Image forming apparatus

Abstract

To solve the problem in which: in a primary transfer simultaneous cleaning system, a toner accumulated in a cleaning unit is scattered on an intermediate transfer body at an unintended timing due to a sudden change of the conveyance speed of the intermediate transfer belt, the toner may contaminate a recording medium at a secondary transfer nip and may be made visible as an image defect on the recording medium.SOLUTION: An image forming apparatus has: an image carrier that carries a toner image; secondary transfer means that includes a secondary transfer roller and secondarily transfers the toner image primarily transferred from the image carrier to an intermediate transfer body from the intermediate transfer body to a recording medium; and a cleaning unit that can be brought into contact with and separated from the intermediate transfer body and is to electrify and remove toner remaining on the intermediate transfer body after the secondary transfer. The image forming apparatus performs control to bring the cleaning unit into contact with the intermediate transfer body after a leading end of the recording medium passes through a contact part of the secondary transfer roller and the intermediate transfer body.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a recording medium. [Background technology]

[0002] In an electrophotographic image forming apparatus, a toner image formed on an electrophotographic photosensitive member is first transferred onto an intermediate transfer member (primary transfer), and then the toner image transferred onto the intermediate transfer member is transferred to a recording medium by a transfer member that comes into contact with the recording medium and transfers the toner image to form an image. By using such an electrophotographic image forming apparatus, a color image with little physical misalignment (color shift) in the superimposition positions of the component color images can be obtained.

[0003] In image forming apparatuses using the above-mentioned intermediate transfer body, removing (cleaning) residual toner from the intermediate transfer body after secondary transfer, in which an image is transferred from the intermediate transfer body to a recording medium such as paper, is important for obtaining a good image. For this reason, a method has been used in which a cleaning blade is provided after the secondary transfer position to scrape off residual toner remaining on the intermediate transfer body after secondary transfer. Another method is to charge the residual toner on the intermediate transfer body after secondary transfer to a potential opposite to that of the photosensitive drum, and then collect the residual toner onto the photosensitive drum at the primary transfer nip while simultaneously performing primary transfer (see Patent Document 1).

[0004] In this simultaneous primary transfer and cleaning method, the remaining toner after secondary transfer passes through the photosensitive drum and is collected by the photosensitive drum cleaning unit. This has the advantage of minimizing the capacity of the waste toner container that collects the remaining toner on the intermediate transfer body, and also extending the life of the intermediate transfer body because the intermediate transfer body is not rubbed hard with a blade or the like.

[0005] Furthermore, as in Patent Document 2, the charging means for the residual toner after secondary transfer can be made to be capable of contacting and separating from the intermediate transfer body, and when there is no residual toner on the intermediate transfer body, the charging means is separated from the intermediate transfer body. This makes it possible to further extend the life of the intermediate transfer body. Hereafter, the charging means for the residual toner after secondary transfer in the above-mentioned simultaneous primary transfer and cleaning method will be referred to as ICL (Intermediate Transfer Apparatus Cleaning) means. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-52748 [Patent Document 2] Patent No. 5954939 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-described simultaneous primary transfer and cleaning method, the ICL device aims to charge the residual toner after secondary transfer to a potential opposite to the photosensitive drum's charging potential. However, some toner is not fully charged and is collected and retained by the ICL device. For example, if the ICL device is a brush, the residual toner on the intermediate transfer body after secondary transfer reaches the brush, which is applied with a potential opposite to the photosensitive drum's charging potential. The residual toner is then divided into toner charged to a potential opposite to the photosensitive drum's charging potential and passing through the brush, and toner that is not fully charged to the photosensitive drum's charging potential and is captured and retained by the brush. The toner retained by the brush is then ejected onto the intermediate transfer body by applying a voltage to the brush at a predetermined timing and is then collected by the photosensitive drum at the primary transfer nip. However, not all of the toner retained by the brush is ejected; a certain amount of toner remains retained on the brush. If this retained toner were to scatter onto the intermediate transfer body at an unintended timing during image formation, the scattered toner would pass through the primary transfer nip and contaminate the secondary transfer member at the secondary transfer nip, or transfer the stains onto the recording medium, resulting in a defective image. The scattering of toner from the brush described above is likely to occur when the brush is in contact with the intermediate transfer body and the transport speed of the intermediate transfer body changes.

[0008] Therefore, the object of the present invention is to provide a technology that prevents toner accumulated in the cleaning section from scattering onto the intermediate transfer body by separating the cleaning section from the intermediate transfer body at times when the transport speed of the intermediate transfer body is likely to change. [Means for solving the problem]

[0009] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention has the following configuration: an image carrier that carries a toner image; a secondary transfer means including a secondary transfer roller for secondarily transferring the toner image, which has been primarily transferred from the image carrier to an intermediate transfer medium, from the intermediate transfer medium to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body, and that charges and cleans the toner remaining on the intermediate transfer body after the secondary transfer; and a control means for controlling the cleaning section to contact the intermediate transfer body after the leading edge of the recording medium has passed through the contact point between the secondary transfer roller and the intermediate transfer body. [Effects of the Invention]

[0010] According to the present invention, by separating the cleaning section from the intermediate transfer body at times when the transport speed of the intermediate transfer body is likely to change, it is possible to prevent toner accumulated in the cleaning section from scattering onto the intermediate transfer body.

[0011] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals. [Brief explanation of the drawings]

[0012] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a schematic cross-sectional configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a schematic configuration of a cleaning device for an intermediate transfer belt according to the first embodiment. [Figure 3] 5A and 5B are schematic diagrams illustrating contact and separation states of the cleaning device for the intermediate transfer belt with respect to the intermediate transfer belt according to the first embodiment. [Figure 4] 2 is a diagram illustrating a control unit in the image forming apparatus 1 according to the first embodiment, and a configuration for controlling contact / separation of the ICL brush by the control unit. FIG. [Figure 5] 3 is a cross-sectional view showing the position of a toner image on an intermediate transfer belt, the position of a sheet S, and the contact / separation state of an ICL brush in the image forming apparatus according to the first embodiment. FIG. [Figure 6] 10 is a cross-sectional view showing the position of a toner image on an intermediate transfer belt, the position of a sheet S, and the contact / separation state of an ICL brush in an image forming apparatus according to a second embodiment. FIG. [Figure 7] 6 is a flowchart illustrating contact / separation control of the ICL brush by the image forming apparatus according to the first embodiment. [Figure 8] 10 is a flowchart illustrating contact / separation control of the ICL brush by the image forming apparatus according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0014] [Embodiment 1] First, the configuration of an image forming apparatus 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4 and 7. In the following description and in each drawing, the vertical direction when the image forming apparatus 1 is installed on a horizontal surface is referred to as the Z direction. The direction intersecting the Z direction and the direction of a rotation axis 90C (FIG. 1) of a rotary main body 90 (described later, the direction of the rotary's rotation axis) is referred to as the Y direction. Furthermore, the direction intersecting both the Z direction and the Y direction is referred to as the X direction. Here, the X direction and the Y direction are preferably horizontal. Furthermore, the X direction, the Y direction, and the Z direction are preferably perpendicular to each other. Furthermore, as necessary, the directions of the arrows X, Y, and Z shown in each drawing will be represented as the +X side, the +Y side, and the +Z side, respectively, and the opposite sides will be represented as the -X side, the -Y side, and the -Z side, respectively.

