Image forming apparatus

Abstract

This design enables the proper removal of adjustment toner images from the intermediate transfer belt while extending the lifespan of the intermediate transfer belt and cleaning components. [Solution] The control unit 110 is capable of controlling the execution of an image forming operation in which the toner image formed on the intermediate transfer belt 31 by the image forming unit 1 is transferred to the recording material S, and an adjustment operation in which the image forming unit 1 forms an adjustment toner image on the intermediate transfer belt 31. In the image forming operation, the control unit 133 is controlled so that the brush 82 rotates at a first peripheral speed Vr when the brush 82 removes the remaining toner from the intermediate transfer belt 31, and the brush 82 rotates at a second peripheral speed Vp which is faster than the first peripheral speed Vr when the brush 82 removes the adjustment toner image from the intermediate transfer belt 31.

Description

Technical Field

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

Background Art

[0002] Conventionally, for example, some image forming apparatuses such as printers and copying machines using an electrophotographic method employ an intermediate transfer method. In an image forming apparatus using the intermediate transfer method, a toner image is formed on an image carrier such as a photosensitive drum, and after the toner image is primarily transferred from the image carrier onto an intermediate transfer member in a primary transfer unit, it is secondarily transferred from the intermediate transfer member onto a recording material such as paper in a secondary transfer unit. As the intermediate transfer member, an intermediate transfer belt formed of an endless belt is often used.

[0003] Toner remaining on the intermediate transfer belt (transfer residual toner) that is not transferred to the recording material in the secondary transfer unit is removed from the intermediate transfer belt by cleaning means in a cleaning unit and recovered. As a method for cleaning the intermediate transfer belt, there is an electrostatic cleaning method. The electrostatic cleaning method is a method in which a voltage is applied to a conductive cleaning member disposed so as to contact the intermediate transfer belt, and toner is electrostatically adsorbed from the intermediate transfer belt onto the cleaning member to clean the intermediate transfer belt. As the cleaning member, a conductive fur brush (conductive fur brush roller) that rotates in contact with the intermediate transfer belt is often used (electrostatic fur cleaning method).

[0004] In Patent Document 1, a configuration has been proposed in which the voltage applied to the fur brush and the rotation speed of the fur brush are controlled according to the detection result of the current flowing through the fur brush.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] Incidentally, in an intermediate transfer type image forming apparatus, a correction toner image (patch pattern) is formed on an intermediate transfer belt, and image density control and color shift correction control are performed by detecting the patch pattern on the intermediate transfer belt with a sensor. Furthermore, the image forming apparatus is sometimes configured so that the patch pattern passes through a secondary transfer section. In this case, the patch pattern that has passed through the secondary transfer section is removed from the intermediate transfer belt in a cleaning section.

[0007] Since patch patterns are not transferred to the recording material, their toner density (amount of toner per unit area) is higher than that of residual toner. Therefore, in order to properly remove patch patterns from the intermediate transfer belt using the electrostatic fur cleaning method, the fur brush requires a relatively high rotation speed. If the rotation speed of the fur brush is insufficient when removing patch patterns from the intermediate transfer belt, cleaning failures may occur, potentially leading to problems such as toner from the patch patterns adhering to subsequent print images. However, if the rotation speed of the fur brush is set to be suitable for removing patch patterns from the intermediate transfer belt, the number of times the fur brush and intermediate transfer belt rub against each other increases, which can reduce the lifespan of parts such as the intermediate transfer belt and fur brush.

[0008] Therefore, the objective of the present invention is to enable the proper removal of the adjustment toner image from the intermediate transfer belt while extending the lifespan of the intermediate transfer belt and cleaning member. [Means for solving the problem]

[0009] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image forming unit comprising a rotatable image carrier that carries a toner image, and an image forming unit that forms a toner image on the image carrier; a rotatable intermediate transfer belt on which the toner image is transferred from the image carrier, the intermediate transfer belt comprising a primary transfer unit on which the toner image is first transferred from the image carrier to the intermediate transfer belt, and a secondary transfer unit on which the toner image is secondarily transferred from the intermediate transfer belt to a recording material; a brush that contacts the intermediate transfer belt in the rotational direction of the intermediate transfer belt at a cleaning unit downstream of the secondary transfer unit and upstream of the primary transfer unit, and removes toner from the intermediate transfer belt by electrostatically adsorbing toner while rotating; a drive unit that drives the brush; and the drive unit The image forming apparatus comprises a control unit capable of controlling the drive unit, wherein the control unit is capable of controlling the execution of an image forming operation in which the toner image formed on the intermediate transfer belt by the image forming unit is transferred to a recording material, and an adjustment operation in which the image forming unit forms an adjustment toner image on the intermediate transfer belt, and the control unit is characterized in that it controls the drive unit so that when the brush removes residual transfer toner remaining on the intermediate transfer belt with the brush, the brush rotates at a first peripheral speed Vr, and when the brush removes the adjustment toner image from the intermediate transfer belt with the brush, the brush rotates at a second peripheral speed Vp which is faster than the first peripheral speed Vr. [Effects of the Invention]

[0010] According to the present invention, it is possible to properly remove the adjustment toner image from the intermediate transfer belt while extending the lifespan of the intermediate transfer belt and cleaning member. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of an image forming apparatus. [Figure 2] This is a schematic diagram of a patch pattern. [Figure 3] This is a block diagram illustrating the control configuration of an image forming apparatus. [Figure 4] This is a schematic cross-sectional view of the secondary transfer region during image formation. [Figure 5] This is a schematic cross-sectional view showing the first configuration of the secondary transfer section during image correction operation. [Figure 6] This is a schematic cross-sectional view showing a second form of the secondary transfer section during image correction operation. [Figure 7] This is a schematic cross-sectional view of a belt cleaning device used during image formation. [Figure 8] This is a schematic cross-sectional view of the belt cleaning device during image correction operation. [Figure 9] This flowchart illustrates the control of the cleaning drive unit during the image correction operation prior to the image formation operation. [Figure 10] This flowchart illustrates the control of the creeking drive unit during image correction operations performed in the middle of continuous printing. [Modes for carrying out the invention]

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

[0013] [Example 1] <Image forming apparatus> Figure 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem printer employing an intermediate transfer method that is capable of forming full-color images using an electrophotographic method. The image forming apparatus 100 can form a full-color image on a sheet-like recording material S in response to an image signal transmitted from an external device such as a host computer.

[0014] The image forming apparatus 100 includes, as a plurality of image forming units, four image forming units (stations) 1Y, 1M, 1C, and 1K that form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The four image forming units 1Y, 1M, 1C, and 1K are arranged in series along the image transfer surface that extends substantially horizontally of the intermediate transfer belt 31. For elements having the same or corresponding functions or configurations provided for each color, the Y, M, C, and K at the end of the symbol indicating that it is an element for any one color may be omitted and they may be collectively described. The image forming unit 1 (1Y, 1M, 1C, 1K) includes a photosensitive drum 11 (11Y, 11M, 11C, 11K), a charger 12 (12Y, 12M, 12C, 12K), an exposure device 13 (13Y, 13M, 13C, 13K), a developing device 14 (14Y, 14M, 14C, 14K), a drum cleaning device 15 (15Y, 15M, 15C, 15K), and the like.

[0015] The photosensitive drum 11, which is a rotatable drum-type (cylindrical) photoreceptor (electrophotographic photoreceptor) as an image carrier, is rotationally driven in the direction of arrow R1 (counterclockwise direction) in the figure. The photosensitive drum 11 is rotationally driven by the driving force being transmitted from the drum driving motor 131a (Fig. 3) of the drum driving unit 131 as the photoreceptor driving means. The surface of the rotating photosensitive drum 11 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the charger 12 as the charging means. At the time of charging, a charging bias (charging voltage) is applied to the charger 12 by a charging power source (high voltage power source) 121 (Fig. 3) as the charging voltage applying unit. The surface of the charged photosensitive drum 11 is irradiated with laser light corresponding to an image signal (image information) by the exposure device 13 as the exposure means and is scanned and exposed, and an electrostatic latent image (electrostatic image) corresponding to the image signal is formed on the surface of the photosensitive drum 11. In this embodiment, the exposure device 13 is configured to include a laser scanner. Note that the exposure device 13 may be configured as one unit that exposes the photosensitive drums 11 of the plurality of image forming units 1. Further, the exposure device 13 is not limited to being configured to include a laser scanner using a laser light source as the light source, and may be configured to include an LED array or the like using an LED as the light source.

