Image forming apparatus and movement amount detection device

Abstract

To correctly detect a movement amount in the width direction of a belt whose position in the thickness direction changes in comparison to a case of detecting the movement amount in the width direction of the belt on the basis of a rotation angle of a rotary member that can rotate around a rotational shaft along the conveyance direction of the belt.SOLUTION: An image formation apparatus comprises: image formation bodies 22, 32 which form images on a belt 52 or a recording medium P conveyed by the belt; movement mechanisms 39, 40, 47, 48 which move the belt in the movement direction MD along the thickness direction TD of the belt; a rotary member 57 which has a rotational shaft along the movement direction and a contact part that can rotate around the rotational shaft and is in contact with a side surface of the belt regardless of the position in the movement direction of the belt; an acquisition unit which acquires a physical amount that changes due to rotation around the rotational shaft of the contact part when the belt is moved in the width direction; and a detection unit which detects the movement amount in the width direction of the belt on the basis of the physical amount acquired by the acquisition unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a movement amount detection device. [Background technology]

[0002] Patent Document 1 discloses a belt meandering amount measuring device that measures the meandering amount of an endless belt that is wound around a plurality of rollers and rotated. In this belt meandering amount measuring device, a measurement reference portion of a predetermined length extending along the belt rotation direction, a first measurement portion that is offset in the belt width direction from the measurement reference portion and extends parallel to the belt rotation direction, and a second measurement portion that is offset in the belt width direction from the measurement reference portion and the first measurement portion and extends parallel to the belt rotation direction, and a sensor that outputs a voltage according to the positions of the measurement reference portion, the first measurement portion, and the second measurement portion in the belt width direction is disposed on one side end of the belt width direction, and data setting before use of the belt is performed. When the belt is rotating without meandering, the voltages at the measurement reference part, the first measurement part, and the second measurement part are measured using the measurement reference part as a reference position, and a conversion formula is calculated to express the relationship between the measurement result and the distance of the first measurement part and the second measurement part in the width direction of the belt from the reference position.When the belt is in use, a sensor measures the voltage at any of the positions of the measurement reference part, the first measurement part, and the second measurement part at predetermined intervals, converts it into a distance from the reference position in the width direction of the belt using the conversion formula, and measures the amount of meandering of the belt by calculating the difference in the distance from the reference position calculated at predetermined intervals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-256789 Summary of the Invention [Problem to be solved by the invention]

[0004] There is an image forming apparatus in which an image forming body that forms an image on the belt and a movement mechanism that moves the belt in its thickness direction are provided near the conveyed belt. Furthermore, in this image forming apparatus, a rotating member that can rotate around a rotation axis along the belt conveyance direction is brought into contact with the side of the belt, and the amount of movement of the belt in the width direction is detected based on a physical quantity that changes depending on the rotation angle of the rotating member.

[0005] In this image forming device, when the position of the belt in the thickness direction changes, the rotation angle of the rotating member per unit movement amount in the width direction of the belt changes, so this image forming device cannot accurately detect the movement amount in the width direction of the belt when the position in the thickness direction changes.

[0006] The object of the present invention is to enable accurate detection of the amount of movement of a belt in the width direction, whose position in the thickness direction changes, compared to when the amount of movement of a belt in the width direction is detected based on a physical quantity that changes due to the rotation of a rotating member that can rotate around a rotation axis along the belt conveying direction. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, an image forming apparatus according to a first aspect of the present invention comprises a conveyed belt, an image forming body that forms an image on the belt or on a recording medium conveyed by the belt, a moving mechanism that moves the belt in a moving direction along the thickness direction of the belt, a rotating member having a rotation axis along the moving direction and a contact portion that is rotatable around the rotation axis and that contacts the side of the belt regardless of the position of the belt in the moving direction, an acquisition unit that acquires a physical quantity that changes due to the rotation of the contact portion around the rotation axis when the belt moves in the width direction, and a detection unit that detects the amount of movement of the belt in the width direction based on the physical quantity acquired by the acquisition unit.

[0008] In order to achieve the above-mentioned object, a second aspect of the image forming apparatus according to the present invention is the image forming apparatus of the first aspect, wherein the contact portion is a linear portion extending in a direction along the rotation axis.

[0009] An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the second aspect, wherein the contact portion is a rounded portion.

[0010] Furthermore, a fourth aspect of the image forming apparatus according to the present invention is the image forming apparatus of the third aspect, wherein the rotating member has a rotating portion that rotates around the rotation axis and extends in a direction along the rotation axis, and the rotating portion has a first plate-shaped portion, a second plate-shaped portion that connects to the first plate-shaped portion so as to intersect with the first plate-shaped portion when viewed along the rotation axis, and the contact portion which is the R-surface portion formed at the connection portion between the first plate-shaped portion and the second plate-shaped portion.

[0011] Furthermore, a fifth aspect of the image forming apparatus according to the present invention is an image forming apparatus according to any one of the first to fourth aspects, wherein the rotating member has a rotating portion that extends in a direction along the rotation axis and rotates around the rotation axis, and a connecting portion that connects the rotation axis and one end of the rotating portion, and the area of a cross section intersecting the direction along the rotation axis is larger at the portion excluding the other end of the rotating portion than at the other end of the rotating portion.