[0015] FIG. 1 is a schematic cross-sectional view illustrating a schematic cross-sectional configuration of an image forming apparatus 1 according to the first embodiment.

[0016] The image forming apparatus 1 is a laser beam printer that forms an image on a sheet S by electrophotography. More specifically, the image forming apparatus 1 is a color laser beam printer equipped with four development units 50y, 50m, 50c, and 50k. As the sheet S, which is the recording material (recording medium), paper such as plain paper and cardboard, plastic film, cloth, and surface-treated sheet materials such as coated paper can be used. Furthermore, a variety of sheet materials with different sizes and materials can be used, including sheet materials with special shapes such as envelopes and index paper.

[0017] Next, a description will be given of the schematic configuration and image forming operation of the image forming apparatus 1 with reference to Fig. 1. As shown in Fig. 1, the image forming apparatus 1 has an image forming apparatus main body (hereinafter referred to as apparatus main body) 1A and toner cartridges 70y, 70m, 70c, and 70k that are detachably attached to the apparatus main body 1A. The apparatus main body 1A according to the first embodiment is the portion of the image forming apparatus 1 excluding the toner cartridges 70y, 70m, 70c, and 70k.

[0018] The apparatus main body 1A of the image forming apparatus 1 has a drum-shaped (cylindrical) electrophotographic photosensitive member (hereinafter referred to as photosensitive drum) 2 as an image carrier that carries an electrostatic latent image. Around the photosensitive drum 2, a charging roller 3, a scanner 4 as an exposure device, and a photosensitive drum cleaning unit 6 are arranged.

[0019] The charging roller 3 is an example of a charging means for uniformly charging the photosensitive drum 2. The scanner 4 is an example of an exposure means for irradiating the photosensitive drum 2 with laser light according to image information to expose it. By irradiating the charged photosensitive drum 2 with laser light from the scanner 4, an electrostatic latent image according to the image information is formed on the surface of the photosensitive drum 2. The photosensitive drum cleaning unit 6 is an example of a cleaning means for removing toner remaining on the surface of the photosensitive drum 2.

[0020] The apparatus main body 1A also has a rotary main body (rotary, rotating body) 90 having development units 50y, 50m, 50c, and 50k. In the first embodiment, trays 80y, 80m, 80c, and 80k are attached to the rotary main body 90. Toner cartridges 70y, 70m, 70c, and 70k are removably attached to the trays 80y, 80m, 80c, and 80k.

[0021] The developing units 50y, 50m, 50c, and 50k are examples of developing means that develop (visualize) the electrostatic latent image formed on the photosensitive drum 2 into a toner image using toner of the corresponding color. The developing units 50y, 50m, 50c, and 50k develop the electrostatic latent image formed on the photosensitive drum 2 using yellow toner, magenta toner, cyan toner, or black toner, respectively.

[0022] The developing unit 50y has a developing roller 51y, a supply roller 52y, and a developing blade (not shown). The developing roller 51y is a developer carrier that carries toner as a developer and rotates to supply yellow toner to the photosensitive drum 2. The supply roller 52y is disposed in contact with the developing roller 51y and is a supply member that supplies yellow toner to the developing roller 51y. The developing blade is a regulating member that regulates the thickness of the yellow toner layer carried by the developing roller 51y. The other developing units 50m, 50c, and 50k each have similar developing rollers 51m, 51c, and 51k, supply rollers 52m, 52c, and 52k, and a developing blade.

[0023] Toner cartridges 70y, 70m, 70c, and 70k corresponding to the developing units 50y, 50m, 50c, and 50k are attached to the rotary body 90. The toner cartridges 70y, 70m, 70c, and 70k contain yellow toner, magenta toner, cyan toner, and black toner, respectively, to be supplied to the developing units 50y, 50m, 50c, and 50k.

[0024] The rotary body 90 is rotatable around a rotation axis (rotation center) 90C. The rotation axis 90C is substantially parallel to the rotation axis (rotation center) of the photosensitive drum 2. By rotating around the rotation axis 90C, the rotary body 90 can assume a development posture in which any one of the developing rollers 51y, 51m, 51c, and 51k faces the photosensitive drum 2. The posture in which the developing roller 51y faces the photosensitive drum 2 is called a yellow development posture. The posture in which the developing roller 51m faces the photosensitive drum 2 is called a magenta development posture. The posture in which the developing roller 51c faces the photosensitive drum 2 is called a cyan development posture. The posture in which the developing roller 51k faces the photosensitive drum 2 is called a black development posture. In other words, the rotary body 90 can rotate around the rotation axis 90C so that the positions of the developing rollers 51y, 51m, 51c, and 51k relative to the photosensitive drum 2 change.

[0025] The apparatus main body 1A has motors M1 (not shown), M2 (not shown), and M3 as drive sources. The motor M1 supplies a drive force for rotating the rotary main body 90 about the rotation axis 90C. The motor M2 moves the trays 80y, 80m, 80c, and 80k relative to the rotary main body 90.

[0026] Motor M3 (FIG. 4) drives components other than those driven by motors M1 and M2. For example, motor M3 drives the photosensitive drum 2, developing units 50y, 50m, 50c, and 50k, pickup roller 310, feed roller 311, conveying roller pair 320, secondary transfer roller 12, belt drive roller 10b, and fixing device (fuser) 40. It is also used to drive the secondary transfer roller 12 and intermediate transfer belt cleaning device (cleaning unit) 13 to contact and separate from the intermediate transfer belt 20a. The components driven by motors M1, M2, and M3 can be changed as appropriate. Alternatively, any two or all three of the functions of motors M1, M2, and M3 can be combined into a single motor. Alternatively, additional drive sources other than motors M1, M2, and M3 may be added.

