Image forming apparatus

Abstract

To prevent occurrence of a difference in an amount of pressing of a pressing member on a belt in a longitudinal direction of the pressing member.SOLUTION: An image forming apparatus 100 has: a belt 31; a plurality of tension rollers; an outer member 41 that is arranged opposite to an inner roller 32 to form a transfer part N2; a pressing member 70; a holding device 82 that is movable and holds the pressing member 70; and a moving device 89 that moves the holding device 82 to move the pressing member 70. The moving device 89 has contact parts 83 that are at least at two points in a direction along a width direction of the belt 31, and are in contact with the holding device 82 to regulate a position in a direction of movement of the holding device 82. The holding device 82 has contact target parts 91 with which the contact parts 83 are in contact at least at two points in the direction along the width direction of the belt 31. At least one of the at least two contact target parts 91 is provided on an adjustment member 90 that can be fixed to a plurality of positions different from each other in a distance from the contact target part 91 to the contact part 83 on the holding device 82.SELECTED DRAWING: Figure 7

Description

Technical Field

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

Background Art

[0002] Conventionally, some image forming apparatuses using an electrophotographic method or the like have a rotatable endless belt (hereinafter also simply referred to as "belt") as an image carrier that carries and conveys 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 photosensitive member as a first image carrier to a sheet-like recording material such as paper for secondary transfer. Hereinafter, mainly, an image forming apparatus of an intermediate transfer system having an intermediate transfer belt will be described as an example.

[0003] In an image forming apparatus using an intermediate transfer belt, a toner image formed on a photoreceptor or the like in the image forming section is first transferred to the intermediate transfer belt in the primary transfer section. The toner image first transferred to the intermediate transfer belt is then secondarily transferred to a recording material in the secondary transfer section. A secondary transfer section is formed by a secondary transfer inner member provided on the inner circumferential surface side of the intermediate transfer belt and a secondary transfer outer member provided on the outer circumferential surface side of the intermediate transfer belt, which is the contact area between the intermediate transfer belt and the secondary transfer outer member. As the secondary transfer inner member, a secondary transfer inner roller, which is one of several tension rollers that tension the intermediate transfer belt, is often used. As the secondary transfer outer member, a secondary transfer outer roller is often used, which is positioned opposite the secondary transfer inner roller across the intermediate transfer belt and is pressed toward the secondary transfer inner roller. Then, a voltage with the opposite polarity to the charge polarity of the toner is applied to the secondary transfer outer roller (or a voltage with the same polarity as the charge polarity of the toner is applied to the secondary transfer inner roller), and the toner image on the intermediate transfer belt is transferred to the recording material in the secondary transfer section. With respect to the recording material, "leading end" and "rear end" refer to the leading and rear ends of the recording material in the direction of transport, respectively. The upstream of the secondary transfer section in the direction of rotation of the intermediate transfer belt is also simply called "upstream of the secondary transfer section."

[0004] To transfer the toner image formed on the intermediate transfer belt to the recording material with high precision, the contact length between the intermediate transfer belt and the recording material in relation to the rotation direction of the intermediate transfer belt upstream of the secondary transfer section is important. If the contact length is long, image defects may occur due to friction between the toner and the recording material caused by the speed difference between the intermediate transfer belt and the recording material. On the other hand, if the contact length is short, image defects may occur due to discharge occurring in the gap between the recording material and the intermediate transfer belt. Therefore, the transport posture of the recording material and the tension layout of the intermediate transfer belt are determined in consideration of the contact position of the leading edge of the recording material with respect to the intermediate transfer belt upstream of the secondary transfer section.

[0005] Patent Document 1 proposes a configuration in which a planar straightening member is provided upstream of the contact position (tacking position) of the leading edge of the recording material with respect to the intermediate transfer belt in the rotational direction of the intermediate transfer belt, and which contacts the inner circumferential surface of the intermediate transfer belt and presses the intermediate transfer belt. In Patent Document 1, a flexible baffle plate or an elastic roll is used as the planar straightening member. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-80926 [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, by bringing a pressing member (backup member) into contact with the inner circumferential surface of the intermediate transfer belt upstream of the secondary transfer section, the shape (position) of the intermediate transfer belt upstream of the secondary transfer section can be set to a desired shape (position). In this configuration, in order to appropriately adjust the contact length between the intermediate transfer belt and the recording material, the inner circumferential surface of the intermediate transfer belt upstream of the secondary transfer section is pressed down by the pressing member, deforming the intermediate transfer belt and forming an appropriate shape (position) of the intermediate transfer belt. The pressing member is held by a holding device, and the amount of pressure the pressing member applies to the intermediate transfer belt can be adjusted by changing the position of the holding device. The position of the holding device can be adjusted, for example, by pressing the holding device with a cam provided on the main body of the image forming apparatus or the intermediate transfer belt unit.

[0008] However, it was found that this configuration presents the following challenges. The pressing member is positioned along the width direction of the intermediate transfer belt (a direction approximately perpendicular to the direction of surface movement), with one end in the longitudinal direction being the front and the other end being the rear. The cam is provided to press the holding device at at least two locations, the front and the rear. In this case, due to tolerances of the parts of the holding device, when the holding device is attached to the main body of the image forming apparatus or the intermediate transfer belt unit, a difference may occur between the front and rear in the distance between the holding device and the rotation axis of the cam, resulting in a difference in the amount the cam presses the holding device between the front and the rear. In this case, a difference occurs between the front and the rear in the amount of pressure (penetration) of the pressing member against the intermediate transfer belt. When a difference occurs between the front and the rear in the amount of pressure of the pressing member against the intermediate transfer belt, it becomes difficult to uniformly adjust the contact length between the intermediate transfer belt and the recording material to an appropriate amount in the width direction of the intermediate transfer belt. As a result, depending on the position of the intermediate transfer belt in the width direction, there is a possibility that areas may be created where discharge occurs due to the gap between the intermediate transfer belt and the recording material, or conversely, areas where image defects occur due to image friction caused by a long contact length between the intermediate transfer belt and the recording material.

[0009] In the above, we have described the conventional problems using the secondary transfer section, which is the part where the toner image is transferred from the intermediate transfer belt to the recording material, as an example. However, similar problems may arise in the transfer section of the toner image from other belt-shaped image carriers, such as photoreceptors, to the recording material.

[0010] Therefore, an object of the present invention is to suppress differences in the amount of pressure applied by the pressing member to the belt in the longitudinal direction of the pressing member. [Means for solving the problem]

[0011] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises a rotatable endless belt for carrying a toner image, a plurality of tension rollers for tensioning the belt, the plurality of tension rollers 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 portion that contacts the outer circumferential surface of the belt and transfers a toner image from the belt to a recording material, and a pressing member that is able to contact the inner circumferential surface of the belt along the width direction of the belt, upstream of the inner roller and downstream of the upstream roller with respect to the rotation direction of the belt, and is capable of pressing the belt from the inner circumferential surface side to the outer circumferential surface side, and the pressing member An image forming apparatus having a movable holding device for holding a pressing member, and a moving device for moving the holding device to move the pressing member, wherein the moving device has at least two contact portions in a direction along the width direction of the belt that contact the holding device and restrict the position of the holding device in the direction of movement, the holding device has at least two contact portions in a direction along the width direction of the belt that the contact portions contact, and at least one of the at least two contact portions is provided on an adjustment member configured to be fixable at multiple positions in the holding device where the contact portion is at a different distance from the contact portion. [Effects of the Invention]

[0012] According to this embodiment, it is possible to suppress differences in the amount of pressure applied by the pressing member to the belt in the longitudinal direction of the pressing member. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view of an image forming apparatus. [Figure 2] This is a schematic cross-sectional view of the vicinity of the secondary transfer region. [Figure 3] This is a schematic perspective drawing illustrating the basic configuration of the mobile mechanism. [Figure 4]It is a schematic side view for explaining the basic configuration of the moving mechanism. [Figure 5] It is a schematic cross-sectional view for explaining the penetration amount of the pressing member. [Figure 6] It is a schematic block diagram for explaining the control mode of the moving mechanism. [Figure 7] It is a schematic perspective view of the moving mechanism. [Figure 8] It is an exploded perspective view of the vicinity of the attachment portion of the cam follower member of the holding device. <x [Figure 9] It is an exploded perspective view of the vicinity of the attachment portion of the cam follower member of the holding device. [[ID=I7]] [Figure 10] It is a perspective view of a jig for adjusting the position of the cam follower member. [Figure 11] It is a schematic diagram for explaining a modified example.