[0012] In addition, a sixth aspect of the image forming apparatus according to the present invention is an image forming apparatus according to any one of the first to fifth aspects, and is equipped with an interlocking part separate from the rotating member that rotates in conjunction with the rotation of the contact part around the rotation axis, and an acquisition part that acquires a physical quantity that changes due to the rotation of the interlocking part.

[0013] Furthermore, a seventh aspect of the image forming apparatus according to the present invention is the sixth aspect of the image forming apparatus, and further includes a first biasing member that applies a force to the interlocking portion in a direction that causes the interlocking portion to contact the rotating member.

[0014] An eighth aspect of the image forming apparatus according to the present invention is an image forming apparatus according to any one of the first to seventh aspects, and has a second biasing member that applies a force to the contact portion in a direction that brings the contact portion into contact with the side of the belt.

[0015] A movement amount detection device according to a ninth aspect of the present invention comprises a rotating member having a rotation axis and a contact portion that is rotatable around the rotation axis and extends in a direction along the rotation axis, and an acquisition unit that acquires a physical quantity that changes due to the rotation of the contact portion when the contact portion is transported in a direction intersecting the extension direction of the rotation axis and rotates around the rotation axis while contacting a side of a detectable object that is movable in its width direction.

[0016] A movement amount detecting device according to a tenth aspect of the present invention is the movement amount detecting device according to the ninth aspect, wherein the contact portion is a linear portion extending in a direction along the rotation axis.

[0017] In addition, a movement amount detection device of an eleventh aspect according to the present invention is a movement amount detection device of the ninth or tenth aspect, and is equipped with a linkage part separate from the rotating member that rotates in conjunction with the rotation of the contact part around the rotation axis, and the acquisition part that acquires a physical quantity that changes due to the rotation of the linkage part. [Effects of the Invention]

[0018] According to the first aspect, the amount of movement in the width direction of a belt whose position in the thickness direction changes can be detected more accurately than when the amount of movement in the width direction of the belt is detected based on a physical quantity that changes due to the rotation of a rotating member that can rotate around a rotation axis along the belt conveying direction.

[0019] According to the second aspect, the amount of movement in the width direction of the belt, whose position in the thickness direction changes, can be detected more accurately than when the contact position of the contact portion with the side surface of the belt changes depending on the rotational position of the contact portion.

[0020] According to the third aspect, the belt is less likely to be damaged by the contact portion than when the contact portion is configured by the edge portion of a plate-like member.

[0021] According to the fourth aspect, the rotational movement of the rotating part becomes smoother compared to when the rotating part is a block body.

[0022] According to the fifth aspect, the mechanical strength of the rotating part can be increased and the rotational movement of the rotating part around the rotation axis can be stabilized compared to when the cross-sectional area of the entire rotating part intersecting the direction along the rotation axis is the same as that of the other end.

[0023] According to the sixth aspect, it is possible to detect the amount of movement in the width direction of a belt whose position in the thickness direction changes, by using a device including an interlocking unit and an acquisition unit.

[0024] According to the seventh aspect, the structure of the image forming apparatus is simpler than when the interlocking portion and the rotating member are connected via a link member.

[0025] According to the eighth aspect, the structure of the image forming apparatus is simpler than when the contact portion and the belt are connected by a mechanism that allows relative displacement.

[0026] According to the ninth aspect, the acquisition unit can acquire the physical quantity more accurately than when the acquisition unit acquires the physical quantity that changes due to the rotation of a rotating member that can rotate around a rotation axis along the transport direction of the object to be detected.

[0027] According to the tenth aspect, the acquisition unit can acquire the physical quantity more accurately than when the acquisition unit acquires the physical quantity that changes due to the rotation of a rotating member that can rotate around a rotation axis along the transport direction of the object to be detected.

[0028] According to the eleventh aspect, the acquisition unit can acquire the physical quantity more accurately than when the acquisition unit acquires the physical quantity that changes due to the rotation of a rotating member that can rotate around a rotation axis along the transport direction of the object to be detected. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic side view showing a transfer belt, a first photosensitive drum, a second photosensitive drum, a primary transfer roll, and a rotating member according to the present embodiment. [Figure 3]FIG. 2 is a schematic side view showing a transfer belt and a rotating member according to the present embodiment. [Figure 4] 1 is a perspective view showing a movement amount detection device according to an embodiment of the present invention; [Figure 5] 5 is a cross-sectional view of the movement amount detection device taken along the arrows VV in FIG. 4. [Figure 6] 6 is a cross-sectional view of the rotating member taken along the arrow line VI-VI in FIG. 3. [Figure 7] 7 is a cross-sectional view of the rotary member taken along the arrow VII-VII in FIG. 3. [Figure 8] 8 is a cross-sectional view of the rotary member taken along the arrow VIII-VIII in FIG. 3. [Figure 9] FIG. 2 is a schematic plan view of a rotating member and a transfer belt according to the present embodiment. [Figure 10] FIG. 10 is a schematic plan view of a rotating member and a transfer belt of a comparative example. [Figure 11] 10 is a schematic plan view of a rotary member, a rotary shaft, and a transfer belt according to a modified example. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Hereinafter, the upstream side of the recording paper P (as an example of a recording medium) in the transport direction may simply be referred to as the "upstream side," and the downstream side of the transport direction may simply be referred to as the "downstream side." Similarly, the upstream side of the transfer belt (belt) (material) 52 in the rotation direction (transport direction) may simply be referred to as the "upstream side," and the downstream side of the rotation direction (transport direction) may simply be referred to as the "downstream side." In the following description, the reference positions for the "upstream side" and "downstream side" of the transfer belt are the secondary transfer position T2 (nip region Np) described below. That is, the direction from the secondary transfer position T2 toward the push roll 49 after passing through the drive roll 44 is the "downstream side" of the transfer belt, and the direction from the secondary transfer position T2 toward the second photosensitive unit 30K after passing through the retract roll 47 is the "upstream side" of the transfer belt.