[0027] The subscripts y, m, c, and k of the reference symbols for the development units 50y, 50m, 50c, and 50k, the toner cartridges 70y, 70m, 70c, and 70k, and the trays 80y, 80m, 80c, and 80k indicate the toner colors corresponding to the corresponding units and components. Here, they represent yellow, magenta, cyan, and black, respectively. The development units 50y, 50m, 50c, and 50k share the same basic configuration and function. The toner cartridges 70y, 70m, 70c, and 70k also share the same basic configuration and function. The trays 80y, 80m, 80c, and 80k also share the same basic configuration and function. Therefore, when it is not necessary to distinguish between them, the subscripts y, m, c, and k are omitted, and the description will be given assuming that each unit is any one of the four units, cartridges, and trays.

[0028] Furthermore, the apparatus main body 1A has a sheet storage section 300, a pickup roller 310, a feed roller 311, a separation roller 312, a pair of conveying rollers 320, a secondary transfer roller 12, a fixing device 40, and an intermediate transfer unit 10. The pickup roller 310 is an example of a feeding means that feeds the sheet S. The feed roller 311 and the separation roller 312 are examples of a separation conveying unit that separates and conveys the sheets S one by one by frictional force. The secondary transfer roller 12 is an example of a transfer means that transfers an image from the intermediate transfer belt 10a to the sheet S.

[0029] The intermediate transfer unit 10 has an intermediate transfer belt 10a, a belt drive roller 10b, a tension roller 10c, an intermediate transfer belt cleaning device 13, and a primary transfer roller 11. The intermediate transfer belt 10a is an example of an intermediate transfer body that carries an image transferred (primary transfer) from the photosensitive drum 2 and transports the image to transfer (secondary transfer) onto a sheet S. The intermediate transfer belt 10a is stretched over the belt drive roller 10b and the tension roller 10c. The belt drive roller 10b is a drive member that is rotationally driven by a motor M3, which is a drive source, to transport the intermediate transfer belt 10a.

[0030] 2 is a schematic diagram showing a schematic configuration of the cleaning device 13 for the intermediate transfer belt 10a according to embodiment 1. The cleaning device 13 for the intermediate transfer belt according to embodiment 1 operates by a simultaneous primary transfer and cleaning method.

[0031] FIG. 2(a) shows a cross-sectional view of the intermediate transfer belt cleaning device 13 in a contact state, as viewed from the Y-axis direction. The intermediate transfer belt cleaning device 13 includes an ICL brush 13a on the outer peripheral side of the intermediate transfer belt 10a and an ICL opposing member (backup member) 13b on the inner peripheral side. The ICL brush 13a includes a support and bristles. It functions to charge the residual toner to a potential opposite to the charge potential of the photosensitive drum 2 and to entangle and temporarily hold a portion of the residual toner. Therefore, the bristles of the ICL brush 13a in the first embodiment are made of a conductive resin such as nylon or rayon and woven into the support at a predetermined bristle density. Specifically, bristles made of conductive nylon resin, each 5 mm long and with a single filament fineness of 5 dtex, are woven into the support at a density of 100 kF / inch2. The ICL opposing member 13b is a cylindrical roller member made of aluminum and is arranged to rotate in response to the transport of the intermediate transfer belt 10a.

[0032] FIG. 2(b) is a longitudinal schematic diagram of the cleaning device 13 for the intermediate transfer belt as viewed from the X-axis direction.

[0033] The length of the ICL brush 13a in the axial direction (Y-axis direction) is long enough to cover the area where toner is transferred to the surface of the intermediate transfer belt 10a. Specifically, the length of the intermediate transfer belt 10a in the Y-axis direction is 236 mm, the length of the ICL brush 13a in the Y-axis direction is 224 mm, and the length of the toner transfer area in the Y-axis direction is 220 mm. The ICL brush 13a can be brought into contact with and separated from the intermediate transfer belt 10a.

[0034] FIG. 3 is a schematic diagram illustrating the contact / separation states of the intermediate transfer belt cleaning device 13 with respect to the intermediate transfer belt 10a according to the first embodiment.

[0035] FIG. 3(a) is a cross-sectional view of the ICL brush 13a in contact with the intermediate transfer belt 10a, and FIG. 3(b) is a cross-sectional view of the ICL brush 13a separated from the intermediate transfer belt 10a. The ICL brush 13a is held by a lever 201, which is rotatable around the Y axis. A spring 202 is attached to the end of the lever 201 opposite the portion holding the ICL brush 13a. The spring 202 presses the lever 201 in a direction that brings the ICL brush 13a into contact with the intermediate transfer belt 10a. Supporting the ICL brush 13a with the pressure of the spring 202 allows the ICL brush 13a to be in stable contact with the intermediate transfer belt 10a. Furthermore, adjusting the contact pressure of the ICL brush 13a against the intermediate transfer belt 10a using the spring 202 can prevent the bristles of the ICL brush 13a from being deformed due to the contact.

[0036] As shown in FIG. 3(b), the cam member 203 as a switching member rotates in the direction of the arrow (clockwise), which presses the lever 201 together with the spring 202, moving the ICL brush 13a to a position separated from the intermediate transfer belt 10a.

[0037] FIG. 4 is a diagram illustrating a control unit in the image forming apparatus 1 according to the first embodiment and a configuration for controlling the contact / separation of the ICL brush 13a by the control unit.

[0038] The cam member 203 is connected to a drive source via a gear train. The final end gear 204, which transmits drive to the cam member 203, disengages its claws when a solenoid 205 performs an attraction operation for a certain period of time, and rotates once by driving a motor M3 serving as a drive source. In the first embodiment, the cam member 203 is configured to rotate one-third of the way when the final end gear 204 rotates once. Therefore, the contact / separation state of the ICL brush 13a transitions depending on the drive of the solenoid 205, and the solenoid 205 is driven via a solenoid drive circuit 206 by a signal output from a CPU 207, which serves as a control unit.

[0039] The CPU 207 is connected to a ROM 209, a RAM 210, a sensor group 211, a timer 212, and the like via a bus. The ROM 209 stores programs executed by the CPU 207, various data, and the like. The RAM 210 functions as a work memory that stores various data when the CPU 207 executes control processing. The sensor group 211 includes, for example, a sensor that detects when a sheet S (described later) has reached a secondary transfer roller 12 or when the sheet S has reached a nip of a fixing unit. The sensor group 211 may also include an encoder that detects the presence or absence of a sheet in a sheet storage unit and the amount of motor rotation, as well as a sensor that detects environmental conditions, and the like. The timer 212 measures time in response to instructions from the CPU 207, and notifies the CPU 207 that a predetermined time instructed by the CPU 207 has elapsed.