Embodiment for Carrying Out the Invention

[0014] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0015] [Example 1] 1. Overall Configuration and Operation of the Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of the present embodiment is a tandem type printer adopting an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a sheet-like recording material (transfer material, sheet, recording medium, medium) P such as paper using an electrophotographic method according to an image signal transmitted from an external device such as a personal computer.

[0016] Regarding the image forming apparatus 100 and its elements, the side closer to the front of the paper of FIG. 1 is defined as the "front" side, and the side deeper into the paper is defined as the "rear" side. The front-rear direction connecting the front side and the rear side is assumed to be substantially parallel to the axial direction of the rotation of the photosensitive drum 11 and the tension rollers of the intermediate transfer belt 31, which will be described later. Also, regarding the image forming apparatus 100 and its elements, the up-down direction refers to the up-down in the gravity direction (vertical direction), and it does not mean only directly above or directly below, but includes the upper side and the lower side relative to the horizontal plane passing through the element or position of interest.

[0017] The image forming apparatus 100 has four image forming units 10Y, 10M, 10C, and 10K that form images of yellow (Y), magenta (M), cyan (C), and black (K) respectively as a plurality of image forming units (stations). These image forming units 10Y, 10M, 10C, and 10K are arranged in a row along the moving direction of the image transfer surface disposed substantially horizontally of the intermediate transfer belt 31, which will be described later. For elements having the same or corresponding functions or configurations in each of the image forming units 10Y, 10M, 10C, and 10K, the Y, M, C, and K at the end of the reference numeral indicating that it is an element for any color may be omitted and described collectively. In this embodiment, the image forming unit 10 includes a photosensitive drum 11 (11Y, 11M, 11C, 11K), a charger 12 (12Y, 12M, 12C, 12K), an exposure device 13 (13Y, 13M, 13C, 13K), a developing device 14 (14Y, 14M, ......

[0018] The image forming apparatus 100 has a photosensitive drum 11, which is a rotatable drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor) that serves as a first image carrier for holding a toner image. The photosensitive drum 11 is driven to rotate at a predetermined peripheral speed (process speed) in the direction of arrow R1 (counterclockwise direction) in Figure 1 by a driving force transmitted from a drum drive motor (not shown) as a driving source. The surface of the rotating photosensitive drum 11 is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by a charger 12 as a charging means. During the charging process, a predetermined charging voltage (charging bias) is applied to the charger 12 by a charging power supply (not shown). The surface of the charged photosensitive drum 11 is scanned and exposed according to an image signal by an exposure apparatus 13 as an exposure means, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 11. In this embodiment, the exposure apparatus 13 is composed of a laser scanner device that irradiates the photosensitive drum 11 with laser light modulated according to an image signal (image information). The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by the developer 14, 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 11. In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 11 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 11, where the absolute value of the potential has decreased after uniform charging treatment and exposure (reverse development method). During development, a predetermined development voltage (development bias) is applied to the developing roller, which is a developer carrier of the developer 14, by a development power supply (not shown). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0019] Opposite the four photosensitive drums 11Y, 11M, 11C, and 11K is an intermediate transfer belt 31, 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 31 is wrapped around a plurality of tension rollers (support rollers), namely a drive roller 33, a tension roller 34, a pre-secondary transfer roller 35, and a secondary transfer inner roller 32, and is stretched at a predetermined tension. The drive roller 33 transmits driving force to the intermediate transfer belt 31. The drive roller 33 is rotationally driven by driving force transmitted from a belt drive motor (not shown) as a drive source. As a result, the intermediate transfer belt 31 receives drive input from the drive roller 33 and rotates (circumferentially moves) in the direction of arrow R2 (clockwise direction) in Figure 1 at a peripheral speed (process speed) corresponding to the peripheral speed of the photosensitive drum 11. The tension roller 34 applies a predetermined tension to the intermediate transfer belt 31 and controls the tension of the intermediate transfer belt 31 to be constant. The tension roller 34 is biased at both ends in the direction of its rotation axis by tension springs 36, which are biasing members composed of compression coil springs that act as tension-applying means (biasing means), from the inner circumferential surface side to the outer circumferential surface side of the intermediate transfer belt 31. The secondary transfer roller 35 forms the surface of the intermediate transfer belt 31 near the upstream of the secondary transfer section N2 (described later) with respect to the rotational direction (direction of surface movement) of the intermediate transfer belt 31. In this embodiment, the secondary transfer inner roller (secondary transfer inner member) 32 functions as a secondary transfer member as a secondary transfer means. Also, on the inner circumferential surface side of the intermediate transfer belt 31, primary transfer rollers 15Y, 15M, 15C, and 15K, which are roller-shaped primary transfer members as primary transfer means, are arranged corresponding to each photosensitive drum 11Y, 11M, 11C, and 11K. In this embodiment, the primary transfer roller 15 is positioned opposite the photosensitive drum 11 via the intermediate transfer belt 31. The primary transfer roller 15 presses the intermediate transfer belt 31 toward the photosensitive drum 11, forming a primary transfer portion (primary transfer nip) N1, which is the contact area between the photosensitive drum 11 and the intermediate transfer belt 31. The tension rollers other than the drive roller 33 among the multiple tension rollers, and each primary transfer roller 15, rotate in accordance with the rotation of the intermediate transfer belt 31.Furthermore, on the inner circumferential surface side of the intermediate transfer belt 31, a pressing member 70 is provided upstream of the secondary transfer inner roller 32 and downstream of the secondary transfer pre-roller 35 in the rotational direction of the intermediate transfer belt 31. The image forming apparatus 100 also has a moving mechanism 81 (Figure 7) for changing the position of the pressing member 70. The pressing member 70 and the moving mechanism 81 will be described in detail later.

[0020] As described above, the toner image formed on the photosensitive drum 11 is primary transferred to the rotating intermediate transfer belt 31 in the primary transfer section N1. During primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 15 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 11 are sequentially primary transferred so that they are superimposed on the same image forming region on the intermediate transfer belt 31. In this embodiment, the primary transfer section N1 is the image forming position where the toner image is formed on the intermediate transfer belt 31. The intermediate transfer belt 31 is an example of a rotatable endless belt that transports the toner image carried at the image forming position.

[0021] On the outer circumferential surface of the intermediate transfer belt 31, a secondary transfer outer roller (secondary transfer outer member) 41 is positioned opposite the secondary transfer inner roller 32. In this embodiment, the secondary transfer outer roller 41 functions as an opposing member (counter electrode) of the secondary transfer inner roller 32. The secondary transfer outer roller 41 is pressed toward the secondary transfer inner roller 32 via the intermediate transfer belt 31, forming a secondary transfer section (secondary transfer nip) N2, which is the contact area between the intermediate transfer belt 31 and the secondary transfer outer roller 41. As described above, the toner image formed on the intermediate transfer belt 31 is secondary transferred in the secondary transfer section N2 onto the recording material P, which is being transported while being held between the intermediate transfer belt 31 and the secondary transfer outer roller 41. In this embodiment, during secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage with the same polarity (negative polarity in this embodiment) as the normal charging polarity of the toner, is applied to the secondary transfer inner roller 32 by a secondary transfer power supply (not shown). In this embodiment, the secondary transfer outer roller 41 is electrically grounded (connected to ground). Alternatively, the secondary transfer outer roller 41 may be used as a secondary transfer member, and a secondary transfer voltage with the opposite polarity to the normal charging polarity of the toner may be applied to it, while the secondary transfer inner roller 32 may be used as a counter electrode and electrically grounded.