[0016] The electrostatic latent image formed on the photosensitive drum 11 is developed (visualized) by supplying toner by a developing device 14 as developing means, and a toner image (toner picture, developer image) is formed on the photosensitive drum 11. In this embodiment, the developing device 14 uses a two-component developer including toner (non-magnetic toner particles) and a carrier (magnetic carrier particles) as the developer. The developing device 14 has a developing sleeve as a developer carrier (developing member), carries the developer on the rotating developing sleeve, conveys it to the opposing portion between the developing sleeve and the photosensitive drum 11, and supplies the toner to the photosensitive drum 11. At the time of development, a developing bias (developing voltage) is applied to the developing sleeve by a developing power source (high-voltage power source) 122 (FIG. 3) as a developing voltage application unit. In this embodiment, the developing device 14 attaches toner charged with the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 11 to the exposed portion on the photosensitive drum 11 where the absolute value of the potential has decreased by being exposed after being uniformly charged (inversion development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner at the time of development, is negative polarity.

[0017] An intermediate transfer belt 31, composed of an endless belt, is positioned opposite the four photosensitive drums 11Y, 11M, 11C, and 11K, serving as an intermediate transfer body. The intermediate transfer belt 31 is stretched over a plurality of tension rollers, namely drive rollers 33, tension rollers 34, a pre-secondary transfer roller 36, and a secondary transfer inner roller 32, and is taut with a predetermined tension. On the inner circumferential surface side of the intermediate transfer belt 31, primary transfer rollers 35Y, 35M, 35C, and 35K, which are roller-type primary transfer members serving as primary transfer means, are positioned opposite the photosensitive drums 11Y, 11M, 11C, and 11K via the intermediate transfer belt 31. The primary transfer rollers 35 are pressed toward the photosensitive drum 11, forming a primary transfer section (primary transfer nip) N1 (N1Y, N1M, N1C, N1K), which is the contact point (contact position) between the photosensitive drum 11 and the intermediate transfer belt 31. The intermediate transfer belt 31 rotates (moves in a circular motion) in the direction of arrow R2 (clockwise) in the figure as the drive roller 33 is rotationally driven. The drive roller 33 is rotationally driven by the transmission of driving force from the belt drive motor 132a (Figure 3) of the belt drive unit 132, which serves as the intermediate transfer body driving means. The tension roller 34 applies a predetermined tension to the intermediate transfer belt 31. The pre-secondary transfer roller 36 forms the surface of the intermediate transfer belt 31 that enters the secondary transfer section N2, which will be described later. The internal secondary transfer roller 32, together with the external secondary transfer roller 41, which will be described later, forms the secondary transfer section N2. The tension rollers other than the drive roller 33 and each primary transfer roller 35 rotate in association with the rotation of the intermediate transfer belt 31.

[0018] In this embodiment, the intermediate transfer belt 31 is composed of a three-layer belt having a base layer, an elastic layer, and a surface layer in order from the inner circumferential surface (back side) to the outer circumferential surface (front side). Suitable materials for the base layer include resins such as polyimide (PI) and polycarbonate (PC), or various types of rubber, with an appropriate amount of carbon black as an antistatic agent. Suitable elastic materials for the elastic layer include various types of rubber such as urethane rubber and silicone rubber, with an appropriate amount of ion conductive material. Suitable materials for the surface layer include resins such as fluororesin. In this embodiment, a belt with an elastic layer was used as the intermediate transfer belt 31; however, for example, a single-layer PI belt without an elastic layer, or a coated PI belt with a fluororesin coating on the PI base layer, may also be used.

[0019] The toner image formed on the photosensitive drum 11 is transferred (primary transfer) to the rotating intermediate transfer belt 31 in the primary transfer section N1 by the action of the primary transfer roller 35. During primary transfer, the primary transfer roller 35 is subjected to a primary transfer bias (primary transfer voltage), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, by the primary transfer power supply (high voltage power supply) 123 (Figure 3), which serves as the primary transfer voltage application unit. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 11 are transferred so as to be superimposed on the same image forming area on the intermediate transfer belt 31. Toner that remains on the photosensitive drum 11 without being transferred to the intermediate transfer belt 31 (primary transfer residue toner) is removed from the photosensitive drum 11 and recovered by the drum cleaning device 15, which serves as a photoreceptor cleaning means.

[0020] On the outer circumferential surface of the intermediate transfer belt 31, a secondary transfer outer roller 41 is positioned opposite the secondary transfer inner roller 32 via the intermediate transfer belt 31. The secondary transfer outer roller 41 is pressed toward the secondary transfer inner roller 32, forming a secondary transfer section (secondary transfer nip) N2, which is the contact point between the intermediate transfer belt 31 and the secondary transfer outer roller 41. The toner image formed on the intermediate transfer belt 31 is transferred (secondary transfer) in the secondary transfer section N2 onto the recording material S, which is being transported while being held between the intermediate transfer belt 31 and the secondary transfer outer roller 41. During secondary transfer, a secondary transfer bias (secondary transfer voltage), which is a DC voltage with the same polarity (negative polarity in this embodiment) as the normal charge polarity of the toner, is applied to the secondary transfer inner roller 32 by a secondary transfer power supply (high voltage power supply) 124 (Figures 3 and 4), which serves as a secondary transfer voltage application unit.

[0021] Recording material S, such as paper or plastic sheets, is stored in cassettes 61, 62, and 63, which serve as recording material storage sections. The recording material S is transported to the transport path 67 by the rotation of one of the transport rollers 64, 65, or 66, which serve as feeders. This recording material S is then transported to the secondary transfer section N2 by a register roller 21, which serves as a transporter, in time with the toner image on the intermediate transfer belt 31.

[0022] Toner that remains on the intermediate transfer belt 31 without being transferred to the recording material S (secondary transfer residue toner) is removed and recovered from the intermediate transfer belt 31 by the belt cleaning device 80, which serves as an intermediate transfer body cleaning means. Details of the belt cleaning device 80 will be described later.

[0023] The recording material S onto which the toner image has been transferred is transported by a transport belt 71, which acts as a transport member, to a fixing device 5, which acts as a fixing means. The fixing device 5 heats and pressurizes the recording material S carrying the unfixed toner image, thereby fixing (melting and solidifying) the toner image to the surface of the recording material S. The recording material S with the fixed image is discharged (output) through the discharge transport path 68 to a tray 69, which acts as a discharge section.

[0024] In this embodiment, the image forming apparatus 100 is configured so that the recording material S supplied to the secondary transfer section N2 is transported from right to left in the figure, but it is not limited to this configuration and may be configured so that it is transported from left to right.

[0025] The image forming apparatus 100 has a sensor unit 90 as a toner image detection means for detecting the adjustment toner image (patch pattern) carried and transported on the intermediate transfer belt 31. The sensor unit 90 is positioned to detect the toner image on the intermediate transfer belt 31 downstream of the primary transfer section N1 (the furthest downstream primary transfer section N1K) and upstream of the secondary transfer section N2 in the rotational direction of the intermediate transfer belt 31. In this embodiment, the sensor unit 90 is positioned opposite the tension roller 34 via the intermediate transfer belt 31. The sensor unit 90 may be configured to detect the toner image at multiple locations in the width direction substantially perpendicular to the direction of movement (transport direction) of the surface of the intermediate transfer belt 31. The sensor unit 90 is configured to have a reflective optical sensor.

[0026] In this embodiment, a density patch pattern for image density control and a registration patch pattern for color shift (registration) correction control are formed on the intermediate transfer belt 31 as patch patterns. In other words, in this embodiment, the image forming apparatus 100 performs image density control (density correction control) and color shift correction control as image correction operations (adjustment operations) to form patch patterns on the intermediate transfer belt 31. Figures 2(a) and 2(b) are schematic diagrams showing examples of density patch pattern 201 and registration patch pattern 202, respectively. As shown in Figure 2(a), in one image density control, multiple patch patterns with different densities for each color, yellow, magenta, cyan, and black, are formed as density patch pattern 201 along the direction of movement on the surface of the intermediate transfer belt 31. Also, as shown in Figure 2(b), in one color shift correction control, patch patterns for each color, yellow, magenta, cyan, and black, are formed as registration patch pattern 202 along the direction of movement on the surface of the intermediate transfer belt 31. The registration patch pattern 202 is formed, for example, on both ends of the intermediate transfer belt 31 in the width direction. The patch pattern is formed on the intermediate transfer belt 31 by being formed on the photosensitive drum 11 and then transferred onto the intermediate transfer belt 31, similar to a printed image that is transferred and output as a result onto the recording material S.

