polarity as the normal charging polarity of the toner) is applied during a predetermined period that includes at least the period when the leading edge of the untransferred toner image first passes through the secondary transfer portion N2. As a result, when the leading edge of the untransferred toner image passes through the secondary transfer portion N2, at least a portion of the toner on the leading edge of the untransferred toner image adheres to the secondary transfer roller 9, thereby reducing the amount of toner carried on the leading edge of the untransferred toner image on the intermediate transfer belt 7.

[0100] In this modification, after applying the tip voltage for a predetermined period, a voltage (cleaning voltage) of the opposite polarity to that during secondary transfer (i.e., negative polarity, which is the same polarity as the normal charging polarity of the toner) is applied to the secondary transfer roller 9. This prevents toner of the untransferred toner image from adhering to the secondary transfer roller 9, and also makes it possible to move (return) the toner adhering to the secondary transfer roller 9 to the intermediate transfer belt 7.

[0101] 14(a) and (b) are timing charts showing an example of the transition of the presence or absence of a toner image on the intermediate transfer belt 7 and the voltage applied to the secondary transfer roller 9 in the vicinity of the period when an untransferred toner image passes through the secondary transfer unit N2 in this modified example. The operation of each unit according to this timing chart is controlled by the CPU 111. Here, it is assumed that the image of each page is formed with toner of at least one color over substantially the entire image forming area.

[0102] As shown in FIG. 14(a), a voltage (leading edge voltage) having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 9 for a predetermined period after the leading edge of the untransferred toner image reaches the secondary transfer portion N2. For example, as shown in FIG. 14(a), the leading edge voltage is applied to the secondary transfer roller 9 for a period corresponding to one rotation of the secondary transfer roller 9. The period during which the leading edge voltage is applied to the secondary transfer roller 9 is not limited to one rotation of the secondary transfer roller 9, and may be shorter or longer. For example, the period during which the leading edge voltage is applied to the secondary transfer roller 9 may be less than one rotation of the secondary transfer roller 9 (e.g., half a rotation of the secondary transfer roller 9). Furthermore, for example, the period during which the leading edge voltage is applied to the secondary transfer roller 9 may be a period exceeding one rotation of the secondary transfer roller 9 (e.g., 2 to 5 rotations of the secondary transfer roller 9). For example, as shown in FIG. 14(b), the period can be set to a length approximately equal to the length of the untransferred toner image in the transport direction of the intermediate transfer belt 7 (or a period approximately equal to the length of the untransferred toner image area). Furthermore, application of the leading edge voltage to the secondary transfer roller 9 can be started before the leading edge of the untransferred toner image or the leading edge of the untransferred toner image area reaches the secondary transfer portion N2. The absolute value of the leading edge voltage can be the same as or different from the absolute value of the voltage during secondary transfer. In this modification, the leading edge voltage is set to +2 kV. Applying the leading edge voltage to the secondary transfer roller 9 causes at least a portion of the toner at the leading edge of the untransferred toner image to adhere to the secondary transfer roller 9, thereby reducing the amount of toner carried at the leading edge of the untransferred toner image on the intermediate transfer belt 9.

[0103] As shown in FIGS. 14A and 14B, after the leading edge voltage is applied to the secondary transfer roller 9 for a predetermined period, a voltage (cleaning voltage) having the same polarity as the normal charging polarity of the toner is applied to the secondary transfer roller 9 for a predetermined period. The period during which the cleaning voltage is applied to the secondary transfer roller 9 preferably includes the period until the trailing edge of the untransferred toner image (which may be the trailing edge of the untransferred toner image area) passes through the secondary transfer section N2. As in the first embodiment, the cleaning voltage can be continuously applied to the secondary transfer roller 9 even after the untransferred toner image area passes through the secondary transfer section N2 (for example, for 1 to 10 revolutions, typically 2 to 5 revolutions, of the secondary transfer roller 9). The absolute value of the cleaning voltage may be the same as or different from the absolute value of the voltage during secondary transfer. In this modification, the cleaning voltage is −300 V. By applying the cleaning voltage to the secondary transfer roller 9, the toner of the untransferred toner image collected by the secondary transfer roller 9 can be expelled onto the intermediate transfer belt 7.

[0104] In this way, when at least the leading edge of the untransferred toner image passes through the secondary transfer portion N2, a voltage of a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 9, and at least a portion of the toner at the leading edge of the untransferred toner image is collected by the secondary transfer roller 9. This reduces the amount of toner carried at the leading edge of the untransferred toner image on the intermediate transfer belt 7, making it possible to prevent toner from adhering to the secondary transfer roller 9 when the leading edge of the untransferred toner image next reaches the secondary transfer portion N2.