[0022] The recording material P is stored in recording material cassettes 61a to 61c, which serve as recording material storage units. The recording material P stored in the recording material cassettes 61a to 61c is sent to the feeding transport path 63 when one of the feeding rollers 62a to 62c, which are feeding members, is rotated. This recording material P is then transported to a pair of registration rollers 21, which are also transport members, by a pair of transport rollers 64, which are also transport members, and is temporarily stopped. When the pair of registration rollers 21 is rotated, the recording material P is sent to the secondary transfer unit N2 in timing with the toner image on the intermediate transfer belt 31.

[0023] Downstream of the pair of resist rollers 21 and upstream of the secondary transfer section N2 in the transport direction of the recording material P, a transport guide (pre-transfer guide) 22 is provided to guide the recording material P to the secondary transfer section N2. The transport guide 22 is composed of a first guide member 22a 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 22), and a second guide member 22b that can contact the back surface of the recording material P (the surface opposite to the front surface). The first guide member 22a and the second guide member 22b are arranged opposite each other, and the recording material P passes between these two members. The first guide member 22a restricts the movement of the recording material P toward the intermediate transfer belt 31. The second guide member 22b restricts the movement of the recording material P toward the intermediate transfer belt 31.

[0024] The recording material P onto which the toner image has been transferred is transported by a transport belt (pre-fixing transport device) 23 to a fixing device 50, which serves as the fixing means. The fixing device 50 heats and pressurizes the recording material P, which is carrying the unfixed toner image, by clamping it with a pair of fixing rotating bodies and transporting it, thereby fixing (melting and solidifying) the toner image onto the surface of the recording material P. The recording material P with the fixed toner image is discharged (output) through the discharge transport path 65 to a discharge tray 66 located outside the main body 110 of the image forming apparatus 100.

[0025] On the other hand, any toner or other deposits remaining on the photosensitive drum 11 after the primary transfer (primary transfer residue toner) are removed from the photosensitive drum 11 and recovered by the cleaning device 16, which serves as a cleaning means. In addition, any toner or other deposits remaining on the intermediate transfer belt 31 after the secondary transfer (secondary transfer residue toner) are removed from the intermediate transfer belt 31 and recovered by the belt cleaning device 37, which serves as an intermediate transfer body cleaning means.

[0026] In this embodiment, the intermediate transfer belt unit 30, which serves as a belt conveying device, comprises an intermediate transfer belt 31, tension rollers 32-35, primary transfer rollers 15, a belt cleaning device 37, and a frame (not shown) that supports these components. In this embodiment, the intermediate transfer belt unit 30 is further provided with a pressing member 70 and a moving mechanism 81, which will be described later. The intermediate transfer belt unit 30 is detachable (or pullable) from the main body 110 of the image forming apparatus 100 for maintenance or replacement.

[0027] Here, the intermediate transfer belt 31 can be made of a single-layer or multi-layer resin-based material, or a multi-layer structure comprising a resin layer made of resin material and an elastic layer made of elastic material. In this embodiment, the secondary transfer inner roller 32 is constructed by providing an elastic layer of electronically conductive rubber on the outer circumference of a metal core. In this embodiment, the secondary transfer pre-roller 35 is made of metal. In this embodiment, the secondary transfer outer roller 41 is constructed by providing an elastic layer of ionically conductive foamed rubber on the outer circumference of a metal core. In this embodiment, bearing members (not shown) that support both ends of the secondary transfer outer roller 41 in the direction of the rotation axis are slidable in the direction toward the secondary transfer inner roller 32 and in the opposite direction. These bearing members are pressed toward the secondary transfer inner roller 32 by a compression spring 42 (Figure 2), which is a biasing member (elastic member) that acts as a biasing means. As a result, the secondary transfer outer roller 41 contacts the secondary transfer inner roller 32 with a predetermined pressure, with the intermediate transfer belt 31 in between, to form the secondary transfer section N2. The rotational axes of the tension rollers of the intermediate transfer belt 31, including the secondary transfer inner roller 32, and the secondary transfer outer roller 41 are substantially parallel to each other.

[0028] 2.2 Secondary Transfer Section Figure 2 is a schematic cross-sectional view (a cross-section approximately perpendicular to the rotation axis direction of the secondary transfer roller 32) for explaining the shape (orientation) of the intermediate transfer belt 31 upstream of the secondary transfer section N2 in the image forming apparatus 100 of this embodiment. Figure 2(a) shows the state before the recording material P moves to the secondary transfer section N2, Figure 2(b) shows the state after the recording material P moves to the secondary transfer section N2, and Figure 2(c) shows a magnified view of the vicinity of the secondary transfer section N2 in Figure 2(b).

[0029] As shown in Figure 2, in this embodiment, the shape of the intermediate transfer belt 31, which is formed by tensioning the secondary transfer inner roller 32 and the secondary transfer pre-roller 35, is elastically biased by the secondary transfer outer roller 41 toward the secondary transfer inner roller 32 by the pressure spring 42. As a result, the intermediate transfer belt 31 is sandwiched between the secondary transfer inner roller 32 and the secondary transfer outer roller 41, forming the secondary transfer portion N2.

[0030] Furthermore, in this embodiment, a pressing member 70 is provided upstream of the secondary transfer section N2, close to the secondary transfer inner roller 32. In this embodiment, during image formation (secondary transfer), the inner circumferential surface of the intermediate transfer belt 31 and the tip of the pressing member 70 are in contact. The pressing member 70 contacts the inner circumferential surface of the intermediate transfer belt 31 and can press the intermediate transfer belt 31 from the inner circumferential surface side to the outer circumferential surface side. As a result, the pressing member 70 can cause the tensioned surface of the intermediate transfer belt 31, formed between the secondary transfer inner roller 32 and the secondary transfer pre-roller 35, to protrude from the inner circumferential surface side to the outer circumferential surface side. In this embodiment, the pressing member 70 is formed of a flexible resin plate-shaped member, and the pressing member 70 elastically biases the intermediate transfer belt 31 by utilizing its bending elasticity. Therefore, the shape (amount of deflection, amount of deformation) or position of the pressing member 70 is determined to be the shape (or position) in which the biasing force of the pressing member 70 that biases the intermediate transfer belt 31 balances the resistance force generated by the tension of the intermediate transfer belt 31. Here, the shape (or position) of the pressing member 70 determined in this way is also called the "statically determined shape (or statically determined position)". The shape (position) of the intermediate transfer belt 31 upstream of the secondary transfer section N2 is then determined by this statically determined shape (statically determined position) of the pressing member 70.

[0031] Furthermore, in this embodiment, the image forming apparatus 100 is configured to change the position of the pressing member 70 by the action of the moving mechanism 81, which will be described later. As a result, in this embodiment, the image forming apparatus 100 is configured to control the static shape (static position) of the pressing member 70, that is, the shape (posture) of the intermediate transfer belt 31 upstream of the secondary transfer section N2.

[0032] In this embodiment, a bias of the same polarity as the charge polarity of the toner constituting the toner image on the intermediate transfer belt 31 is applied to the secondary transfer inner roller 32, and the secondary transfer outer roller 41 is connected to earth. This creates a transfer electric field in the secondary transfer section N2. The recording material P is transported to the secondary transfer section N2, where the transfer electric field has been formed, guided by the transport guide 22 (Figure 1). As shown in Figure 2(a), the recording material P is transported toward the secondary transfer section N2 with its leading edge in contact with the intermediate transfer belt 31 upstream of the secondary transfer section N2, and further in contact with the toner image formed on the surface of the intermediate transfer belt 31. Then, as shown in Figure 2(b), when the recording material P is transported to the secondary transfer section N2, the toner image is transferred from the intermediate transfer belt 31 to the recording material P by the pressurizing action between the secondary transfer inner roller 32 and the secondary transfer outer roller 41, and the electrical action of the transfer electric field.