[0027] The image forming apparatus 100 interrupts the image forming operation to form a density patch pattern and read it using the sensor unit 90, for example, every time it forms a printed image on 100 sheets of A4-sized recording material S. Then, the image forming apparatus 100 performs image density control using the results and then resumes the image forming operation. In addition, the image forming apparatus 100 interrupts the image forming operation to form a registration patch pattern and read it using the sensor unit 90, for example, when the temperature rise (ΔT) of the exposure apparatus 13 becomes ΔT > 3℃. Then, the image forming apparatus 100 performs color shift correction control using the results and then resumes the image forming operation.

[0028] In this embodiment, the patch pattern supported on the intermediate transfer belt 31 passes through the secondary transfer section N2 without being removed from the intermediate transfer belt 31, and is removed from the intermediate transfer belt 31 by the belt cleaning device 80. In this embodiment, there is no cleaning configuration that transfers the patch pattern to a member (roller or belt) that contacts the outer circumferential surface of the intermediate transfer belt 31 to form the secondary transfer section N2, and then removes and recovers the patch pattern from this member.

[0029] In this embodiment, the image forming apparatus 100 is a color image forming apparatus capable of forming full-color images, but the present invention is not limited thereto. The image forming apparatus may be, for example, a monochrome image forming apparatus that has only an image forming unit for black as its image forming unit and is capable of forming black and white images. In that case, no color shift occurs, so operations associated with color shift correction control are unnecessary.

[0030] <Control Configuration> Figure 3 is a block diagram illustrating the schematic control configuration of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 has a control unit (control circuit) 110 that controls the image forming apparatus 100. The control unit 110 is composed of a CPU 111 as an arithmetic processing unit, a memory (storage medium) 112 such as ROM, RAM, or non-volatile memory as a storage unit, and an input / output unit (not shown) for inputting and outputting signals (information) between the control unit 110 and external devices. The CPU 111 and the memory 112 can transfer and read data from each other. The ROM stores the control program, a pre-determined data table, etc. The RAM, which is a rewritable memory, stores information input to the control unit 110, detected information, calculation results, etc. The non-volatile memory stores various setting information and various history information. Various parts of the image forming apparatus 100 are connected to the control unit 110. The control unit 110 can control the operation of each part of the image forming apparatus 100 so that the image forming apparatus 100 performs various operations such as image forming, image density control, and color shift correction control.

[0031] For example, the control unit 110 is connected to various power supplies, such as a charging power supply 121, a developing power supply 122, a primary transfer power supply 123, a secondary transfer power supply 124, and a first cleaning power supply 124 and a second cleaning power supply 125, which will be described later. The control unit 110 is also connected to various drive units, such as a drum drive unit 131, a belt drive unit 132, and a cleaning drive unit 133, which will be described later. The control unit 110 is also connected to an exposure device 13 (13Y, 13M, 13C, 13K), a sensor unit 90, etc. Furthermore, the control unit 110 may be connected to an image reading device (not shown) provided in or connected to the image forming apparatus 100, or to an external device such as a host computer.

[0032] Although not shown in the illustration, in this embodiment, the charging power supply 121, the developing power supply 122, and the primary transfer power supply 123 are each independently provided for each image forming unit 1. Furthermore, the drum drive unit 131, the belt drive unit 132, and the cleaning drive unit 133 are each configured with a drive motor as a drive source and gears as drive transmission members. The drum drive unit 131 (or its drive motor) may be independently provided for each photosensitive drum 11, or it may be common to all or some of the photosensitive drums 11. Also, at least some components (such as the drive motor) may be common to various drive units, such as the drum drive unit 131 and the belt drive unit 132.

[0033] The image forming apparatus 100 executes a print job, which is a series of operations that form and output an image on one or more recording materials S, initiated by a single start instruction. A print job generally consists of an image forming process (image forming operation), a pre-rotation process (pre-rotation operation), a paper-to-paper process (paper-to-paper operation), and a post-rotation process (post-rotation operation). The image forming process is the period during which an electrostatic latent image is formed (exposure), a toner image is formed (development), and the toner image is transferred to the primary and secondary images, with respect to the image forming area on the photosensitive drum 11 or the intermediate transfer belt 31 where a print image can be formed. The term "image forming time" refers to this period. More specifically, the timing of image forming time differs depending on the position where each of these processes—electrostatic latent image formation, toner image formation, and primary and secondary toner image transfer—is performed. The pre-rotation process is the period from when a start instruction is input until the formation of the print image begins (exposure begins), during which preparatory operations are performed before the image forming process. The inter-paper process is the period between recording materials S when image formation is performed on multiple recording materials S in succession (continuous printing, continuous image formation). The post-rotation process is the period during which tidying operations (preparation operations) are performed after the image formation process. Non-image formation time refers to periods other than the image formation time, and includes the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation process (pre-rotation operation), which is a preparatory operation when the image forming apparatus 100 is powered on or resumes from sleep mode.

[0034] <Secondary Transfer Section> Figure 4 is a schematic cross-sectional view showing the secondary transfer section N2 during image formation (when a printed image is formed on the intermediate transfer belt 31) (the cross-section is approximately perpendicular to the rotation axis direction of the secondary transfer roller 32).

[0035] The secondary transfer outer roller 41 comes into contact with the surface (nip-pre-tension surface) L of the intermediate transfer belt 31, which is formed by tensioning the secondary transfer inner roller 32 and the secondary transfer pre-roller 36. The secondary transfer outer roller 41 is pressed toward the secondary transfer inner roller 32 by a pressure spring 42 acting as a biasing member. This forms the secondary transfer section N2.

[0036] During image formation (secondary transfer of the printed image), a secondary transfer bias (secondary transfer voltage) with the same polarity as the charge polarity of the toner constituting the toner image on the intermediate transfer belt 31 (the normal charge polarity of the toner) is applied to the secondary transfer inner roller 32 by the secondary transfer power supply 124. The secondary transfer outer roller 41 is connected to earth (electrically grounded). As a result, a transfer electric field is formed in the secondary transfer section N2. In this embodiment, since the toner constituting the toner image on the intermediate transfer belt 31 carries a negative polarity (-) charge, a negative polarity (-) voltage is applied to the secondary transfer inner roller 32. Upstream of the secondary transfer section N2 in the transport direction of the recording material S, a secondary transfer pre-guide 43 is provided as a recording material guide member that guides the recording material S toward the secondary transfer section N2. The secondary transfer pre-guide 43 is composed of an upper guide 43a and a lower guide 43a. The upper guide 43a restricts the movement of the recording material S toward the intermediate transfer belt 31. The lower guide 43a restricts the movement of the recording material S away from the intermediate transfer belt 31. Then, in the secondary transfer section N2, the toner image Ti constituting the print image is transferred (secondary transfer) onto the recording material S, which is sent to the secondary transfer section N2 guided by the pre-secondary transfer guide 43 from the intermediate transfer belt 31. In this embodiment, the secondary transfer device 44 as a secondary transfer means is composed of a secondary transfer inner roller 32 as a secondary transfer member and a secondary transfer outer roller 41 as a secondary transfer opposing member. Alternatively, a secondary transfer bias with the opposite polarity to the normal charging polarity of the toner may be applied to the secondary transfer outer roller 41 as a secondary transfer member, and the secondary transfer inner roller 32 as a secondary transfer opposing member may be connected to earth (electrically grounded).

[0037] On the intermediate transfer belt 31, residual toner (secondary transfer toner) Tr is generated that remains on the intermediate transfer belt 31 without being transferred to the recording material S in the secondary transfer section N2. This residual toner Tr remains supported on the intermediate transfer belt 31 and is transported downstream of the secondary transfer section N2 in the direction of movement of the surface of the intermediate transfer belt 31.

[0038] In the image forming apparatus 100 of this embodiment, the percentage of a solid (maximum density) monochromatic toner image transferred from the intermediate transfer belt 31 onto the recording material S in the secondary transfer section N2 (secondary transfer efficiency) is approximately 97%. In other words, in the image forming apparatus 100 of this embodiment, approximately 3% of the toner in the solid monochromatic toner image remains on the intermediate transfer belt 31 as residual toner Tr.

[0039] Figure 5 is a schematic cross-sectional view showing the first configuration of the secondary transfer section N2 during image correction operation (when forming a patch pattern on the intermediate transfer belt 31) (the cross-section is shown approximately perpendicular to the rotation axis direction of the secondary transfer roller 32).

[0040] When forming the patch pattern Tp on the intermediate transfer belt 31, the recording material S is not transported to the secondary transfer section N2, and the secondary transfer outer roller 41 is separated from the intermediate transfer belt 31. As a result, the patch pattern Tp can pass through the secondary transfer section N2 while remaining supported on the intermediate transfer belt 31. This suppresses the adhesion of toner to the secondary transfer outer roller 41, and prevents toner from adhering to the back surface of the recording material S during subsequent image formation.