[0040] 1, the cleaning device 13 for the intermediate transfer belt is disposed downstream (on the tension roller 10c side) of the secondary transfer nip (contact portion with the secondary transfer roller 12) in the transport direction of the intermediate transfer belt 10a. In the first embodiment, the cleaning device 13 is disposed downstream of the intermediate position between the belt drive roller 10b and the tension roller 10c.

[0041] Next, an image forming operation in embodiment 1 will be described. First, the photosensitive drum 2 is rotated in the direction of the arrow (counterclockwise) in Fig. 1 in synchronization with the rotation of the intermediate transfer belt 10a. Then, the surface of the photosensitive drum 2 is uniformly charged by the charging roller 3.

[0042] When a color image is formed on the sheet S, the rotary body 90 rotates in the direction of the arrow in Figure 1 (clockwise) while supporting the developing units 50y, 50m, 50c, and 50k. Then, the electrophotographic process is repeatedly performed while the developing rollers 51y, 51m, 51c, and 51k are moved one by one to the developing position.

[0043] First, the scanner 4 irradiates the photosensitive drum 2 with laser light based on image data corresponding to a yellow image, forming an electrostatic latent image corresponding to the yellow image on the surface of the photosensitive drum 2. In parallel with the formation of this electrostatic latent image, the motor M1 rotates the rotary body 90, causing the rotary body 90 to assume a yellow developing position. When the rotary body 90 is in the yellow developing position, the developing roller 51y is in the developing position and develops the electrostatic latent image formed on the photosensitive drum 2 with yellow toner. A developing voltage of opposite polarity to the charging polarity of the photosensitive drum 2 is applied to the developing roller 51y so that the toner adheres to the latent image on the photosensitive drum 2.

[0044] In the first embodiment, each of the developing rollers 51y, 51m, 51c, and 51k is an elastic roller having a metal shaft coated with rubber. At the developing position, each of the developing rollers 51y, 51m, 51c, and 51k develops an electrostatic latent image while in contact with the photosensitive drum 2. In other words, the image forming apparatus 1 according to the first embodiment employs a contact development method. However, each of the developing rollers 51y, 51m, 51c, and 51k may also develop an electrostatic latent image while a gap is formed between the developing rollers 51y, 51m, 51c, and 51k and the photosensitive drum 2 at the developing position. In other words, the image forming apparatus 1 may employ a non-contact development method.

[0045] Once the yellow toner image is developed, the yellow toner image on the photosensitive drum 2 is primarily transferred onto the intermediate transfer belt 10a by the primary transfer roller 11 disposed inside the intermediate transfer belt 10a. At this time, a primary transfer voltage of the opposite polarity to that of the toner image formed on the photosensitive drum 2 is applied to the primary transfer roller 11.

[0046] Thereafter, the rotary body 90 is rotated to sequentially move the developing rollers 51m, 51c, and 51k to the developing positions, thereby sequentially forming toner images of each color on the photosensitive drum 2. That is, after the yellow toner image is transferred to the intermediate transfer belt 10a, the rotary body 90 assumes the magenta developing position, and the magenta toner image is transferred to the intermediate transfer belt 10a. After the magenta toner image is transferred to the intermediate transfer belt 10a, the rotary body 90 assumes the cyan developing position, and the cyan toner image is transferred to the intermediate transfer belt 10a. After the cyan toner image is transferred to the intermediate transfer belt 10a, the rotary body 90 assumes the black developing position, and formation of a black toner image on the intermediate transfer belt 10a begins. Until the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 10a pass through the secondary transfer section and the cleaning device, the secondary transfer roller 12 and the intermediate transfer belt cleaning device 13 are separated from the intermediate transfer belt 10a. The secondary transfer roller 12 is brought into contact with the intermediate transfer belt 10a after the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 10a have passed through the secondary transfer section and before the leading edge of the color toner image on the intermediate transfer belt 10a, on which the fourth color, black toner image, has been formed, reaches the secondary transfer section again.

[0047] Meanwhile, a sheet S is fed by a pickup roller 310 from a sheet storage unit 300 provided at the bottom of the apparatus main body 1A. The sheets S are separated into individual sheets by a feed roller 311 and a separation roller 312 and then fed to a pair of conveying rollers 320. The sheet S fed to the pair of conveying rollers 320 waits until a toner image is formed on the intermediate transfer belt 10a. After the toner image is formed on the intermediate transfer belt 10a, the sheet S that has been waiting by the pair of conveying rollers 320 is conveyed and sent to a transfer unit (secondary transfer unit), which is a nip between the intermediate transfer belt 10a and a secondary transfer roller 12. In this way, the color image on the intermediate transfer belt 10a is transferred (secondary transfer) onto the surface of the conveyed sheet S. At this time, a secondary transfer voltage of a polarity opposite to the charge polarity of the toner image is applied to the secondary transfer roller 12.

[0048] The sheet S onto which the color image has been transferred in this manner is sent to the fixing device 40. In the fixing device 40, the sheet S is heated and pressurized, and the image is fixed onto the sheet S. After passing through the fixing device 40, the sheet S is discharged outside the image forming apparatus 1 as a finished product.

[0049] Residual toner remaining on the surface of the intermediate transfer belt 10a after the secondary transfer is cleaned by the cleaning device 13 for the intermediate transfer belt as follows.

[0050] The ICL brush 13a serves to charge the transfer residual toner on the intermediate transfer belt 10a to a potential opposite to the charge potential of the photosensitive drum 2, and to temporarily hold some of the transfer residual toner by entangling it in the brush. The transfer residual toner on the intermediate transfer belt 10a is charged to a potential opposite to the charge potential of the photosensitive drum 2 by passing through the ICL brush 13a. In the first embodiment, the photosensitive drum 2 is negatively charged, and a positive (plus) voltage is applied to the ICL brush 13a, so the transfer residual toner that passes through the ICL brush 13a is positively charged. The transfer residual toner, now positively charged, is transferred to the surface of the photosensitive drum 2, which is negatively charged, at the primary transfer nip and is collected by the cleaning unit 6 of the photosensitive drum 2.