[0031] 1, an image forming apparatus 10 of this embodiment is an electrophotographic type that forms a toner image (one example of an image) on a recording paper P. The image forming apparatus 10 includes an image forming unit 12, a storage unit 14, a conveying unit 16, and a fixing device 18 within an apparatus main body (not shown). Each unit of the image forming apparatus 10 will be described below.

[0032] In the following description, the width direction (horizontal direction) of the device body is defined as the X direction, the up-down direction (vertical direction) of the device body is defined as the Y direction, and the front-to-rear direction (direction perpendicular to the paper surface) perpendicular to the X and Y directions is defined as the Z direction. Note that in Figure 1, the front side of the paper surface is the front, and the back side of the paper surface is the rear.

[0033] <Image forming section> The image forming section 12 has a function of forming a toner image on a recording paper P. The image forming section 12 has a first photosensitive unit 20, a second photosensitive unit 30, and a transfer device 50.

[0034] [Photosensitive unit] 1, the image forming apparatus 10 is provided with two first photoconductor units 20 and two second photoconductor units 30. Each first photoconductor unit 20 and each second photoconductor unit 30 is detachable from the apparatus main body. The image forming apparatus 10 has first photoconductor units 20Y and 20M for yellow (Y) and magenta (M), and second photoconductor units 30C and 30K for cyan (C) and black (K).

[0035] In the following description, when it is necessary to distinguish between the colors yellow (Y), magenta (M), cyan (C), and black (K), the letters Y, M, C, and K are added after the symbol of each component, and when it is not necessary to distinguish between the colors, the letters Y, M, C, and K may be omitted.

[0036] The transfer belt 52 of the transfer device 50, which will be described later and is made of an elastic material, has two linear portions that form a straight line when viewed from the Z direction. These two linear portions are an upper portion 52A and a lower portion 52B. When viewed from the Z direction, the upper portion 52A is aligned with the X direction, and the lower portion 52B is inclined with respect to the X direction. That is, when viewed from the Z direction, the angle θB (see FIG. 1) formed between the lower portion 52B and the X direction is an acute angle, and the angle θB is greater than the angle θA (not shown) formed between the upper portion 52A and the X direction. The angle θA is an acute angle of 0° or slightly larger than 0°. When viewed from the Z direction, the upper portion 52A and the lower portion 52B are aligned with each other in the Y direction. Note that the term "linear portion" in this specification and claims is not limited to a completely linear shape. For example, the upper portion 52A located between the retract roll 39 and the retract roll 48 described below has a slight recess in the area pressed by the two first photosensitive drums 22 and the primary transfer roll 41, but the upper portion 52A corresponds to a "straight portion." Similarly, the lower portion 52B located between the retract roll 40 and the retract roll 47 has a slight recess in the area pressed by the two second photosensitive drums 32 and the primary transfer roll 41, but the lower portion 52B corresponds to a "straight portion." The width direction of the transfer belt 52 is along the Z direction.

[0037] The two first photoconductor units 20 face the outer peripheral surface (top surface) of the upper portion 52A and are aligned in the X direction along the upper portion 52A. Each first photoconductor unit 20 has a first photoconductor drum 22 that rotates in one direction (e.g., counterclockwise in FIG. 1). Each first photoconductor drum 22 is rotatable around a rotation axis 20X extending in the Z direction. Each first photoconductor unit 20 also has, in order from the upstream side in the rotation direction of the first photoconductor drum 22, a first charging unit 24, a first exposure unit 25, a first developing unit 26, and a first removal unit 27. Each first photoconductor unit 20 also has a pair of support plates 28 spaced apart from each other in the Z direction. Note that one of the support plates 28 is not shown in FIG. 1. The first charging unit 24, the first exposure unit 25, the first developing unit 26, and the first removal unit 27 are members that extend in the Z direction. Both ends in the Z direction of the first charging unit 24, the first exposing unit 25, the first developing unit 26, and the first removing unit 27 are supported by a pair of support plates 28. Furthermore, the relative movement of the pair of support plates 28 is restricted. As shown in FIG. 1, the dimension in the X direction of each first photosensitive unit 20 is a horizontal dimension 20L.

[0038] The two second photosensitive units 30 face the outer peripheral surface (lower surface) of the lower portion 52B and are aligned along the lower portion 52B. Each second photosensitive unit 30 has a second photosensitive drum 32 that rotates in one direction (e.g., counterclockwise in FIG. 1). Each second photosensitive drum 32 is rotatable about a rotation axis 30X extending in the Z direction. Each second photosensitive unit 30 also has, in order from the upstream side in the rotation direction of the second photosensitive drum 32, a second charging unit 34, a second exposure unit 35, a second developing unit 36, and a second removing unit 37. Each second photosensitive unit 30 also has a pair of second support plates 38 spaced apart from each other in the Z direction. Note that one of the second support plates 38 is not shown in FIG. 1. The second charging unit 34, the second exposure unit 35, the second developing unit 36, and the second removing unit 37 are members that extend in the Z direction. Both ends in the Z direction of the second charging section 34, the second exposing section 35, the second developing section 36, and the second removing section 37 are supported by a pair of second support plates 38. Furthermore, the relative movement of the pair of second support plates 38 is restricted. As shown in FIG. 1, the dimension in the X direction of each second photosensitive unit 30 is a horizontal dimension 30L.