[0041] When multiple patch patterns are formed on the intermediate transfer belt 31 in a single image correction operation, typically, the secondary transfer outer roller 41 is separated from the intermediate transfer belt 31 from a predetermined timing before the foremost part of the multiple patch patterns (the leading edge of the first patch pattern) in the direction of movement of the surface of the intermediate transfer belt 31 reaches a position corresponding to the secondary transfer section N2, until a predetermined timing after the last part of the multiple patch patterns (the trailing edge of the last patch pattern) in the direction of movement of the surface of the intermediate transfer belt 31 has passed the position corresponding to the secondary transfer section N2.

[0042] In this first embodiment, the image forming apparatus 100 is provided with a contact-separation mechanism 140, which is a means of moving the secondary transfer outer roller 41 into contact with and away from the intermediate transfer belt 31.

[0043] Figure 6 is a schematic cross-sectional view showing a second configuration of the secondary transfer section N2 during image correction operation (when forming a patch pattern on the intermediate transfer belt 31) (the cross-section is approximately perpendicular to the rotation axis direction of the secondary transfer roller 32).

[0044] When forming the patch pattern Tp on the intermediate transfer belt 31, the recording material S is not transported to the secondary transfer section N2. Instead, a positive (+) voltage (a voltage opposite to the normal charging polarity of the toner) is applied to the secondary transfer roller 32 by the secondary transfer power supply 124. As a result, the patch pattern Tp, which carries a negative (-) charge, can pass through the secondary transfer section N2 while remaining supported on the intermediate transfer belt 31. This suppresses the adhesion of toner to the secondary transfer roller 41, and prevents toner from adhering to the back surface of the recording material S during subsequent image formation.

[0045] When multiple patch patterns are formed on the intermediate transfer belt 31 in a single image correction operation, typically, a positive voltage is applied to the secondary transfer roller 41 from a predetermined timing before the foremost part of the multiple patch patterns (the leading edge of the first patch pattern) in the direction of movement of the surface of the intermediate transfer belt 31 reaches the secondary transfer section N2, until a predetermined timing after the last part of the multiple patch patterns (the trailing edge of the last patch pattern) in the direction of movement of the surface of the intermediate transfer belt 31 has passed the secondary transfer section N2.

[0046] When this second configuration is adopted, the secondary transfer power supply 124 is configured to be able to apply both a negative voltage and a positive voltage to the secondary transfer roller 32.

[0047] In this embodiment, either the first or second embodiment described above may be adopted.

[0048] <Configuration of the belt cleaning device and belt cleaning operation during image formation> Next, the belt cleaning device (hereinafter also simply referred to as the "cleaning device") 80 in this embodiment will be described.

[0049] Figure 7 is a schematic cross-sectional view of the cleaning device 80 during image formation (when the printed image is formed on the intermediate transfer belt 31) in this embodiment (showing a cross-section approximately perpendicular to the rotation axis direction of the secondary transfer roller 32).

[0050] The cleaning device 80 is positioned downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 (the uppermost primary transfer section N1Y) in the rotational direction of the intermediate transfer belt 31. In this embodiment, the cleaning device 80 is positioned opposite the drive roller 33 via the intermediate transfer belt 31. In this embodiment, the cleaning device 80 employs an electrostatic cleaning method, particularly an electrostatic fur brush cleaning method, to electrostatically recover toner from the intermediate transfer belt 31.

[0051] The cleaning device 80 has a housing 88 positioned near the intermediate transfer belt 31. The following components are provided inside the housing 88. First, there are first and second fur brushes (cleaning brushes) 81 and 82, which serve as first and second cleaning components. Also, there are first and second bias rollers 83 and 84, which serve as first and second recovery components (voltage application components). Furthermore, there are first and second blades 85 and 86, which serve as first and second scraping components. Finally, there is a toner recovery screw 87, which serves as a toner transport component.

[0052] The first and second fur brushes 81 and 82 are composed of conductive fur brush rollers, which are conductive, rotatable, brush-shaped cleaning members. The brush fibers of the first and second fur brushes 81 and 82 have, for example, an electrical resistance value of 3 × 10⁻¹⁰. 5 ~1 × 10 13 It is composed of carbon-dispersed nylon, acrylic, or polyester fibers with a fiber thickness of 2 to 15 denier and a density of Ω / cm. The first and second fur brushes 81 and 82 are, for example, made of these brush fibers (conductive fibers) with a bristle density of 50,000 to 500,000 fibers / inch. 2The brush is constructed by implanting bristles onto a metal roller, which serves as the base material (core metal, core material), in a specific ratio. The length of the brush fibers is, for example, about 3 to 5 mm. The first and second fur brushes 81 and 82 are positioned to contact the intermediate transfer belt 31. In this embodiment, the first and second fur brushes 81 and 82 are positioned to maintain a penetration depth of approximately 1.0 to 2.0 mm into the intermediate transfer belt 31. This penetration depth is represented by the value obtained by subtracting the shortest distance between the base material of the fur brush and the intermediate transfer belt 31 from the length of the brush fibers. The first and second fur brushes 81 and 82 are rotated in the direction of arrow R3 (clockwise direction) in the figure by a driving force transmitted from the cleaning motor 133a (Figure 3) of the cleaning drive unit 133, which serves as the cleaning drive means. In other words, the first and second fur brushes 81 and 82 rotate in a counter-direction to the direction of movement of the surface of the intermediate transfer belt 31, that is, in the opposite direction to the direction of movement of the intermediate transfer belt 31 at the contact point (contact position) with the intermediate transfer belt 31. As a result, the first and second fur brushes 81 and 82 rub against the surface of the intermediate transfer belt 31.

[0053] In this embodiment, the first and second fur brushes 81 and 82 are in contact with a drive roller 33, which functions as an opposing member, via an intermediate transfer belt 31. The drive roller 33 is connected to earth (electrically grounded). The rotational axis direction of the first and second fur brushes 81 and 82 is substantially parallel to the width direction of the intermediate transfer belt 31 (the rotational axis direction of the secondary transfer roller 32). The length of the rotational axis direction of the first and second fur brushes 81 and 82 is longer than the width of the region on the intermediate transfer belt 6 in the width direction of the intermediate transfer belt 31 where a toner image can be formed. The contact area between the first fur brush 81 and the intermediate transfer belt 31 is the first cleaning section CL1 where toner is removed from the intermediate transfer belt 31 by the first fur brush 81. The contact area between the second fur brush 82 and the intermediate transfer belt 31 is the second cleaning section CL2 where toner is removed from the intermediate transfer belt 31 by the second fur brush 82. The first and second cleaning sections CL1 and CL2 are located downstream of the secondary transfer section N2 and upstream of the primary transfer section N1 (the uppermost primary transfer section N1Y) in the rotational direction of the intermediate transfer belt 6. In this embodiment, in the direction of movement of the surface of the intermediate transfer belt 31, the first cleaning section CL1 is located upstream of the second cleaning section CL2, and the second cleaning section CL2 is located downstream of the first cleaning section CL1. In other words, in this embodiment, in the direction of movement of the surface of the intermediate transfer belt 31, the first fur brush 81 is located upstream of the second fur brush 82, and the second fur brush 82 is located downstream of the first fur brush 81.

[0054] The first and second bias rollers 83 and 84 are composed of rotatable metal rollers (e.g., made of aluminum). The first and second bias rollers 83 and 84 are positioned to contact the first and second fur brushes 81 and 82. In this embodiment, the first and second bias rollers 83 and 84 are positioned to penetrate the first and second fur brushes 81 and 82 by approximately 1.5 to 2.5 mm. The first and second bias rollers 83 and 84 are rotated in the direction of arrow R4 (counterclockwise) in the figure by a driving force transmitted from the cleaning motor 133a (Figure 3) of the cleaning drive unit 133, which serves as the driving means. In other words, the first and second bias rollers 83 and 84 rotate in the width direction relative to the rotation direction of the first and second fur brushes 81 and 82, that is, in the direction of movement of the first and second fur brushes 81 and 82 at the contact point with the first and second fur brushes 81 and 82. The rotation axis direction of the first and second bias rollers 83 and 84 is approximately parallel to the width direction of the intermediate transfer belt 6 (the rotation axis direction of the secondary transfer inner roller 32). The length of the rotation axis direction of the first and second bias rollers 83 and 84 is equivalent to the length of the rotation axis direction of the first and second fur brushes 81 and 82.