[0051] On the other hand, the transfer residual toner that does not pass through the ICL brush 13a and is temporarily held by the ICL brush 13a is discharged from the ICL brush 13a onto the intermediate transfer belt 10a again in the operation after image formation. It is then transferred to the surface of the photosensitive drum 2 at the primary transfer nip and collected by the photosensitive drum cleaning unit 6. However, not all of the toner temporarily held by the ICL brush 13a is discharged onto the intermediate transfer belt 10a, and a certain amount of residual toner remains after secondary transfer on the ICL brush 13a. Next, the contact / separation timing of the ICL brush 13a in this embodiment 1 will be described with reference to FIG. 5.

[0052] FIG. 5 is a cross-sectional view showing the position of the toner image on the intermediate transfer belt 10a, the position of the sheet S, and the contact / separation state of the ICL brush 13a in the image forming apparatus 1 according to the first embodiment.

[0053] 5(a) shows the state after the primary transfer of the yellow, magenta, and cyan toner images onto the intermediate transfer belt 10a is completed and the toner images on the intermediate transfer belt 10a pass through the intermediate transfer belt cleaning unit 13 (ICL brush 13a and ICL opposing member 13b). At this time, the ICL brush 13a is in a separated state and not in contact with the intermediate transfer belt 10a.

[0054] 5(b) shows the state where the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 10a have passed the secondary transfer unit and the transfer of the fourth color, black toner image, onto the intermediate transfer belt 10a has begun. At this time, the secondary transfer roller 12 is in contact with the intermediate transfer belt 10a until the yellow, magenta, cyan, and black toner images reach the secondary transfer unit.

[0055] 5(c) shows a state in which, after the secondary transfer roller 12 contacts the intermediate transfer belt 10a, the sheet S, which has been waiting until the YMCK toner image is formed on the intermediate transfer belt 10a, is transported in synchronization with the toner image on the intermediate transfer belt 10a and reaches the secondary transfer nip. At this time, the ICL brush 13a is still spaced from the intermediate transfer belt 10a. In this way, secondary transfer of the YMCK toner image onto the sheet S begins.

[0056] 5(d) shows a state in which secondary transfer is being performed while the sheet S passes through the secondary transfer nip, with the ICL brush 13a still spaced apart from the intermediate transfer belt 10a.

[0057] 5(e) shows the state in which secondary transfer is being performed as the sheet S passes through the secondary transfer nip, until the transfer residual toner remaining on the surface of the intermediate transfer belt 10a reaches the intermediate transfer belt cleaning unit 13. At this time, the ICL brush 13a is in contact with the intermediate transfer belt 10a.

[0058] FIG. 5(f) shows a state where the residual toner has passed through the cleaning unit 13 for the intermediate transfer belt, and the ICL brush 13a is again separated from the intermediate transfer belt 10a in preparation for the next image formation.

[0059] 7 is a flowchart illustrating contact / separation control of the ICL brush 13a by the image forming apparatus 1 according to the first embodiment. The processing shown in this flowchart is realized by the CPU 207 executing a program stored in the ROM 209. This flowchart mainly describes the control processing by the CPU 207 that relates to contact / separation control of the ICL brush 13a, and omits details of other processing.

[0060] 7 begins when image formation is started. First, in S701, the CPU 207 drives the solenoid 205, motor M3, etc. to separate the ICL brush 13a from the intermediate transfer belt 10a. Next, the process proceeds to S702, where the CPU 207 separates the secondary transfer roller 12 from the intermediate transfer belt 10a. Note that if the ICL brush 13 and secondary transfer roller 12 are already separated from the intermediate transfer belt 10a, steps S701 and S702 may be omitted.

[0061] Next, the process proceeds to S703, where the CPU 207 executes primary transfer of the yellow, magenta, and cyan toner images onto the intermediate transfer belt 10a, and then the process proceeds to S704, where the primary transfer of the fourth color, black toner image, onto the intermediate transfer belt 10a begins. Then, the process proceeds to S705, where the CPU 207 brings the secondary transfer roller 12 into contact with the intermediate transfer belt 10a and starts conveying the sheet S in synchronization with the primary transfer of the fourth color, black toner image. Then, in S706, when the leading edge of the sheet S reaches the secondary transfer nip in synchronization with the primary transfer of the black toner image, the CPU 207 starts secondary transfer onto the sheet S by the secondary transfer roller 12 and the secondary transfer roller 12. Note that the determination of whether the leading edge of the sheet S has reached the secondary transfer nip may be made based on the detection result from the sensor described above. The process then proceeds to S707, where the CPU 207 determines whether a predetermined time has elapsed since the start of secondary transfer, i.e., whether the timing has come for the transfer residual toner remaining on the surface of the intermediate transfer belt 10a to reach the cleaning unit 13 of the intermediate transfer belt while secondary transfer to the sheet S is being performed (the state shown in FIG. 5(e)). This timing may be determined by determining in advance, through experiments or the like, the time from the start of secondary transfer until the transfer residual toner reaches the cleaning unit 13 according to the rotation speed of the motor, and determining whether the timer 212 has timed that time. Alternatively, the amount of motor rotation from the start of secondary transfer until the transfer residual toner reaches the cleaning unit 13 may be determined, and the amount of rotation of the motor that has actually been driven to rotate may be determined.

[0062] If it is determined in S707 that the time has come for the residual toner to reach the cleaning unit 13 after the start of secondary transfer, the process proceeds to S708, where the CPU 207 drives the solenoid 205 and motor M3 to bring the ICL brush 13a into contact with the intermediate transfer belt 10a. This results in the state shown in FIG. 5(e). The process proceeds to S709, where the CPU 207 waits until the secondary transfer onto the sheet S is complete, and then the process proceeds to S710, where the CPU 207 separates the secondary transfer roller 12 from the intermediate transfer belt 10a. The process proceeds to S711, where the CPU 207 determines whether a predetermined time has elapsed since the secondary transfer onto the sheet S was completed, i.e., whether the residual toner remaining on the surface of the intermediate transfer belt 10a after the secondary transfer has completely passed through the cleaning unit 13 for the intermediate transfer belt. If it is determined that the transfer residual toner has passed through the cleaning unit 13 of the intermediate transfer belt in this way, the process proceeds to S712, where the CPU 207 drives the solenoid 205 and motor M3 to separate the ICL brush 13a from the intermediate transfer belt 10a (FIG. 5(f)). Similarly, the predetermined time in S711 may be determined in advance by experiment or the like, based on the motor rotation speed or the like, from the time from the end of the secondary transfer until the transfer residual toner passes through the cleaning unit 13, and the determination may be made based on whether the timer 212 has timed that time. Alternatively, the amount of motor rotation from the end of the secondary transfer until the transfer residual toner passes through the cleaning unit 13 may be determined, and the determination may be made based on whether that amount of rotation has been reached. The process then proceeds to S713, where the CPU 207 determines whether all printing has been completed. If completed, the process ends. If not, the process proceeds to S703, where image formation on the next sheet S is performed.