[0033] Here, for high-precision secondary transfer, the length of contact between the intermediate transfer belt 31 and the recording material P in the direction of rotation of the intermediate transfer belt 31 upstream of the secondary transfer section N2, when the recording material P is transported to the secondary transfer section N2 (also referred to here as the "contact length"), is important. If the contact length is long, image defects may occur due to friction between the toner image formed on the surface of the intermediate transfer belt 31 and the recording material P. On the other hand, if the contact length is short, the gap G (Figure 2(c)) between the intermediate transfer belt 31 and the recording material P becomes large, and image defects may occur due to discharge phenomena occurring in the gap G. Furthermore, when a recording material P with high rigidity, such as cardboard or coated paper, is used, the intermediate transfer belt 31 is more likely to deform when the recording material P enters the contact position of the leading edge of the recording material P against the intermediate transfer belt 31 upstream of the secondary transfer section N2. This makes it easier for the above-mentioned gap G to occur, and image defects due to discharge in the gap G may occur.

[0034] As in this embodiment, by providing the pressing member 70, it becomes easier to appropriately set the contact length between the intermediate transfer belt 31 and the recording material P upstream of the secondary transfer section N2. In particular, in this embodiment, the shape (position) of the intermediate transfer belt 31 upstream of the secondary transfer section N2 can be controlled by variably controlling the position of the pressing member 70 with the moving mechanism 81 described later. As a result, the toner image can be stably transferred to the secondary transfer by optimizing the contact length between the intermediate transfer belt 31 and the recording material P upstream of the secondary transfer section N2. Furthermore, even when a recording material P with high rigidity, such as cardboard or coated paper, is used, the deformation of the intermediate transfer belt 31 when it comes into contact with the recording material P can be suppressed by the effect of the elastic biasing of the pressing member 70. As a result, it is possible to suppress the increase in the gap G between the intermediate transfer belt 31 and the recording material P.

[0035] In this embodiment, the image forming apparatus 100 is designed to achieve high productivity, and the intermediate transfer belt 31 is transported at a speed of 400 mm / s. In this embodiment, the toner is negatively charged. To ensure appropriate transfer performance even at the transport speed of the intermediate transfer belt 31, a high-voltage bias of -10 kV is applied to the secondary transfer roller 32 as a secondary transfer voltage. However, the transport speed of the intermediate transfer belt 31, the charge polarity of the toner, and the value of the secondary transfer voltage are not limited to these.

[0036] 3. Pressing member In this embodiment, as described above, the image forming apparatus 100 has a pressing member (backup member, backup sheet) 70 on the inner circumferential surface side of the intermediate transfer belt 31, near the upstream side of the secondary transfer section N2. The pressing member 70 can press the inner circumferential surface of the intermediate transfer belt 31 near the entrance of the secondary transfer section N2, causing the intermediate transfer belt 31 to protrude outwards. The pressing member 70 is positioned to be able to contact the inner circumferential surface of the intermediate transfer belt 31 upstream of the secondary transfer inner roller 32 and downstream of the secondary transfer pre-roller 35 with respect to the rotational direction of the intermediate transfer belt 31. In particular, in this embodiment, the pressing member 70 is positioned to be able to contact the inner circumferential surface of the intermediate transfer belt 31 upstream of the secondary transfer inner roller 32 and downstream of the downstream end of the transport guide 22 (first guide member 22a) with respect to the transport direction of the recording material P.

[0037] In this embodiment, the pressing member 70 is composed of a plate-like (sheet-like) member that is approximately rectangular in plan view, having a predetermined length in the longitudinal direction which is approximately parallel to the width direction of the intermediate transfer belt 31, and a predetermined thickness in the short direction which is approximately perpendicular to the longitudinal direction. The width direction of the intermediate transfer belt 31 is approximately perpendicular to the direction of movement of the surface of the intermediate transfer belt 31 and is approximately parallel to the rotation axis direction of the secondary transfer internal roller 32. The length of the pressing member 70 in the longitudinal direction is equivalent to the length of the intermediate transfer belt 31 in the width direction. The free end (tip) of the pressing member 70, which is one end in the short direction (the downstream end with respect to the rotation direction of the intermediate transfer belt 31), can contact the inner circumferential surface of the intermediate transfer belt 31 over approximately the entire width of the intermediate transfer belt 31, and can press the intermediate transfer belt 31. Furthermore, the pressing member 70 is held by the holding device 82 (Figure 7), which is a holding device that constitutes the moving mechanism 81 described later. A portion of the fixed end (base end), which is the other end in the shorter direction (the end on the upstream side with respect to the rotational direction of the intermediate transfer belt 31), is fixed to the holding device 82.

[0038] In this embodiment, the pressing member 70 is formed using a resin material. In particular, in this embodiment, the pressing member 70 is made of PPS (polyphenylene sulfide) with a thickness of 0.5 mm, and the pressing member 70 elastically biases the intermediate transfer belt 31 by utilizing its flexibility. Note that the pressing member 70 is not limited to the configuration of this embodiment, and any material that can elastically bias the intermediate transfer belt 31 is acceptable. For example, the thickness of the pressing member 70 is not limited to 0.5 mm, but is preferably around 0.4 to 1.5 mm, and may be 1.0 mm, for example. Also, the material of the pressing member 70 is not limited to PPS, but may be PEEK (polyetheretherketone), PET (polyethylene terephthalate), etc.

[0039] Here, it is desirable that the pressing member 70, more specifically the free end (tip) side of the pressing member 70 in the short direction (here, also simply referred to as the "tip") be positioned as close as possible to the secondary transfer internal roller 32. However, the pressing member 70 is positioned so as not to come into contact with the secondary transfer internal roller 32. The pressing member 70 is positioned, for example, to contact the inner circumferential surface of the intermediate transfer belt 31 at a position, for example, about 2 mm or more, typically about 10 mm or more, upstream of the intermediate transfer belt 31 in the rotational direction from the position where the secondary transfer internal roller 32 and the intermediate transfer belt 31 come into contact. Alternatively, the pressing member 70 is positioned, for example, to contact the inner circumferential surface of the intermediate transfer belt 31 at a position, for example, about 40 mm or less, typically about 25 mm or less, upstream of the intermediate transfer belt 31 in the rotational direction from the position where the secondary transfer internal roller 32 and the intermediate transfer belt 31 come into contact.

[0040] 4. Basic configuration and operation of the moving mechanism Next, the moving mechanism for changing the position of the pressing member 70 will be described. Here, in order to facilitate understanding of the problems and solutions of the present invention, the basic configuration and operation of the moving mechanism will first be described based on the configuration of an example of a conventional moving mechanism. Figure 3 is a perspective view of a conventional moving mechanism 71. Figure 4 is a schematic side view of the vicinity of the pressing member 70, taken from one end side (the front side of the paper in Figure 1) in the direction of the rotation axis of the secondary transfer internal roller 32, and approximately parallel to the rotation axis direction, for the purpose of explaining the operation of the moving mechanism 71. Figure 4 shows a state in which the intermediate transfer belt 31 is not provided for illustrative purposes. Furthermore, this conventional moving mechanism 71 will be described assuming that it is incorporated into the image forming apparatus 100 of this embodiment.

[0041] The moving mechanism 71 can control the static shape (static position) of the pressing member 70, that is, the shape (orientation) of the intermediate transfer belt 31 upstream of the secondary transfer section N2, by changing the position of the pressing member 70. This allows the moving mechanism 71 to optimize the contact length between the intermediate transfer belt 31 and the recording material P upstream of the secondary transfer section N2. In other words, the moving mechanism 71 can control the amount of pressure (penetration amount, described later) applied by the pressing member 70 to the intermediate transfer belt 31 by changing the position of the pressing member 70. Furthermore, the moving mechanism 71 may be configured to change the contact or separation state of the pressing member 70 from the intermediate transfer belt 31 by changing the position of the pressing member 70.