[0055] The first and second blades 85 and 86 are positioned to contact the first and second bias rollers 83 and 84. The first and second blades 85 and 86 are made of a rubber material such as urethane rubber as an elastic member. The first and second blades 85 and 86 are plate-shaped members having a predetermined length in the longitudinal direction, which is positioned substantially parallel to the rotation axis direction of the first and second bias rollers 83 and 84, and a predetermined thickness in the short direction, which is substantially perpendicular to the longitudinal direction. The first and second blades 85 and 86 are in contact with the first and second bias rollers 83 and 84 in the counter-direction (direction in which the free ends face upstream in the rotation direction) with respect to the rotation direction of the first and second bias rollers 83 and 84. The length of the first and second blades 85 and 86 in the longitudinal direction is equivalent to the length of the first and second bias rollers 83 and 84 in the rotation axis direction.

[0056] In this embodiment, a first cleaning bias (first cleaning voltage) of negative polarity (-), which is the same polarity as the normal charging polarity of the toner, is applied to the first fur brush 81 located on the upstream side in the direction of movement of the surface of the intermediate transfer belt 31. In this embodiment, a first cleaning power supply (high voltage power supply) 125 applies a DC voltage of negative polarity (-) to the first bias roller 83. As a result, a DC voltage of negative polarity (-) is applied to the first fur brush 81 via the first bias roller 83. On the other hand, in this embodiment, a second cleaning bias (second cleaning voltage) of positive polarity (+), which is the opposite polarity to the normal charging polarity of the toner, is applied to the second fur brush 82 located on the downstream side in the direction of movement of the surface of the intermediate transfer belt 31. In this embodiment, a second cleaning power supply (high voltage power supply) 126 applies a DC voltage of positive polarity (+) to the second bias roller 84. As a result, a positive (+) DC voltage is applied to the second fur brush 82 via the second bias roller 84.

[0057] Most of the residual toner Tr that has passed through the secondary transfer section N2 is positively charged (+). This is because most of the residual toner Tr is positively charged (+) toner that remained on the intermediate transfer belt 31 without being transferred to the recording material S by the positively charged (+) secondary transfer bias. As the intermediate transfer belt 31 rotates, this residual toner Tr is electrostatically attracted to the first fur brush 81 to which a negatively charged (-) first cleaning bias is applied, and is removed from the intermediate transfer belt 31. For example, when a voltage of -3.5kV is applied to the first bias roller 83, the potential of the first fur brush 81 becomes -2.0kV, and the positively charged (+) residual toner Tr on the intermediate transfer belt 31 is transferred from the intermediate transfer belt 31 to the first fur brush 81. The toner transferred to the first fur brush 81 is transferred from the first fur brush 81 to the first bias roller 83 due to the potential difference between the first fur brush 81 and the first bias roller 83. The toner transferred to the first bias roller 83 is scraped off from the first bias roller 83 by the first blade 85.

[0058] As described above, the first fur brush 81 removes the remaining toner Tr on the intermediate transfer belt 31. However, there is still a possibility that some remaining toner Tr may remain on the intermediate transfer belt 31 after passing through the first cleaning section CL1. The remaining toner Tr that has passed through the first cleaning section CL1 is charged to a negative polarity (-) by the first cleaning bias of negative polarity (-) applied to the first fur brush 81. This is thought to be because the toner is charged by charge injection or discharge.

[0059] The remaining toner Tr that has passed through the first cleaning section CL1 is electrostatically attracted to the second fur brush 82, to which a positive polarity (+) second cleaning bias is applied, as the intermediate transfer belt 31 rotates, and is removed from the intermediate transfer belt 31. This allows the second fur brush 82 to remove any remaining toner Tr that could not be removed from the intermediate transfer belt 31 by the first fur brush 81. For example, when a voltage of +3.5kV is applied to the second bias roller 84, the potential of the second fur brush 82 becomes +2.0kV, and the negative polarity (-) remaining toner Tr on the intermediate transfer belt 31 is transferred from the intermediate transfer belt 31 to the second fur brush 82. The toner transferred to the second fur brush 82 is then transferred from the second fur brush 82 to the second bias roller 84 due to the potential difference between the second fur brush 82 and the second bias roller 84. The toner that has been transferred to the second bias roller 84 is scraped off from the second bias roller 84 by the second blade 86.

[0060] The first and second cleaning biases may be controlled by constant voltage or constant current. It is sufficient to supply a sufficient cleaning current (for example, 10-80 μA in absolute value) to the first and second cleaning units CL1 and CL2. Here, constant current control is a control method that adjusts the output of the power supply so that the current supplied to the target is approximately constant at a target current. Constant voltage control is a control method that adjusts the output of the power supply so that the voltage applied to the target is approximately constant at a target voltage.

[0061] The toner scraped off the first and second bias rollers 83 and 84 by the first and second blades 85 and 86 is contained within the housing 88. The toner contained within the housing 88 is transported by a recovery toner screw 87 provided within the housing 88 and discharged from the housing 88. The recovery toner screw 87 is rotationally driven by a driving force transmitted from the cleaning motor 133a (Figure 3) of the cleaning drive unit 133, which serves as the driving means. The toner discharged from the housing 88 is transported via a transport path (not shown) provided within the image forming apparatus 100 to, for example, a recovery toner container (not shown) provided within the image forming apparatus 100, and is collected in the recovery toner container.

[0062] In this embodiment, the first fur brush 81, the second fur brush 82, the first bias roller 83, the second bias roller 84, and the recovered toner screw 87 are driven and connected by a gear train. These are driven by a common cleaning motor 133a (Figure 3) of the cleaning drive unit 133. Here, the peripheral speed of the first fur brush 81 is denoted as V1, and the peripheral speed of the second fur brush 82 is denoted as V2. The peripheral speeds of the first and second fur brushes 81 and 82 are represented by the moving speeds of the first and second fur brushes 81 and 82 at the contact point with the intermediate transfer belt 31 (the surface position of the intermediate transfer belt where the distance between the substrate of the fur brush and the intermediate transfer belt is the shortest distance).

[0063] In this embodiment, the drive roller 33 that transports the intermediate transfer belt 31 is driven by the belt drive motor 132a (Figure 3) of the belt drive unit 132. The transport speed (surface movement speed) of the intermediate transfer belt 31 is denoted as V0.

[0064] In this embodiment, the peripheral speeds (rotational speeds) of the first and second fur brushes 81 and 82 when the cleaning device 80 removes the remaining toner Tr from the intermediate transfer belt 31 are set according to the rotational speed (rpm) of the cleaning motor 133a as follows. That is, the rotational speed of the cleaning motor 133a is set to a first rotational speed Nr such that the peripheral speed V1 of the first fur brush 81 and the peripheral speed V2 of the second fur brush 82 have the following relationship with respect to the transport speed V0 of the intermediate transfer belt 31. V1 = 0.25 × V0 V2 = 0.25 × V0

[0065] This setting is necessary to sufficiently remove the maximum expected concentration of residual toner Tr from the intermediate transfer belt 31 (effectively leaving none on the intermediate transfer belt 31). If the peripheral speeds V1 and V2 of the first and second fur brushes 81 and 82 are increased beyond this setting, the number of times the first and second fur brushes 81 and 82 rub against the intermediate transfer belt 31 will increase, which may reduce the lifespan of the intermediate transfer belt 31 and the first and second fur brushes 81 and 82 due to wear and tear.

[0066] <Belt cleaning operation during image correction> Figure 8 is a schematic cross-sectional view of the cleaning device 80 during the image correction operation in this embodiment (when forming a patch pattern on the intermediate transfer belt 31) (showing a cross-section approximately perpendicular to the rotation axis direction of the secondary transfer roller 32).

[0067] Most of the toner in the patch pattern Tp that has passed through the secondary transfer section N2 is negatively charged (-). This is because the patch pattern Tp passes through the secondary transfer section N2 while essentially still transferred to the intermediate transfer belt 31. Therefore, the patch pattern Tp passes through the first cleaning section CL1 without being transferred to the first fur brush 81, to which a first cleaning bias of negative polarity (-) is applied. When the patch pattern Tp reaches the second cleaning section CL2, it is transferred to the second fur brush 82, to which a second cleaning bias of positive polarity (+) is applied. The toner transferred to the second fur brush 82 is collected in the housing 88 and recovered in a toner recovery container (not shown), in the same manner as the image formation process described above.