[0039] In this specification and claims, the term "image forming body" refers to a body that deposits toner or ink on a substrate (e.g., transfer belt 52). Specifically, the first photoconductor drum 22 of the first photoconductor unit 20 corresponds to the "image forming body," and the second photoconductor drum 32 of the second photoconductor unit 30 corresponds to the "image forming body." Specifically, the first charging unit 24, the first exposing unit 25, the first developing unit 26, and the first removing unit 27 do not correspond to the "image forming body." Similarly, the second charging unit 34, the second exposing unit 35, the second developing unit 36, and the second removing unit 37 do not correspond to the "image forming body." Note that, as will be described later, when the image forming apparatus 10 is an inkjet system, the inkjet head corresponds to the "image forming body."

[0040] The first distance 20B is the distance (adjacent distance) between two portions on the outer circumferential surface of the upper portion 52A where images are formed by the two first photosensitive drums 22 or two inkjet heads, as viewed in the Z direction. When the first photosensitive drums 22 correspond to the "image forming body," two line segments connecting each first photosensitive drum 22 and each primary transfer roll 41 corresponding to each first photosensitive drum 22 intersect with the outer circumferential surface of the upper portion 52A at two intersecting portions on the outer circumferential surface. When the first photosensitive drums 22 correspond to the "image forming body," the first distance 20B is the distance between the two intersecting portions as viewed in the Z direction. When the image forming apparatus 10 is an inkjet system, the first distance 20B is the distance between the centers of the inkjet heads (image forming bodies) corresponding to the first photosensitive units 20.

[0041] Furthermore, the distance between two portions of the outer peripheral surface of the lower portion 52B where images are formed by the two second photosensitive units 30 or two inkjet heads, as viewed in the Z direction, is the second distance 30B. When the second photosensitive drum 32 corresponds to the "image forming body," two line segments connecting each second photosensitive drum 32 and each primary transfer roll 41 corresponding to each second photosensitive drum 32 intersect with the outer peripheral surface of the lower portion 52B at two intersecting portions on the outer peripheral surface. When the second photosensitive drum 32 corresponds to the "image forming body," the distance between the two intersecting portions, as viewed in the Z direction, is the second distance 30B. When the image forming apparatus 10 is an inkjet system, the distance between the centers of the inkjet heads (image forming bodies) corresponding to the second photosensitive units 30 is the second distance 30B.

[0042] As shown in FIG. 1, the first developing unit 26 is provided with a developing roll 26A, a collecting auger 26B, a supply auger 26C, and an agitating auger 26D. Similarly, the second developing unit 36 is provided with a developing roll 36A, a collecting auger 36B, a supply auger 36C, and an agitating auger 36D. The supply auger 26C and the agitating auger 26D are aligned in the X direction. On the other hand, the supply auger 36C and the agitating auger 36D are aligned in the Y direction. Therefore, the horizontal dimension of the second developing unit 36 is shorter than the horizontal dimension of the first developing unit 26. Therefore, the horizontal dimension 30L is shorter than the horizontal dimension 20L.

[0043] As shown in FIG. 1, when viewed from the Z direction, the two first photosensitive units 20 are aligned in the X direction. That is, the two first photosensitive units 20 are not aligned in the Y direction. On the other hand, when viewed from the Z direction, portions of the two second photosensitive units 30 are aligned in the Y direction. The horizontal dimension 30V shown in FIG. 1 is the X direction dimension of the portions of the two second photosensitive units 30. 30E shown in FIG. 1 is the horizontal dimension of the portion consisting of the two second photosensitive units 30. 30G shown in FIG. 1 is the horizontal dimension of the portion consisting of the lower portion 52B and the two second photosensitive units 30.

[0044] The first charging unit 24 of each first photoconductor unit 20 charges the outer circumferential surface of the first photoconductor drum 22. Then, the first exposure unit 25 exposes the outer circumferential surface of the first photoconductor drum 22 charged by the first charging unit 24 to light, thereby forming an electrostatic latent image on the outer circumferential surface of the first photoconductor drum 22. Furthermore, the first developing unit 26 develops the electrostatic latent image formed on the outer circumferential surface of the first photoconductor drum 22 by the first exposure unit 25, thereby forming a toner image. Then, after the toner image is transferred to the transfer belt 52, the first removing unit 27 removes the toner remaining on the outer circumferential surface of the first photoconductor drum 22.

[0045] The second charging section 34 of each second photosensitive unit 30 charges the outer circumferential surface of the second photosensitive drum 32. Then, the second exposure section 35 exposes the outer circumferential surface of the second photosensitive drum 32 charged by the second charging section 34 to light, thereby forming an electrostatic latent image on the outer circumferential surface of the second photosensitive drum 32. Furthermore, the second developing section 36 develops the electrostatic latent image formed on the outer circumferential surface of the second photosensitive drum 32 by the second exposure section 35, thereby forming a toner image. Then, after the toner image is transferred to the transfer belt 52, the second removing section 37 removes the toner remaining on the outer circumferential surface of the second photosensitive drum 32.