[0042] The moving mechanism 71 has a holding device (holding member) 72 that extends along the width direction of the intermediate transfer belt 31. The pressing member 70 is held by the holding device 72. The pressing member 70 has a free end (tip) 70a in the short direction that can contact the inner circumferential surface of the intermediate transfer belt 31 over substantially the entire width of the intermediate transfer belt 31, and can press the intermediate transfer belt 31. In this example, a part of the fixed end (base end) 70b side in the short direction of the pressing member 70 is fixed to a mounting fixture 70c. The mounting fixture 70c is made of sheet metal having a plate-like portion that extends along the width direction of the intermediate transfer belt 31 (the longitudinal direction of the pressing member 70), and is used to attach the pressing member 70 to the holding device 72. The pressing member 70 has a portion of its fixed end 70b in the short direction fixed to a mounting fixture 70c by adhesive or the like over substantially its entire width in the longitudinal direction, and this mounting portion 70c is fixed to the holding device 72 by screws or the like. The holding device 72 is provided with cylindrical support holes 72a at both ends in the longitudinal direction. The holding device 72 is supported by the frame (not shown) of the intermediate transfer belt unit 30 so as to be able to rotate around a pivot axis that is substantially parallel to the width direction of the intermediate transfer belt 31, with respect to the support holes 72a. In this way, by rotating the holding device 72 around a pivot axis substantially parallel to the width direction of the intermediate transfer belt 31, the pressing member 70 can be rotated around the pivot axis and its position can be changed.

[0043] The moving mechanism 71 also has a camshaft 74, which is a cylindrical member extending along the width direction of the intermediate transfer belt 31. The camshaft 74 is supported by the frame (not shown) of the intermediate transfer belt unit 30 so as to be able to rotate around a rotation axis that is substantially parallel to the width direction of the intermediate transfer belt 31. The moving mechanism 71 also has a cam 73, a transmission gear 76, and a flag (cam position flag) 77. These cam 73, transmission gear 76, and flag 77 are each fixed to the camshaft 74. There are two cams 73, one at each end of the camshaft 74 in the direction of its rotation axis. The moving mechanism 71 also has a cam drive motor 75, which is a stepping motor, as a drive source. The cam drive motor 75 is fixed to the frame (not shown) of the intermediate transfer belt unit 30 so as to the frame (not shown) of the intermediate transfer belt unit 30 so as to have a drive gear 75a fixed to its output shaft mesh with a transmission gear 76 fixed to the camshaft 74. When the cam drive motor 75 rotates, the drive is transmitted to the camshaft 74 via the transmission gear 76, and the cam 73, transmission gear 76, and flag 77 rotate together with the camshaft 74 around a rotation axis that is substantially parallel to the width direction of the intermediate transfer belt 31.

[0044] The cam 73, acting as the contact portion, contacts the cam follower 72b, which is the contacted portion provided on the holding device 72. The cam 73 forms a stepless surface in which the radius from the center of rotation changes uniformly according to its rotation angle. Therefore, when the cam 73 rotates due to the rotation of the cam drive motor 75, the holding device 72 rotates around the support hole 72a. As a result, the moving mechanism 71 can move the pressing member 70 and change the position of the pressing member 70. Here, changing the position of the pressing member 70 means, more specifically, changing the position of the tip of the pressing member 70 (hereinafter also simply referred to as the "tip position") assuming that the intermediate transfer belt 31 is absent. Specifically, in this example, changing the position of the pressing member 70 means changing the position of the movable holding device 72 of the moving mechanism 71.

[0045] Furthermore, the moving mechanism 71 has a position sensor (cam position sensor, cam HP sensor) 78 as a position detection means for detecting the rotational position of the cam 73, in particular, the home position (HP) in the rotational direction in this example. The position sensor 78 is supported by the frame (not shown) of the intermediate transfer belt unit 30. The position sensor 78 and the flag 77, which serves as an indicator means (indicator part) fixed to the cam shaft 74, constitute an optical position detection mechanism. Through the action of the position sensor 78 and the flag 77, the attitude of the moving mechanism 71 can be set to a preset neutral state.

[0046] As shown in Figure 4(a), when the pressing member 70 is moved in the direction that presses the intermediate transfer belt 31, the cam 73 is driven by the cam drive motor 75 and rotates clockwise. As a result, the holding device 72 rotates counterclockwise around the support hole 72a, and the position of the pressing member 70 (more specifically, the tip position) moves toward the outer circumferential surface of the intermediate transfer belt 31. Also, as shown in Figure 4(b), when the pressing member 70 is moved in the opposite direction, that is, away from the intermediate transfer belt 31, the cam 73 is driven by the cam drive motor 75 and rotates counterclockwise. As a result, the holding device 72 rotates clockwise around the support hole 72, and the position of the pressing member 70 (more specifically, the tip position) moves toward the inner circumferential surface of the intermediate transfer belt 31.

[0047] The retaining device 72 is biased to rotate in a direction in which the cam follower 72b engages with the cam 73. The retaining device 72 is biased by the tension of the intermediate transfer belt 31 via the pressing member 70, and may also be provided with a spring or other biasing member as a biasing means for biasing the retaining device 72. This allows the pressing member 70 to be separated from the intermediate transfer belt 31.

[0048] In this example, a moving device 79 is formed by a cam 73, a camshaft 74, a cam drive motor 75, a transmission gear 76, etc., which moves the holding device 72. The moving mechanism 71 is then formed by having the moving device 79 and the holding device 72.

[0049] Figure 5 is a schematic cross-sectional view (a cross-section approximately perpendicular to the rotation axis direction of the secondary transfer roller 32) for explaining the amount of penetration of the pressing member 70 into the intermediate transfer belt 31. The amount of pressure applied by the pressing member 70 to the intermediate transfer belt 31 can be expressed as the amount of penetration of the pressing member 70 into the intermediate transfer belt 31. This amount of penetration of the pressing member 70 is roughly the amount by which the pressing member 70 causes the intermediate transfer belt 31 to protrude outward relative to the tensioned surface of the intermediate transfer belt 31 formed by tensioning the secondary transfer roller 32 and the secondary transfer roller 35. The secondary transfer roller 35 is an example of an upstream roller among a plurality of tensioning rollers, which is positioned upstream of the secondary transfer roller 32 in the rotation direction of the intermediate transfer belt 31 and adjacent to the secondary transfer roller 32. In other words, in the cross-section shown in Figure 5, the common tangent line between the secondary transfer roller 32 and the secondary transfer roller 35 on the side in contact with the intermediate transfer belt 31 is called the common tangent line 31a. In this case, the penetration amount D of the pressing member 70 can be defined as the normal distance from the common tangent 31a to the tip of the pressing member 70 when the intermediate transfer belt 31 is not stretched (the distance between the common tangent 31a and a line passing through the tip of the pressing member 70 and parallel to the common tangent 31a).

[0050] Figure 6 is a schematic block diagram showing an example of a control method for setting (adjusting) the position of the pressing member 70. The image forming apparatus 100 is equipped with a storage unit 112 and a control unit 111. The control unit 111 can control the position of the support member 72 in relation to the rotation direction of the support member 72 by controlling the rotation angle of the cam 73, thereby controlling the position of the pressing member 70 (more specifically, the tip position). In other words, the control unit 111 can detect the neutral state of the moving mechanism 71 (the home position of the cam 73) based on the signal (information) from the position sensor 78. The control unit 111 can also pulse control the cam drive motor 75. Then, from the neutral state, the control unit 111 can move the support member 72 to an arbitrary position and move the pressing member 70 to an arbitrary position by inputting an arbitrary number of pulses to the cam drive motor 75. For example, the relationship between the penetration amount D of the pressing member 70 and the number of pulses input to the cam drive motor 75 can be stored in advance in the storage unit 112. As a result, the control unit 111 can variably control the penetration amount D of the pressing member 70 by inputting an arbitrary number of pulses to the cam drive motor 75.

