Image forming apparatus

Abstract

In a configuration in which the position (shape) of the transfer area or the shape (orientation) of the belt near the transfer area can be changed, the color shift associated with such change is suppressed. [Solution] The image forming apparatus is configured such that, in a configuration in which the relative position between the inner roller and the outer roller that form the transfer section is variable, the control unit controls the system to perform an adjustment operation (color resist adjustment) when the relative position is changed.

Description

Technical Field

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

Background Art

[0002] Conventionally, some image forming apparatuses using an electrophotographic method or the like have an endless belt (hereinafter also simply referred to as "belt") as an image carrier for carrying a toner image. As such a belt, for example, there is an intermediate transfer belt as a second image carrier that conveys a toner image primarily transferred from a photoreceptor or the like as a first image carrier to a sheet-like recording material such as paper for secondary transfer.

[0003] In an image forming apparatus using an intermediate transfer belt, a toner image formed on a photoreceptor or the like in an image forming section is primarily transferred to the intermediate transfer belt in a primary transfer section. Further, the toner image primarily transferred to the intermediate transfer belt is secondarily transferred to a recording material in a secondary transfer section. A secondary transfer section (secondary transfer nip), which is a contact portion between the intermediate transfer belt and an external member, is formed by an internal member (secondary transfer internal member) provided on the inner peripheral surface side of the intermediate transfer belt and an external member (secondary transfer external member) provided on the outer peripheral surface side of the intermediate transfer belt. As the internal member, a secondary transfer inner roller (hereinafter also simply referred to as "inner roller"), which is one of a plurality of tension rollers for stretching the intermediate transfer belt, is used. As the external member, a secondary transfer outer roller (hereinafter also simply referred to as "outer roller") that is disposed at a position facing the inner roller across the intermediate transfer belt and is pressed toward the inner roller is often used. Then, by applying a voltage having a polarity opposite to the charging polarity of the toner to the outer roller (or applying a voltage having the same polarity as the charging polarity of the toner to the inner roller), the toner image on the intermediate transfer belt is secondarily transferred onto the recording material in the secondary transfer section. Generally, a conveyance guide for guiding the recording material to the secondary transfer section is provided upstream of the secondary transfer section with respect to the conveyance direction of the recording material.

[0004] It is known that the stiffness of the recording material affects the behavior of the recording material near the upstream and downstream areas of the secondary transfer section in relation to the direction of transport of the recording material, thereby affecting the resulting image. For example, in the case of "thin paper," which is an example of a recording material with low stiffness, the intermediate transfer belt and the recording material may stick together near the downstream area of ​​the secondary transfer section in relation to the direction of transport of the recording material, causing a jam (paper jam) due to poor separation of the recording material from the intermediate transfer belt. On the other hand, in the case of "thick cardboard," which is an example of a recording material with high stiffness, the trailing end of the recording material in the direction of transport may collide with the intermediate transfer belt when it passes through the transport guide. This can disrupt the posture of the intermediate transfer belt near the upstream area of ​​the secondary transfer section in relation to the direction of transport of the recording material, and may cause image defects (such as streaky image distortions extending in a direction approximately perpendicular to the direction of transport of the recording material) at the trailing end of the recording material in the direction of transport.

[0005] In recent years, these challenges have often become apparent in the commercial printing market, for example, where there is a need to accommodate a diversification of recording materials. Therefore, a configuration has been proposed in which the shape of the secondary transfer section (position of the secondary transfer section) is changed according to the type of recording material (Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5935699 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As described above, in order to improve the separation of the recording material from the intermediate transfer belt and to suppress image defects at the trailing end of the recording material, it is effective to change the shape (nip shape) or position (nip position) of the secondary transfer section depending on the type of recording material. This change in the shape (position) of the secondary transfer section can be made by moving at least one of the inner roller or the outer roller to change the relative position between the inner roller and the outer roller in the circumferential direction of the inner roller (for example, represented by the "offset amount" described later).

[0008] However, moving the roller (or a component in contact with it) that tensions the intermediate transfer belt can change the alignment of one end and the other end (front and back) of the roller with respect to its rotational axis. When such a change in alignment occurs, the posture in which the intermediate transfer belt can travel stably changes.

[0009] Furthermore, there is a configuration in which a pressing member is provided near the upstream side of the secondary transfer section to press against the inner circumferential surface of the intermediate transfer belt, and the amount of pressure applied by this pressing member to the intermediate transfer belt is made variable to change the shape (tension shape, posture) of the intermediate transfer belt upstream of the secondary transfer section. The effect of such a change in the shape of the intermediate transfer belt near the secondary transfer section on the running posture of the intermediate transfer belt is the same as in the case of changing the relative position of the inner roller and outer roller as described above.

[0010] In a tandem-type image forming apparatus, a change in the stable orientation of the intermediate transfer belt causes a change in the amount of movement of the intermediate transfer belt in the width direction from the upstream image forming section to the downstream image forming section with respect to the rotation direction of the intermediate transfer belt. As a result, a relative positional shift (so-called "color shift") occurs in the toner images formed in each image forming section. Hereafter, the relative positional shift of the toner images formed in each image forming section will also be referred to as "color shift".

[0011] Therefore, the object of the present invention is to suppress color shifts that occur when the position (shape) of the transfer portion or the shape (position) of the belt near the transfer portion is changed. [Means for solving the problem]

[0012] The above objective is achieved by the image forming apparatus according to the present invention. In summary, one typical configuration of the present invention is a plurality of image forming units that form a toner image, a rotatable endless belt on which the toner image is formed by the image forming units, a plurality of tension rollers that tension the belt, including an inner roller, an outer member positioned opposite the inner roller and forming a transfer unit that contacts the outer surface of the belt and transfers the toner image from the belt to the recording material, a position changing mechanism that can change the position of at least one of the inner roller or the outer member to change the relative position between the inner roller and the outer member in the circumferential direction of the inner roller, and the plurality of image forming units The image forming apparatus comprises: a toner detection unit that detects an adjustment toner image for detecting a relative positional shift of toner images formed on a belt; and a control unit that can perform an adjustment operation to obtain an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units, based on the detection result of the adjustment toner image by the toner detection unit, wherein the control unit can be controlled to perform the adjustment operation when the relative position is changed by the position changing mechanism.

[0013] Another representative configuration of the present invention is a plurality of image forming units that form a toner image, a rotatable endless belt on which the toner image is formed by the image forming units, a plurality of tension rollers that tension the belt, including an inner roller, an outer member positioned opposite the inner roller and forming a transfer unit that contacts the outer surface of the belt and transfers the toner image from the belt to a recording material, a position changing mechanism that can change the position of at least one of the inner roller or the outer member to change the relative position between the inner roller and the outer member in the circumferential direction of the inner roller, a toner detection unit that detects an adjustment toner image for detecting a relative positional shift of the toner image formed on the belt by the plurality of image forming units, and the plurality of image forming units that form the adjustment toner image on the belt, and based on the detection result of the adjustment toner image by the toner detection unit The image forming apparatus comprises: a control unit capable of performing an adjustment operation to acquire an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units; a first storage unit that stores a first adjustment value acquired by the control unit when the relative position is a first relative position; and a second storage unit that stores a second adjustment value acquired by the control unit when the relative position is a second relative position different from the first relative position, wherein the control unit is controllable to adjust the image writing position using the first adjustment value stored in the first storage unit when forming a toner image with the relative position as the first relative position, and to adjust the image writing position using the second adjustment value stored in the second storage unit when forming a toner image with the relative position as the second relative position.

[0014] Another representative configuration of the present invention is a plurality of image forming units that form a toner image, a rotatable endless belt on which the toner image is formed by the image forming units, a plurality of tension rollers that tension the belt, including an inner roller and an upstream roller positioned upstream of the inner roller and adjacent to the inner roller with respect to the rotation direction of the belt, an outer member positioned opposite the inner roller and forming a transfer unit that contacts the outer circumferential surface of the belt and transfers the toner image from the belt to the recording material, a pressing member that is able to contact the inner circumferential surface of the belt upstream of the inner roller and downstream of the upstream roller with respect to the rotation direction of the belt and can press the belt from the inner circumferential surface side to the outer circumferential surface side, and the position of the pressing member is changed to position the pressing member on the belt The image forming apparatus comprises: a position changing mechanism capable of changing at least one of the amount of pressure applied and the state of contact or separation of the pressing member with respect to the belt; a toner detection unit that detects an adjustment toner image for detecting a relative positional shift of the toner image formed on the belt by the plurality of image forming units; and a control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units and to acquire an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit, wherein the control unit can be controlled to perform the adjustment operation when the position of the pressing member is changed by the position changing mechanism.

[0015] Another representative configuration of the present invention is a plurality of image forming units that form a toner image, a rotatable endless belt on which the toner image is formed by the image forming units, a plurality of tension rollers that tension the belt, including an inner roller and an upstream roller positioned upstream of the inner roller and adjacent to the inner roller with respect to the rotation direction of the belt, an outer member positioned opposite the inner roller and forming a transfer unit that contacts the outer circumferential surface of the belt to transfer the toner image from the belt to a recording material, a pressing member that is able to contact the inner circumferential surface of the belt upstream of the inner roller and downstream of the upstream roller with respect to the rotation direction of the belt, and can press the belt from the inner circumferential surface side to the outer circumferential surface side, a position changing mechanism that can change the position of the pressing member to change at least one of the amount of pressure the pressing member applies to the belt and the state of contact or separation of the pressing member from the belt, and an adjustment mechanism for detecting the relative positional displacement of the toner image formed on the belt by the plurality of image forming units. The image forming apparatus comprises: a toner detection unit for detecting a toner image; a control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units, and to acquire an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit; a first storage unit for storing a first adjustment value acquired by the control unit when the pressing member is in a first position; and a second storage unit for storing a second adjustment value acquired by the control unit when the pressing member is in a second position different from the first position, wherein the control unit is capable of controlling the adjustment of the image writing position using the first adjustment value stored in the first storage unit when forming a toner image with the position of the pressing member in a first position, and adjusting the image writing position using the second adjustment value stored in the second storage unit when forming a toner image with the position of the pressing member in a second position. [Effects of the Invention]

[0016] According to the present invention, in a configuration in which the position (shape) of the transfer unit or the shape (posture) of the belt in the vicinity of the transfer unit can be changed, color shift associated with the change can be suppressed.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic cross-sectional view of an image forming apparatus. [Figure 2] It is a schematic block diagram showing a control mode of an image forming apparatus. [Figure 3] It is a schematic cross-sectional view showing a secondary transfer unit. [Figure 4] It is a schematic cross-sectional side view showing an offset mechanism. [Figure 5] It is a schematic perspective view showing a steering mechanism. [Figure 6] It is a schematic diagram for explaining color shift due to a change in the posture of an intermediate transfer belt. [Figure 7] It is a schematic diagram for explaining the configuration of a toner detection sensor. [Figure 8] It is a schematic diagram showing a pattern image in color registration adjustment. [Figure 9] It is a flowchart of the control of Example 1. [Figure 10] It is a schematic cross-sectional view of another example of an image forming apparatus. [Figure 11] It is a schematic block diagram showing a control mode of another example of an image forming apparatus. [Figure 12] It is a schematic cross-sectional view for explaining the conveyance posture of a recording material. [Figure 13] It is a schematic cross-sectional view for explaining the intrusion amount (pressing amount). [Figure 14] It is a schematic cross-sectional side view showing a pressing mechanism.​​​​​​​​​​​​

[0018] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0019] [Example 1] 1. Overall configuration and operation of the 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-type multifunction device (having the functions of a copier, printer, and facsimile machine) employing an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a sheet-like recording material (paper, transfer material, sheet material, recording medium, media) P, such as paper, using an electrophotographic method in response to an image signal transmitted from an external device such as a personal computer.

[0020] The image forming apparatus 100 has four image forming units 10Y, 10M, 10C, and 10K, each forming images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. These image forming units 10Y, 10M, 10C, and 10K are arranged in series along the direction of movement of the image transfer surface, which is positioned approximately horizontally on the intermediate transfer belt 21, which will be described later. Elements in each image forming unit 10Y, 10M, 10C, and 10K that have the same or corresponding function or configuration may be described collectively by omitting the Y, M, C, and K at the end of the symbols indicating that they are elements for one of the colors. In this embodiment, the image forming unit 10 is composed of a photosensitive drum 1 (1Y, 1M, 1C, 1K), a charging roller 2 (2Y, 2M, 2C, 2K), an exposure device 3 (3Y, 3M, 3C, 3K), a developing device 4 (4Y, 4M, 4C, 4K), a primary transfer roller 23 (23Y, 23M, 23C, 23K), a cleaning device 5 (5Y, 5M, 5C, 5K), and the like, which will be described later.

[0021] The image forming unit 10 is provided with a photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor) serving as a first image carrier for holding a toner image. The photosensitive drum 1 is driven to rotate in the direction of arrow R1 (counterclockwise) in Figure 1 by a driving force transmitted from a drum drive unit 111 (Figure 2), which is a driving means equipped with a drum drive motor 111a as a driving source. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-shaped charging member serving as a charging means (charger). During the charging process, a predetermined charging voltage is applied to the charging roller 2 by a charging power supply (not shown). The charged surface of the photosensitive drum 1 is scanned and exposed according to an image signal by an exposure device 3, which is an exposure means (electrostatic image forming means), and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. In this embodiment, the exposure device 3 is composed of a laser scanner device 3 that irradiates the photosensitive drum 1 with laser light modulated according to an image signal. The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4, which is a developing means, when toner is supplied as a developer, and a toner image (toner image, developer image) is formed on the photosensitive drum 1. In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 1, where the absolute value of the potential has decreased after uniform charging treatment and exposure (reverse development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity. The developing device 4 has a developing roller (not shown), which is a rotatable developer carrier that carries the developer and transports it to the development position, which is the part opposite to the photosensitive drum 1. The developing roller is rotated by, for example, a driving force transmitted from the drive system of the photosensitive drum 1. Also, during development, a predetermined developing voltage is applied to the developing roller by a developing power supply (not shown).

[0022] Opposite the four photosensitive drums 1Y, 1M, 1C, and 1K is an intermediate transfer belt 21, a rotatable intermediate transfer body composed of an endless belt, which serves as a second image carrier for holding the toner image. The intermediate transfer belt 21 is wrapped around a plurality of tension rollers (support rollers), namely a drive roller 22, an upstream auxiliary roller 25a, a downstream auxiliary roller 25b, a tension roller 24, a pre-secondary transfer roller 29, and an inner roller 26, and is stretched with a predetermined tension. The drive roller 22 transmits driving force to the intermediate transfer belt 21. The tension roller 24 is positioned downstream of the primary transfer section N1 (described later) and upstream of the secondary transfer section N2 (described later) with respect to the rotational direction (conveying direction, moving direction, running direction) of the intermediate transfer belt 21, and applies a predetermined tension to the intermediate transfer belt 21. The secondary transfer roller 29 forms the surface of the intermediate transfer belt 21 near the upstream of the secondary transfer section N2 (described later) with respect to the rotational direction of the intermediate transfer belt 21. The inner roller (secondary transfer inner roller, inner member, secondary transfer opposing roller) 26 functions as an opposing member (opposing electrode) of the outer roller 41 (described later). The upstream auxiliary roller 25a and downstream auxiliary roller 25b form an image transfer surface that is arranged substantially horizontally. The drive roller 22 is rotationally driven by the transmission of driving force from the belt drive unit 113 (Figure 2), which is a driving means equipped with a belt drive motor 113a as a driving source. As a result, the intermediate transfer belt 21 receives drive input from the drive roller 22 and rotates (circumvents) in the direction of arrow R2 in Figure 1 (clockwise direction). On the inner circumferential surface of the intermediate transfer belt 21, primary transfer rollers 23Y, 23M, 23C, and 23K, which are roller-shaped primary transfer members serving as primary transfer means, are arranged corresponding to each photosensitive drum 1Y, 1M, 1C, and 1K. The primary transfer rollers 23 press the intermediate transfer belt 21 toward the photosensitive drum 1, forming a primary transfer portion (primary transfer nip) N1, which is the contact area between the photosensitive drum 1 and the intermediate transfer belt 21. The tension rollers other than the drive roller 22, and each primary transfer roller 23, rotate in accordance with the rotation of the intermediate transfer belt 21. In this embodiment, the tension roller 24 also functions as a steering roller.In other words, in this embodiment, the tension roller 24 applies a predetermined tension to the intermediate transfer belt 21 and, by tilting, corrects the deviation of the intermediate transfer belt 21 (deviation of the running position in the width direction which is substantially perpendicular to the direction of movement of the surface of the intermediate transfer belt 21).