[0063] As described above, in the first embodiment, the ICL brush 13a contacts the intermediate transfer belt 10a after the sheet S reaches the secondary transfer nip. When the sheet S enters the secondary transfer nip, the frictional force acting on the intermediate transfer belt 10a at the secondary transfer nip changes significantly. This causes a sudden change in the transport speed of the intermediate transfer belt 10a. Therefore, if the ICL brush 13a is in contact with the intermediate transfer belt 10a when the sheet S enters the secondary transfer nip, toner accumulated on the ICL brush 13a may be unintentionally scattered onto the intermediate transfer belt 10a. The polarity of the toner scattered onto the intermediate transfer belt 10a cannot be controlled, and this can interfere with the primary transfer of the next page in continuous printing at the primary transfer nip. Furthermore, if the scattered toner does not transfer to the photosensitive drum 2 but remains on the intermediate transfer belt 10a, it can result in image defects in the printed output.

[0064] Conventionally, the ICL brush is configured so that the belt drive roller 10b, which is the opposing member in the secondary transfer, also serves as a backup member, and is located immediately after the secondary transfer nip. In this configuration, considering the operating time of the ICL brush contact / separation mechanism, if the ICL brush is not in contact with the intermediate transfer belt before the sheet S reaches the secondary transfer section, it will not be able to clean the remaining toner after the secondary transfer in time.

[0065] However, in the cleaning device 13 for the intermediate transfer belt according to the first embodiment, the belt drive roller 10b, which is the opposing member for secondary transfer, is not used as a backup member, but is arranged at a position further downstream of the intermediate transfer belt. In other words, it is possible to ensure time for the ICL brush to come into contact with the sheet S after it enters the secondary transfer nip (time for the transfer residual toner from the secondary transfer portion to reach the ICL brush 13a).

[0066] Therefore, according to the first embodiment, the ICL brush is brought into contact with the intermediate transfer belt after the sheet S reaches the secondary transfer nip, which prevents toner from scattering from the ICL brush due to a change in the conveyance speed of the intermediate transfer belt when the sheet S enters the secondary transfer nip. This has the effect of providing an output product with good image quality without being affected by toner scattering from the ICL brush.

[0067] Although the first embodiment has been described using the example of color print image formation, the same effects can be obtained in monochrome print image formation, and this is not excluded from the scope of the invention. Furthermore, the configuration of separating the ICL brush from the intermediate transfer belt also has the effect of improving the durability of the intermediate transfer belt, and it is preferable to keep the ICL brush separated as much as possible. Therefore, even in monochrome printing, the problem of unintended toner scattering on the intermediate transfer belt due to contact / separation of the ICL brush exists, and the configuration of the present invention can achieve the same effects.

[0068] Furthermore, in the first embodiment, an image forming apparatus that performs multiple development using one photosensitive drum has been described as an example, but the same effects can also be obtained with a so-called inline type image forming apparatus that performs image formation using photosensitive drums of each color arranged side by side on an intermediate transfer belt, and these are not excluded from the scope of the invention.

[0069] [Embodiment 2] Next, a second embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the second embodiment are the same as those of the first embodiment. Therefore, elements having the same or equivalent functions and configurations as those of the image forming apparatus 1 of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. A feature of the second embodiment is that the contact operation of the ICL brush 13a against the intermediate transfer belt 10a is performed after the sheet S reaches the fixing nip.

[0070] As explained in the first embodiment, unintended scattering of toner from the ICL brush 13a onto the intermediate transfer belt 10a is likely to occur when there is a sudden change in the transport speed of the intermediate transfer belt 10a. One example is the timing when the sheet S reaches the secondary transfer nip, as explained in the first embodiment. The fixing device 40 is disposed downstream in the transport path of the sheet S, and there are cases where the timing when the sheet S reaches the fixing device 40 also causes a sudden change in the transport speed of the intermediate transfer belt 10a.

[0071] In recent years, the distance from the secondary transfer unit to the fixing device has become shorter due to the miniaturization of image forming devices, and shocks and changes in conveyance speed when the sheet S enters the fixing device are more likely to be transmitted to the intermediate transfer belt. In such image forming devices, the ICL brush 13a contacts the intermediate transfer belt 10a after the sheet S reaches the fixing nip, thereby preventing toner from scattering from the ICL brush 13a.

[0072] Next, an image forming apparatus according to the second embodiment and an image forming operation will be described.

[0073] The sheet S onto which the toner image has been transferred in the secondary transfer nip is sent to a fixing device 40 (FIG. 1). In the fixing device 40, the sheet S is heated and pressed, and the image is fixed onto the sheet S.

[0074] As shown in FIG. 1, the fixing device 40 according to the second embodiment includes a pressure roller (pressure member) 401 and a fixing film (fixing rotator) 402. The pressure roller 401 and the fixing film 402 are pressed against each other to form a fixing nip. A heater member serving as a heat source is disposed inside the fixing film 402, and the heater member heats the fixing film 402, thereby heating and pressurizing the toner image on the sheet S passing through the fixing nip, thereby fixing the image. The pressure roller 401 has an elastic layer made of a heat-resistant material formed on a metal core metal serving as a base material, and is pressed by the fixing film 402 to ensure the fixing nip width. The pressure roller 401 receives driving force from a motor M3 via a gear provided at the end of the core metal, and is driven to rotate in the direction of the arrow (counterclockwise). The fixing film 402 is driven to rotate by frictional force generated at the nip with the pressure roller 401.