[0051] While not limited to this, the penetration depth D of the pressing member 70 is preferably about 1.0 mm to 3.5 mm or less. This stabilizes the shape of the intermediate transfer belt 31 upstream of the secondary transfer section N2 and reduces the possibility that the smooth rotation of the intermediate transfer belt 31 may be hindered by an excessive increase in the load on the contact surface between the pressing member 70 and the intermediate transfer belt 31. Furthermore, the amount of pressure D of the pressing member 70 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 31 from the position where the pressing member 70 contacts the intermediate transfer belt 31 to the secondary transfer section N2, with respect to the transport direction of the recording material P. Furthermore, for example, in the standby state of the image forming apparatus 100 (power ON and waiting for job input), or in the power OFF state or sleep state, the pressing member 70 can be positioned at a distance from (or simply in contact with) the intermediate transfer belt 31. For example, the neutral state of the moving mechanism 71 may be set to a state in which the pressing member 70 is at a distance from the intermediate transfer belt 31.

[0052] 5. Challenges For example, in the conventional moving mechanism 71 described above, the cams 73, which act as contact points, are provided at two locations, the front and the rear, in the width direction of the intermediate transfer belt 31 (the longitudinal direction of the pressing member 70). Each cam 73 then contacts the cam follower 72b, which acts as the contact point of the holding device 72. In this case, because the distance between the two cam followers 72b at the front and rear is relatively long, the distance of the cam follower 72b relative to the rotation axis of the cam 73 may differ between the front and rear depending on the precision of the parts of the holding device 72, such as the shape of the contact point with the cam 73. In this case, the final tip position of the pressing member 70 on the intermediate transfer belt 31 and the amount of pressure (penetration) on the intermediate transfer belt 31 may differ between the front and the rear. As a result, it may become difficult to make the contact distance between the intermediate transfer belt 31 and the recording material P uniform in the width direction of the intermediate transfer belt 31 (the longitudinal direction of the pressing member). Furthermore, for example, image defects may occur on either the front or rear side of the intermediate transfer belt 31 in the width direction (longitudinal direction of the pressing member 70) due to air gaps or friction caused by a long contact distance.

[0053] Therefore, in this embodiment, at least one of the at least two contact points provided on the holding device, which the contact point of the moving device that moves the holding device contacts, is provided on an adjustment member fixed to the holding device and configured to adjust the distance to the contact point. This makes it possible to suppress the effect of the difference in distance between the contact point and the contact point on the front and rear sides as described above. Further details will be explained below.

[0054] 6. Moving mechanism of this embodiment Next, the moving mechanism 81 of this embodiment will be described. Figure 7 is a perspective view of the moving mechanism 81 of this embodiment. The basic configuration and operation of the moving mechanism 81 of this embodiment are substantially the same as those of the conventional moving mechanism 71 described above. In Figure 7, the moving mechanism 81 of this embodiment is shown in the same way as the conventional moving mechanism 71 described above when viewed from the cam 73 side.

[0055] The moving mechanism 81 has a holding device (holding member) 82 that extends along the width direction of the intermediate transfer belt 31. The pressing member 70 is held by the holding device 82. The pressing member 70 has a free end (tip) 70a in the short direction that can contact the inner circumferential surface of the intermediate transfer belt 31 over substantially the entire width of the intermediate transfer belt 31, and can press the intermediate transfer belt 31. In this embodiment, a part of the fixed end (base end) 70b side in the short direction of the pressing member 70 is fixed to a mounting fixture 70c. The mounting fixture 70c is made of sheet metal having a plate-like portion that extends along the width direction of the intermediate transfer belt 31 (the longitudinal direction of the pressing member 70), and is used to attach the pressing member 70 to the holding device 82. The pressing member 70 has a portion of its fixed end 70b in the short direction fixed to a mounting fixture 70c by adhesive or the like over substantially its entire width in the longitudinal direction, and this mounting portion 70c is fixed to the holding device 82 by screws or the like. The pressing member 70 may also be directly fixed to the holding device 82. Rotating shafts 82a are provided at both ends in the longitudinal direction of the holding device 82. The holding device 82 is supported by the frame (not shown) of the intermediate transfer belt unit 30 via the rotating shafts 82a so that it can rotate around a rotation axis substantially parallel to the width direction of the intermediate transfer belt 31. In this way, by rotating the holding device 82 around a rotation axis substantially parallel to the width direction of the intermediate transfer belt 31, the pressing member 70 can be rotated around the rotation axis and its position can be changed.

[0056] The moving mechanism 81 also has a camshaft 84, which is a cylindrical member extending along the width direction of the intermediate transfer belt 31. The camshaft 84 is supported by the frame (not shown) of the intermediate transfer belt unit 30 so as to be able to rotate around a rotation axis that is substantially parallel to the width direction of the intermediate transfer belt 31. The moving mechanism 81 also has a cam 83, a drive gear 86a, and a flag (cam position flag) 87. These cam 83, drive gear 86a, and flag 87 are each fixed to the camshaft 84. There are two cams 83, one at each end in the rotation axis direction of the camshaft 84. The drive gear 86a is provided at the rear end in the rotation axis direction of the camshaft 84. The moving mechanism 81 also has a cam drive motor 85, which is a stepping motor, and a transmission gear train 86b as a drive source. The cam drive motor 85 and the transmission gear train 86b are provided on the rear side in the rotation axis direction of the camshaft 84. A drive gear 86a fixed to the camshaft 84 is driven and connected via a transmission gear train 86b to an output gear 85a fixed to the output shaft of the cam drive motor 85. The cam drive motor 85 and the transmission gear train 86b are supported by the frame (not shown) of the intermediate transfer belt unit 30. When the cam drive motor 85 rotates, the drive is transmitted to the camshaft 84 via the transmission gear train 86b and the drive gear 86a, and the cam 73 and the flag 87 rotate together with the camshaft 84 around a rotation axis that is substantially parallel to the width direction of the intermediate transfer belt 31.

[0057] The cam 83, acting as a contact portion, contacts a contact surface 91, which is provided on a cam follower member 90, an adjustment member fixed to the holding device 82, and acts as a contacted portion. The cam follower member 90 will be described in more detail later. The cam 73 forms a stepless surface whose radius from the center of rotation changes uniformly according to its rotation angle. This stepless surface contacts the contact surface 91 of the cam follower member 90. There are two cam follower members 90, one at each end in the longitudinal direction of the holding device 82. Each cam 83, provided at each end in the rotation axis direction of the cam shaft 84, contacts each cam follower member 90. Therefore, when the cam drive motor 85 rotates and the cam 73 rotates, the holding device 82 rotates around the pivot axis 82a due to the rotation of the cam 73. As a result, the moving mechanism 81 can move the pressing member 70 and change the position of the pressing member 70. As described above, changing the position of the pressing member 70 means, more specifically, changing the tip position of the pressing member 70 as if the intermediate transfer belt 31 were absent. Specifically, in this embodiment, changing the position of the pressing member 70 means changing the position of the movable holding device 82 of the moving mechanism 81.

[0058] Furthermore, the moving mechanism 81, like the conventional moving mechanism 71 described above, has a position sensor (not shown) supported by the frame (not shown) of the intermediate transfer belt unit 30. And, like the conventional moving mechanism 71 described above, the moving mechanism 81 can be set to a preset neutral state by the action of the position sensor and the flag 87. The operation of changing the position of the pressing member 70 by the moving mechanism 81 is the same as that of the conventional moving mechanism 71 described above, so a description will be omitted.

[0059] In this embodiment, a moving device 89 for moving the holding device 82 is constructed using a cam 83, a camshaft 84, a cam drive motor 85, a drive gear 86a, a transmission gear train 86b, and the like. The moving mechanism 81 is then constructed with the moving device 89 and the holding device 82.