[0023] As described above, the toner image formed on the photosensitive drum 1 is first transferred to the rotating intermediate transfer belt 21 in the primary transfer section N1 by the action of the primary transfer roller 23. During primary transfer, a 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, is applied to the primary transfer roller 23 by a primary transfer power supply (not shown). For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially first transferred so that they are superimposed on the same image forming region on the intermediate transfer belt 21. In this embodiment, the primary transfer section N1 is the image forming position where the toner image is formed on the intermediate transfer belt 21. The intermediate transfer belt 21 is an example of a rotatable endless belt that transports the toner image carried at the image forming position.

[0024] On the outer circumferential surface of the intermediate transfer belt 21, an outer roller (secondary transfer outer roller, outer member, secondary transfer roller) 41, which is a roller-shaped secondary transfer member (transfer rotating body), is positioned opposite the inner roller 26 as a secondary transfer means. The outer roller 41 is pressed toward the inner roller 26 via the intermediate transfer belt 21, forming a secondary transfer section (secondary transfer nip) N2, which is the contact point between the intermediate transfer belt 21 and the outer roller 41. In this embodiment, the outer roller 41 rotates in conjunction with the rotation of the intermediate transfer belt 21, but it may also be rotationally driven independently of the intermediate transfer belt 21. As described above, the toner image formed on the intermediate transfer belt 21 is secondary transferred in the secondary transfer section N2 to the recording material P, which is being transported sandwiched between the intermediate transfer belt 21 and the outer roller 41, by the action of the outer roller 41. In this embodiment, during secondary transfer, a secondary transfer voltage, which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the outer roller 41 by a secondary transfer power supply (not shown). In this embodiment, the inner roller 26 is electrically grounded (connected to ground). Alternatively, the inner roller 26 may be used as a secondary transfer member and a secondary transfer voltage with the same polarity as the normal charging polarity of the toner may be applied to it, and the outer roller 41 may be used as a counter electrode and electrically grounded.

[0025] The recording material P is transported to the secondary transfer section N2 in a manner that matches the timing with the toner image on the intermediate transfer belt 21. The recording material P is stored in advance in a recording material storage unit (cassette) 11. This recording material P is fed out by a feeding unit (feeding rollers, etc.) provided in the recording material storage unit 11, and after its orientation is adjusted in the resist adjustment unit 12, it is transported to the secondary transfer section N2 at a predetermined timing (resist ON timing). Here, the resist adjustment unit 12 includes a pair of resist rollers (resist roller pair) 13, which are roller-shaped transport members as a transport means, and a resist drive unit (transport drive unit) 114 (Figure 2) as a drive means for driving the resist rollers 13. The resist rollers 13 are rotated by the resist drive unit 114, and the recording material P is transported at the contact portion (nip portion) of the pair of resist rollers 13. The resist drive unit 114 is equipped with a resist drive motor 114a (Figure 2) as a drive source, and the resist drive unit 114 drives at least one (or both) of the pair of resist rollers 13. In this embodiment, the control unit 150 (Figure 2) can change the start timing of transport of the recording paper P (remote ON timing) using the register ON timing changing means. The control unit 150 can also change the transport speed of the recording material P in the secondary transfer unit N2 by controlling the rotation speed of the resist drive motor 114a of the resist drive unit 114 and controlling the rotation speed of the resist roller 13. The recording material P supplied from the recording material storage unit 11 is temporarily stopped by the register roller 13. Then, the recording material P is fed into the secondary transfer unit N2 by the registration roller 13 being rotated so that the toner image on the intermediate transfer belt 21 and the desired image forming area on the recording material P coincide.

[0026] Regarding the transport direction of the recording material P, a transport guide 27 is provided downstream of the register roller 13 and upstream of the secondary transfer section N2 to guide the recording material P to the secondary transfer section N2. The transport guide 27 is composed of a first guide member 27a that can contact the front surface of the recording material P (the surface on which the toner image is transferred immediately after passing through the transport guide 27) and a second guide member 27b that can contact the back surface of the recording material P (the surface opposite to the front surface). The first guide member 27a and the second guide member 27b are arranged opposite each other, and the recording material P passes between these two members. The first guide member 27a restricts the movement of the recording material P toward the intermediate transfer belt 21. The second guide member 27b restricts the movement of the recording material P toward the intermediate transfer belt 21.

[0027] The recording material P onto which the toner image has been transferred is transported by a transport belt 14 to a fixing device 15, which serves as a fixing means. The transport belt 14 is driven by a transport drive motor (not shown). A suction fan (not shown) is positioned on the inner circumferential side of the transport belt 14 to attract the recording material P, and attracts the recording material P toward the transport belt 14. The fixing device 15 heats and pressurizes the recording material P carrying the unfixed toner image to fix (melt and solidify) the toner image to the surface of the recording material P. After that, the recording material P with the fixed toner image is discharged (output) by a discharge device 16 to a discharge tray 17 located outside the main body 110 of the image forming apparatus 100 (outside the machine).

[0028] On the other hand, toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 1 and recovered by the cleaning device 5, which is a cleaning means. In addition, toner remaining on the intermediate transfer belt 21 after the secondary transfer (secondary transfer residual toner) and any adhering materials such as paper dust from the recording material P are removed from the intermediate transfer belt 21 and recovered by the belt cleaning device 28, which is an intermediate transfer body cleaning means.

[0029] In this embodiment, the intermediate transfer belt unit 20, which serves as a belt conveying device, comprises an intermediate transfer belt 21 stretched over multiple tension rollers, each primary transfer roller 23, a belt cleaning device 28, and a frame that supports these components. The intermediate transfer belt unit 20 is detachable from the main device body 110 for maintenance or replacement.

[0030] 2. Offset Figure 3 is a schematic cross-sectional view (a cross-section approximately perpendicular to the rotation axis direction of the inner roller 26) for explaining the behavior of the recording material P in the vicinity of the secondary transfer section N2. In Figure 3, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 in this embodiment are denoted by the same reference numerals. In this embodiment, the outer roller 41 is rotatably supported at both ends in the direction of its rotation axis by bearings 43. The bearings 43 are slidable in the direction toward the inner roller 26 and in the opposite direction, and are pressed toward the inner roller 26 by a compression spring 44, which is a biasing member (elastic member) acting as a biasing means. As a result, the outer roller 41 contacts the inner roller 26 with a predetermined pressure across the intermediate transfer belt 21, forming the secondary transfer section N2. In this embodiment, the outer roller 41 rotates in conjunction with the rotation of the intermediate transfer belt 21. Here, the rotational axis directions of the tension rollers of the intermediate transfer belt 21, including the inner roller 26, and the outer roller 41 are approximately parallel to each other.

[0031] As mentioned above, the behavior of the recording material P near the upstream and downstream of the secondary transfer section N2 changes depending on the shape of the secondary transfer section N2 (position of the secondary transfer section N2) and the stiffness of the recording material P. For example, if the recording material P is "thin paper," which is an example of a recording material P with low stiffness, jams (paper jams) may occur due to poor separation of the recording material P from the intermediate transfer belt 21. This phenomenon is more pronounced when the stiffness of the recording material P is low, because the recording material P is less rigid and therefore more likely to stick to the intermediate transfer belt 21.

[0032] In other words, in the cross-section shown in Figure 3, the line indicating the tensioned surface (tensioned surface) of the intermediate transfer belt 21 formed by tensioning the inner roller 26 and the secondary transfer roller 29 is defined as the pre-nip tension line T. The secondary transfer roller 29 is an example of an upstream roller among a plurality of tension rollers, positioned upstream of the inner roller 26 in the rotational direction of the intermediate transfer belt 21 and adjacent to the inner roller 26. In the same cross-section, the straight line passing through the rotational center of the inner roller 26 and the rotational center of the outer roller 41 is defined as the nip center line Lc. In the same cross-section, the line passing through the secondary transfer section N2 and approximately perpendicular to the nip center line Lc is defined as the nip line Ln. Figure 3 shows a state in which the rotational center of the outer roller 41 is offset upstream of the rotational center of the intermediate transfer belt 21 in the direction along the pre-nip tension line T compared to the rotational center of the inner roller 26.

[0033] When the recording material P is held between the inner roller 26 and the outer roller 41 in the secondary transfer section N2, it tends to maintain a posture approximately along the nip line Ln. Therefore, generally, when the rotation centers of the inner roller 26 and the outer roller 41 are close together in the direction along the pre-nip tensioning wire T, the discharge angle θa of the recording material P becomes small, as shown by the dashed line A in Figure 3. In other words, when the leading edge of the recording material P in the transport direction is discharged from the secondary transfer section N2, it takes a posture that is close to the intermediate transfer belt 21. This makes it easier for the recording material P to stick to the intermediate transfer belt 21. Conversely, the further upstream the rotation center of the outer roller 41 is positioned relative to the rotation center of the inner roller 26 in the direction along the pre-nip tensioning wire T, the larger the discharge angle θb of the recording material P becomes, as shown by the solid line in Figure 3. In other words, the leading edge of the recording material P in the transport direction is positioned such that it is discharged away from the intermediate transfer belt 21 when it is discharged from the secondary transfer section N2. This makes it less likely for the recording material P to stick to the intermediate transfer belt 21.

[0034] On the other hand, as mentioned above, if the recording material P is, for example, "cardboard," which is an example of a recording material P with high rigidity, the rear end of the recording material P in the transport direction may collide with the intermediate transfer belt 21 when it passes through the transport guide 27. This can cause image defects at the rear end of the recording material P in the transport direction. This phenomenon is more pronounced when the recording material P has high rigidity, as the stiffness of the recording material P makes it easier for the rear end of the recording material P in the transport direction to collide with the intermediate transfer belt 21 with considerable force.

[0035] In other words, as described above, in the cross-section shown in Figure 3, when the recording material P is held between the inner roller 26 and the outer roller 41 in the secondary transfer section N2, it tends to maintain its orientation almost along the nip line Ln. Therefore, the further upstream the rotation center of the outer roller 41 is positioned in the direction of rotation of the intermediate transfer belt 21 compared to the rotation center of the inner roller 26 in the direction along the nip pre-tensioning wire T, the more the nip line Ln bites into the nip pre-tensioning wire T. As a result, when the rear end of the recording material P in the transport direction passes through the transport guide 27, the rear end of the recording material P in the transport direction will collide with the intermediate transfer belt 21, as shown by the dashed line B in Figure 3, making it easier for image defects to occur at the rear end of the recording material P in the transport direction. In contrast, if the rotation centers of the inner roller 26 and the outer roller 41 are brought closer together in the direction along the nip pre-tensioning wire T, collision with the intermediate transfer belt 21 when the rear end of the recording material P in the transport direction passes through the transport guide 27 can be suppressed. This makes it less likely for image defects to occur at the rear end of the recording material P in the transport direction.

[0036] Therefore, in order to improve the separation of the recording material P from the intermediate transfer belt 21 and to suppress image defects at the rear end of the recording material P in the transport direction, the following is effective. That is, depending on the type of recording material P, the relative position of the inner roller 26 and the outer roller 41 in the circumferential direction of the inner roller 26 (the rotation direction of the intermediate transfer belt 21) is changed, and the shape of the secondary transfer section N2 (the position of the secondary transfer section N2) is changed.

[0037] Referring to Figure 3, the definition of the offset amount X, which indicates the relative position of the inner roller 26 and the outer roller 41, will be explained. In the cross-section shown in Figure 3, the reference line L1 is the common tangent line between the inner roller 26 on the side around which the intermediate transfer belt 21 is wrapped (the side to which the intermediate transfer belt 21 is in contact) and the secondary transfer roller 29. The reference line L1 corresponds to the nip pre-tensioning wire T mentioned above. Also in the same cross-section, the inner roller centerline L2 is the straight line passing through the rotation center of the inner roller 26 and approximately perpendicular to the reference line L1. Also in the same cross-section, the outer roller centerline L3 is the straight line passing through the rotation center of the outer roller 41 and approximately perpendicular to the reference line L1. At this time, the distance (vertical distance) between the inner roller centerline L2 and the outer roller centerline L3 is defined as the offset amount X (a positive value is taken when L3 is upstream of L2 in the rotation direction of the intermediate transfer belt 21). The offset amount X can take negative, zero, or positive values. By increasing the offset amount X, the width of the secondary transfer portion N2 in the direction of rotation of the intermediate transfer belt 21 widens on the upstream side in the direction of rotation of the intermediate transfer belt 21. In other words, the upstream end of the contact area between the outer roller 41 and the intermediate transfer belt 21 in the direction of rotation is located further upstream than the upstream end of the contact area between the inner roller 26 and the intermediate transfer belt 21 in the direction of rotation of the intermediate transfer belt 21. In this way, by changing the position of at least one of the inner roller 26 or the outer roller 41, the relative position of the inner roller 26 and the outer roller 41 in the circumferential direction of the inner roller 26 can be changed, thereby changing the position of the secondary transfer portion N2 (the shape of the secondary transfer portion N2).

[0038] In Figure 3, the outer roller 41 is shown virtually as being in contact with the reference line L1 (nip front tensioning wire T) without deformation. However, the outermost layer of the outer roller 41 is made of an elastic material such as rubber or sponge, and in reality, it is deformed by being pressed by the compression spring 44 in the direction toward the inner roller 26. When the outer roller 41 is positioned offset upstream of the rotational direction of the intermediate transfer belt 21 relative to the inner roller 26, and is pressed by the compression spring 44 to sandwich the intermediate transfer belt 21 between the outer roller 41 and the inner roller 26, a roughly S-shaped secondary transfer section N2 is formed. The orientation of the recording material P, which is sent guided by the transport guide 27, is then determined according to the shape of the secondary transfer section N2. The larger the offset amount X, the greater the bending of the recording material P. Therefore, for example, if the recording material P is "thin paper", increasing the offset amount X can improve the separation of the recording material P from the intermediate transfer belt 21 after passing through the secondary transfer section N2. However, if the offset amount X is large, the amount of bending of the recording material P is large. For example, if the recording material P is "cardboard," when the rear end of the recording material P in the transport direction passes through the transport guide 27, collision of the rear end of the recording material P in the transport direction with the intermediate transfer belt 21 is more likely to occur. This can degrade the image quality of the rear end of the recording material P in the transport direction, but in this case, the offset amount X can be reduced.

[0039] In this embodiment, the image forming apparatus 100 changes the offset amount X by changing the position of at least one of the inner roller 26 or the outer roller 41. In particular, in this embodiment, the image forming apparatus 100 changes the offset amount X by changing the position of the inner roller 26. In this embodiment, the image forming apparatus 100 also changes the offset amount X based on the stiffness of the recording material P and information about the basis weight of the recording material (paper) P, which is information about the type of recording material P. For example, if the recording material P is "thick paper", the inner roller 26 is positioned at a second inner roller position where the offset amount X becomes a second offset amount X2. Then, for example, if the recording material P is "thin paper", the inner roller 26 is positioned at a first inner roller position where the offset amount X becomes a first offset amount X1 which is greater than the second offset amount X2. The second offset amount X2 may be a positive value, 0, or a negative value, and the first offset amount X1 is typically a positive value. In this embodiment, the relative position between the inner roller 26 and the outer roller 41 when the offset amount X is the first offset amount X1 is the first relative position, and the relative position between the inner roller 26 and the outer roller 41 when the offset amount X is the second offset amount X2 is the second relative position. That is, in this embodiment, the position of the secondary transfer section N2 when the offset amount X is the first offset amount X1 is the first position of the transfer section, and the position of the secondary transfer section N2 when the offset amount X is the second offset amount X2 is the second position of the transfer section.