[0046] [Transfer device] 1, the transfer device 50 includes four primary transfer rolls 41 as primary transfer bodies, a transfer belt 52 as intermediate transfer body, and a transfer cylinder 85 as secondary transfer body. That is, the transfer device 50 primarily transfers the toner images formed on the outer peripheral surfaces of the first photosensitive drums 22 onto the transfer belt 52 in an overlapping manner, and then secondarily transfers the overlapped toner images onto the recording paper P.

[0047] (Primary transfer roll) 1, each primary transfer roll 41 facing the upper portion 52A transfers the toner image formed on the outer circumferential surface of the corresponding first photosensitive drum 22 to the outer circumferential surface of the transfer belt 52 at a primary transfer position T1 between the first photosensitive drum 22 and the primary transfer roll 41. Each primary transfer roll 41 facing the lower portion 52B transfers the toner image formed on the outer circumferential surface of the corresponding second photosensitive drum 32 to the outer circumferential surface of the transfer belt 52 at a primary transfer position T1 between the second photosensitive drum 32 and the primary transfer roll 41. In this embodiment, a primary transfer voltage is applied between the primary transfer roll 41 and the first photosensitive drum 22, so that the toner image formed on the outer circumferential surface of the first photosensitive drum 22 is transferred to the outer circumferential surface of the transfer belt 52 at the primary transfer position T1. Similarly, when a primary transfer voltage is applied between the primary transfer roll 41 and the second photosensitive drum 32, the toner image formed on the outer surface of the second photosensitive drum 32 is transferred to the outer surface of the transfer belt 52 at the primary transfer position T1.

[0048] Furthermore, each primary transfer roll 41 is movable in the thickness direction TD (see arrow in FIG. 1) of the transfer belt 52. In this specification, the thickness direction TD of the transfer belt 52 refers to the thickness direction of the transfer belt 52 when each of retract rolls 39, 40, 47, and 48, which will be described later, is located at the pressing position. Furthermore, the rotation shaft of the primary transfer roll 41 is biased by a biasing member (not shown) in a direction approaching the inner circumferential surface of the transfer belt 52.

[0049] (Transfer belt) The circular transfer belt 52 shown in FIG. 1 is wound around four retract rolls 39, 40, 47, 48, a drive roll 44, a steering roll 45, a backup roll 46, and a push roll 49 to determine its position.

[0050] The retract rolls 39, 40, 47, and 48, which constitute the movement mechanisms of this embodiment, are in rotatable contact with the inner circumferential surface of the transfer belt 52 and are movable in a predetermined forward / backward direction RD. Each of the retract rolls 39, 40, 47, and 48 is movable in the forward / backward direction RD between a pressing position and a retracted position, which is a position on the inner circumferential side of the transfer belt 52 from the pressing position. The retract roll 39 is located downstream of the first photosensitive unit 20Y and upstream of the steering roll 45. The retract roll 40 is located upstream of the second photosensitive unit 30C and downstream of the steering roll 45. The retract roll 47 is located downstream of the second photosensitive unit 30K and upstream of the backup roll 46. The retract roll 48 is located upstream of the first photosensitive unit 20Y and downstream of the drive roll 44.

[0051] An upper portion 52A and a lower portion 52B of the transfer belt 52 are movable in a moving direction MD (see FIG. 1) along the thickness direction TD. As shown in FIG. 2, when the transfer belt 52 moves in the moving direction MD, the primary transfer roll 41 moves in the thickness direction TD following the transfer belt 52.

[0052] For example, when the retract rolls 40 and 47 are in the pressing position, the lower portion 52B is located at the first transport position PM1 shown by the solid lines in FIGS. 2 and 3. At this time, the second photoconductor unit 30C and the second photoconductor unit 30K can transfer a toner image to the transfer belt 52. When the retract rolls 40 and 47 are in the retracted position, the lower portion 52B is located at the second transport position PM2 shown by the phantom lines in FIGS. 2 and 3. At this time, the second photoconductor unit 30C and the second photoconductor unit 30K cannot transfer a toner image to the transfer belt 52. Although not shown, when the retract rolls 39 and 48 are in the pressing position, the upper portion 52A is located at the first transport position PM1, which corresponds to the first transport position PM1 in FIGS. 2 and 3. At this time, the first photoconductor unit 20Y and the first photoconductor unit 20M can transfer a toner image to the transfer belt 52. When the retract rolls 39 and 48 are in the retracted position, the upper portion 52A is located at the second transport position PM2, which corresponds to the second transport position PM2 in Figures 2 and 3. At this time, the first photosensitive unit 20Y and the first photosensitive unit 20M cannot transfer a toner image to the transfer belt 52. Note that by individually controlling the positions of the retract rolls 39, 40, 47, and 48, it is possible to set any one to three of the second photosensitive units 30 to a state in which they can transfer an image to the transfer belt 52.

[0053] The movement direction MD, which is a direction along the thickness direction TD of the transfer belt 52, includes a direction completely parallel to the thickness direction TD and a direction slightly inclined with respect to the thickness direction TD. When the movement direction MD is inclined with respect to the thickness direction TD, the inclination angle between the movement direction MD and the thickness direction TD when viewed along the Z direction is any value equal to or less than 10 degrees.