[0060] In this embodiment, the moving mechanism 81 is configured such that a cam follower member 90, which is configured as a separate component, is fixed to the holding device 82, and the cam 83 is brought into contact with this cam follower member 90. This cam follower member 90 can be fixed after its position has been adjusted relative to the holding device 82.

[0061] Figures 8 and 9 are exploded perspective views showing the vicinity of the mounting portion of the cam follower member 90 on the front side of the retaining device 82. Figure 8 shows the state in which the cam follower member 90 has been removed from the retaining device 82, and Figure 9 shows the state in which the reinforcing plate 82c, which will be described later, has been removed.

[0062] The holding device 82 has a base member 82b that extends along the width direction of the intermediate transfer belt 31. The base member 82b is made of a resin material and has the aforementioned pivot shafts 82a at both ends in its longitudinal direction. The base member 82b is rotatably supported by the frame 30a of the intermediate transfer belt unit 30 via its pivot shafts 82a. The frame 30a may be the frame of a subunit equipped with a pressing member 70 and a holding device 82 that are detachable from the intermediate transfer belt unit 30. The pressing member 70 is fixed to the base member 82b by fastening means such as screws via the aforementioned mounting fixture 70c. The mounting fixture 70c is fixed to the lower side in the figure, which is the side of the base member 82b facing the intermediate transfer belt 31. In addition, a reinforcing plate 82c is fixed to the upper side in the figure, which is the side of the base member 82b opposite to the side to which the mounting fixture 70c is fixed, by fastening means such as screws. The reinforcing sheet metal 82c is made of sheet metal having a plate-like portion that extends along the longitudinal direction of the base member 82b, and in this embodiment it is provided for purposes such as reinforcing the holding device 82. However, a configuration without the reinforcing sheet metal 82c is also possible.

[0063] Then, near the longitudinal end of the holding device 82, the cam follower member 90 is positioned so as to overlap the reinforcing sheet metal 82c, which is fixed to the base member 82b, from above in the figure. This cam follower member 90 is fixed to the base member 82b by a screw (flanged screw) 95, which is a fastener (fixing device) that serves as a fixing means. In other words, the cam follower member 90 has a main part 92 on which a contact surface 91 is provided as a contacted part that the cam 83 contacts, as described above, and a base part 93 for fixing the cam follower member 90 to the holding device 82. The base part 93 is formed to follow the surface of the reinforcing sheet metal 82c, and the main part 92 is formed to stand upright in a direction intersecting the surface of the base part 93. The base portion 93 is provided with an adjustment hole 94, which is an elongated hole that intersects (in this embodiment is approximately perpendicular to) the rotation axis direction of the camshaft 84 (the longitudinal direction of the holding device 82 and the width direction of the intermediate transfer belt 31). On the other hand, the base member 82b is provided with a fixing hole 96 into which a screw 95 is screwed (Figure 9). The reinforcing plate 82c is also provided with a through hole 97 into which the screw 95 can pass through with some play. The reinforcing plate 82c is fixed to the base member 82b1 by fitting a positioning projection 82b1 provided on the base member 82b into a positioning hole 82c1 provided on the reinforcing plate 82c. As a result, the through hole 97 of the reinforcing plate 82c is positioned to match the fixing hole 96 of the base member 82b so that the screw 95 can be screwed into the fixing hole 96 of the base member 82b.

[0064] As described above, the adjustment hole 94 provided in the base 93 of the cam follower member 90 is an elongated hole that is long in a direction that intersects (approximately perpendicular in this embodiment) with the rotation axis direction of the cam shaft 84. Therefore, after adjusting the position of the cam follower member 90 relative to the base member 82b by moving the cam follower member 90 toward or toward the cam shaft 84 (the rotation axis of the cam 83), the cam follower member 90 can be fixed to the base member 82b with a screw 95.

[0065] Although Figures 8 and 9 only show the configuration of the front cam follower member 90, the configuration of the rear cam follower member 90 is similar in this embodiment (approximately symmetrical with respect to the center in the width direction of the intermediate transfer belt 31).

[0066] The position of the cam follower member 90 can be fixed using an adjustment jig so that it is at a sufficiently equal distance from the common rotation axis of the two cams 83. Subsequently, components such as the pressing member 70 can be assembled to the holding device 82 with the position of the cam follower member 90 fixed, and the holding device 82 can be assembled to the image forming apparatus 100 or the intermediate transfer belt unit 30.

[0067] Figure 10 is a perspective view of an example of a jig 200 for adjusting the position of the cam follower member 90. In this embodiment, the holding device 82 is set on the jig 200 with the reinforcing plate 82c attached to the base member 82b, and the adjustment assembly of the cam follower member 90 is performed. The jig 200 has a base portion 201 on which the holding device 82 is placed. The jig 200 also has two pivot axis positioning portions 201 provided on the base portion 201 that determine the position of the pivot axes 82a provided at both ends in the longitudinal direction of the base member 82 of the holding device 82. The jig 200 also has two jig contact portions 203 provided on the base portion 201, which are modeled after the cam 83 in the moving mechanism 81. The positions of the jig contact portions 203 relative to the pivot axis positioning portions 201 are determined so as to sufficiently match the positional relationship in the moving mechanism 81.

[0068] When assembling the cam follower member 90 to the holding device 82, the base member 82b, to which the reinforcing plate 82c is fixed, is set on the base portion 201 by holding the pivot shafts 82a at both ends in the longitudinal direction of the base member 82b in the pivot shaft positioning portion 201. Then, the cam follower member 90 is positioned on the reinforcing plate 82c so that the adjustment hole 94 of the cam follower member 90, the through hole 97 of the reinforcing plate 82c, and the fixing hole 96 of the base member 82b are aligned, and temporarily fastened with screws 95. In other words, the screws 95 are passed through the through hole 97 and the fixing hole 94 to position the cam follower member 90 so that it can move in the longitudinal direction of the adjustment hole 94, which is composed of elongated holes. After that, the cam follower member 90 is moved relative to the base member 82b so that the contact surface 91 of the cam follower member 90 contacts the jig contact portion 203. Then, with the cam follower member 90 in proper contact with the jig contact portion 203, the screw 95 is fully screwed into the fixing hole 96 of the base member 82b, thereby fixing the cam follower member 90 to the base member 82b with the screw 95.

[0069] Furthermore, the jig 200 is provided with a pressing portion 204 for pressing the base member 82b against the base portion 201 of the jig 200 in order to prevent the base member 82b from shifting position in the rotational direction around the pivot axis 82a, for example, when adjusting the position of the cam follower member 90.

[0070] In this embodiment, each of the two contact points is provided on a cam follower member 90 whose position can be adjusted. However, one of the contact points may be provided on a cam follower member 90 whose position can be adjusted, while the other is provided on a holding device (e.g., a base member) in a position that cannot be adjusted. Alternatively, one of the cam follower members 90 to which each of the two contact points is provided may be adjustable, while the other is fixed in a fixed position in a position that cannot be adjusted.

[0071] Furthermore, in this embodiment, the cam follower member 90 was configured to be fixed in place by the holding device 82 by continuously changing its position steplessly within a predetermined range, but it is not limited to this, and it may be configured to be fixed by changing its position stepwise.

[0072] Furthermore, in this embodiment, the relief portion that allows the screw 95 to move so that the cam follower member 90 can move was made up of an elongated hole, but it is not limited to a hole that is closed all around, and may be a groove or the like with a part of the periphery open. Also, conversely to this embodiment, a relief portion such as an elongated hole may be provided in the base member 82b, and a fixing hole may be provided in the cam follower member 90, and it may be fixed, for example, from the base member 82b side with a screw 95 or the like.

[0073] Furthermore, in this embodiment, the contact portion of the moving device 89 was provided on a rotatable cam 83, but for example, as shown in Figure 11, the contact portion of the moving device 89 may be provided on a movable part 89a that can slide using a solenoid or the like. Similarly, the holding device 82 is not limited to being rotatable, and may be, for example, slidable, as long as the position of the pressing member 70 can be changed according to the purpose.