[0040] 3. Offset mechanism Next, the offset mechanism 101 in this embodiment will be described. Here, "thin paper" will be used as an example of a recording material P with low rigidity, and "thick paper" will be used as an example of a recording material P with high rigidity.

[0041] Figures 4(a) and 4(b) are schematic cross-sectional side views (a cross-section approximately perpendicular to the rotation axis direction of the inner roller 26) taken from one end of the inner roller 26 in the direction of its rotation axis (the front side of the paper in Figure 1) and approximately parallel to the rotation axis direction. Here, Figure 4(a) shows the condition of the recording material P passing through the secondary transfer section N2 when it is "thin paper", and Figure 4(b) shows the condition when it is "thick paper".

[0042] As shown in Figures 4(a) and (b), in this embodiment, the image forming apparatus 100 has an offset mechanism (offset amount changing means) 101 as a position changing mechanism that changes the relative position of the inner roller 26 with respect to the outer roller 41 to make the offset amount X variable. Figures 4(a) and (b) show the configuration of one end of the inner roller 26 in the direction of the rotation axis, but the configuration of the other end is similar (approximately symmetrical with respect to the center in the direction of the rotation axis of the inner roller 26).

[0043] Both ends of the inner roller 26 in the direction of its rotation axis are rotatably supported by an inner roller holder 38, which serves as a support member. The inner roller holder 38 is supported by the frame of the intermediate transfer belt unit 20 or the like so as to be rotatable around the inner roller pivot axis 38a. In this way, by rotating the inner roller holder 38 around the inner roller pivot axis 38a and thereby rotating the inner roller 26 around the inner roller pivot axis 38a, the relative position of the inner roller 26 with respect to the outer roller 41 can be changed, thereby changing the offset amount X.

[0044] The internal roller holder 38 is configured to rotate by the action of an offset cam 39 acting as an operating member. The offset cam 39 is supported by the frame of the intermediate transfer belt unit 20 or the like so as to be able to rotate around the offset cam pivot axis 39a. The offset cam 39 is able to rotate around the offset cam pivot axis 39a by receiving drive from an offset motor (offset cam drive motor) 115 acting as a drive source. The offset cam 39 is also in contact with an offset cam follower (arm portion) 38c provided on the internal roller holder 38. Furthermore, as will be described later, the internal roller holder 38 is biased by the tension of the intermediate transfer belt 21 so as to rotate in a direction in which the offset cam follower 38c contacts the offset cam 39. However, it is not limited to this, and the internal roller holder 38 may be biased by a biasing member (elastic member) such as a spring so as to rotate the offset cam follower 38c in a direction in which it contacts the offset cam 39.

[0045] Furthermore, in this embodiment, the image forming apparatus 100 is provided with an offset cam position sensor 37, which detects the rotational position of the offset cam 39, as a position detection means for detecting the relative position between the inner roller 26 and the outer roller 41 (the position of the inner roller 26 in this embodiment). The offset cam position sensor 37 is configured to include, for example, the offset cam 39 or a flag as an indicator unit provided coaxially with the offset cam 39, and an optical sensor (photointerrupter) as a detection unit. The offset cam position sensor 37 may be configured to detect, for example, the home position (HP) of the offset cam 39, that is, the home position of the inner roller 26. The signal indicating the detection result of the offset cam position sensor 37 is input to the control unit 150 (Figure 2). Based on the detection result of the offset cam position sensor 37, the control unit 150 can determine the position of the offset cam 39 (rotational position), that is, the position of the inner roller 26.

[0046] As described above, in this embodiment, the offset mechanism 101 is configured with an internal roller holder 38, an offset cam 39, an offset motor 115, an offset cam position sensor 37, and the like.

[0047] As shown in Figure 4(a), in the case of "thin paper," the offset cam 39 is driven by the offset motor 115 and rotates, for example, counterclockwise. This causes the inner roller holder 38 to rotate clockwise around the inner roller pivot axis 38a, determining the relative position of the inner roller 26 with respect to the outer roller 41. As a result, the inner roller 26 is positioned at the first inner roller position, which is the first offset amount X1, where the offset amount X is relatively large. In this state, the recording material P is more easily bent within the secondary transfer section N2, and as mentioned above, the separation of the "thin paper" from the intermediate transfer belt 21 after passing through the secondary transfer section N2 is improved.

[0048] As shown in Figure 4(b), in the case of "cardboard," the offset cam 39 is driven by the offset motor 115 and rotates, for example, clockwise. This causes the inner roller holder 38 to rotate counterclockwise around the inner roller pivot axis 38a, determining the relative position of the inner roller 26 with respect to the outer roller 41. As a result, the inner roller 26 is positioned at a second inner roller position, which is a second offset amount X2 with a relatively small offset amount X. In this state, bending of the recording material P within the secondary transfer section N2 can be reduced, and as mentioned above, the deterioration of image quality at the rear end in the transport direction of the "cardboard" can be suppressed.

[0049] In this example, the offset amount X(X1, X2) is set to be one of the following two patterns based on the basis weight M(gsm) of the recording material P. Here, gsm is g / m². 2 It means... (a) M ≤ 300 gsm: X1 = +2.5 mm (b) M>300gsm: X2=-1.3mm

[0050] In this embodiment, the position of the inner roller 26 (relative position between the inner roller 26 and the outer roller 41) in the above setting (a) shown in Figure 4(a) is the home position of the inner roller 26 (relative position between the inner roller 26 and the outer roller 41). Here, the home position of the inner roller 26 refers to the position when the image forming apparatus 100 is in sleep mode (described later) or when the main power is turned OFF. However, it is not limited to this, and the position of the inner roller 26 in the above setting (b) shown in Figure 4(b) may similarly be considered the home position of the inner roller 26.

[0051] Furthermore, the offset amount X and the type of recording material P assigned to each offset amount X (here, the basis weight of the recording material P) are not limited to the specific examples described above. These can be appropriately set through experiments, etc., from the viewpoint of improving the separation of the recording material P from the intermediate transfer belt 21 and suppressing image defects that occur near the secondary transfer section N2, as described above. In this embodiment, an offset amount X of approximately -3 mm to +3 mm is preferable. Also, the patterns of offset amount X are not limited to two patterns, and three or more patterns may be set. Following this embodiment, an appropriate setting can be selected from three or more settings based on information such as the basis weight of the recording material P as information related to the type of recording material P, which is related to the stiffness of the recording material P.

[0052] As described above, in the cross-section shown in Figure 4, the inner roller holder 38 is constantly subjected to a counterclockwise moment around the inner roller pivot axis 38a due to the tension of the intermediate transfer belt 21. In other words, in this embodiment, the inner roller holder 38 is constantly subjected to a moment in the direction that causes the offset cam follower 38c to rotate so that it engages with the offset cam 39, due to the tension of the intermediate transfer belt 21. Also, in the cross-section shown in Figure 4, the inner roller pivot axis 38a is positioned downstream in the direction of transport of the recording material P with respect to the straight line (nip center line) Lc connecting the rotation center of the inner roller 26 and the rotation center of the outer roller 41. As a result, when the outer roller 41 is in contact with the inner roller 26 via the intermediate transfer belt 21, the reaction force that the inner roller holder 38 receives from the outer roller 41 is also a counterclockwise moment in Figure 4. With this configuration, a cam mechanism can be constructed without using a separate biasing member such as a spring.

[0053] Furthermore, in order to avoid hindering the workability of operations such as attaching or removing the intermediate transfer belt 21 to the intermediate transfer belt unit 20 for the purpose of replacing the intermediate transfer belt 21, it is desirable that the inner roller holder 38 be positioned on the inside of the tensioned surface of the intermediate transfer belt 21. For this reason, in the cross-section shown in Figure 4, it is desirable that the inner roller pivot axis 38a be positioned in region A between the straight line (nip center line) Lc and the post-nip tensioning line U. Here, the post-nip tensioning line U is a line that indicates the tensioned surface of the intermediate transfer belt 21 formed by tensioning the inner roller 26 and the drive roller 22 (see Figure 1) in the cross-section shown in Figure 4. The drive roller 22 is an example of a downstream roller among a plurality of tensioning rollers that is positioned downstream of the inner roller 26 with respect to the rotational direction of the intermediate transfer belt 21 and adjacent to the inner roller 26.

[0054] 4. Changing the offset amount and color shift Next, we will explain the color shift that occurs when the offset amount is changed.

[0055] (Control of the intermediate transfer belt's alignment) First, let's explain the control of the intermediate transfer belt 21.

[0056] The intermediate transfer belt 21 can become misaligned due to factors such as the position (alignment) of the tension rollers and imbalances in the applied pressure. This misalignment of the intermediate transfer belt 21 can be controlled by designating at least one of the multiple tension rollers as a steering roller (misalignment control roller) and tilting it so that its rotation axis is inclined relative to the rotation axes of the other tension rollers, thereby changing the direction of travel of the intermediate transfer belt 21.

[0057] In this embodiment, the image forming apparatus 100 has a steering mechanism as a steering control means for controlling the alignment of the intermediate transfer belt 21. In this embodiment, the steering mechanism uses the signal from a sensor provided at the widthwise end of the intermediate transfer belt 21 to control the alignment by changing the alignment of the tension roller (which also serves as a steering roller) 24 so that the value of the signal from the sensor remains constant. Further details will be explained below.

[0058] Figure 5 is a schematic perspective view illustrating the steering mechanism 62 in this embodiment. As described above, in this embodiment, the tension roller 24 also serves as the steering roller. In this embodiment, the tension roller 24 is positioned downstream of the primary transfer nip N1 (the furthest downstream primary transfer nip N1K) and upstream of the secondary transfer section N2 with respect to the rotational direction of the intermediate transfer belt 21. The tension roller 24 is rotatably held by the intermediate transfer belt unit 20 at both ends in the direction of its rotational axis via bearing members (not shown). The bearing members at both ends of the tension roller 24 in the direction of its rotational axis are supported so as to be able to slide in the direction from the inner circumferential surface side to the outer circumferential surface side and in the opposite direction of the intermediate transfer belt 21. Furthermore, the bearing members at both ends are each pressurized (biased) in the direction from the inner circumferential surface side to the outer circumferential surface side of the intermediate transfer belt 21 by a biasing force such as a compression spring, which is a biasing member (elastic member) acting as a biasing means. As a result, the tension roller 24 applies a predetermined tension to the intermediate transfer belt 21. Furthermore, the bearing member at one end of the tension roller 24 in the direction of its rotation axis (the far side in Figure 5) is supported by the frame of the intermediate transfer belt unit 20 so as to be rotatable around a pivot axis that is substantially perpendicular to the rotation axis of the tension roller 24. The bearing member at the other end of the tension roller 24 in the direction of its rotation axis (the near side in Figure 5) is supported by the frame of the intermediate transfer belt unit 20 via a bias correction arm 57. This bias correction arm 57 is rotatable (oscillating) around a pivot axis that is substantially parallel to the rotation axis of the tension roller 24. As a result, the tension roller 24 can be rotated so that the near end in Figure 5 moves in the vertical direction in Figure 5. By rotating the tension roller 24 in this way, the tension roller 24 can be tilted so that its rotation axis is inclined with respect to the rotation axis of other tension rollers such as the drive roller 22.

[0059] When the intermediate transfer belt 21 moves towards the front or back side in Figure 5, the widthwise end of the intermediate transfer belt 21 causes the shift detection sensor 56 to move in the direction of arrow IF or arrow IR in Figure 5. The signal indicating the detection result of the shift detection sensor 56 is input to the control unit 150 (Figure 2). The control unit 150 drives the shift correction motor 60, which acts as a drive source (steering drive unit), according to the widthwise running position of the intermediate transfer belt 21 detected by the shift detection sensor 56 (more specifically, the position of the widthwise end of the intermediate transfer belt 21 at the point where the shift detection sensor 56 contacts it). When the shift correction motor 60 is driven, the shift correction cam 58 rotates, causing the shift correction arm 57 to swing. As a result, the front end of the tension roller 24 in Figure 5 moves up and down (in the direction of arrow SF or arrow SR), causing the tension roller 24 to tilt. In this way, the tilting of the tension roller 24 causes the intermediate transfer belt 21 to move in the direction of arrow IF or arrow IR in Figure 5. By continuing these operations, the misalignment of the intermediate transfer belt 21 is corrected.

[0060] The position of the tension roller 24 (position in the tilting direction, inclined position) is detected by a position information acquisition unit, a tilt correction cam position sensor 61, which is provided coaxially with the rotation axis of the tilt correction cam 58. The tilt correction cam position sensor 61 is configured to include, for example, a flag as an indicator unit provided coaxially with the tilt correction cam 58 or the tilt correction cam 58, and an optical sensor (photo interrupter) as a detection unit. The tilt correction cam position sensor 61 may be configured to detect, for example, the home position (HP) of the tilt correction cam 58, i.e., the home position of the tension roller 24. The signal indicating the detection result of the tilt correction cam position sensor 61 is input to the control unit 150 (Figure 2). Based on the detection result of the tilt correction cam position sensor 61, the control unit 150 can determine the position of the tilt correction cam 61 (position in the rotation direction), i.e., the position of the tension roller 24 (inclined position). Furthermore, the alignment detection sensor 56 is configured to include, for example, a flag that contacts the end of the intermediate transfer belt 21 in the width direction, an LED as a light-emitting part, and two photodiodes as light-receiving parts. The amount of light received by the two photodiodes changes depending on the position of the flag of the alignment detection sensor 56. By detecting this amount of light received, it is possible to determine the running position of the intermediate transfer belt 21 in the width direction (more specifically, the position of the end of the intermediate transfer belt 21 in the width direction at the point where the alignment detection sensor 56 makes contact).

[0061] In this embodiment, the steering mechanism 62 is configured with a steering correction motor 60, a steering correction cam position sensor 61, a steering detection sensor 56, a steering correction arm 57, a steering correction cam 58, and the like.

[0062] The configuration for controlling the alignment of the intermediate transfer belt 31 is not limited to that of this embodiment, and known configurations can be used as appropriate. For example, the steering rollers may consist of multiple rollers among a plurality of tension rollers. The steering rollers may also have both ends in the direction of the rotation axis that move, for example, around a pivot axis in the center of the rotation axis direction. There are also systems that use an automatic centering method that controls the alignment automatically using frictional force without using sensors.

[0063] (Impact of changes in offset amount on alignment control) As described above, in this embodiment, the balance of the running posture of the intermediate transfer belt 21 is maintained by changing the alignment of the tension roller 24. However, due to the change in the offset amount caused by moving the inner roller 26 that tensions the intermediate transfer belt 21, it is necessary to readjust the adjusted balance position. This is because moving the inner roller 26 changes the alignment of one end and the other end of the inner roller 26 in the direction of its rotation axis, which can change the posture in which the intermediate transfer belt 21 can run stably. As described above, in this embodiment, only the alignment of the tension roller 24 is adjusted in the steering control. Therefore, the posture of the intermediate transfer belt 21 is uniquely determined by this adjustment. Consequently, readjusting the position of the tension roller 24 means a change in the posture of the intermediate transfer belt 21.

[0064] Figure 6 is a schematic diagram of the intermediate transfer belt 21 as seen from the image transfer surface side, illustrating the change in the orientation of the intermediate transfer belt 21. The lower part of Figure 6 is the front side of the paper in Figure 1 (the front side of the image forming apparatus 100), and the upper part of Figure 6 is the back side of the paper in Figure 1 (the back side of the image forming apparatus 100). As shown in Figure 6, the orientation of the intermediate transfer belt 21 changes, for example, from state (a) to state (b). At this time, it is assumed that the image writing position (image writing timing) has been adjusted by the color resist adjustment described later so that no color shift occurs in state (a). When it changes to state (b), the toner image Ty formed on the intermediate transfer belt 21 in the upstream image forming unit 10Y moves to the position of Tyb when it reaches the primary transfer unit N1M of the downstream image forming unit 10M. Therefore, it shifts A [μm] inward from the position of Tya, which had been adjusted by the color resist adjustment. This is the color shift.