[0054] The drive roll 44, which has a circular cross section, is configured to be driven to rotate around an axis 44X extending in the Z direction by a drive unit (not shown), and rotates the transfer belt 52 in the direction indicated by arrow A at a predetermined speed.

[0055] The diameter of the steering roll 45, which has a circular cross section, is the same as the diameter of the drive roll 44 within the tolerance range. In other words, the outer circumferential length 45C of the steering roll 45 and the outer circumferential length 44C of the drive roll 44 are the same within the tolerance range. The steering roll 45 is rotatable around a rotation axis 45X extending in one direction. The steering roll 45 is an example of a deflecting roll. Furthermore, the steering roll 45 is rotatable around a rotation central axis provided at the center of the steering roll 45 in the direction of the rotation axis 45X and intersecting the rotation axis 45X. The neutral position of the steering roll 45 is the position in the rotation direction around the rotation central axis when the rotation axis 45X is parallel to the Z direction. Furthermore, the transfer device 50 includes a drive mechanism (not shown) that applies a drive force to the steering roll 45 to rotate the steering roll 45. When the drive mechanism applies a drive force to the steering roll 45 according to the amount of movement (amount of meandering) of the transfer belt 52 in the width direction detected by the movement amount detection devices 17A and 17B described later, the rotating steering roll 45 suppresses the meandering of the transfer belt 52.

[0056] The first distance 20B between the two first photosensitive drums 22 and the second distance 30B between the two second photosensitive drums 32 are set to be integer multiples of the outer circumferential length 44C of the drive roll 44 and the outer circumferential length 45C of the steering roll 45. The second distance 30B is shorter than the first distance 20B. For example, in this embodiment, the first distance 20B is set to be four times the outer circumferential length 44C and the outer circumferential length 45C, and the second distance 30B is set to be three times the outer circumferential length 44C and the outer circumferential length 45C.

[0057] The distance along the transfer belt 52 between the primary transfer position T1 of the downstream first photosensitive drum 22 and the primary transfer position T1 of the upstream second photosensitive drum 32 is a distance different from the first distance 20B and the second distance 30B. The distance along the transfer belt 52 between the primary transfer position T1 of the downstream first photosensitive drum 22 and the primary transfer position T1 of the upstream second photosensitive drum 32 is also set to an integer multiple of the outer circumferential length 44C of the drive roll 44 and the outer circumferential length 45C of the steering roll 45.

[0058] The backup roll 46 faces the transfer cylinder 85 across the transfer belt 52. The area where the transfer cylinder 85 and the transfer belt 52 contact is the nip area Np (see FIG. 1). The nip area Np is the secondary transfer position T2 where the toner image is transferred from the transfer belt 52 to the recording paper P.

[0059] Furthermore, a push-in roll 49, which is located upstream of the retract roll 48 and downstream of the drive roll 44, is in rotatable contact with the outer circumferential surface of the transfer belt 52 and presses the transfer belt 52 toward its inner circumferential side.

[0060] <Movement amount detection device> Two movement amount detection devices 17A and 17B are provided on a base plate 50A (not shown in FIG. 1; see FIG. 4) that supports the primary transfer roll 41, retract rolls 39, 40, 47, and 48, and drive roll 44. One of the movement amount detection devices 17A is disposed near one side surface 52G of the upper portion 52A in the width direction, and is located downstream of the first photoconductor unit 20Y and upstream of the first photoconductor unit 20M. The other movement amount detection device 17B is disposed near one side surface 52G of the lower portion 52B in the width direction, and is located downstream of the second photoconductor unit 30C and upstream of the second photoconductor unit 30K. As shown in FIGS. 4 and 5, the movement amount detection devices 17A and 17B include a rotation unit 55 and a detection unit 60.

[0061] The rotation unit 55 has a support member 56, a rotation member 57, a rotation shaft 58, and a coil spring 59. The support member 56, which is a press-molded metal product, has a first connection portion 56A, a fixed portion 56B, and a second connection portion 56C. The first connection portion 56A and the fixed portion 56B intersect with each other, and the first connection portion 56A and the second connection portion 56C intersect with each other.

[0062] The rotating member 57, which is a press-molded metal product, has a base 57A, a connecting portion 57B, a rotating portion 57C, and a pressing portion 57D. The base 57A has a vertical wall portion 57A1, a lower portion 57A2, and an upper portion 57A3. The lower portion 57A2 and the upper portion 57A3 are connected to both ends of the vertical wall portion 57A1, respectively. The lower portion 57A2 and the upper portion 57A3 intersect with the vertical wall portion 57A1. In other words, the cross section of the base 57A is substantially U-shaped.

[0063] One end of a metallic rotation shaft 58 extending in a direction intersecting the Z direction is fixed to the first connection portion 56A. The rotation shaft 58 penetrates the lower portion 57A2 and the upper portion 57A3. The base portion 57A (rotation member 57) is rotatable around the rotation shaft 58 relative to the support member 56.

[0064] One end of connecting portion 57B, which is flat and extends in one direction, is connected to upper portion 57A3. Upper portion 57A3 and connecting portion 57B are located on the same plane. One end of rotating portion 57C, which extends in a direction intersecting connecting portion 57B, is connected to the other end of connecting portion 57B. When viewed along rotating shaft 58, rotating portion 57C is located on the outer periphery of rotating shaft 58.