[0068] Since the patch pattern Tp is not transferred to the recording material S, its toner density (amount of toner per unit area) is greater than that of the residual toner Tr. Therefore, in order to sufficiently remove the patch pattern Tp from the intermediate transfer belt 31 (without leaving virtually any residue on the intermediate transfer belt 31), it is necessary to increase the number of times the surface of the intermediate transfer belt 31 and the conductive fibers constituting the second fur brush 82 come into contact and rub against each other. In other words, when removing the patch pattern Tp from the intermediate transfer belt 31, the peripheral speed V2 of the second fur brush 82 needs to be greater than when removing the residual toner Tr from the intermediate transfer belt 31. In this embodiment, the peripheral speed of the second fur brush 82 when the cleaning device 80 removes the patch pattern Tp from the intermediate transfer belt 31 is set by the rotation speed of the cleaning motor 133a as follows. In other words, the rotation speed of the cleaning drive motor 133a is set to the second rotation speed Np such that the peripheral speed V2 of the second fur brush 82 has the following relationship with respect to the transport speed V0 of the intermediate transfer belt 31. V2 = 0.5 × V0

[0069] Thus, in this embodiment, the second rotation speed Np of the cleaning motor 133a during image correction operation (when removing the patch pattern Tp) is greater than the first rotation speed Nr of the cleaning motor 133a during image formation (when removing the remaining toner Tr) (Np > Nr). In other words, in this embodiment, the rotation speed of the cleaning motor 133a is switched between image formation and image correction operation.

[0070] In this embodiment, the first fur brush 81, the second fur brush 82, the first bias roller 83, the second bias roller 84, and the toner recovery screw 87 are driven and connected by a gear train. Therefore, during image correction operation, their rotational speeds are also greater than during image formation. In other words, in this embodiment, during image correction operation, the peripheral speeds V1 and V2 of the first and second fur brushes 81 and 82 are set by the rotational speed of the cleaning motor 133a as follows. V1 = 0.5 × V0 V2 = 0.5 × V0

[0071] In this embodiment, the transport speed V0 of the intermediate transfer belt 31 is substantially the same during image formation (removal of residual toner Tr) and during image correction operation (removal of patch pattern Tp). Also, in this embodiment, the settings of the first and second cleaning biases are substantially the same during image formation (removal of residual toner Tr) and during image correction operation (removal of patch pattern Tp), but these may be different.

[0072] The first rotational speed Nr of the cleaning motor 133a is represented by the rotational speed of the cleaning motor 133a when the remaining toner Tr is removed from the intermediate transfer belt 31 by the second fur brush 82. In other words, the first rotational speed Nr of the cleaning motor 133a is represented by the rotational speed of the cleaning motor 133a during the period when the image formation region (the region where a printed image can be formed) on the intermediate transfer belt 31 is passing through the second cleaning section CL2 during image formation.

[0073] Furthermore, the second rotational speed Np of the cleaning motor 133a is represented by the rotational speed of the cleaning motor 133a when the patch pattern Tp is removed from the intermediate transfer belt 31 by the second fur brush 82. In other words, the second rotational speed Np of the cleaning motor 133a is represented by the rotational speed of the cleaning motor 133a during the period when the region on the intermediate transfer belt 31 where the patch pattern Tp is formed is passing through the second cleaning unit CL2 during the image correction operation. The period during which the region where the patch pattern Tp is formed is passing through the second cleaning unit CL2 may be the period from when the foremost part of the multiple patch patterns in the direction of movement of the surface of the intermediate transfer belt 31 reaches the second cleaning unit CL2 until the last part of the multiple patch patterns in the direction of movement of the surface of the intermediate transfer belt 31 has finished passing through the second cleaning unit CL2, if multiple patch patterns Tp are formed on the intermediate transfer belt 31 in a single image correction operation.

[0074] This can also be rephrased as follows: The peripheral speed of the second fur brush 82 during image formation (when removing residual toner Tr) is the first peripheral speed Vr, and the peripheral speed of the second fur brush 82 during image correction operation (when removing the patch pattern Tp) is the second peripheral speed Vp. In this embodiment, the second peripheral speed Vp is faster than the first peripheral speed Vr (Vp > Vr). In other words, in this embodiment, the peripheral speed of the second fur brush 82 is switched between image formation and image correction operation. To put it another way, in this embodiment, the ratio of the peripheral speed of the second fur brush 82 to the transport speed V0 of the intermediate transfer belt 31 during image formation (when removing residual toner Tr) is less than the ratio Vp / V0 during image correction operation (when removing the patch pattern Tp) (Vp / V0 > Vr / V0). In other words, in this embodiment, the ratio is switched between image formation and image correction operation. The peripheral speed of the second fur brush 82 can typically be changed (controlled) by changing (controlling) the rotational speed of the drive motor, as in this embodiment. However, it is not limited to this, and the peripheral speed of the second fur brush 82 may also be changed (controlled) by a speed change mechanism, which is a speed change means provided in the drive transmission section that transmits power from the drive motor to the second fur brush 82. Furthermore, from the viewpoint of extending the lifespan of the components and ease of cleaning, the first peripheral speed Vr is preferably 20% or more and 80% or less of the second peripheral speed Vp (0.2 × Vp ≤ Vr ≤ 0.8 × Vp). Typically, the first peripheral speed Vr is 30% or more and 70% or less of the second peripheral speed Vp (0.3 × Vp ≤ Vr ≤ 0.7 × Vp). As described above, in this embodiment, the peripheral speed of the first fur brush 81 during image correction operation (when removing the patch pattern Tp) is faster than the peripheral speed of the first fur brush 81 during image formation (when removing the remaining toner Tr) in conjunction with the second fur brush 82.

[0075] <Timing for switching cleaning speeds> When switching the rotation speed of the cleaning motor 133a, the peripheral speeds V1 and V2 of the first and second fur brushes 81 and 82 change, which alters the drive load of the intermediate transfer belt 31. This can cause temporary fluctuations in the transport speed V0 of the intermediate transfer belt 31 and the rotation speed of the photosensitive drum 11, which is driven in contact with the intermediate transfer belt 31. Therefore, switching the rotation speed of the cleaning motor 133a during image formation (secondary transfer of the print image, exposure of the print image) may result in image defects such as horizontal streaks (shock images).

[0076] To suppress the occurrence of such image defects, it is preferable to switch the rotation speed of the cleaning motor 133a (peripheral speeds V1 and V2 of the first and second fur brushes 81 and 82) at the following timings.

[0077] When switching the rotation speed of the cleaning motor 133a (peripheral speeds V1 and V2 of the first and second fur brushes 81 and 82) while the photosensitive drum 11 and intermediate transfer belt 31 are rotating, it is preferable to perform the switching when no image is being formed, that is, when the formation of the print image (exposure, development), primary transfer of the print image, and secondary transfer of the print image are not being performed.

[0078] For example, it is preferable to switch the rotational speed of the cleaning motor 133a from the first rotational speed Nr to the second rotational speed Np after the recording material S on which the last print image formed immediately before the interruption of the image correction operation has finished passing through the secondary transfer section N2. In other words, it is preferable to switch the peripheral speed of the second fur brush 82a from the first peripheral speed Vr to the second peripheral speed Vp after the recording material S on which the last print image formed immediately before the interruption of the image correction operation has finished passing through the secondary transfer section N2. This makes it possible to suppress the occurrence of image defects such as horizontal streaks due to fluctuations in the transport speed of the intermediate transfer belt 31 caused by changes in the drive load of the intermediate transfer belt 31 as described above.

[0079] Furthermore, for example, it is preferable to switch the rotational speed of the cleaning motor 133a from the second rotational speed Np to the first rotational speed Nr before exposure (image writing) for the print image formed on the first recording material S immediately after the interruption of the image correction operation begins. In other words, it is preferable to switch the peripheral speed of the second fur brush 82 from the second peripheral speed Vp to the first peripheral speed Vr before exposure (image writing) for the print image formed on the first recording material S immediately after the interruption of the image correction operation begins. This makes it possible to suppress the occurrence of image defects such as horizontal streaks due to fluctuations in the transport speed of the intermediate transfer belt 31 due to changes in the drive load of the intermediate transfer belt 31 and fluctuations in the rotational speed of the photosensitive drum 11.

[0080] Using Figure 9, we will further explain the switching operation of the rotation speed (drive speed) of the cleaning motor 133a in conjunction with the image correction operation performed before the image formation operation. Figure 9 is a flowchart illustrating the control of this operation.

[0081] When a print job is fed into the image forming apparatus 100 (S101), the control unit 110 starts driving the photosensitive drum 11 and the intermediate transfer belt 31, and controls the cleaning motor 133a to start driving at a first rotation speed Nr (S102). Print jobs are fed into the image forming apparatus 100 based on user operations on external devices such as a host computer. Subsequently, the control unit 110 acquires information about the image forming apparatus 100, such as the waiting time since the previous print job (S103), and determines whether or not an image correction operation is necessary based on that information (S104). This is because, for example, if the waiting time is long, the amount of charge of the toner in the developing unit 14 may change, and if the settings of the previous print job are left as they are, the density of the printed image may not be appropriate. The control unit 110 can, for example, determine the waiting time of the image forming apparatus 100 from the end time of the previous print job and the start time of the current print job stored in the memory 112 (non-volatile memory). The control unit 110 then determines, for example, that image density control is necessary if the waiting time exceeds a predetermined time.