[0065] In Figure 6, the change in the posture of the intermediate transfer belt 21 is simplified, showing only the tilt changing from state (a) to state (b). However, in more detail, as the offset amount is changed, fluctuations in the alignment of the intermediate transfer belt 21 also occur until the running posture of the intermediate transfer belt 21 stabilizes. In other words, in this embodiment, the alignment is corrected so that the position of the alignment detection sensor 56 shown by the solid line in state (a) and the position of the alignment detection sensor 56 shown by the dashed line in state (b) become approximately constant. Therefore, when the offset amount is changed, the intermediate transfer belt 21 changes its running posture (tilt) while experiencing fluctuations in alignment as it moves from state (a) to state (b). Since this alignment is corrected by the alignment control described above, the position of the end of the intermediate transfer belt 21 detected by the alignment detection sensor 56 stabilizes to an approximately constant position. However, as the alignment of the inner roller 26 changes, the position of the tension roller 24 in this stable state changes, and the running posture (tilt) of the intermediate transfer belt 21 changes from state (a) to state (b).

[0066] 5. Color Resist Adjustment Next, we will explain color resist adjustment as an adjustment operation. In the image forming apparatus 100, if the relative positions of the images of different colors are misaligned when images of different colors are superimposed and transferred, changes in the color of the image formed on the recording material P will occur. Therefore, the image forming apparatus 100 forms a pattern image on the intermediate transfer belt 21 using multiple image forming units 10, and performs color resist adjustment (color misalignment correction control) to correct the image writing position (image writing timing) at each image forming unit 10 based on the result of detecting the pattern image with a sensor.

[0067] As shown in Figure 1, the image forming apparatus 100 has a toner detection unit 116 equipped with a toner detection sensor 116a (Figure 2) for detecting pattern images (adjustment toner images, toner patches) on the intermediate transfer belt 21. The toner detection unit 116 is located between the primary transfer unit N1K and the secondary transfer unit N2 of the downstream image forming unit 10K with respect to the rotational direction of the intermediate transfer belt 21. In particular, in this embodiment, the toner detection unit 116 is positioned opposite the downstream auxiliary roller 25b.

[0068] Figure 7 is a schematic diagram illustrating the configuration of the toner detection sensor 116a. The toner detection sensor 116a is an optical sensor that detects reflected light from a pattern image formed on the intermediate transfer belt 21. For example, the toner detection sensor 116a detects diffusely reflected light from the pattern image. The toner detection sensor 116a comprises a light-emitting unit 601 that irradiates (projects) light toward the intermediate transfer belt 21, and a light-receiving unit 602 that receives reflected light from the intermediate transfer belt 21 or the pattern image. The light-receiving unit 602 is positioned so that it can receive diffusely reflected light from the light-emitting unit 601 irradiated toward the intermediate transfer belt 21, with the angle of incidence and the angle of reflection not being equal. The light-receiving unit 602 is positioned so that it does not receive light that has been specularly reflected from the pattern image. The toner detection sensor 116a outputs a signal of a level corresponding to the intensity of the light (amount of light received) received by the light-receiving unit 602. The toner detection sensor 116a has a lens 603 that collects reflected light from the detection area 604 within the region 605 illuminated by light from the light-emitting unit 601. In other words, the light-receiving unit 602 selectively receives diffusely reflected light from the detection area 604.

[0069] Figure 8 is a schematic diagram of an example of a pattern image 300 formed on the intermediate transfer belt 21. The pattern image 300 includes a magenta pattern image 302, a yellow pattern image 301, a cyan pattern image 303, and a superimposed pattern image 304 in which the magenta pattern image is exposed through the gaps of the black pattern image. Since the reflected light from the black pattern image is small, the superimposed pattern image 304 is formed to detect the position of the black pattern image. In the illustrated example, the reference color pattern image is assumed to be the magenta pattern image 302. Note that the reference color pattern image may be a pattern image of another color, such as yellow. The image writing position of each color is corrected based on the time at which each pattern image is detected by the toner detection sensor 116a. A detailed explanation of the specific method of color resist adjustment is omitted here, as any known method can be arbitrarily used, but it can be done as follows, for example.

[0070] The pattern image 300 in Figure 8 includes a first group of pattern images 300a inclined in a first direction with respect to the transport direction of the intermediate transfer belt 21, and a second group of pattern images 300b inclined in a second direction different from the first direction with respect to the transport direction of the intermediate transfer belt 21. The first and second group of pattern images 300a and 300b each include a pattern image of a reference color and a pattern image of other colors, respectively. This pattern image 300 is formed on and transported on the rotating intermediate transfer belt 21. Therefore, for example, the time at which the pattern image of the reference color was detected and the time at which the pattern image of the target color was detected are obtained for each of the first and second group of pattern images 300a and 300b. Then, for example, based on the interval of these times, the positional shift of the target color pattern image relative to the reference color with respect to the transport direction (sub-scanning direction) of the intermediate transfer belt 21 can be detected. This makes it possible to detect the relative positional shift of each color with respect to the sub-scanning direction, i.e., color shift. Furthermore, the pattern images of the first pattern image group 300a and the pattern images of the second pattern image group 300b are tilted in different directions. Therefore, for example, the time at which each color pattern image of the first pattern image group 300a is detected and the time at which the corresponding color pattern image of the second pattern image group 300b is detected are obtained. Then, for example, based on these time intervals, it is possible to detect the positional shift of each color pattern image with respect to the width direction (main scanning direction) of the intermediate transfer belt 21 until it moves to the detection area of ​​the toner detection sensor 116a. This makes it possible to detect the relative positional shift of each color with respect to the main scanning direction, i.e., color shift.

[0071] The control unit 150 (Figure 2) calculates an adjustment value for at least one image forming unit 10 that requires correction to reduce the color misalignment in the sub-scanning direction and the main scanning direction. Then, during subsequent image formation, this adjustment value is used to correct the image output position in at least one of the sub-scanning or main scanning directions for at least one image forming unit 10 that requires correction. This reduces the relative positional misalignment, i.e., color misalignment, of each color image when images of different colors are superimposed and transferred. For example, as explained with reference to Figure 6, if the yellow image is shifted Aμm behind the magenta image in the main scanning direction, the image output position of the magenta image should be corrected so that the magenta image is shifted Aμm behind. Specifically, in this embodiment, the output position (output timing) of the electrostatic image by the exposure device 3 on the photosensitive drum 1 in the image forming unit 10, i.e., the light irradiation position (light irradiation timing) on ​​the photosensitive drum 1 by the exposure device 3, is corrected. The amount by which this image output position (image output timing) is shifted corresponds to the adjustment value. In this embodiment, it is sufficient to correct the image output position (image output timing) in the main scanning direction at least to correct the color misalignment in the width direction (main scanning direction) of the intermediate transfer belt 21.

[0072] 6. Control Modes Figure 2 is a schematic block diagram showing the control configuration of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 is equipped with a control unit 150 as a control means. The control unit 150 is composed of a CPU 151 as a arithmetic control means, which is a central element for performing arithmetic processing; a storage unit (memory, storage medium) 152 such as ROM, RAM, and non-volatile memory as a storage means; and an interface unit 153. The RAM, which is a rewritable memory, stores information input to the control unit 150, detected information, and calculation results, while the ROM stores the control program and pre-determined data tables. The CPU 151 and the memory 152 can transfer and read data from each other. The interface unit 153 controls the input and output (communication) of signals between the control unit 150 and the devices connected thereto.

[0073] The control unit 150 is connected to various parts of the image forming apparatus 100 (image forming unit 10, intermediate transfer belt 21 and drive devices for components related to the transport of recording material P, various power supplies, etc.). For example, the control unit 150 is connected to the drum drive unit 111, laser scanner devices 3Y, 3M, 3C, 3K, belt drive unit 113, resist drive unit 114, etc. The control unit 150 is also connected to the offset mechanism 101, steering mechanism 62, toner detection unit 116, etc. Furthermore, the control unit 150 is connected to the operation unit (operation panel) 160 provided on the image forming apparatus 100. The operation unit 160 has a display unit as a display means for displaying information under the control of the control unit 150, and an input unit as an input means for inputting information to the control unit 150 through operation by an operator such as a user or service person. The operation unit 160 may be configured to have a touch panel that has the functions of a display unit and an input unit. Furthermore, the control unit 150 may be connected to an external device 200, such as an image reading device (not shown) provided in or connected to the image forming apparatus 100, or a personal computer connected to the image forming apparatus 100.

[0074] The control unit 150 controls each part of the image forming apparatus 100 based on the job information to perform image formation. The job information includes a start instruction (start signal) input from the operation unit 160 or external device 200, and information regarding image formation conditions such as the type of recording material P (command signal). The job information also includes image information (image signal) input from the image reader or external device 200. The information regarding the recording material (information regarding the type of recording material) includes attributes based on general characteristics such as plain paper, fine paper, glossy paper, coated paper, embossed paper, cardboard, thin paper, etc. (so-called paper type category), numerical values ​​or ranges of numerical values ​​such as basis weight, thickness, and rigidity, or brand name (including manufacturer, product name, part number, etc.), and any other information that can distinguish the recording material. Each recording material distinguished by the information regarding the recording material can be considered to constitute a type of recording material. Furthermore, information regarding the recording material may be included in or replaced by print mode information, which specifies the operating settings of the image forming apparatus 100, such as "plain paper mode," "thick paper mode," or "embossed paper mode."

[0075] Here, the image forming apparatus 100 executes a job, which is a series of operations that start with a single start instruction and form and output an image on one or more recording materials P. A job generally includes an image forming process, a pre-rotation process, an inter-paper process when forming an image on multiple recording materials P, and a post-rotation process. The image forming process is the period during which the electrostatic image, toner image, primary transfer, and secondary transfer of the toner image are performed for the image that will actually be formed and output on the recording materials P. The image forming time (image forming period) refers to this period. More specifically, the timing of the image forming time differs depending on the position where each of these processes—electrostatic image formation, toner image formation, primary transfer, and secondary transfer of the toner image—is performed. The pre-rotation process is the period during which preparatory operations are performed before the image forming process, from when a start instruction is input until the image is actually formed. The inter-paper process (inter-recording material process, inter-image process) is the period corresponding to the space between recording materials P when image forming is performed continuously on multiple recording materials P (continuous image forming). The post-rotation process is the period during which the image forming process is followed by a tidying operation (preparation operation). Non-image forming time (non-image forming period) refers to the period other than the image forming time, and includes the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation process, which is a preparatory operation when the image forming apparatus 100 is powered on or when it returns from sleep mode. Furthermore, non-image forming time includes the power-off state, sleep state, standby state, and the period from the standby state until the start of the pre-rotation process or pre-multi-rotation process. Note that the sleep state is a state in which, for example, power supply to each part of the image forming apparatus 100 other than the control unit 150 (or a part thereof) is stopped, and power consumption is reduced compared to the standby state. In this embodiment, the image forming apparatus 100 performs the operation to change the offset amount described above during non-image forming time.

[0076] 7. Control Procedure Next, the operation of the job in this embodiment will be described. Figure 9 is a flowchart showing an overview of the job procedure in this embodiment. As mentioned above, color misalignment may occur due to a change in the posture of the intermediate transfer belt 21 when the offset amount is changed. Therefore, in this embodiment, the image forming apparatus 100 performs color resist adjustment when the offset amount is changed. Here, a job using multiple types of recording material P with different basis weights (mixed load job) will be explained as an example. In this embodiment, the inner roller 26 (relative position between the inner roller 26 and the outer roller 41) is in the home position when the offset amount X is +2.5 mm. Therefore, for example, when starting a job from the sleep state of the image forming apparatus 100, the job operation, such as driving the intermediate transfer belt 21, starts from the state where the inner roller 26 is in the home position where the offset amount X is +2.5 mm.

[0077] When the control unit 150 receives a request to start a job, it starts driving the photosensitive drum 1 and the intermediate transfer belt 21, and determines, based on the job information, whether the basis weight of the recording material P on which the next image will be formed is 300 gsm or less (S101). If the control unit 150 determines in S101 that the basis weight is 300 gsm or less ("Yes"), it determines whether the current offset amount X is +2.5 mm (S102). If the control unit 150 determines in S102 that the current offset amount X is +2.5 mm ("Yes"), it performs image formation without changing the offset amount X (S103). After that, the control unit 150 determines whether all images for the job have been formed (S104). Then, if the control unit 150 determines in S104 that all images have been formed ("Yes"), it terminates the job operation, and if it determines that all images have not been formed ("Yes"), it returns to the process in S101.

[0078] Furthermore, if the control unit 150 determines in S101 that the basis weight is greater than 300 gsm ("No"), it determines whether the current offset amount X is +2.5 mm or not (S105). If the control unit 150 determines in S105 that the current offset amount X is +2.5 mm ("Yes"), it proceeds as follows: In order to accommodate the recording material P with a basis weight greater than 300 gsm, it moves the inner roller 26 using the offset mechanism 101 to change the offset amount X to -1.3 mm (S107). Next, since the offset amount X has been changed, the control unit 150 performs color resist adjustment (S108). Here, the control unit 150 waits for time to pass after changing the offset amount X (more specifically, after the position change of the inner roller 26 is completed) until the shifting behavior of the intermediate transfer belt 21 stabilizes, before starting color resist adjustment (more specifically, the formation of a pattern image on the intermediate transfer belt 21). In this case, color resist adjustment will be performed in the inter-paper process, but the duration of the inter-paper process will be extended as needed compared to the inter-paper process when color resist adjustment is not performed. After that, the control unit 150 performs image formation (S103). Subsequent operations are the same as described above. On the other hand, if the control unit 150 determines in S105 that the current offset amount X is -1.3 mm ("No"), it performs image formation without changing the offset amount X (S103). Subsequent operations are the same as described above.

[0079] Furthermore, if the control unit 150 determines in S102 that the current offset amount X is -1.3 mm ("No"), it proceeds as follows: In other words, to accommodate recording material P with a basis weight of 300 gsm or less, the control unit 150 moves the inner roller 26 using the offset mechanism 101 to change the offset amount X to +2.5 mm (S106). Next, since the offset amount X has been changed, the control unit 150 performs color resist adjustment (S108). Subsequent operations are the same as described above.

[0080] Thus, in this embodiment, when the offset amount X is changed while the image formation of a job is continuous, color resist adjustment is performed. On the other hand, when the image formation of a job is continuous and the same type of recording material (basis weight greater than or less than 300 gsm) is used to form an image, the offset amount X is not changed, and therefore, image formation is performed without color resist adjustment.

[0081] As described above, in this embodiment, the image forming apparatus 100 includes a plurality of image forming units 10 that form a toner image, a rotatable endless belt 21 on which the toner image is formed by the image forming units 10, a plurality of tension rollers that tension the belt 21, including an inner roller 26, an outer member 41 positioned opposite the inner roller 26 and forming a transfer unit N2 that contacts the outer circumferential surface of the belt 21 to transfer the toner image from the belt 21 to the recording material P, and a position changing mechanism 101 that can change the relative position between the inner roller 26 and the outer member 41 in the circumferential direction of the inner roller 26 by changing the position of at least one of the inner roller 26 or the outer member 41. The system includes a toner detection unit 116 that detects adjustment toner images for detecting the relative positional shift of toner images formed on the belt 21 by multiple image forming units 10, and a control unit 150 that can perform an adjustment operation to obtain an adjustment value for adjusting the image writing position in the width direction of the belt 21 in at least one of the multiple image forming units 10, based on the detection result of the adjustment toner image by the toner detection unit 116, wherein the control unit 150 can be controlled to perform the adjustment operation when the relative position is changed by the position change mechanism 101. In this embodiment, the control unit 150 can be controlled to perform the adjustment operation before forming a toner image to be transferred to a subsequent recording material P if the relative position is changed by the position change mechanism 101 after a toner image has been transferred to a preceding recording material P during the execution of a job to transfer toner images to multiple recording materials P. As will be explained in more detail in Example 3, the control unit 150 can perform the adjustment operation before forming the toner image to be transferred to the subsequent recording material P if, during the execution of a job to transfer toner images to multiple recording materials P, the relative position is changed by the position change mechanism 101 after the toner image has been transferred to the preceding recording material P, provided that predetermined conditions are met. If the predetermined conditions are not met, the control unit 150 can form the toner image to be transferred to the next recording material P without performing the adjustment operation.