[0075] The rotation speed of the pressure roller 401 is set to match the speed at which the sheet S, onto which the toner image has been transferred, is conveyed through the secondary transfer nip. In the second embodiment, the pressure roller 401 and the belt drive roller 10b, which drives the intermediate transfer belt 10a, share a common drive source, motor M3. Therefore, their speeds are adjusted by a gear ratio so that they are equivalent. However, the pressure roller 401 is pressed by the fixing film 402, and its rotation speed varies depending on the temperature of the pressure roller 401. This is because the elastic layer of the pressure roller 401 in the second embodiment is made of silicone rubber, and the outer diameter of the elastic layer changes due to thermal expansion. Therefore, depending on the temperature of the pressure roller 401, a discrepancy occurs between the conveyance speed of the pressure roller 401 and the conveyance speed of the intermediate transfer belt 10a. As a result, when the sheet S, onto which the toner image has been transferred at the secondary transfer nip, enters the fixing nip, the conveyance speed of the sheet S changes considerably. This change in the speed of the sheet S is transmitted to the intermediate transfer belt 10a at the secondary transfer nip, causing a change in the transport speed of the intermediate transfer belt 10a. Therefore, if the ICL brush 13a is in contact with the intermediate transfer belt 10a when the sheet S enters the fixing nip, there is a possibility that toner accumulated on the ICL brush 13a will be unintentionally scattered onto the intermediate transfer belt 10a. To prevent toner from scattering from the ICL brush 13a, the ICL brush 13a is brought into contact with the intermediate transfer belt 10a after the sheet S reaches the fixing nip.

[0076] Next, the contact and separation timing of the ICL brush 13a according to the second embodiment will be described with reference to FIG.

[0077] FIG. 6 is a cross-sectional view showing the positions of the toner image on the intermediate transfer belt 10a, the position of the sheet S, and the contact / separation states of the ICL brush 13a in the image forming apparatus 1 according to the second embodiment.

[0078] 6(a) shows the state after the primary transfer of the yellow, magenta, and cyan toner images onto the intermediate transfer belt 10a is completed and before the toner images on the intermediate transfer belt 10a pass through the intermediate transfer belt cleaning unit 13. At this time, the ICL brush 13a is in a separated state, not in contact with the intermediate transfer belt 10a.

[0079] 6(b) shows the state where the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 10a have passed the secondary transfer unit, and the transfer of the fourth color, black toner image, onto the intermediate transfer belt 10a has begun. At this time, the secondary transfer roller 12 remains in contact with the intermediate transfer belt 10a until the yellow, magenta, cyan, and black toner images reach the secondary transfer unit.

[0080] 6(c) shows a state in which the sheet S, which has been waiting until the YMCK toner image is formed on the intermediate transfer belt 10a after the secondary transfer roller 12 has contacted the intermediate transfer belt 10a, is transported in synchronization with the YMCK toner image on the intermediate transfer belt 10a and reaches the secondary transfer nip, with the ICL brush 13a still spaced apart from the intermediate transfer belt 10a.

[0081] 6(d) shows a state in which the secondary transfer onto the sheet S has started, the sheet S has passed through the secondary transfer nip, and has reached the fixing nip. At this time, the ICL brush 13a is still separated from the intermediate transfer belt 10a.

[0082] Figure 6(e) shows the state in which the sheet S is passing through the fixing nip and the residual toner remaining on the surface of the intermediate transfer belt 10a reaches the cleaning section 13 of the intermediate transfer belt, and at this time the ICL brush 13a is in contact with the intermediate transfer belt 10a.

[0083] FIG. 6(f) shows a state where the residual toner has passed through the cleaning unit 13 of the intermediate transfer belt, and at this time the ICL brush 13a is again separated from the intermediate transfer belt 10a to prepare for the next image formation.

[0084] 8 is a flowchart illustrating contact / separation control of the ICL brush 13a by the image forming apparatus 1 according to the second embodiment. The processing shown in this flowchart is realized by the CPU 207 executing a program stored in the ROM 209. In FIG. 8, processing common to the processing in FIG. 7 is indicated by the same reference numerals, and description thereof will be omitted.

[0085] In S706, when the leading edge of sheet S reaches the secondary transfer nip, CPU 207 starts secondary transfer onto sheet S using secondary transfer roller 12. Then, in S801, CPU 207 determines whether a predetermined time has elapsed since the start of secondary transfer, i.e., whether it is time for the leading edge of sheet S to pass through the fixing nip while secondary transfer onto sheet S is being performed. This timing can be determined, for example, by using the aforementioned sensor to detect that the leading edge of sheet S has passed through the fixing nip. Alternatively, the time (predetermined time) from the start of secondary transfer until the leading edge of sheet S passes through the fixing nip of fixing device 40 may be determined in advance through experiments or the like based on the motor rotation speed, and the time measured by timer 212 from the start of secondary transfer may be determined based on whether the time reached the predetermined time. Alternatively, the amount of motor rotation from the start of secondary transfer until the leading edge of sheet S reaches fixing device 40 may be determined in advance, and a sensor such as the aforementioned encoder may be used to determine whether the amount of motor rotation from the start of secondary transfer has reached the determined amount of rotation. When the CPU 207 determines in S801 that the leading edge of the sheet S has passed through the fixing nip, the process proceeds to S708, where the CPU 207 drives the solenoid 205 and motor M3 to bring the ICL brush 13a into contact with the intermediate transfer belt 10a (FIG. 6(e)). Note that it is assumed here that the distance from the secondary transfer nip to the ICL brush 13a is longer than the distance from the secondary transfer nip to the fixing device 40. Therefore, in S708, the ICL brush 13a may be brought into contact with the intermediate transfer belt 10a a short time after the sheet S has reached the fixing nip.

[0086] As described above, according to the second embodiment, the ICL brush can be brought into contact with the intermediate transfer belt after the sheet S reaches the fixing nip. This makes it possible to prevent toner from scattering from the ICL brush onto the intermediate transfer belt even if a sudden change in the conveying speed of the intermediate transfer belt occurs when the sheet S reaches the fixing nip.

[0087] The intermediate transfer belt cleaning device 13 according to the second embodiment is disposed at a position on the intermediate transfer belt 10a at a distance from the secondary transfer nip longer than the distance from the secondary transfer nip to the fixing device 40 along the transport path of the sheet S. Here, the transport speed of the sheet S is the same as that of the intermediate transfer belt 40a. Therefore, this arrangement allows the sheet S to reach the fixing device before the residual toner generated at the secondary transfer nip reaches the ICL brush 13a. In other words, the ICL brush 13a can contact the intermediate transfer belt 10a after the sheet S reaches the fixing nip. This prevents toner from scattering from the ICL brush 13a onto the intermediate transfer belt 10a, even if the transport speed of the intermediate transfer belt 10a changes, providing an output with high image quality.