[0065] The rotating portion 57C has a first plate-shaped portion 57C1, a second plate-shaped portion 57C2, and a contact portion 57C3. The rotating portion 57C (first plate-shaped portion 57C1, second plate-shaped portion 57C2, and contact portion 57C3) extends in a direction along the rotation axis 58. Here, "extending in a direction along the rotation axis 58" includes the rotating portion 57C extending in a direction completely parallel to the rotation axis 58 and the rotating portion 57C extending in a direction slightly inclined with respect to the rotation axis 58. When the rotating portion 57C is inclined with respect to the rotation axis 58, the inclination angle formed between the rotating portion 57C and the rotation axis 58 when viewed along the Z direction is an arbitrary value of 10° or less.

[0066] As shown in FIGS. 6 to 8, when viewed along the rotation axis 58, the first plate-shaped portion 57C1 and the second plate-shaped portion 57C2 intersect with each other. The intersection angle θc between the first plate-shaped portion 57C1 and the second plate-shaped portion 57C2 is an obtuse angle. The first plate-shaped portion 57C1 has a wide portion 57C1a and a narrow portion 57C1b. The wide portion 57C1a is one end portion of the first plate-shaped portion 57C1 in the longitudinal direction. The narrow portion 57C1b, which is the portion of the first plate-shaped portion 57C1 excluding the one end portion, is narrower than the wide portion 57C1a. The second plate-shaped portion 57C2 has a wide portion 57C2a and a narrow portion 57C2b. The narrow portion 57C2b is narrower than the wide portion 57C2a. The longitudinal dimension of the wide portion 57C2a is greater than the longitudinal dimension of the wide portion 57C1a. A contact portion 57C3 is formed on a part of one surface of the rotating portion 57C. As will be described later, one surface of the rotating portion 57C faces one side surface 52G of the transfer belt 52. The linear contact portion 57C3 extending in the direction along the rotation shaft 58 is a connection portion between the first plate-shaped portion 57C1 and the second plate-shaped portion 57C2. As shown in FIGS. 6 to 8, the contact portion 57C3 has a rounded surface.

[0067] One end of a pressing portion 57D, which has a flat plate shape and extends in one direction, is connected to the upper portion 57A3. That is, the upper portion 57A3, the connecting portion 57B, and the pressing portion 57D are located on the same plane.

[0068] 4, both ends of a coil spring (second biasing member) 59 are fixed to the first connecting portion 56A of the support member 56 and the vertical wall portion 57A1 of the rotation member 57. The coil spring 59 is constantly elastically deformed. Therefore, the biasing force generated by the coil spring 59 biases the rotation member 57 to rotate counterclockwise in FIG.

[0069] The detection unit 60 includes a case 61, an optical sensor 67, an interlocking member 72, and a coil spring (first biasing member) 77.

[0070] The case 61 has a shape obtained by processing a portion of a rectangular parallelepiped. That is, a recess 62 is formed on one surface (the left surface in FIG. 5 ) of the case 61. One end 62A of the recess 62, which is along the rotation axis 58, is closed at both ends in the Z direction by a pair of support walls 63. Although not shown, the pair of support walls 63 are formed with bearings. Meanwhile, both ends in the Z direction of the recess 62, excluding the end 62A, are open. Furthermore, a space 64 is formed inside the case 61. As shown in FIG. 5 , the space 64 is in communication with the portion of the recess 62 excluding the end 62A. An optical sensor 67 is fixed to the inner surface of the space 64. The optical sensor 67 has a light-emitting element 68 and a light-receiving element 69 facing each other. The inspection light emitted by the light-emitting element 68 is received by the light-receiving element 69. The light-emitting element 68, the light-receiving element 69, and the drive mechanism are connected to a control device (detection unit) 80 shown in FIG. 5 .

[0071] The control device 80 has a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), storage, a communication I / F (Interface), and an input / output I / F. The CPU, ROM, RAM, storage, communication I / F, and input / output I / F are connected to each other via a bus so that they can communicate with each other. The CPU is a central processing unit that executes various programs and controls each component. That is, the CPU reads programs from the ROM or storage and executes the programs using the RAM as a working area. The CPU controls the drive mechanism and performs various arithmetic processing according to the programs. This arithmetic processing includes calculating the amount of movement of the transfer belt 52 in the width direction based on the amount of inspection light received by the light receiving element 69.

[0072] The interlocking member 72 is an integrally molded product having a supported shaft 73, a pressed portion 74, and a detected portion 75. One end of the pressed portion 74 and one end of the detected portion 75 are connected to the supported shaft 73, which extends along the Z direction. As shown in FIG. 5, the cross-sectional shape of the pressed portion 74 is approximately V-shaped, and the cross-sectional shape of the detected portion 75 is approximately L-shaped.

[0073] 5, both ends of interlocking member 72 are rotatably supported by bearings on the pair of support walls 63. The tip of detected portion 75 is located inside space 64. Most of pressed portion 74 is located outside case 61.

[0074] Furthermore, as shown in Figure 5, both ends of coil spring 77 are fixed to the inner surface of one end 62A and to supported shaft 73, respectively. Coil spring 77 is constantly elastically deformed. Therefore, the biasing force generated by coil spring 77 biases interlocking member 72 to rotate clockwise in Figure 5. The biasing force of coil spring 77 is smaller than the biasing force of coil spring 59.