[0082] 8. Effects of this embodiment As explained above, according to this embodiment, by adjusting the color resist in conjunction with the change in the offset amount, it is possible to suppress color shifts caused by changes in the orientation of the intermediate transfer belt 21. In other words, according to this embodiment, in a configuration in which the position (shape) of the secondary transfer section N2 can be changed, color shifts associated with such changes can be suppressed. As a result, according to this embodiment, color shifts can be suppressed while accommodating a wide range of recording materials P with different stiffnesses and other properties.

[0083] In this embodiment, we have described the case where two offset amounts can be used, but similar effects can be obtained in cases where three or more offset amounts can be used by adjusting the color resist after changing to each offset amount.

[0084] [Example 2] Next, other embodiments of the present invention will be described. In the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0085] 1. Overview of this embodiment To obtain sufficient transferability even for recording materials with uneven surfaces such as cardboard or embossed paper, a configuration is known in which a pressing member is provided near the upstream side of the secondary transfer section to press against the inner surface of the intermediate transfer belt. The pressing member improves transferability by ensuring close contact between the recording material and the intermediate transfer belt in the area where a strong electric field is applied near the secondary transfer section. Therefore, pressure is required to change the shape (position) of the intermediate transfer belt near the secondary transfer section in order to ensure close contact with the recording material. The presence or absence of contact by this pressing member, and changes in the contact force, can affect the tension state of the intermediate transfer belt, similar to the change in the offset amount in Example 1, which can result in color shifts.

[0086] 2. Configuration of the image forming apparatus Figure 10 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment has the same configuration as the image forming apparatus 100 of Embodiment 1 shown in Figure 1. However, in this embodiment, a pressing member 70 is provided on the inner circumferential surface side of the intermediate transfer belt 21, upstream of the inner roller 26 and downstream of the secondary transfer roller 29 with respect to the rotational direction of the intermediate transfer belt 21. The pressing member 70 contacts the inner circumferential surface of the intermediate transfer belt 21 and can press the intermediate transfer belt 21 from the inner circumferential surface side to the outer circumferential surface side. As a result, the pressing member 70 can cause the tensioned surface (tensioned surface) T (Figure 14) of the intermediate transfer belt 21, which is formed between the inner roller 26 and the secondary transfer roller 29, to protrude from the inner circumferential surface side to the outer circumferential surface side of the intermediate transfer belt 21. The pressing member 70 and the pressing mechanism 102 (Figure 14) for changing the position of the pressing member 70 will be described further later.

[0087] Figure 11 is a schematic block diagram showing the control configuration of the image forming apparatus 100 in this embodiment. The control configuration shown in Figure 11 is the same as that of Embodiment 1 shown in Figure 2. However, this embodiment differs from Embodiment 1 in that a pressing mechanism 102, which will be described later, is connected to the control unit 150.

[0088] 3.Amount of penetration Figure 12 is a schematic cross-sectional view (a cross-section approximately perpendicular to the rotation axis direction of the inner roller 26) illustrating the transport posture of the recording material P in the vicinity of the secondary transfer section (secondary transfer nip) N2. Note that Figure 12 shows a state in which the rotation center of the inner roller 26 and the rotation center of the outer roller 41 are positioned approximately at the same location with respect to the direction along the tension wire T.

[0089] As mentioned above, the rigidity of the recording material P changes the orientation of the recording material P as it is transported from the transport guide 27 to the secondary transfer section N2. For example, if the recording material P is "cardboard," a gap G is more likely to form between the intermediate transfer belt 21 and the recording material P near the entrance of the secondary transfer section N2, making "scattering" more likely to occur.

[0090] In other words, in Figure 12, the contact distance D is defined as the distance at which the intermediate transfer belt 21 and the recording material P are in contact along the direction of movement of the intermediate transfer belt 21 near the entrance of the secondary transfer section N2 (near the upstream of the inner roller 26 with respect to the rotation direction of the intermediate transfer belt 21). More specifically, the contact distance D is the distance between the contact start position between the inner roller 26 and the intermediate transfer belt 21 and the contact start position between the recording material P and the intermediate transfer belt 21, with respect to the direction of movement of the intermediate transfer belt 21. For example, if the recording material P is "cardboard", the contact distance D becomes smaller because the rigidity of the recording material P is large, making it difficult to bend near the entrance of the secondary transfer section N2. As a result, a gap G is created between the intermediate transfer belt 21 and the recording material P, and discharge occurs in that gap G due to the influence of the transfer electric field, causing the toner image to scatter and resulting in image defects ("scattering").

[0091] To address these issues, it is effective to provide a pressing member 70 that contacts the inner circumferential surface of the intermediate transfer belt 21 near the entrance of the secondary transfer section N2 and presses the intermediate transfer belt 21. By causing the tensioned surface T of the intermediate transfer belt 21 to protrude outward with the pressing member 70, the contact distance D can be increased, thereby reducing the gap G between the intermediate transfer belt 21 and the recording material P near the entrance of the secondary transfer section N2. This helps to suppress "scattering".

[0092] The amount of penetration (pressure) of the pressing member 70 into the intermediate transfer belt 21 will be described below. The amount of pressure applied by the pressing member 70 to the intermediate transfer belt 21 can be expressed as the amount of penetration of the pressing member 70 into the intermediate transfer belt 21 as follows. This penetration amount is roughly the amount by which the pressing member 70 causes the intermediate transfer belt 21 to protrude outward from the tensioned surface (tensioned surface) T of the intermediate transfer belt 21, which is formed by tensioning the intermediate transfer belt 21 with the inner roller 26 or outer roller 41 and the secondary transfer roller 29. The secondary transfer roller 29 is an example of an upstream roller among a plurality of tensioned rollers, which is positioned upstream of the inner roller 26 in the rotational direction of the intermediate transfer belt 21 and adjacent to the inner roller 26. More specifically, the definition of this penetration amount changes depending on the offset amount X, which indicates the relative position of the inner roller 26 and the outer roller 41 in the circumferential direction of the inner roller 26. The definition of the offset amount X is as described in Example 1.

[0093] Figures 13(a) and (b) are schematic cross-sectional views of the vicinity of the secondary transfer section N2 (a cross-section approximately perpendicular to the rotation axis direction of the inner roller 26) to explain the definition of the penetration amount Y of the pressing member 70 into the intermediate transfer belt 21. Note that the definition of the penetration amount Y differs depending on whether the offset amount X is positive or 0 or negative. Generally, the tension surface T of the intermediate transfer belt 21 when not pressed by the pressing member 70 is formed by the inner roller 26 and the pre-secondary transfer roller 29, or by the outer roller 41 and the pre-secondary transfer roller 29, which depends on the offset amount X. Figure 13(a) shows the case where the offset amount X is 0 or a negative value (especially a negative value), and Figure 13(b) shows the case where the offset amount X is a positive value.

[0094] First, we will explain the case where the offset amount X is 0 or a negative value. In the cross-section shown in Figure 13(a), the reference line L1 is defined as the common tangent between the inner roller 26 on the side around which the intermediate transfer belt 21 is wrapped and the secondary transfer roller 29. The reference line L1 corresponds to the tension line (tension surface) T of the intermediate transfer belt 21 when the intermediate transfer belt 21 is not extended outwards towards the outer surface by the pressing member 70. In the same cross-section, the pressing tangent L4 is defined as the tangent to the intermediate transfer belt 21 that contacts the outer surface of the intermediate transfer belt 21 in the region where the pressing member 70 contacts the intermediate transfer belt 21, and is approximately parallel to the reference line L1. In this case, when the offset amount X is 0 or a negative value, the distance (vertical distance) between the reference line L1 and the pressing tangent L4 is defined as the amount of penetration Y of the pressing member 70 into the intermediate transfer belt 21 (however, a positive value when the pressing tangent L4 is on the outer surface side of the intermediate transfer belt 21 than the reference line L1). This intrusion amount Y can take values ​​of 0 or positive values.

[0095] Next, we will explain the case where the offset amount X is a positive value. In the cross-section shown in Figure 13(b), the common tangent between the outer roller 41 on the side around which the intermediate transfer belt 21 is wrapped and the secondary transfer roller 29 is defined as the reference line L1'. Also, in the same cross-section, the tangent to the intermediate transfer belt 21 that contacts the outer circumferential surface of the intermediate transfer belt 21 in the region where the pressing member 70 contacts the intermediate transfer belt 21, which is approximately parallel to the reference line L1', is defined as the pressing portion tangent L4'. In this case, when the offset amount X is a positive value, the distance (vertical distance) between the reference line L1' and the pressing portion tangent L4' is defined as the penetration amount Y of the pressing member 70 into the intermediate transfer belt 21 (however, the value is positive when the pressing portion tangent L4' is on the outer circumferential surface side of the intermediate transfer belt 21 than the reference line L1'). This penetration amount Y can take values ​​of 0 or a positive value.

[0096] 4. Pressing member, pressing mechanism Next, the pressing member 70 and the pressing mechanism 102 for changing the position of the pressing member 70 in this embodiment will be described. Figures 14(a) and (b) are schematic cross-sectional side views of the main parts of the inner roller 26, viewed from one end side in the direction of the rotation axis of the inner roller 26 (the front side of the paper in Figure 10) and approximately parallel to the direction of the rotation axis, near the secondary transfer section N2 in this embodiment. Figure 14(a) shows the state in which the pressing member 70 presses the intermediate transfer belt 21 with a predetermined pressing force, and Figure 14(b) shows the state in which the pressing member 70 is separated from the intermediate transfer belt 21. Figures 14(a) and (b) show the configuration of one end of the inner roller 26 in the direction of the rotation axis, but the configuration of the other end is similar (approximately symmetrical with respect to the center in the direction of the rotation axis of the inner roller 26).

[0097] In this embodiment, the image forming apparatus 100 has a sheet-shaped pressing member (backup sheet) 70. The pressing member 70 can press the inner circumferential surface of the intermediate transfer belt 21 near the entrance of the secondary transfer section N2, causing the intermediate transfer belt 21 to protrude outwards. The pressing member 70 is positioned to contact the inner circumferential surface of the intermediate transfer belt 21 upstream of the inner roller 26 and downstream of the secondary transfer roller 29 with respect to the rotational direction of the intermediate transfer belt 21. In particular, in this embodiment, the pressing member 70 is positioned to contact the inner circumferential surface of the intermediate transfer belt 21 at a position upstream of the inner roller 26 and downstream of the downstream end of the transport guide 27 (first guide member 27a) with respect to the transport direction of the recording material P.

[0098] The pressing member 70 can be formed using a resin material. Suitable resin materials for forming the pressing member 70 include, for example, polyester resins such as PET resin. In this embodiment, the pressing member 70 is composed of a plate-shaped member having a predetermined length in a longitudinal direction (approximately parallel to the width direction of the intermediate transfer belt 21, and a predetermined thickness in a short direction (approximately perpendicular to the longitudinal direction)). The longitudinal length of the pressing member 70 is equivalent to the width direction of the intermediate transfer belt 21. The free end of the pressing member 70, which is one end in the short direction (the downstream end in the rotation direction of the intermediate transfer belt 21), can contact the inner circumferential surface of the intermediate transfer belt 21 over approximately its entire width, thereby enabling it to press the intermediate transfer belt 21. As an example, the thickness of the pressing member 70 is approximately 0.4 to 0.6 mm. In this embodiment, the pressing member 70 is an elastic body and is positioned to conform to the intermediate transfer belt 21 through elastic deformation.

[0099] Here, the pressing member 70 is, for example, an electrical resistance with medium resistance (for example, a volume resistivity of 1 × 10⁻⁶). 5 ~1 × 10 9 A PET resin sheet adjusted to Ω·cm can be used. This suppresses the flow of current through the pressing member 70 and also prevents the intermediate transfer belt 21 from being attracted to the pressing member 70 by static electricity (triboelectric charging) generated by friction between the pressing member 70 and the intermediate transfer belt 21, thereby preventing the rotation of the intermediate transfer belt 21 from being hindered.

[0100] Furthermore, the pressing member 70 is not limited to a sheet-like material made of resin. The pressing member 70 may be, for example, a sheet-like material made of a thin metal plate. Also, the pressing member 70 is not limited to a sheet-like material. The pressing member 70 may be, for example, an elastic material (such as a pad) such as sponge or rubber. Also, the pressing member 70 may be a rigid body such as a rotatable roller made of resin or metal. Furthermore, the pressing member 70 is not limited to being positioned at a predetermined location and in contact with the intermediate transfer belt 21 as in this embodiment. For example, when a rigid body such as the above-mentioned rotatable roller is used as the pressing member 70, the pressing member 70 may be biased toward the intermediate transfer belt 21 by a spring or the like as a biasing means.

[0101] In this embodiment, the image forming apparatus 100 has a pressing mechanism (pressure amount changing means) 102 as a position changing mechanism. The pressing mechanism 102 changes the position of the pressing member 70 to change at least one of the amount of penetration (pressure amount) of the pressing member 70 into the intermediate transfer belt 21, and the state of contact or separation of the pressing member 70 with the intermediate transfer belt 21. For simplicity, here it may be explained that changing the amount of penetration (pressure amount) of the pressing member 70 into the intermediate transfer belt 21 includes changing the state of contact or separation of the pressing member 70 with the intermediate transfer belt 21.

[0102] The pressing member 70 is supported by a pressing member holder 71, which acts as a support member. The pressing member 70 has a fixed end, which is one end in its shorter direction (the upstream end in the rotational direction of the intermediate transfer belt 21), fixed to the pressing member holder 71 over substantially its entire width in the longitudinal direction. The pressing member holder 71 is held by the frame of the intermediate transfer belt unit 20 or the like so that it can rotate around the pressing member pivot axis 71a. In this way, the position of the pressing member 70 can be changed by rotating the pressing member holder 71 around the pressing member pivot axis 71a and the pressing member 70 around the pressing member pivot axis 71a. This makes it possible to change at least one of the amount of penetration (pressure) of the pressing member 70 into the intermediate transfer belt 21 and the state of contact or separation of the pressing member 70 with the intermediate transfer belt 21.

[0103] The pressing member holder 71 is configured to rotate by the action of a pressing cam 73, which acts as an operating member. The pressing cam 73 is held by the frame of the intermediate transfer belt unit 20 or the like so that it can rotate around the pressing cam pivot axis 73a. The pressing cam 73 rotates around the pressing cam pivot axis 73a by receiving drive from a pressing motor (pressing cam drive motor) 75, which acts as a drive source. The pressing cam 73 is also in contact with a cam follower 71b provided on the pressing member holder 71. The pressing member holder 71 is also biased by a rotation spring 72, which is a biasing member (elastic member) such as a tension spring, so that the cam follower 71b rotates in a direction in which it engages with the pressing cam 73. In this embodiment, the image forming apparatus 100 is also provided with a pressing cam position sensor 74 as a position detection means for detecting the position of the pressing cam 73 in the rotation direction, and in this embodiment, the home position (HP) in the rotation direction. The pressing cam position sensor 74 can be configured, for example, with a pressing cam 73 or a flag as an indicator unit provided coaxially with the pressing cam 73, and an optical sensor (photointerrupter) as a detection unit.

[0104] As described above, in this embodiment, the pressing mechanism 102 is configured with a pressing member holder 71, a pressing cam 73, a pressing cam motor 75, a pressing cam position sensor 74, a rotating spring 72, and the like.

[0105] As shown in Figure 14(a), when the pressing member 70 presses the intermediate transfer belt 21, the pressing cam 73 is driven by the pressing cam motor 75 and rotates clockwise. As a result, the pressing member holder 71 rotates counterclockwise around the pressing member pivot axis 71a, and the pressing member 70 is positioned so that the amount of penetration of the pressing member 70 into the intermediate transfer belt 21 is a predetermined amount. At this time, the tip of the pressing member 70 contacts the inner circumferential surface of the intermediate transfer belt 21 near the entrance of the secondary transfer section N2, causing the intermediate transfer belt 21 to protrude outwards.