[0082] If the control unit 110 determines in S104 that image correction operation (image density control) is not necessary, it proceeds to the process in S110. On the other hand, if the control unit 110 determines in S104 that image correction operation (image density control) is necessary, it controls the rotation speed of the cleaning motor 133a to increase from the first rotation speed Nr to the second rotation speed Np (S105). After that, the control unit 110 controls the operation to form the density patch pattern for image density control and to perform the image density control operation described above (S106). The timing for increasing the speed of the cleaning motor 133a is before the foremost part of the patch pattern on the intermediate transfer belt 31 reaches the second cleaning section CL2 (in this embodiment, before exposure of the photosensitive drum 11 for forming the patch pattern).

[0083] Subsequently, after the last part of the patch pattern on the intermediate transfer belt 31 reaches the second cleaning section CL2 (S107), the control unit 110 controls the rotation speed of the cleaning motor 133a to decrease from the second rotation speed Np to the first rotation speed Nr (S108). As a result, the patch pattern is properly removed from the intermediate transfer belt 31.

[0084] Then, after the rotation speed of the cleaning motor 133a switches to the first rotation speed Nr, the control unit 110 starts the exposure of the print image by the exposure device 13 (S109). In other words, it controls the process to start the formation of an electrostatic latent image of the print image on the surface of the photosensitive drum 11Y by irradiating the photosensitive drum 11Y with laser light from the uppermost image forming unit 1Y in the direction of movement of the surface of the intermediate transfer belt 31. After that, the control unit 110 controls the process to perform secondary transfer (printing operation) of the print image (S110). This suppresses temporary fluctuations in the transport speed of the intermediate transfer belt 31 and the rotation speed of the photosensitive drum 11, thereby suppressing the occurrence of image defects such as horizontal streaks in the print image (product). After that, the control unit 110 terminates the print job.

[0085] Next, using Figure 10, we will further explain the switching operation of the rotation speed (drive speed) of the cleaning motor 133a in conjunction with the image correction operation performed during continuous printing. Figure 10 is a flowchart illustrating the control of this operation.

[0086] When a print job is fed into the image forming apparatus 100 (S201), the control unit 110 starts driving the photosensitive drum 11 and the intermediate transfer belt 31, and controls the cleaning motor 133a to start driving at a first rotation speed Nr (S202). The image forming apparatus 100 receives print jobs based on user operations on external devices such as a host computer. Subsequently, the control unit 110 controls the apparatus to perform the formation of the print image and the secondary transfer (print operation) of the print image (S203). After that, the control unit 110 acquires information about the image forming apparatus 100, such as the temperature of the exposure device 13 (S204), and determines whether or not an image correction operation is necessary based on that information (S205). For example, the control unit 110 acquires the temperature detection result of the exposure device 13 from a temperature sensor (not shown) that is a temperature detection means of the exposure device 13. Then, for example, the control unit 110 determines that color shift correction control is necessary when the temperature rise (ΔT) of the exposure device 13 becomes ΔT > 3℃.

[0087] If the control unit 110 determines in S205 that image correction operation (color shift correction control) is not necessary, it proceeds to the process in S213. On the other hand, if the control unit 110 determines in S205 that image correction operation (color shift correction control) is necessary, it starts forming the registration patch pattern for the aforementioned color shift correction control (S206). The control unit 110 then performs color shift correction control operations as appropriate, such as detecting the patch pattern. After the trailing end of the recording material S, to which the last printed image formed before the start of patch pattern formation has been secondarily transferred has passed the secondary transfer section N2 in the transport direction (S207), the control unit 110 controls the rotation speed of the cleaning motor 133a to increase from the first rotation speed Nr to the second rotation speed Np (S208). The timing for increasing the speed of the cleaning motor 133a is before the foremost part of the patch pattern on the intermediate transfer belt 31 reaches the second cleaning section CL2. This suppresses fluctuations in the transport speed of the intermediate transfer belt 31 while the recording material S is passing through the secondary transfer section N2, thereby suppressing the occurrence of image defects such as horizontal streaks in the print image that is secondarily transferred to the recording material S.

[0088] Subsequently, the control unit 110 controls the rotation speed of the cleaning motor 133a to decrease from the second rotation speed Np to the first rotation speed Nr (S211) after the leading edge of the patch pattern on the intermediate transfer belt 31 reaches the second cleaning section CL2 (S209), and then the trailing edge of the patch pattern on the intermediate transfer belt 31 reaches the second cleaning section CL2 (S210). As a result, the patch pattern is properly removed from the intermediate transfer belt 31.

[0089] Then, after the rotation speed of the cleaning motor 133a switches to the first rotation speed Nr, the control unit 110 starts (resumes) the exposure of the print image by the exposure device 13 (S212). In other words, it controls the process to start the formation of an electrostatic latent image of the print image on the surface of the photosensitive drum 11Y by irradiating the photosensitive drum 11Y with laser light from the uppermost image forming unit 1Y in the direction of movement of the surface of the intermediate transfer belt 31. After that, the control unit 110 controls the process to perform secondary transfer (printing operation) of the print image (S203). This suppresses temporary fluctuations in the transport speed of the intermediate transfer belt 31 and the rotation speed of the photosensitive drum 11, thereby suppressing the occurrence of image defects such as horizontal streaks in the print image (output). Also, when the output of all print images in the print job is completed (S213), the control unit 110 terminates the print job.

[0090] Thus, in this embodiment, the image forming apparatus 100 includes a rotatable image carrier (photosensitive drum) 11 that carries a toner image, an image forming unit 1 that forms a toner image on the image carrier 11, and a rotatable intermediate transfer belt 31 onto which the toner image is transferred from the image carrier 11, the intermediate transfer belt 31 forming a primary transfer unit N1 into which the toner image is first transferred from the image carrier 11 to the intermediate transfer belt 31, and a secondary transfer unit N2 into which the toner image is secondarily transferred from the intermediate transfer belt 31 to the recording material S, and a cleaning unit (second cleaning unit) CL2 located downstream of the secondary transfer unit N2 and upstream of the primary transfer unit N1 in the rotational direction of the intermediate transfer belt 31 that contacts the intermediate transfer belt 31 and removes toner from the intermediate transfer belt 31 by electrostatically attracting toner while rotating. The system includes a brush 82, a drive unit (cleaning drive unit) 133 that drives the brush 82, and a control unit 110 that can control the drive unit 133. The control unit 110 can control the system to perform an image forming operation in which the toner image formed on the intermediate transfer belt 31 by the image forming unit 1 is transferred to the recording material S, and an adjustment operation in which the image forming unit 1 forms an adjustment toner image (patch pattern) on the intermediate transfer belt 31. The system controls the drive unit 133 so that when the brush 82 removes residual transfer toner remaining on the intermediate transfer belt 31 with the brush 82, the brush 82 rotates at a first peripheral speed Vr, and when the brush 82 removes the adjustment toner image from the intermediate transfer belt 31 with the brush 82, the brush 82 rotates at a second peripheral speed Vp which is faster than the first peripheral speed Vr.

[0091] In this embodiment, the control unit 110 controls the drive unit 133 such that when removing residual toner from the intermediate transfer belt 31 with the brush 82, the motor (cleaning motor) 133a of the drive unit 133 rotates at a first rotational speed Nr, and when removing the adjustment toner image from the intermediate transfer belt 31 with the brush 82, the motor 133a rotates at a second rotational speed Np which is greater than the first rotational speed Nr. Here, the image forming unit 1 includes an exposure device 13 that exposes the image carrier 11 to form an electrostatic image on the image carrier 11, and a developing device 14 that supplies toner to the electrostatic image formed on the image carrier 11 to form a toner image on the image carrier 11. In this case, it is preferable that the control unit 110 controls the timing of changing the rotation speed of the motor 133a from the second rotation speed Np to the first rotation speed Nr when performing the image forming operation after the adjustment operation is performed, so that the last part of the adjustment toner image formed by the adjustment operation in the direction of movement of the surface of the intermediate transfer belt 31 reaches the cleaning unit CL2, and before the formation of an electrostatic image by the exposure device 13 in the image forming operation is started. Alternatively, it is preferable that the control unit 110 controls the timing of changing the rotation speed of the motor 133a from the first rotation speed Nr to the second rotation speed Np when performing the adjustment operation after the image forming operation is performed, so that the last recording material S in the image forming operation passes the secondary transfer unit N2, and before the foremost part of the adjustment toner image formed by the adjustment operation in the direction of movement of the surface of the intermediate transfer belt 31 reaches the cleaning unit CL2. Furthermore, when performing the image forming operation after the adjustment operation, it is preferable to change the peripheral speed of the brush 82 from the second peripheral speed Vp to the first peripheral speed Vr at the same timing as described above.