[0074] Thus, in this embodiment, the image forming apparatus 100 includes a rotatable endless belt 31 that carries a toner image, a plurality of tension rollers that tension the belt 31, including an inner roller 32 and an upstream roller 35 positioned upstream of the inner roller 32 and adjacent to the inner roller 32 with respect to the rotational direction of the belt 31, an outer member 41 positioned opposite the inner roller 32 and forming a transfer section N2 that contacts the outer peripheral surface of the belt 31 to transfer a toner image from the belt 31 to the recording material P, a pressing member 70 that is able to contact the inner peripheral surface of the belt 31 along the width direction of the belt 31, upstream of the inner roller 32 and downstream of the upstream roller 35 with respect to the rotational direction of the belt 31, and can press the belt 31 from the inner peripheral surface side to the outer peripheral surface side, a movable holding device 82 that holds the pressing member 70, and a moving device 89 that moves the pressing member 70 by moving the holding device 82. In this embodiment, the moving device 89 has contact portions 83 at least two locations along the width direction of the belt 31 that abut against the holding device 82 and restrict the position of the holding device 82 in the direction of movement, and the holding device 82 has contact portions 91 at least two locations along the width direction of the belt 31 that the contact portions 83 abut against, and at least one of the at least two contact portions 91 is provided on an adjustment member 90 that is configured to be fixable at multiple positions on the holding device 82 where the distance of the contact portion 91 from the contact portion 83 is different.

[0075] In this embodiment, at least two contact portions 91 are provided on separate adjustment members 90 configured to be fixable at multiple positions on the holding device 82 where the distance of the contact portion 91 from the contact portion 83 is different. However, at least one of the at least two contact portions 91 may be configured so that its position on the holding device 82 cannot be changed. In this embodiment, the holding device 82 has a base member 82b to which the adjustment member 90 is fixed, and a fixing device 95 for fixing the adjustment member 90 to the base member 82b. The base member 82b or the adjustment member 90 is provided with a relief portion 94 that allows the fixing device 95 to move away from the adjustment member 90 relative to the base member 82b. In this embodiment, the holding device 82 is rotatable about a pivot axis that extends along the width direction of the belt 31. In this embodiment, the moving device 89 is configured to have a cam 83 with the contact portion described above, which is rotatable around a pivot axis extending along the width direction of the belt 31, and the adjustment member 90 is configured to be fixable at multiple positions in the holding device 82 where the contact portion 91 of the holding device 82 is at a different distance from the pivot axis of the cam 83. In this embodiment, the pressing member 70 is configured to have its longitudinal direction substantially parallel to the width direction of the belt 31, with the upstream end of the belt 31 in the rotation direction in the short direction being held by the holding device 82, and the downstream end of the belt 31 in the rotation direction in the short direction being able to contact the inner circumferential surface of the belt 31.

[0076] As described above, in this embodiment, the moving mechanism 81 changes the orientation of the holding device 82 by bringing the cam 83 into contact with the cam follower member 90 provided on the holding device 82. In this embodiment, the front and rear cam follower members 90 that define the amount of pressure (penetration) of the pressing member 70 against the intermediate transfer belt 31 are each made of separate components from the holding device 82, and the position of these cam follower members 90 with respect to the rotation axis of the cam 83 is adjustable. Because the holding device 82 has a relatively large number of parts, the accuracy of the positional relationship between the contacted parts may decrease due to overlapping tolerances. Therefore, by adjusting the distance of the contacted parts from the contacted parts on the holding device 82 side, the decrease in the accuracy of the positional relationship can be effectively suppressed (improved). On the other hand, because the cam 83 side has relatively few parts, the deviation in the positional relationship that can be adjusted on the cam 83 side is often sufficiently small. As described above, the cam follower member 90 can change its position, and when assembling the device, its position can be adjusted so that there is no difference between the front and rear sides of the amount of pressure (penetration) applied by the pressing member 70 to the intermediate transfer belt 31. This makes it possible to suppress the effect of the difference between the front and rear sides of the amount of pressure (penetration) applied by the pressing member 70 to the intermediate transfer belt 31.

[0077] [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.

[0078] In the above embodiment, the number of cams for moving the holding device was set to two, one at the front and one at the rear, but this number may be increased as needed. For example, a configuration with cams at three locations—the front, the rear, and one in between—may be used. In that case, a cam follower member whose position can be adjusted can be provided corresponding to each cam.

[0079] Furthermore, in the above embodiment, the cam was given a shape with a stepless surface whose radius from the center of rotation changes uniformly, but any shape that allows the orientation of the holding device to be adjusted (changed) according to the purpose is acceptable.

[0080] Furthermore, the pressing member may be a roller made of an elastic material such as sponge or rubber, or a roller made of a rigid material such as resin or metal. However, from the viewpoint of positioning the pressing member sufficiently close to the secondary transfer section, the pressing member is preferably a plate-shaped member as in the above-described embodiment. Also, a thin metal plate can be used as the pressing member.

[0081] 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. For example, the outer roller can be configured to contact the outer circumferential surface of the intermediate transfer belt via the secondary transfer belt. In such a configuration, the intermediate transfer belt and the secondary transfer belt are sandwiched 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, thereby forming the secondary transfer portion. In this case, the contact portion between the intermediate transfer belt and the secondary transfer belt is the secondary transfer portion (secondary transfer nip).

[0082] 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.

[0083] 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]

[0084] 31 Intermediate transfer belt 32 Secondary transfer inner roller 35 Secondary transfer roller 41 Secondary transfer outer roller 70 Pressing member 81 Moving mechanism 82 Holding device 83 Cam 84 Camshaft 85 Cam drive motor 89 Mobile device 90 Cam follower member 100 Image forming apparatus 200 jigs

Claims

1. A rotatable, endless belt that carries the toner image, 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, with respect to the rotational direction of the belt, is capable of contacting the inner circumferential surface of the belt along the width direction of the belt, upstream of the inner roller and downstream of the upstream roller, and is capable of pressing the belt from the inner circumferential surface side toward the outer circumferential surface side. A movable holding device for holding the pressing member, A moving device that moves the pressing member by moving the holding device, In an image forming apparatus having, The moving device has at least two contact portions in a direction along the width direction of the belt that contact the holding device and restrict the position of the holding device in the direction of movement. The holding device has at least two contact portions that the contact portion contacts in a direction along the width direction of the belt, An image forming apparatus characterized in that at least one of the at least two contact portions is provided on an adjustment member configured to be fixable at multiple positions in the holding device where the contact portion is at a different distance from the contact portion.

2. The image forming apparatus according to claim 1, characterized in that the at least two contact portions are provided on separate adjustment members configured to be fixable at a plurality of positions in the holding device where the distance of the contact portion to the contact portion is different.

3. The image forming apparatus according to claim 1, characterized in that at least one of the at least two contact portions is provided in such a way that its position in the holding device cannot be changed.

4. The holding device comprises a base member to which the adjustment member is fixed, and a fastener for fixing the adjustment member to the base member. The image forming apparatus according to claim 1, characterized in that the base member or the adjustment member is provided with a relief portion that allows the fixing device to be released and the adjustment member to be moved relative to the base member.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that the holding device is rotatable about a pivot axis extending along the width direction of the belt.

6. The moving device is configured to have a cam equipped with the contact portion, which is rotatable around a pivot axis extending along the width direction of the belt. The image forming apparatus according to any one of claims 1 to 4, characterized in that the adjustment member is configured to be fixable at a plurality of positions in the holding device where the contact portion of the cam is at different distances from the rotation axis.

7. The image forming apparatus according to any one of claims 1 to 4, characterized in that the pressing member is arranged such that its longitudinal direction is substantially parallel to the width direction of the belt, the upstream end in the short direction in the direction of rotation of the belt is held by the holding device, and the downstream end in the short direction in the direction of rotation of the belt is made of a plate-like member that can contact the inner circumferential surface of the belt.

Images