[0106] Furthermore, as shown in Figure 14(b), when the pressing member 70 is moved away from the intermediate transfer belt 21, the pressing cam 73 is driven by the pressing cam motor 75 and rotates counterclockwise. As a result, the pressing member holder 71 rotates clockwise around the pressing member pivot axis 71a, and the pressing member 70 is positioned so that it is separated from the intermediate transfer belt 21.

[0107] While not limited to this, the penetration amount Y is preferably 3.5 mm or less. If the penetration amount (pressure amount) is greater than this, the load on the contact surface between the pressing member 70 and the intermediate transfer belt 21 will increase, which may make it difficult for the intermediate transfer belt 21 to rotate smoothly. In addition, it is desirable to position the pressing member 70 as close as possible to the inner roller 26, but it is desirable to position it so that it does not come into contact with the inner roller 26. The pressing member 70 can be positioned such that the tip of the pressing member 70 comes into contact with the inner circumferential surface of the intermediate transfer belt 21 at a distance of, for example, about 2 mm or more, typically about 10 mm or more, upstream in the rotational direction of the intermediate transfer belt 21 from the position where the inner roller 26 and the intermediate transfer belt 21 come into contact. Furthermore, the pressing member 70 can be positioned such that the tip of the pressing member 70 contacts the inner circumferential surface of the intermediate transfer belt 21 at a distance of approximately 40 mm or less, typically 25 mm or less, upstream in the rotational direction of the intermediate transfer belt 21 from the position where the inner roller 26 and the intermediate transfer belt 21 come into contact. The penetration amount Y should be at a desired value when the recording material P is near the entrance of the secondary transfer section N2 and when it is passing through the secondary transfer section N2. More specifically, the area near the entrance of the secondary transfer section N2 corresponds to the region of the intermediate transfer belt 21 from the position where the pressing member 70 comes into contact with the intermediate transfer belt 21 to the secondary transfer section N2, with respect to the transport direction of the recording material P.

[0108] As described above, for example, if the recording material P is cardboard, the tip of the pressing member 70 can be brought into contact with the inner circumferential surface of the intermediate transfer belt 21 near the entrance of the secondary transfer section N2, causing the tension wire T to protrude outward. This increases the contact distance D between the intermediate transfer belt 21 and the recording material P near the entrance of the secondary transfer section N2, thereby suppressing scattered images.

[0109] Furthermore, as mentioned above, it is important to ensure that the intermediate transfer belt 21 is in close contact with the recording material P. Therefore, depending on the difference in stiffness and the depth of the irregularities, the shape of the secondary transfer section N2 can be changed, and the position of the pressing member 70 can be changed to increase the pressing force. Specifically, if the recording material P is ordinary paper (such as plain paper), the pressing member 70 can be placed in the first position, and if the recording material P is embossed paper, the pressing member 70 can be placed in the second position, where the penetration amount Y is increased compared to the penetration amount Y in the first position. In other words, when using a recording material P with irregularities on its surface, such as embossed paper, the transferability in the recesses (for example, 80-140 μm deep) may decrease. This is due to the following reason: In other words, during secondary transfer, gap discharge occurs in the recesses of the recording material P where the intermediate transfer belt 21 upstream of the secondary transfer section N2 and the recording material P are not in close contact. This discharge causes the toner on the intermediate transfer belt 21 before it enters the secondary transfer section N2 to become toner that is difficult to transfer in the secondary transfer. This can result in a scattered or fragmented image. In contrast, when using embossed paper, pressing the inner surface of the intermediate transfer belt 21 with the pressing member 70 causes the recording material P and the intermediate transfer belt 21 to adhere closely to a point upstream from the secondary transfer section N2. As a result, gap discharge in the recesses of the recording material P is suppressed, and the transfer performance is improved.

[0110] In this embodiment, the home position of the pressing member 70 is set to a position where the pressing member 70 is either separated from the intermediate transfer belt 21 or in contact with the intermediate transfer belt 21 with a penetration amount Y (e.g., 0 to 1 mm) smaller than that during image formation (secondary transfer). When the image forming apparatus 100 is in standby mode, power-off mode, or sleep mode, the pressing member 70 is positioned in the home position. When a job request is input to the control unit 150, it sets the pressing member 70 to a first position corresponding to plain paper (e.g., a position where the penetration amount Y is 1.5 mm) and starts driving the intermediate transfer belt 21. When transferring a toner image to embossed paper, the pressing member 70 is set to a second position (e.g., a penetration amount Y of 3.0 mm). The first position may be set to a position where the penetration amount is 0 mm (e.g., separated).

[0111] 5. Control Procedure Next, the operation of the job in this embodiment will be described. Figure 15 is a flowchart showing an overview of the job procedure in this embodiment. As mentioned above, color misalignment may occur due to a change in the position of the intermediate transfer belt 21 when the penetration amount of the pressing member 70 is changed. Therefore, in this embodiment, the image forming apparatus 100 performs color resist adjustment when the penetration amount of the pressing member 70 is changed. Here, a job in which embossed paper and recording materials other than embossed paper, such as plain paper, are used as recording material P (mixed job) will be described as an example. In this embodiment, for example, when starting a job from the sleep state of the image forming apparatus 100, the pressing member 70 is positioned to a first position corresponding to plain paper, etc. (for example, a position where the penetration amount Y is 1.5 mm) as described above, and then the driving of the intermediate transfer belt 21 is started.

[0112] When the control unit 150 receives a request to start a job, it starts driving the photosensitive drum 1 and the intermediate transfer belt 21, and determines whether the recording material P on which the image will be formed next is embossed paper or not based on the job information (S201). If the control unit 150 determines in S201 that it is not embossed paper ("Yes"), it determines whether the current position of the pressing member 70 is the first position corresponding to the first penetration amount (penetration amount "small") (S202). If the control unit 150 determines in S202 that the current position of the pressing member 70 is the first position ("Yes"), it performs image formation without changing the penetration amount Y (S203). After that, the control unit 150 determines whether all images for the job have been formed or not (S204). Then, if the control unit 150 determines in S204 that all image formation has been completed ("Yes"), it terminates the job operation, and if it determines that all image formation has not been completed ("Yes"), it returns to the process in S201.

[0113] Furthermore, if the control unit 150 determines in S201 that it is embossed paper ("No"), it determines whether the current position of the pressing member 70 is the first position corresponding to the first penetration amount (penetration amount "small") (S205). If the control unit 150 determines in S205 that the current position of the pressing member 70 is the first position ("Yes"), it proceeds as follows: In other words, in order to accommodate embossed paper, it moves the pressing member 70 using the pressing mechanism 102 to change the position of the pressing member 70 to the second position corresponding to the second penetration amount (penetration amount "large") (S207). Next, since the position of the pressing member 70 has been changed, the control unit 150 performs color resist adjustment (S208). Here, the control unit 150 changes the penetration amount Y (more specifically, from the time the position of the pressing member 70 is changed), waits for a sufficient amount of time to pass for the bending behavior of the intermediate transfer belt 21 to stabilize, and then starts color resist adjustment (more specifically, forming a pattern image on the intermediate transfer belt 21). After that, the control unit 150 performs image formation (S203). The subsequent operations are the same as described above. On the other hand, if the control unit 150 determines in S205 that the current position of the pressing member 70 is the second position corresponding to the second penetration amount (penetration amount "large") ("No"), it performs image formation without changing the penetration amount Y (S203). The subsequent operations are the same as described above.

[0114] Furthermore, if the control unit 150 determines in S202 that the current position of the pressing member 70 is the second position corresponding to the second penetration amount (penetration amount "large") ("No"), it proceeds as follows: In other words, in order to accommodate recording materials P other than embossed paper such as plain paper, the pressing mechanism 102 moves the pressing member 70 to change the position of the pressing member 70 to the first position corresponding to the first penetration amount (penetration amount "small") (S206). Next, since the position of the pressing member 70 has been changed, the control unit 150 performs color resist adjustment (S208). Subsequent operations are the same as described above.

[0115] Thus, since changing the penetration amount Y has the same effect as changing the offset amount X in Example 1, in this example, if the penetration amount Y is changed, color resist adjustment is performed.

[0116] As described above, in this embodiment, the image forming apparatus 100 includes a plurality of tension rollers for tensioning the belt 21, including an inner roller 26 and an upstream roller 29 positioned upstream of the inner roller 21 and adjacent to the inner roller 21 with respect to the rotational direction of the belt 21; a pressing member 70 that can contact the inner circumferential surface of the belt 21 upstream of the inner roller 21 and downstream of the upstream roller 29 with respect to the rotational direction of the belt 21, and can press the belt 21 from the inner circumferential surface side to the outer circumferential surface side; and a mechanism for changing the position of the pressing member 70. The system includes a position change mechanism 102 that can change at least one of the amount of pressure the pressing member 70 applies to the belt 21, and the state of contact or separation of the pressing member 70 from the belt 21, and a control unit 150 that can perform an adjustment operation to obtain an adjustment value for adjusting the image writing position in the width direction of the belt 21 in at least one of the multiple image forming units 10, based on the detection result of the adjustment toner image by the toner detection unit 116, which forms an adjustment toner image on the belt 21 using multiple image forming units 10. In this embodiment, the control unit 150 can be controlled to perform the above adjustment operation when the position of the pressing member 70 is changed by the position change mechanism 102. In this embodiment, the control unit 150 can be controlled to perform the above adjustment operation before forming a toner image to be transferred to a subsequent recording material P if the position of the pressing member 70 is changed by the position change mechanism 102 after the toner image has been transferred to a preceding recording material P while the job of transferring toner images to multiple recording materials P is being executed. As will be explained in detail in Example 3, during the execution of a job to transfer toner images to multiple recording materials P, if the position of the pressing member 70 is changed by the position changing mechanism 102 after the toner image has been transferred to the preceding recording material P, the control unit 150 can perform the above adjustment operation before forming the toner image to be transferred to the subsequent recording material P if predetermined conditions are met. If the above predetermined conditions are not met, the control unit 150 can form the toner image to be transferred to the next recording material P without performing the above adjustment operation.

[0117] 6. Effects of this embodiment As described above, in this embodiment, the change in the amount of penetration of the pressing member 70 corresponds to the change in the offset amount in Embodiment 1, and whether or not to make this change is determined by whether it is embossed paper or plain paper. However, the overall flow is the same as in Embodiment 1. According to this embodiment, in a configuration in which the shape (position) of the intermediate transfer belt 21 near the secondary transfer section N2 can be changed, color shift associated with this change can be suppressed. As a result, this embodiment can also suppress color shift while accommodating a wide range of recording materials P with different thicknesses (basis weights) and surface properties.

[0118] In this embodiment, the case where the penetration depth of the pressing member 70 is changed depending on whether it is embossed paper or plain paper was described as an example, but it is not limited to this. For example, the same judgment can be made when changing the penetration depth of the pressing member 70 according to the basis weight of the recording material P, and when the penetration depth is changed, it is possible to suppress color shift by performing color resist adjustment.

[0119] Furthermore, although this embodiment describes a case where the amount of penetration during image formation (secondary transfer) can be changed to two amounts, similar effects can be obtained in cases where it is possible to change to three or more amounts by adjusting the color resist after changing to each amount.

[0120] In addition to changing the offset amount in Example 1, the shape of the intermediate transfer belt 21 near the secondary transfer section N2 may be further changed by the pressing member 70 in order to obtain sufficient transferability even on recording materials P with uneven surfaces such as embossed paper. In other words, the image forming apparatus 100 may have both the offset mechanism 101 in Example 1 and the pressing mechanism 102 in this embodiment. If the offset amount and the penetration amount are changed synchronously at the same timing (e.g., between the same sheets of paper), similar control can be performed according to the procedure of Example 1 or this embodiment. Also, if only one of the offset amount or the penetration amount is changed at a single timing (e.g., between the same sheets of paper), similar control can be performed according to the procedure of Example 1 or this embodiment, respectively.

[0121] For example, the aforementioned "scattering" that occurs when the recording material P has high rigidity (high thickness), and image defects at the leading and trailing ends of the recording material P ("shock images") can be effectively suppressed by placing a pressing member 70 upstream of the secondary transfer section N2 with respect to the rotational direction of the intermediate transfer belt 21, thereby causing the intermediate transfer belt 21 to protrude outward. Therefore, when the offset amount X is changed to be smaller when the rigidity (high thickness) of the recording material P is high, it is desirable to synchronize the pressing member 70 with the adjustment to protrude the intermediate transfer belt 21 outward. On the other hand, for example, if the rigidity (thickness) of the recording material P is low, and the offset amount X is increased, and the intermediate transfer belt 21 is protruded towards the outer circumferential surface by the pressing member 70, the following occurs. In other words, the contact distance D becomes too large, and image defects, so-called "roughness" (or "torn image misalignment"), may occur due to the friction between the toner image on the intermediate transfer belt 21 and the recording material P, causing the toner image to be mechanically disturbed. Therefore, if the offset amount X is significantly changed by changing the position of at least one of the inner roller 26 or the outer roller 41 (in this embodiment, the position of the inner roller 26), the position of the pressing member 70 can be changed in synchronously to change the penetration amount Y so that the penetration amount Y becomes smaller. Note that changing the offset amount X and the penetration amount Y in synchronously means the following: Typically, when forming an image on a recording material P, if the offset amount X is changed before the recording material P reaches the secondary transfer section N2, then the penetration amount Y is also changed before the recording material P reaches the secondary transfer section N2.

[0122] Furthermore, in this embodiment, the pressing member 70 can be separated from the inner circumferential surface of the intermediate transfer belt 21, but it is not limited to this. When the penetration amount Y is 0 mm, the pressing member 70 may be in contact with the intermediate transfer belt 21. Alternatively, the penetration amount Y can be changed to a different state, and the configuration may be such that the penetration amount Y does not take the value of 0.

[0123] [Example 3] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0124] 1. Overview of this embodiment In Example 1, color shift was suppressed by performing a color resist adjustment each time the offset amount was changed. However, depending on how the user uses the system, it may be necessary to frequently mix different types of recording materials that require changes in the offset amount when forming images. In that case, the control in Example 1 would require frequent color resist adjustments. At this time, in addition to changing the offset amount, performing a color resist adjustment each time can lead to a decrease in productivity. Therefore, this embodiment provides a control system that suppresses color shift while minimizing the decrease in productivity.

[0125] 2. Conditions for performing color resist adjustment As explained above, color resist adjustment needs to be performed by changing the orientation of the intermediate transfer belt. In addition, the image forming apparatus may be set to perform color resist adjustment when the number of images formed reaches a predetermined number, or when the internal temperature of the image forming apparatus changes by more than a predetermined temperature. In other words, color resist adjustment is sometimes performed to compensate for the thermal deformation of each component during the process of superimposing the toner image from exposure, caused by the heat generated by repeated image formation. Generally, the biggest change is due to the thermal deformation of the lens inside the exposure apparatus that forms the latent image on the photoreceptor, and depending on the configuration of the image forming apparatus, color resist adjustment may be performed as often as once every few minutes. However, color resist adjustment is not performed between every sheets of paper, but is generally performed when the number of images formed satisfies predetermined conditions, or when the temperature of a separately installed thermistor satisfies predetermined conditions. The thermistor mentioned above is an example of an environmental sensing means that detects at least one of the temperature or humidity inside or outside the image forming apparatus. Thus, color resist adjustment can be broadly divided into two types: those performed periodically and those performed in response to certain changes. This section explains the adjustments required for each color resist.

[0126] The periodic color resist adjustment addresses changes over time due to thermal deformation, as described above. The color resist adjustment value is performed each time the number of images formed or the internal temperature of the image forming apparatus meets predetermined conditions. As shown in Figure 2, when a color resist adjustment is performed, the adjustment value is stored in the storage unit 152. The adjustment value stored in the storage unit 152 is used until the next color resist adjustment is performed, but when a new color resist adjustment is performed, the adjustment value is overwritten with the new value.