[0092] Furthermore, in this embodiment, the image forming apparatus 100 has an application unit (second cleaning power supply) 126 that applies a bias to the cleaning unit CL2 that moves toner charged with the opposite polarity to the normal charging polarity of the toner from the intermediate transfer belt 31 to the brush 82. Furthermore, in this embodiment, the image forming apparatus 100 includes a separate cleaning unit (first cleaning unit) CL1 located downstream of the secondary transfer unit N2 and upstream of the primary transfer unit N1 in the rotational direction of the intermediate transfer belt 31, which contacts the intermediate transfer belt 31 and removes toner from the intermediate transfer belt 31 by electrostatically attracting toner while rotating; and a separate application unit (first cleaning power supply) 125 which applies a bias to the separate cleaning unit CL1 to move toner charged with the normal charging polarity of the toner from the intermediate transfer belt 31 to the separate brush 81. The drive unit 133 drives the brush 82 and the separate brush 81, and when the brush 82 rotates at the first peripheral speed, the separate brush 81 rotates at the third peripheral speed, and when the brush 82 rotates at the second peripheral speed, the separate brush 81 rotates at a fourth peripheral speed that is faster than the third peripheral speed.

[0093] As described above, this embodiment makes it possible to properly remove the patch pattern from the intermediate transfer belt 31 while extending the lifespan of parts such as the intermediate transfer belt 31 and the first and second fur brushes 81 and 82.

[0094] [Other examples] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the embodiments described above.

[0095] In the above embodiment, the drive roller 33 is used as a common opposing roller for the first and second fur brushes 81 and 82, but opposing rollers may be provided independently for the first and second fur brushes 81 and 82, respectively.

[0096] Furthermore, in the above-described embodiment, a voltage is applied to the first and second bias rollers 83 and 84, but the method of supplying the cleaning current is not limited to this. For example, rollers facing each of the first and second fur brushes 81 and 82 may be independently provided via the intermediate transfer belt 31, and a voltage may be applied to these rollers. In this case, the first and second fur brushes 81 and 82 can be used as opposing members and electrically grounded via the first and second bias rollers 83 and 84. In this case, a voltage with the opposite polarity to the voltage applied to the first and second bias rollers 83 and 84 in the above-described embodiment may be applied to each roller facing the first and second fur brushes 81 and 82. Alternatively, the first and second fur brushes 81 and 82 may be directly voltage-applied (or directly electrically grounded).

[0097] Furthermore, in the above-described embodiment, the cleaning device 80 has two fur brushes, a first fur brush 81 and a second fur brush 82, but the present invention is not limited to such a configuration. If it is possible to sufficiently remove the remaining toner Tr from the intermediate transfer belt 31 with one fur brush, then only one fur brush is needed. In that case, for example, during image formation, a negative polarity (-) cleaning bias is applied to the fur brush in order to remove the remaining toner Tr from the intermediate transfer belt 31. Then, for example, during image correction operation, the system can be switched to apply a positive polarity (+) cleaning bias to the fur brush in order to remove the patch pattern Tp from the intermediate transfer belt 31. [Explanation of Symbols]

[0098] 31 Intermediate transfer belt 80 Belt cleaning device 81. First Fur Brush 82. Second fur brush 90 Sensor Unit 110 Control Unit 125 First cleaning power supply 126 Second cleaning power supply 133 Cleaning drive unit 133a Cleaning motor

Claims

1. The image forming unit comprises a rotatable image carrier that holds a toner image, and the image forming unit that forms a toner image on the image carrier, A rotatable intermediate transfer belt on which a toner image is transferred from the image carrier, comprising: a primary transfer section on which a toner image is first transferred from the image carrier to the intermediate transfer belt; and a secondary transfer section on which a toner image is secondarily transferred from the intermediate transfer belt to a recording material; A brush that contacts the intermediate transfer belt in the rotational direction of the intermediate transfer belt at a cleaning section downstream of the secondary transfer section and upstream of the primary transfer section, and removes toner from the intermediate transfer belt by electrostatically attracting it while rotating, A drive unit that drives the aforementioned brush, A control unit capable of controlling the aforementioned drive unit, It has, The control unit, It is possible to control the image forming operation, in which the image forming unit transfers the toner image formed on the intermediate transfer belt to the recording material, and the adjustment operation, in which the image forming unit forms an adjustment toner image on the intermediate transfer belt. An image forming apparatus characterized in that, when removing residual transfer toner remaining on the intermediate transfer belt with the brush during the image forming operation, the brush rotates at a first peripheral speed Vr, and when removing the adjustment toner image from the intermediate transfer belt with the brush, the brush rotates at a second peripheral speed Vp which is faster than the first peripheral speed Vr, by controlling the drive unit.

2. The image forming apparatus according to claim 1, characterized in that the control unit controls the drive unit such that when the transfer residue toner is removed from the intermediate transfer belt by the brush, the motor provided in the drive unit rotates at a first rotational speed Nr, and when the adjustment toner image is removed from the intermediate transfer belt by the brush, the motor rotates at a second rotational speed Np which is greater than the first rotational speed Nr.

3. The image forming unit includes an exposure device that exposes the image carrier to form an electrostatic image on the image carrier, and a developing device that supplies toner to the electrostatic image formed on the image carrier to form a toner image on the image carrier. The image forming apparatus according to claim 2, characterized in that the control unit controls the timing of changing the rotation speed of the motor from the second rotation speed Np to the first rotation speed Nr when performing the image forming operation after performing the adjustment operation, so that the timing is after the rear end of the adjustment toner image formed by the adjustment operation in the direction of movement of the surface of the intermediate transfer belt reaches the cleaning unit, and before the formation of an electrostatic image by the exposure apparatus in the image forming operation begins.

4. The image forming apparatus according to claim 2, characterized in that the control unit controls the timing for changing the rotation speed of the motor from the first rotation speed Nr to the second rotation speed Np when performing the adjustment operation after performing the image forming operation, so that the timing is after the last recording material in the image forming operation has passed the secondary transfer section and before the foremost part of the adjustment toner image formed by the adjustment operation in the direction of movement of the surface of the intermediate transfer belt reaches the cleaning section.

5. The image forming unit includes an exposure device that exposes the image carrier to form an electrostatic image on the image carrier, and a developing device that supplies toner to the electrostatic image formed on the image carrier to form a toner image on the image carrier. The image forming apparatus according to claim 1, characterized in that the control unit controls the timing of changing the peripheral speed of the brush from the second peripheral speed Vp to the first peripheral speed Vr when performing the image forming operation after performing the adjustment operation, such that the timing is after the rear end of the adjustment toner image formed by the adjustment operation in the direction of movement of the surface of the intermediate transfer belt reaches the cleaning unit, and before the formation of an electrostatic image by the exposure apparatus in the image forming operation begins.

6. The image forming apparatus according to claim 1, characterized in that the control unit controls the timing of changing the peripheral speed of the brush from the first peripheral speed Vr to the second peripheral speed Vp when performing the adjustment operation after performing the image forming operation, so that the timing is after the last recording material in the image forming operation has passed the secondary transfer section and before the foremost part of the adjustment toner image formed by the adjustment operation in the direction of movement of the surface of the intermediate transfer belt reaches the cleaning section.

7. The image forming apparatus according to claim 1, characterized in that it has an application unit that applies a bias to the cleaning unit to move toner, which is charged with a polarity opposite to the normal charging polarity of the toner, from the intermediate transfer belt to the brush.

8. A separate cleaning section located downstream of the secondary transfer section and upstream of the primary transfer section in the rotational direction of the intermediate transfer belt, contacts the intermediate transfer belt, and removes toner from the intermediate transfer belt by electrostatically attracting it while rotating; Another application unit applies a bias to the other cleaning unit to move toner, which has been charged to the correct charging polarity of the toner, from the intermediate transfer belt to the other brush, It has, The image forming apparatus according to claim 7, characterized in that the drive unit drives the brush and the other brush, and when the brush rotates at the first peripheral speed, the other brush rotates at the third peripheral speed, and when the brush rotates at the second peripheral speed, the other brush rotates at a fourth peripheral speed faster than the third peripheral speed.

Images