[0105] It should be noted that the control of applying a leading edge voltage to the secondary transfer roller 9 as in this modified example can also be combined with the control of the comparative example described above. That is, by applying a leading edge voltage to the secondary transfer roller 9, the amount of toner carried at the leading edge of the untransferred toner image on the intermediate transfer belt 7 can be reduced. This makes it possible to suppress damage to the blocking layer when the leading edge of the untransferred toner image reaches the cleaning nip Q. Therefore, it is possible to suppress toner slip-through at the leading edge of the untransferred toner image. Therefore, even in the control of the comparative example in which the leading edge of the untransferred toner image may overlap with the image formation area after image formation is resumed, it is expected that the occurrence of slip-through images due to toner slip-through of the untransferred toner image can be suppressed.

[0106] <Variation 2> This modification differs from the first modification in the cleaning voltage.

[0107] 15(a) is a timing chart showing an example of the transition of the presence or absence of a toner image on the intermediate transfer belt 7 and the voltage applied to the secondary transfer roller 9 around the time when the untransferred toner image passes through the secondary transfer unit N2 in this modified example. The operation of each unit according to this timing chart is controlled by the CPU 111. Here, it is assumed that the image of each page is formed with toner of at least one color over substantially the entire image forming area.

[0108] In this modification, a leading edge voltage (+2 kV in this embodiment) is applied to the secondary transfer roller 9 for a predetermined period, and then a voltage ranging from 0 V to −300 V is applied to the secondary transfer roller 9 in a stepwise manner. In this modification, the 0 V voltage is also referred to as a cleaning voltage. Specifically, with each rotation of the secondary transfer roller 9, the cleaning voltage applied to the secondary transfer roller 9 is reduced by −100 V (the absolute value increases toward the negative polarity) from 0 V to −100 V, −200 V, and −300 V. As in the first embodiment, the final cleaning voltage of −300 V continues to be applied to the secondary transfer roller 9 even after the untransferred toner image area has passed the secondary transfer portion N2. The entire period during which the cleaning voltage is applied to the secondary transfer roller 8 preferably includes the period until the trailing edge of the untransferred toner image (which may be the trailing edge of the untransferred toner image area) passes the secondary transfer portion N2. The number of voltage steps, the length of each step, and the voltage value of each step are not limited to those in this embodiment. For example, the voltage may be changed during one rotation of the secondary transfer roller 9. By gradually increasing the absolute value of the cleaning voltage in this way, the amount of toner of the untransferred toner image collected by the secondary transfer roller 9 and expelled toward the intermediate transfer belt 7 can be gradually increased from the leading edge of the untransferred toner image to the trailing edge. This makes it possible to gradually increase the amount of toner transported to the cleaning nip Q from the area close to the leading edge of the untransferred toner image, where toner is more likely to slip through, to the area farther away.

[0109] <Variation 3> This modification differs from the first and second modifications in tip voltage.

[0110] 15(b) is a timing chart showing an example of the transition of the presence or absence of a toner image on the intermediate transfer belt 7 and the voltage applied to the secondary transfer roller 9 around the time when the untransferred toner image passes through the secondary transfer unit N2 in this modified example. The operation of each unit according to this timing chart is controlled by the CPU 111. Here, it is assumed that the image of each page is formed with toner of at least one color over substantially the entire image forming area.

[0111] In this modified example, when the leading edge of the untransferred toner image reaches the secondary transfer portion N2, a voltage is applied to the secondary transfer roller 9, gradually increasing from +2 kV to 0 V. The final voltage of 0 V can be considered a cleaning voltage. Specifically, with each rotation of the secondary transfer roller 9, the leading edge voltage applied to the secondary transfer roller 9 is reduced by 500 V (the absolute value is reduced so that the voltage becomes more negative). The number of voltage steps, the length of each step, and the voltage value of each step are not limited to those in this embodiment. For example, the voltage may be changed over one rotation of the secondary transfer roller 9. By gradually decreasing the absolute value of the leading edge voltage in this manner, the amount of toner of the untransferred toner image collected by the secondary transfer roller 9 can be gradually reduced from the leading edge to the trailing edge of the untransferred toner image. This allows the secondary transfer roller 9 to collect more toner in areas closer to the leading edge of the untransferred toner image, where toner slippage is more likely to occur. By making it more difficult for toner in an area farther from the leading edge of the untransferred toner image to adhere to the secondary transfer roller 9, it is possible to prevent the secondary transfer roller 9 from being soiled by toner from the untransferred toner image.

[0112] In this modification, after the tip voltage is changed in stages and applied, a cleaning voltage (−300 V in this modification) is applied to the secondary transfer roller 9 for a predetermined period. At this time, the cleaning voltage may be changed in stages as in the second modification.