[0127] Furthermore, in this embodiment, as shown in Figure 2, the number of memory units (storage areas) corresponding to the number of possible offset amounts is used to store the adjustment values ​​for color resist adjustment. In this embodiment, since there are two possible offset amounts, two memory units 152a and 152b are used. The adjustment value of the color resist adjustment performed when the offset amount X is the first offset amount X1, which is +2.5 mm, is stored in the first memory unit 152a. The adjustment value of the color resist adjustment performed when the offset amount X is the second offset amount X2, which is -1.3 mm, is stored in the second memory unit 152b. When a new color resist adjustment is performed with the corresponding offset amount X, the adjustment values ​​stored in the first and second memory units 152a and 152b are updated (overwritten) with the newly acquired adjustment values.

[0128] Here, when changing from a predetermined offset amount to another predetermined offset amount, the effect of that change on color shift is uniquely determined, provided that it is not accompanied by the aforementioned changes due to thermal deformation over time. Therefore, if the offset amount is changed and a color shift occurs, the color shift will be eliminated when the offset amount is returned to its original value. At least during the intervals between the periodic color resist adjustments mentioned above, the effect of thermal deformation is small and can be considered a reversible change.

[0129] Based on these considerations, in this embodiment, in order to suppress the occurrence of color misalignment while suppressing the decrease in productivity which can be a problem depending on how the user uses the system, for example, the following control is implemented.

[0130] 3. Control Procedure Next, the operation of the job in this embodiment will be described. Figure 16 is a flowchart showing an overview of the job procedure in this embodiment. Here, a job using multiple types of recording materials P with different basis weights (a mixed-load job) will be described as an example. Similar to Embodiment 1, the home position is when the offset amount X is +2.5 mm, and for example, when starting a job from a sleep state, the job operation, such as driving the intermediate transfer belt 21, will start from the offset amount X +2.5 mm. Note that in the procedure in Figure 16, the explanation of processes that are the same as those in the procedure in Figure 9 described in Embodiment 1 will be omitted as appropriate.

[0131] The processes S301 to S307 in Figure 16 are the same as the processes S101 to S107 in Figure 9 in Embodiment 1. In this embodiment, after changing the offset amount X in S306 or S307, the control unit 150 stores the adjustment value for the changed offset amount X in the previous storage unit 152, and then determines whether a periodic color resist adjustment has been performed (S308). If a periodic color resist adjustment has not been performed, the effect of thermal deformation is considered to be small as described above, so the adjustment value obtained in the previous color resist adjustment performed can be used for the changed offset amount X. In this case, if the changed offset amount X is the first offset amount X1 (+2.5 mm), the adjustment value previously stored in the first storage unit 152a can be used. Also, if the changed offset amount X is the second offset amount X2 (-1.3 mm), the adjustment value previously stored in the second storage unit 152a can be used. Therefore, if the control unit 150 determines in S308 that periodic color resist adjustment has not been performed ("Yes"), it will not perform color resist adjustment and will use the adjustment value obtained in the previous color resist adjustment (S309). On the other hand, if the control unit 150 determines in S308 that periodic color resist adjustment has been performed ("No"), it will perform color resist adjustment considering the effects of thermal deformation (S310). The subsequent operations are the same as in Example 1.

[0132] For example, first, a color resist adjustment is performed with an offset amount X of +2.5mm, and the adjustment value obtained at that time is stored in the first storage unit 152a as the adjustment value for offset amount X = +2.5mm. Subsequently, when a color resist adjustment is performed due to a change in the offset amount X to -1.3mm, the obtained adjustment value is stored in the second storage unit 152b as the adjustment value for offset amount X = -1.3mm. If it becomes necessary to return the offset amount X to +2.5mm again in this state, the following procedure is followed. In other words, if no periodic color resist adjustment has been performed since the last color resist adjustment when the offset amount X was +2.5mm, the adjustment value stored in the first storage unit 152a can be used as is when returning the offset amount X to +2.5mm. This eliminates the need to perform a color resist adjustment. Conversely, if periodic color resist adjustments are performed, the adjustment value for the previous offset amount X = +2.5 mm stored in the first memory unit 152a is discarded to account for the effects of thermal deformation, and the color resist adjustment is performed. The adjustment value stored in the first memory unit 152a is then updated with the newly acquired adjustment value obtained from that color resist adjustment.

[0133] For simplicity's sake, the explanation above has been omitted, but in S308, the control unit 150 also determines whether or not the adjustment value is stored in the first and second storage units 152a and 152b. If the previous adjustment value for the offset amount X after the current change is not stored, the control unit 150 controls the process to proceed to S310 and perform the color resist adjustment, even if the conditions for using the previous adjustment value as described above exist.

[0134] Here, for example, in the pre-rotation or pre-multi-rotation process of a job, color resist adjustment can be performed with at least one offset amount X (e.g., the offset amount X at the start of the job, such as the home position), and the adjustment value can be stored in the storage unit 152. In the pre-rotation or pre-multi-rotation process of a job, color resist adjustment can be performed with multiple (e.g., all possible) offset amounts X, and each adjustment value can be stored in the storage unit 152. Furthermore, the adjustment values ​​stored in the storage unit 152 that are available for use in the job are not limited to adjustment values ​​obtained during the execution of the job (between sheets) or in the pre-rotation or pre-multi-rotation process of the job. They may also be adjustment values ​​obtained during the execution of a previous job (between sheets), or in the pre-rotation or pre-multi-rotation process of a previous job, or even during color resist adjustment performed at the time of factory shipment of the image forming apparatus 100, the first adjustment after installation, or during the current or previous power-on. In addition, even if adjustment values ​​are not obtained in advance, if the above-mentioned periodic color resist is performed during the execution of the job, the adjustment value for the offset amount at that time will be obtained.

[0135] As described above, in this embodiment, the image forming apparatus 100 has a first storage unit 152a that stores a first adjustment value acquired by the control unit 150 when the relative position between the inner roller 26 and the outer member 41 in the circumferential direction of the inner roller 26 is a first relative position, and a second storage unit 152b that stores a second adjustment value acquired by the control unit 150 when the relative position is a second relative position different from the first relative position. The control unit 150 can be controlled to adjust the image writing position using the first adjustment value stored in the first storage unit 152a when forming a toner image with the relative position as the first relative position, and to adjust the image writing position using the second adjustment value stored in the second storage unit 152b when forming a toner image with the relative position as the second relative position. In this embodiment, if the relative position has changed from the first relative position to the second relative position and then returned to the first relative position, and a predetermined condition is met, the control unit 150 controls the system to perform an adjustment operation before forming the toner image to be transferred to the recording material P next, thereby updating the first adjustment value stored in the first storage unit 152a. In this embodiment, the predetermined condition is that an adjustment operation, which is performed periodically regardless of the relative position, has been executed between the time the first adjustment value was previously stored in the first storage unit 152a and the time the relative position returned to the first relative position. Furthermore, in this embodiment, if the relative position has changed from the first relative position to the second relative position and then returned to the first relative position, and the predetermined condition is not met, the control unit 150 forms the toner image to be transferred to the recording material P next without performing the adjustment operation. Furthermore, in this embodiment, if the relative position is changed from the second relative position to the first relative position and then returned to the second relative position, and a predetermined condition is met, the control unit 150 controls the system to perform an adjustment operation before forming the toner image to be transferred to the recording material P next, and to update the second adjustment value stored in the second storage unit 152b. In this embodiment, the predetermined condition is that an adjustment operation, which is performed periodically regardless of the relative position, has been executed between the time the second adjustment value was last stored in the second storage unit 152b and the time the relative position is returned to the second relative position.

[0136] 4. Effects of this embodiment As described above, according to this embodiment, if available, the need to perform color resist adjustment is eliminated by using the previous adjustment value stored in the memory unit 152. Therefore, even if, for example, depending on how the user uses the system, the control in Embodiment 1 requires frequent adjustment of the offset amount, it is possible to suppress the occurrence of color misalignment while suppressing a decrease in productivity.

[0137] Furthermore, in this embodiment, it is assumed that thermal deformation cannot be said to have no effect on the orientation of the intermediate transfer belt 21, and therefore, the presence or absence of periodic color resist adjustments is used as a criterion for determining whether the previous adjustment value can be used. However, it is conceivable that the thermal effect on the change in the orientation of the intermediate transfer belt 21 due to the change in the offset amount may be sufficiently small and always be considered to be a reversible change. In this case, for example, the adjustment values ​​for color resist adjustment at each offset amount can be acquired and stored in advance, or the change in the orientation of the intermediate transfer belt 21 due to the change in the offset amount can be stored. Then, by using this information, it is possible to correct color misalignment without performing any color resist adjustments depending on the change in the offset amount.

[0138] In this embodiment, the condition for using the previous adjustment value is that periodic color resist adjustment has not been performed. However, more directly, the conditions could also be that the number of images formed has not reached a predetermined number, or that the internal temperature of the image forming apparatus has not changed by more than a predetermined temperature. For example, in S308 of Figure 16, after storing the previous adjustment value in the previous storage unit 152 for the changed offset amount X, it is determined whether the number of images formed has reached a predetermined number, or whether the internal temperature of the image forming apparatus has changed by more than a predetermined temperature. If the number of images formed has not reached a predetermined number, or if the internal temperature of the image forming apparatus has not changed by more than a predetermined temperature, the previous adjustment value can be used to avoid performing color resist adjustment. In this way, any conditions can be used as appropriate, as long as the effect of the change in offset amount on the change in the attitude of the intermediate transfer belt 21 is sufficiently small and it can be determined that the change is reversible.

[0139] Furthermore, although this embodiment was described based on a change in the offset amount, similar to Embodiment 1, the principle of this embodiment can also be applied to a change in the position (penetration amount) of the pressing member 70, as described in Embodiment 2, instead of a change in the offset amount, and the same effects as described above can be obtained. For a detailed explanation of this case, refer to the explanation of this embodiment by replacing the change in the offset amount with a change in the position (penetration amount) of the pressing member 70.

[0140] [Example 4] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0141] 1. Overview of this embodiment In Example 3, it was assumed that the change in the orientation of the intermediate transfer belt 21 due to the change in the offset amount would be affected by thermal deformation. However, if the change in the orientation of the intermediate transfer belt 21 is not affected by thermal deformation, it is possible to reduce the frequency of color resist adjustment by storing the difference in the adjustment value of the color resist before and after the change in orientation.

[0142] 2. Control Overview When adjustment values ​​for color resist adjustment are obtained for both the +2.5mm offset X state and the -1.3mm offset X state, the difference value is calculated and stored in the memory unit 152. For example, until the adjustment values ​​for each offset X state are obtained and the difference value is calculated, each adjustment value may be stored in the memory units 152a and 152b respectively, as in Example 3. Once the difference value is calculated, color misalignment correction can be performed using this difference value. This eliminates the need to perform color resist adjustment even if the posture of the intermediate transfer belt 21 changes due to a change in the offset X.

[0143] The adjustment values ​​for color resist adjustment at each offset amount X can be obtained by performing color resist adjustment in advance, or by performing color resist adjustment when each offset amount X is used for the first time. For example, as mentioned above, in the previous rotation process or previous multi-rotation process of a job, color resist adjustment can be performed at at least one offset amount X (e.g., the offset amount X at the start of the job, such as the home position), and the adjustment values ​​can be stored in the storage unit 152. In the previous rotation process or previous multi-rotation process of a job, color resist adjustment can be performed at multiple (e.g., all possible) offset amounts X, and the respective adjustment values ​​can be stored in the storage unit 152. Furthermore, the adjustment values ​​stored in the storage unit 152 that are available for use in the job are not limited to adjustment values ​​obtained during the execution of the job (between pages) or in the previous rotation process or previous multi-rotation process of the job. They may also be adjustment values ​​obtained in color resist adjustments performed during the execution of a previous job (between pages), in the previous rotation process or previous multi-rotation process of a previous job, or even at the time of factory shipment of the image forming apparatus 100, the first adjustment after installation, or at the time of power-on in the current or previous job. Furthermore, even if adjustment values ​​are not obtained in advance, if the aforementioned periodic color resist is performed during job execution, adjustment values ​​for the offset amount at that time will be obtained. In other words, it is possible to use the difference value after the adjustment value for each offset amount X has been obtained. Until the difference value becomes available, the control can be the same as in Example 1.

[0144] 3. Control Procedure Next, the operation of the job in this embodiment will be described. Figure 17 is a flowchart showing an overview of the job procedure in this embodiment. Here, the procedure is shown from the point where each offset amount X, which is a characteristic of this embodiment, is acquired. In the procedure in Figure 17, the explanation of the same process as in the procedure in Figure 9 described in Embodiment 1 will be omitted as appropriate.

[0145] The processes S401 to S707 in Figure 17 are the same as the processes S101 to S107 in Figure 9 in Embodiment 1. In this embodiment, after changing the offset amount X in S406 or S407, the control unit 150 performs color shift correction as follows (S408). That is, the difference between the adjustment value of the color resist adjustment performed when the offset amount X is +2.5 mm and the adjustment value of the color resist adjustment performed when the offset amount X is -1.3 mm is used as the correction value to adjust the image writing position (image writing timing) at the changed offset amount X. This difference value is stored in the storage unit 152 as described above. The subsequent operations are the same as in Embodiment 1.

[0146] For example, when the offset amount is changed from the first offset amount X1 to the second offset amount X2, color shift correction is performed by delaying the image writing timing in the main scanning direction by the absolute value of the difference. In this case, when the offset amount is changed from the second offset amount X2 to the first offset amount X1, color shift correction can be performed by advancing the image writing timing in the main scanning direction by the absolute value of the difference. It is also possible to store both the difference value including positive and negative signs when changing from the first offset amount X1 to the second offset amount X2, and the difference value including positive and negative signs when changing from the second offset amount X2 to the first offset amount X1.

[0147] As described above, in this embodiment, the image forming apparatus 100 has a storage unit 152 that stores the difference between a first adjustment value obtained by the control unit 150 when the relative position between the inner roller 26 and the outer member 41 in the circumferential direction of the inner roller 26 is a first relative position, and a second adjustment value obtained by the control unit 150 when the relative position is a second relative position different from the first relative position. The control unit 150 can be controlled to adjust the image writing position using the difference value stored in the storage unit 152 when forming a toner image after changing the relative position from the first relative position to the second relative position, and when forming a toner image after changing the relative position from the second relative position to the first relative position.

[0148] 4. Effects of this embodiment As explained above, in cases where, for example, the change in the posture of the intermediate transfer belt 21 is not affected by thermal deformation, the control of this embodiment makes it possible to suppress color misalignment without performing color resist adjustment.

[0149] Furthermore, although this embodiment was described based on a change in the offset amount, similar to Embodiment 1, the principle of this embodiment can also be applied to a change in the position (penetration amount) of the pressing member 70, as described in Embodiment 2, instead of a change in the offset amount, and the same effects as described above can be obtained. For a detailed explanation of this case, refer to the explanation of this embodiment by replacing the change in the offset amount with a change in the position (penetration amount) of the pressing member 70.

[0150] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the embodiments described above.

[0151] In the above-described embodiment, the basis weight input to the operating unit was obtained as information regarding the thickness of the recording material, but the present invention is not limited to this embodiment. For example, it is also possible to provide a detection means for detecting the thickness of the recording material within the image forming apparatus and perform control based on the information of the recording material thickness detected by this detection means. For example, a sensor that utilizes ultrasonic attenuation is known as a detection means for detecting an index value correlated with the basis weight and thickness of the recording material. It should be noted that any means capable of detecting an index value correlated with the basis weight and thickness of the recording material is not limited to those using ultrasound, and for example, those using light can also be used.

[0152] Furthermore, in the above-described embodiment, information regarding the surface properties of the recording material was obtained by inputting information about the type of recording material at the operation unit, but the present invention is not limited to this embodiment. For example, it is also possible to make numerical information of the surface roughness of the recording material input from the operation unit and perform control based on the acquired numerical information of surface roughness. It is also possible to provide a detection means for detecting the surface roughness of the recording material within the image forming apparatus and perform control based on the surface roughness information of the recording material detected by this detection means. For example, as a detection means for detecting an index value correlated with the surface properties of the recording material, a specular and diffuse reflected light sensor is known, which irradiates the recording material with light and reads the intensity of specular reflected light and diffuse reflected light with a light intensity sensor. It should be noted that as long as it can detect an index value correlated with the smoothness of the surface of the recording material, it is not limited to the above-described light intensity sensor, and for example, a device using an image sensor can also be used. The index value correlated with the smoothness of the surface of the recording material is not limited to a value converted to a value that conforms to a predetermined standard such as Beck smoothness, but can be any value that correlates with the smoothness of the surface of the recording material.