[0088] In the second embodiment, the pressure roller, which is a fixing member, and the belt drive roller 10b, which drives the intermediate transfer belt 10a, share a common drive source, motor M3. However, a configuration having separate drive sources can achieve the same effects. Therefore, such a configuration is not excluded from the scope of the present invention. Even in a configuration having separate drive sources, it is difficult to perfectly match the conveyance speeds of the pressure roller and the intermediate transfer belt due to variations in the outer diameters of the components and the degree of thermal expansion of the components. In the second embodiment, the fixing device 40 has a heater inside the fixing film. However, similar effects can be achieved with a fixing configuration using a heat roller, an external heating system, or an IH (electromagnetic induction heating) system, and these configurations are not excluded from the scope of the present invention.

[0089] (Other embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0090] The present specification and drawings disclose the following image forming apparatus and a control method thereof.

[0091] (Item 1) an image carrier that carries a toner image; a secondary transfer means including a secondary transfer roller for secondarily transferring the toner image, which has been primarily transferred from the image carrier to an intermediate transfer medium, from the intermediate transfer medium to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body, and that charges and cleans the toner remaining on the intermediate transfer body after the secondary transfer; a control unit that controls the cleaning unit to contact the intermediate transfer body after the leading edge of the recording medium has passed through a contact portion between the secondary transfer roller and the intermediate transfer body; An image forming apparatus comprising:

[0092] (Item 2) 2. The image forming apparatus according to claim 1, wherein the cleaning unit has a brush member that charges the toner remaining on the intermediate transfer body after the secondary transfer by applying a voltage thereto.

[0093] (Item 3) 3. The image forming apparatus according to claim 2, wherein the brush member holds toner on the surface of the area in contact with the intermediate transfer body.

[0094] (Item 4) a motor serving as a drive source for transporting the intermediate transfer body; a sensor for detecting that the recording medium has reached the secondary transfer roller. The image forming apparatus according to any one of items 1 to 3, characterized in that after the sensor detects the recording medium, the control unit drives the motor a predetermined amount of rotation and then contacts the cleaning unit with the intermediate transfer body.

[0095] (Item 5) an image carrier that carries a toner image; a primary transfer means for primarily transferring the toner image formed on the image carrier to an intermediate transfer medium; a secondary transfer unit including a secondary transfer roller for secondarily transferring the toner image from the intermediate transfer body to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body, and that charges and cleans the toner remaining on the intermediate transfer body after the secondary transfer; a fixing unit that fixes the toner image secondarily transferred onto the recording medium by applying heat and pressure to the toner image in a fixing nip formed between a fixing rotary body and a pressure body that are in pressure contact with each other; a control unit that controls the cleaning unit to contact the intermediate transfer body after the leading edge of the recording medium, onto which the secondary transfer has been performed by the secondary transfer unit, has passed through the fixing nip portion of the fixing device; An image forming apparatus comprising:

[0096] (Item 6) 6. The image forming apparatus according to item 5, wherein the cleaning unit has a brush member that charges the toner remaining on the intermediate transfer body after the secondary transfer by applying a voltage thereto.

[0097] (Item 7) 7. The image forming apparatus according to item 5 or 6, wherein the distance from the secondary transfer roller to the cleaning unit on the intermediate transfer body is longer than the distance from the secondary transfer roller to the fixing device.

[0098] (Item 8) 8. The image forming apparatus according to any one of items 5 to 7, wherein the cleaning unit retains toner on the surface of the area in contact with the intermediate transfer body.

[0099] (Item 9) The fixing device further includes a sensor for detecting that the recording medium has passed through a fixing nip portion of the fixing device. 9. The image forming apparatus according to any one of items 5 to 8, wherein the control unit brings the cleaning unit into contact with the intermediate transfer body based on detection by the sensor.

[0100] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention. [Explanation of symbols]

[0101] 1...image forming apparatus, 2...photosensitive drum, 10...intermediate transfer unit, 10a...intermediate transfer belt, 12...secondary transfer roller, 13...cleaning device for intermediate transfer belt, 13a...ICL brush, 40...fixing device, 50...developing unit, S...sheet

Claims

1. an image carrier that carries a toner image; a secondary transfer means including a secondary transfer roller for secondarily transferring the toner image, which has been primarily transferred from the image carrier to an intermediate transfer medium, from the intermediate transfer medium to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body, and that charges and cleans the toner remaining on the intermediate transfer body after the secondary transfer; a control unit that controls the cleaning unit to contact the intermediate transfer body after the leading edge of the recording medium has passed through a contact portion between the secondary transfer roller and the intermediate transfer body; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the cleaning unit has a brush member that charges the toner remaining on the intermediate transfer body after the secondary transfer by applying a voltage thereto.

3. 3. The image forming apparatus according to claim 2, wherein the brush member holds toner on the surface of the area where the brush member contacts the intermediate transfer member.

4. a motor serving as a drive source for transporting the intermediate transfer body; a sensor for detecting that the recording medium has reached the secondary transfer roller.

2. The image forming apparatus according to claim 1, wherein the control unit drives the motor a predetermined number of rotations after the sensor detects the recording medium, and then brings the cleaning unit into contact with the intermediate transfer body.

5. an image carrier that carries a toner image; a primary transfer means for primarily transferring the toner image formed on the image carrier to an intermediate transfer medium; a secondary transfer unit including a secondary transfer roller for secondarily transferring the toner image from the intermediate transfer body to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body, and that charges and cleans the toner remaining on the intermediate transfer body after the secondary transfer; a fixing unit that fixes the toner image secondarily transferred onto the recording medium by applying heat and pressure to the toner image in a fixing nip formed between a fixing rotary body and a pressure body that are in pressure contact with each other; a control unit that controls the cleaning unit to contact the intermediate transfer body after the leading edge of the recording medium, onto which the secondary transfer has been performed by the secondary transfer unit, has passed through the fixing nip portion of the fixing device; An image forming apparatus comprising:

6. 6. The image forming apparatus according to claim 5, wherein the cleaning unit has a brush member that charges the toner remaining on the intermediate transfer body after the secondary transfer by applying a voltage thereto.

7. 6. The image forming apparatus according to claim 5, wherein the distance from the secondary transfer roller to the cleaning unit on the intermediate transfer body is longer than the distance from the secondary transfer roller to the fixing unit.

8. 6. The image forming apparatus according to claim 5, wherein the cleaning unit retains toner on the surface of the area in contact with the intermediate transfer body.

9. The fixing device further includes a sensor for detecting that the recording medium has passed through a fixing nip portion of the fixing device.

6. The image forming apparatus according to claim 5, wherein the control unit brings the cleaning unit into contact with the intermediate transfer body based on the detection by the sensor.

Images