[0113] As described above, in this embodiment, the control unit 111 controls the secondary transfer unit N2 to apply a voltage of the same polarity as the voltage used when transferring the toner image to the recording material S during a predetermined period that includes the period when the leading edge of the untransferred toner image first passes through the secondary transfer unit N2. The control unit 111 can control the secondary transfer unit N2 to apply, as the same-polarity voltages, a first same-polarity voltage and a second same-polarity voltage having an absolute value smaller than that of the first same-polarity voltage during the predetermined period, to the secondary transfer unit N2, and the second same-polarity voltage is applied after the first same-polarity voltage. Furthermore, in this embodiment, the control unit 111 controls the secondary transfer unit N2 to apply a voltage of the opposite polarity to the voltage used when transferring the toner image to the recording material S during a second predetermined period that is after the predetermined period and before the recording material S onto which the first toner image is secondarily transferred after image formation resumes when automatic feed unit switching is performed reaches the secondary transfer unit N2. The control unit 111 can control the application of the reverse polarity voltages, that is, a first reverse polarity voltage and a second reverse polarity voltage having an absolute value greater than that of the first reverse polarity voltage, to the secondary transfer unit N2 during the second predetermined period, and the second reverse polarity voltage is applied after the first reverse polarity voltage.

[0114] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0115] In the above embodiment, the case where the leading edge of the untransferred toner image passes through the secondary transfer unit, the intermediate transfer belt rotates idly one revolution, and then the area on the intermediate transfer belt corresponding to the leading edge of the image after restart reaches the secondary transfer unit, has been described. However, this idling may be repeated multiple times.

[0116] The value of the voltage applied to the secondary transfer roller is not limited to the values ​​described in the above embodiment. The voltage that is changed stepwise in the modified example described in the third embodiment may be changed gradually in a linear or curved manner.

[0117] Furthermore, the image forming apparatus may be configured to be capable of forming an image based on an image signal from an image reading unit provided in or connected to the image forming apparatus (for example, a multifunction device having the functions of a copier, printer, and facsimile machine).

[0118] Furthermore, the number of feeding units (cassettes, etc.) provided in the image forming apparatus is not limited to two, and more feeding units, such as three, may be provided.

[0119] Furthermore, in cleaning the secondary transfer roller, a voltage of the opposite polarity to the voltage used when transferring the toner image onto the recording material and a voltage of the same polarity may be applied alternately.

[0120] In addition, the outer roller corresponding to the secondary transfer roller in the above-described embodiment may be electrically grounded, and a voltage of the same polarity as the normal charging polarity of the toner may be applied to the inner roller corresponding to the secondary transfer opposing roller in the above-described embodiment, thereby applying a secondary transfer voltage to the secondary transfer section.

[0121] Furthermore, the secondary transfer member is not limited to a roller-shaped member, but may be a brush-shaped, sheet-shaped, film-shaped, pad-shaped member, etc. The same applies to the primary transfer member.

[0122] Furthermore, the image forming area may be approximately the same size as the recording material, or may be smaller or larger than the size of the recording material. When the image forming area is smaller than the size of the recording material, typically, margins where no image is formed are provided at the leading and trailing ends of the recording material in the conveying direction and at both ends in a direction approximately perpendicular to the conveying direction of the recording material. When the image forming area is larger than the size of the recording material, typically, portions of the image forming area that extend beyond the size of the recording material are provided at the leading and trailing ends of the recording material in the conveying direction and at both ends in a direction approximately perpendicular to the conveying direction of the recording material. However, the margins or protruding portions may be provided only at either the leading and trailing ends of the recording material in the conveying direction or at both ends in a direction approximately perpendicular to the conveying direction of the recording material. [Explanation of symbols]

[0123] 1 Photosensitive drum 2 Charging roller 3 Exposure equipment 5 Primary transfer roller 7 Intermediate transfer belt 8 Belt cleaning device 12 Cassette (feed unit) 82 Cleaning blade

Claims

1. an image forming unit including a rotatable image carrier and performing image formation to form a toner image on the image carrier; a rotatable intermediate transfer member onto which a toner image is primarily transferred from the image carrier at a primary transfer section; a secondary transfer member forming a secondary transfer section that secondarily transfers a toner image from the intermediate transfer body to a recording material; a cleaning device that removes toner from the intermediate transfer body downstream of the secondary transfer unit and upstream of the primary transfer unit in the movement direction of the intermediate transfer body, the cleaning device having a cleaning blade that contacts the surface of the intermediate transfer body along the width direction of the intermediate transfer body; a first feeding section and a second feeding section that feed a recording material toward the secondary transfer section; a control unit that, when it is detected that there is no recording material in the first feeding unit after the image formation has started, controls to change the recording material feeding source from the first feeding unit to the second feeding unit and controls to resume the image formation that forms a toner image to be secondarily transferred onto the recording material fed from the second feeding unit; and an untransferred toner image; a leading edge of the untransferred toner image on the intermediate transfer body in the transport direction; and a leading edge of the image forming area on the image carrier on which the first toner image can be formed after the image formation is resumed. When the source of the recording material is changed from the first feeding unit to the second feeding unit, the control unit controls the image formation to resume so that the leading edge of the post-resumption image reaches the primary transfer unit first after the leading edge of the untransferred toner image has first passed through the primary transfer unit.