[0153] Furthermore, as in the above-described embodiment, when inputting information about the recording material (information about thickness and surface properties) from the operating unit, it is not limited to directly inputting information about the recording material from the operating unit (including selecting from multiple options). For example, by selecting a predetermined final density of recording material from multiple recording material storage units, information about the recording material stored in the recording material storage unit, which is pre-associated with the recording material storage unit and stored in the storage unit, may be obtained.

[0154] Furthermore, information such as information regarding recording materials is not limited to being input from the operating unit of the image forming apparatus. This information may also be input from an external device that is communicatively connected to the image forming apparatus. In this case, the aforementioned interface unit (input / output circuit), etc., functions as an input unit for inputting information to the control unit.

[0155] Furthermore, in the above-described embodiment, the image forming apparatus was configured to change the offset amount by changing the position of the inner roller, but it may also be configured to change the offset amount by changing the position of the outer roller. Moreover, the configuration is not limited to moving either the inner roller or the outer roller, but may be configured to change the offset amount by moving both the inner roller and the outer roller.

[0156] Furthermore, in the above-described embodiment, an outer roller that directly contacts the outer circumferential surface of the intermediate transfer belt was used as an outer member that forms the secondary transfer portion together with the inner roller as an inner member. In contrast, the configuration may use an outer roller and a secondary transfer belt stretched between the outer roller and other rollers as the outer member. In other words, the image forming apparatus may have a tension roller, an outer roller, and a secondary transfer belt stretched between these rollers as the outer members. The outer roller can then contact the outer circumferential surface of the intermediate transfer belt via the secondary transfer belt. In such a configuration, the secondary transfer portion is formed by sandwiching the intermediate transfer belt and the secondary transfer belt between the inner roller that contacts the inner circumferential surface of the intermediate transfer belt and the outer roller that contacts the inner circumferential surface of the secondary transfer belt. In this case, the contact portion between the intermediate transfer belt and the secondary transfer belt is the secondary transfer portion (secondary transfer nip). In this case as well, the offset amount X is defined by the relative position of the inner roller and the outer roller, as described above. Furthermore, the penetration amount Y is defined in the same manner as described above, using the reference line L1 and the tangent line L4 of the pressing portion formed by the inner roller and the roller before secondary transfer, or the reference line L1' and the tangent line L4' of the pressing portion formed by the outer roller and the roller before secondary transfer.

[0157] Furthermore, in the above-described embodiments, actuators that operate the movable part using a cam were used as the offset mechanism and the pressing mechanism, but the invention is not limited to this. The offset mechanism and the pressing mechanism can be any mechanism that can achieve the same operation as in the above-described embodiments, and for example, actuators that operate the movable part using a solenoid may be used.

[0158] Furthermore, although the above-described embodiment described a case where the belt-shaped image carrier is an intermediate transfer belt, the present invention can be applied to any image carrier composed of an endless belt that transports the toner image carried at the image formation position. Examples of such belt-shaped image carriers include, in addition to the intermediate transfer belt in the above-described embodiment, a photoreceptor belt and an electrostatic recording dielectric belt.

[0159] Furthermore, the present invention can also be implemented in other embodiments in which some or all of the configurations of the above-described embodiments are replaced with alternative configurations. Therefore, as long as the image forming apparatus uses a belt-shaped image carrier, it can be implemented regardless of whether it is a tandem type / single-drum type, a charging method, an electrostatic image forming method, a developing method, a transfer method, or a fixing method. In the above-described embodiments, the main parts related to the formation / transfer of toner images have been explained, but the present invention can be implemented in various applications such as printers, various printing machines, copiers, fax machines, and multifunction devices by adding the necessary equipment, equipment, and housing structures. [Explanation of Symbols]

[0160] 21 Intermediate transfer belt 26 Secondary transfer inner roller 29 Secondary transfer roller 41 Secondary transfer outer roller 62 Steering mechanism 70 Pressing member 100 Image forming apparatus 101 Offset mechanism 102 Pressing mechanism

Claims

1. Multiple image forming units that form a toner image, A rotatable, endless belt on which a toner image is formed by the image forming unit, A plurality of tension rollers for tensioning the belt, comprising a plurality of tension rollers including an inner roller, An outer member is positioned opposite the inner roller and forms a transfer section that contacts the outer surface of the belt to transfer a toner image from the belt to the recording material, A position changing mechanism that can change the relative position between the inner roller and the outer member in the circumferential direction by changing the position of at least one of the inner roller or the outer member, A toner detection unit that detects an adjustment toner image for detecting the relative positional shift of the toner image formed on the belt by the plurality of image forming units, A control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units, and to obtain an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit, It has, The image forming apparatus is characterized in that the control unit can be controlled to execute the adjustment operation when the relative position is changed by the position changing mechanism.

2. The image forming apparatus according to claim 1, characterized in that the control unit can be controlled to perform the adjustment operation before forming a toner image to be transferred to a subsequent recording material if the relative position is changed by the position changing mechanism after the toner image has been transferred to a preceding recording material while the job of transferring a toner image to a plurality of recording materials is being executed.

3. The image forming apparatus according to claim 2, characterized in that, during the execution of a job to transfer toner images to a plurality of recording materials, if the relative position is changed by the position changing mechanism after the toner image has been transferred to the preceding recording material, and if predetermined conditions are met, the control unit performs the adjustment operation before forming the toner image to be transferred to the subsequent recording material.

4. The image forming apparatus according to claim 3, characterized in that, during the execution of a job to transfer toner images to a plurality of recording materials, if the relative position is changed by the position changing mechanism after the toner image has been transferred to the preceding recording material, and the predetermined conditions are not met, the control unit forms the toner image to be transferred to the next recording material without performing the adjustment operation.

5. Multiple image forming units that form a toner image, A rotatable, endless belt on which a toner image is formed by the image forming unit, A plurality of tension rollers for tensioning the belt, comprising a plurality of tension rollers including an inner roller, An outer member is positioned opposite the inner roller and forms a transfer section that contacts the outer surface of the belt to transfer a toner image from the belt to the recording material, A position changing mechanism that can change the relative position between the inner roller and the outer member in the circumferential direction by changing the position of at least one of the inner roller or the outer member, A toner detection unit that detects an adjustment toner image for detecting the relative positional shift of the toner image formed on the belt by the plurality of image forming units, A control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units, and to obtain an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit, A first storage unit that stores a first adjustment value obtained by the control unit when the relative position is the first relative position, A second storage unit that stores a second adjustment value obtained by the control unit when the relative position is a second relative position different from the first relative position, It has, The control unit is capable of adjusting the image writing position using the first adjustment value stored in the first storage unit when forming a toner image with the relative position as the first relative position, and adjusting the image writing position using the second adjustment value stored in the second storage unit when forming a toner image with the relative position as the second relative position.

6. The image forming apparatus according to claim 5, characterized in that, when the relative position has been changed from the first relative position to the second relative position and then returned to the first relative position, and a predetermined condition is met, the control unit controls the operation to update the first adjustment value stored in the first storage unit by performing the adjustment operation before forming the toner image to be transferred to the recording material next.

7. The image forming apparatus according to claim 6, characterized in that the predetermined condition is that the adjustment operation, which is performed periodically regardless of the relative position, is executed between the time the first adjustment value is previously stored in the first storage unit and the time the relative position is returned to the first relative position.

8. The image forming apparatus according to claim 6, characterized in that, when the relative position is changed from the first relative position to the second relative position and then returned to the first relative position, and the predetermined conditions are not met, the control unit forms the toner image to be transferred to the recording material next without performing the adjustment operation.

9. The image forming apparatus according to claim 5, characterized in that the control unit controls the adjustment operation to update the second adjustment value stored in the second storage unit when the relative position has been changed from the second relative position to the first relative position and then returned to the second relative position, provided that predetermined conditions are met, before forming the toner image to be transferred to the recording material next.

10. The image forming apparatus according to claim 9, characterized in that the predetermined condition is that the adjustment operation, which is performed periodically regardless of the relative position, is executed between the time the second adjustment value is previously stored in the second storage unit and the time the relative position is returned to the second relative position.

11. Multiple image forming units that form a toner image, A rotatable, endless belt on which a toner image is formed by the image forming unit, A plurality of tension rollers for tensioning the belt, comprising a plurality of tension rollers including an inner roller, An outer member is positioned opposite the inner roller and forms a transfer section that contacts the outer surface of the belt to transfer a toner image from the belt to the recording material, A position changing mechanism that can change the relative position between the inner roller and the outer member in the circumferential direction by changing the position of at least one of the inner roller or the outer member, A toner detection unit that detects an adjustment toner image for detecting the relative positional shift of the toner image formed on the belt by the plurality of image forming units, A control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units, and to obtain an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit, A storage unit that stores the difference between a first adjustment value obtained by the control unit when the relative position is a first relative position and a second adjustment value obtained by the control unit when the relative position is a second relative position different from the first relative position. It has, The image forming apparatus is characterized in that the control unit can control the adjustment of the image writing position using the difference value stored in the storage unit when forming a toner image after changing the relative position from the first relative position to the second relative position, and when forming a toner image after changing the relative position from the second relative position to the first relative position.

12. Multiple image forming units that form a toner image, A rotatable, endless belt on which a toner image is formed by the image forming unit, A plurality of tension rollers for tensioning the belt, comprising an inner roller and a plurality of upstream rollers positioned upstream of the inner roller and adjacent to the inner roller with respect to the rotational direction of the belt, An outer member is positioned opposite the inner roller and forms a transfer section that contacts the outer surface of the belt to transfer a toner image from the belt to the recording material, A pressing member is provided that can contact the inner surface of the belt upstream of the inner roller and downstream of the upstream roller with respect to the rotational direction of the belt, and can press the belt from the inner surface side to the outer surface side. A position-changing mechanism that can change the position of the pressing member to change at least one of the amount of pressure the pressing member applies to the belt and the state in which the pressing member is in contact with or separated from the belt, A toner detection unit that detects an adjustment toner image for detecting the relative positional shift of the toner image formed on the belt by the plurality of image forming units, A control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units, and to obtain an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit, It has, The image forming apparatus is characterized in that the control unit can be controlled to execute the adjustment operation when the position of the pressing member is changed by the position changing mechanism.

13. The image forming apparatus according to claim 12, characterized in that the control unit can be controlled to perform the adjustment operation before forming a toner image to be transferred to a subsequent recording material if the position of the pressing member is changed by the position changing mechanism after the toner image has been transferred to a preceding recording material while the job of transferring a toner image to a plurality of recording materials is being executed.

14. The image forming apparatus according to claim 13, characterized in that, during the execution of a job to transfer toner images to a plurality of recording materials, if the position of the pressing member is changed by the position changing mechanism after the toner image has been transferred to the preceding recording material, and if predetermined conditions are met, the control unit performs the adjustment operation before forming the toner image to be transferred to the subsequent recording material.

15. The image forming apparatus according to claim 14, characterized in that, during the execution of a job to transfer toner images to a plurality of recording materials, if the position of the pressing member is changed by the position changing mechanism after the toner image has been transferred to the preceding recording material, and the predetermined conditions are not met, the control unit forms the toner image to be transferred to the next recording material without performing the adjustment operation.

16. Multiple image forming units that form a toner image, A rotatable, endless belt on which a toner image is formed by the image forming unit, A plurality of tension rollers for tensioning the belt, comprising an inner roller and a plurality of upstream rollers positioned upstream of the inner roller and adjacent to the inner roller with respect to the rotational direction of the belt, An outer member is positioned opposite the inner roller and forms a transfer section that contacts the outer surface of the belt to transfer a toner image from the belt to the recording material, A pressing member is provided that can contact the inner surface of the belt upstream of the inner roller and downstream of the upstream roller with respect to the rotational direction of the belt, and can press the belt from the inner surface side to the outer surface side. A position-changing mechanism that can change the position of the pressing member to change at least one of the amount of pressure the pressing member applies to the belt and the state in which the pressing member is in contact with or separated from the belt, A toner detection unit that detects an adjustment toner image for detecting the relative positional shift of the toner image formed on the belt by the plurality of image forming units, A control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units, and to obtain an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit, A first storage unit that stores a first adjustment value obtained by the control unit while the pressing member is in the first position, A second storage unit that stores a second adjustment value obtained by the control unit when the pressing member is in a second position different from the first position, It has, The image forming apparatus is characterized in that the control unit can adjust the image writing position using the first adjustment value stored in the first storage unit when forming a toner image with the position of the pressing member set to the first position, and adjust the image writing position using the second adjustment value stored in the second storage unit when forming a toner image with the position of the pressing member set to the second position.

17. The image forming apparatus according to claim 16, characterized in that the control unit controls the adjustment operation to update the first adjustment value stored in the first storage unit when the position of the pressing member is changed from the first position to the second position and then returned to the first position, provided that predetermined conditions are met, before forming the toner image to be transferred to the recording material next.

18. The image forming apparatus according to claim 17, characterized in that the predetermined condition is that the adjustment operation, which is performed periodically regardless of the position of the pressing member, is executed between the time the first adjustment value is previously stored in the first memory unit and the time the position of the pressing member is returned to the first position.

19. The image forming apparatus according to claim 17, characterized in that, when the position of the pressing member is changed from the first position to the second position and then returned to the first position, and the predetermined conditions are not met, the control unit forms the toner image to be transferred to the recording material next without performing the adjustment operation.

20. The image forming apparatus according to claim 16, characterized in that the control unit controls the adjustment operation to update the second adjustment value stored in the second storage unit when the position of the pressing member is changed from the second position to the first position and then returned to the second position, provided that predetermined conditions are met, before forming the toner image to be transferred to the recording material next.

21. The image forming apparatus according to claim 20, characterized in that the predetermined condition is that the adjustment operation, which is performed periodically regardless of the position of the pressing member, is executed between the time the second adjustment value is previously stored in the second memory unit and the time the position of the pressing member is returned to the second position.

22. Multiple image forming units that form a toner image, A rotatable, endless belt on which a toner image is formed by the image forming unit, A plurality of tension rollers for tensioning the belt, comprising an inner roller and a plurality of upstream rollers positioned upstream of the inner roller and adjacent to the inner roller with respect to the rotational direction of the belt, An outer member is positioned opposite the inner roller and forms a transfer section that contacts the outer surface of the belt to transfer a toner image from the belt to the recording material, A pressing member is provided that can contact the inner surface of the belt upstream of the inner roller and downstream of the upstream roller with respect to the rotational direction of the belt, and can press the belt from the inner surface side to the outer surface side. A position-changing mechanism that can change the position of the pressing member to change at least one of the amount of pressure the pressing member applies to the belt and the state in which the pressing member is in contact with or separated from the belt, A toner detection unit that detects an adjustment toner image for detecting the relative positional shift of the toner image formed on the belt by the plurality of image forming units, A control unit capable of performing an adjustment operation to form the adjustment toner image on the belt using the plurality of image forming units, and to obtain an adjustment value for adjusting the image writing position in the width direction of the belt in at least one of the plurality of image forming units based on the detection result of the adjustment toner image by the toner detection unit, A storage unit that stores the difference between a first adjustment value obtained by the control unit when the pressing member is in a first position and a second adjustment value obtained by the control unit when the pressing member is in a second position different from the first position. It has, The image forming apparatus is characterized in that the control unit can control the adjustment of the image writing position using the difference value stored in the storage unit when forming a toner image after changing the position of the pressing member from the first position to the second position, and when forming a toner image after changing the position of the pressing member from the second position to the first position.

23. The image forming apparatus according to any one of claims 1 to 22, characterized in that the plurality of tension rollers include a steering roller that can tilt relative to other tension rollers among the plurality of tension rollers to move the belt in the width direction of the belt.

24. The image forming apparatus according to claim 23, characterized in that it has a steering drive unit for tilting the steering roller.

Images