2. 2. The image forming apparatus according to claim 1, wherein the cleaning device comprises a container, a support member fixed to the container, and the cleaning blade fixed to the support member.

3. the cleaning blade is in contact with the intermediate transfer body in a counter direction to the moving direction of the intermediate transfer body; 3. The image forming apparatus according to claim 2, wherein the cleaning blade has a rubber hardness of 65 to 75°, a set angle θ1 of the cleaning blade of 12 to 18°, and an intrusion amount δ of the cleaning blade into the intermediate transfer body of 0.3 to 1.2 mm.

4. The image forming apparatus according to claim 1, characterized in that the cleaning device comprises a container, a support member attached to the container so as to be swingable around a swing axis, and the cleaning blade fixed to the support member and swingable around the swing axis so as to move toward and away from the intermediate transfer body as the support member swings.

5. the cleaning blade is in contact with the intermediate transfer body in a counter direction to the moving direction of the intermediate transfer body; the swing shaft is disposed downstream of a contact portion between the cleaning blade and the intermediate transfer body in the moving direction of the intermediate transfer body, 5. The image forming apparatus according to claim 4, wherein, in a cross section substantially perpendicular to the width direction of the intermediate transfer body, when the contact point between the cleaning blade and the intermediate transfer body is defined as contact point G, the tangent to the intermediate transfer body at the contact point G is defined as tangent line L3, the straight line passing through the contact point G and the oscillation axis is defined as line L4, and the angle formed by the tangent line L3 and the line L4 with the contact point G as the reference point is defined as oscillation angle θ2, the oscillation angle θ2 is set so that the line L4 is on the intermediate transfer body side with respect to the tangent line L3.

6. The image forming apparatus according to any one of claims 1 to 5, characterized in that the control unit controls the resumption of image formation so that the leading edge of the image after resumption reaches the primary transfer unit first before the leading edge of the untransferred toner image that first passed through the primary transfer unit next reaches the secondary transfer unit.

7. An image forming apparatus according to any one of claims 1 to 5, characterized in that when the image forming area on the intermediate transfer body where the untransferred toner image may exist is defined as the untransferred toner image area, the control unit controls the resumption of image formation so that the leading edge of the image after resumption first reaches the primary transfer unit before the trailing end in the transport direction of the untransferred toner image area first reaches the primary transfer unit.

8. an application unit that applies a voltage to the secondary transfer unit; 6. The image forming apparatus according to claim 1, wherein the control unit controls the secondary transfer unit to apply a voltage of the same polarity as a voltage used when transferring the toner image to the recording material during a predetermined period including a period during which the leading edge of the untransferred toner image first passes through the secondary transfer unit.

9. 9. The image forming apparatus according to claim 8, wherein the control unit controls the application of a first same-polarity voltage and a second same-polarity voltage having an absolute value smaller than that of the first same-polarity voltage to the secondary transfer unit during the predetermined period, and the second same-polarity voltage is applied after the first same-polarity voltage.

10. 9. The image forming apparatus according to claim 8, wherein the control unit controls the secondary transfer unit to apply a voltage of opposite polarity to the voltage used when transferring the toner image to the recording material during a second predetermined period after the predetermined period and before the recording material onto which the first toner image after the resumption of image formation is secondarily transferred reaches the secondary transfer unit.

11. 11. The image forming apparatus according to claim 10, wherein the control unit controls the application of a first reverse polarity voltage and a second reverse polarity voltage having an absolute value greater than that of the first reverse polarity voltage to the secondary transfer unit as the reverse polarity voltage during the second predetermined period, and the second reverse polarity voltage is applied after the first reverse polarity voltage.

12. 6. The image forming apparatus according to claim 1, wherein the leading edge of the untransferred toner image is at least one of the leading edges of the toner images formed at any position in the width direction of the intermediate transfer body.

13. 6. An image forming apparatus according to claim 1, wherein the leading edge of the untransferred toner image is the leading edge position of the toner image that is located furthest rearward in the transport direction among the leading edge positions of the toner images formed at any position in the width direction of the intermediate transfer body.

Images