[0075] As shown in FIGS. 4 and 5, the rotation unit 55 and the detection unit 60 are connected to each other. Specifically, the first connection portion 56A of the support member 56 is fixed to one surface (the top surface in FIG. 5) of the case 61, and the second connection portion 56C is fixed to another surface (the left surface in FIG. 5) of the case 61. When the rotation unit 55 and the detection unit 60 are connected to each other, the pressing portion 57D of the rotation member 57 and the pressed portion 74 of the interlocking member 72 come into contact with each other. As described above, the biasing force of the coil spring 77 is smaller than the biasing force of the coil spring 59. Therefore, the pressing portion 57D (the rotation member 57) is rotated counterclockwise in FIG. 9 by the coil spring 59, and the interlocking member 72 (pressed portion 74) in contact with the pressing portion 57D is rotated counterclockwise in FIG. 5 against the biasing force of the coil spring 77. When no external force other than that exerted by coil springs 59 and 77 is applied to rotating member 57 and interlocking member 72, rotating member 57 is located at an initial position 57IP shown by an imaginary line in Fig. 9, and interlocking member 72 is located at an initial position 72IP shown by an imaginary line in Fig. 5. Rotating unit 55 is provided with a stopper (not shown) for restricting counterclockwise rotation of rotating member 57 around rotation shaft 58 at initial position 57IP. Furthermore, fixed portions 56B of support members 56 of movement amount detecting devices 17A and 17B formed by connecting rotating unit 55 and detection unit 60 are fixed to base plate 50A with bolts or the like.

[0076] When the fixed portion 56B is fixed to the base plate 50A, the extension direction of the rotation shaft 58 is aligned with the movement direction MD. In other words, the extension directions of the rotating portion 57C and the rotation shaft 58 intersect with the conveyance direction of the transfer belt 52. Here, the "direction aligned with the movement direction MD" includes a direction completely parallel to the movement direction MD and a direction slightly inclined with respect to the movement direction MD. When the rotation shaft 58 is inclined with respect to the movement direction MD, the inclination angle between the movement direction MD and the axis of the rotation shaft 58 when viewed along the Z direction is any value equal to or less than 10°.

[0077] When the detected portion 75 is not located between the light-emitting element 68 and the light-receiving element 69, the light-receiving element 69 receives all of the inspection light emitted by the light-emitting element 68. When the detected portion 75 is located between the light-emitting element 68 and the light-receiving element 69, the light-receiving element 69 cannot receive all or part of the inspection light emitted by the light-emitting element 68. In other words, the amount of inspection light received by the light-receiving element 69 changes depending on the rotation angle of the detected portion 75 (interlocking member 72) about the supported shaft 73. In other words, the amount of inspection light received by the light-receiving element 69 changes depending on the rotation angle of the rotating member 57 (rotating portion 57C), which rotates in conjunction with the detected portion 75, about the rotation shaft 58.

[0078] 1 and 9, contact portion 57C3 of rotating portion 57C of movement amount detecting device 17A disposed near upper portion 52A contacts side surface 52G of upper portion 52A. Similarly, as shown in FIGS. 2, 3, and 9, contact portion 57C3 of rotating portion 57C of movement amount detecting device 17B disposed near lower portion 52B contacts side surface 52G of lower portion 52B. Furthermore, regardless of the position of retract rolls 39, 40, 47, and 48 in the movement direction MD, the contact state between contact portion 57C3 of movement amount detecting device 17A and side surface 52G of upper portion 52A is maintained, and the contact state between contact portion 57C3 of movement amount detecting device 17B and side surface 52G of lower portion 52B is also maintained.

[0079] Here, the position in the width direction of the transfer belt 52 shown by the solid line in Fig. 9 is defined as the reference position 52SP. When the transfer belt 52 is located at the reference position 52SP, the rotating member 57 (rotating portion 57C) is located at the reference rotation position 57SP shown by the solid line in Fig. 9 in a plan view. The reference rotation position 57SP is a position rotated by a predetermined angle clockwise in a plan view from the initial position 57IP shown by the imaginary line in Fig. 9. At this time, the interlocking member 72 is located at the reference rotation position 72SP shown by the solid line in Fig. 5.

[0080] The transfer belt 52 is movable in the width direction. That is, the transfer belt 52 is movable in the vertical direction in FIG. 9 from a reference position 52SP. When the transfer belt 52 moves to a first position 52P1 shown by a virtual line in FIG. 9, the rotating portion 57C (contact portion 57C3) of the movement amount detection devices 17A and 17B, which contacts a side surface 52G of the transfer belt 52, moves from the reference rotation position 57SP to the first rotation position 57P1 shown by a virtual line, following the transfer belt 52. As a result, the interlocking member 72 moves from the reference rotation position 72SP to the first rotation position 72P1 shown by a virtual line in FIG. 5. On the other hand, when the transfer belt 52 moves to the second position 52P2 shown by the imaginary line in FIG. 9, the rotating portion 57C (contact portion 57C3) of the movement amount detection device 17A, which contacts the side surface 52G of the transfer belt 52, moves from the reference rotation position 57SP to the second rotation position 57P2 shown by the imaginary line, following the transfer belt 52. As a result, the interlocking member 72 moves from the reference rotation position 72SP to the second rotation position 72P2 shown by the imaginary line in FIG. 5. The first position 52P1 is the position of the transfer belt 52 when the transfer belt 52 of this embodiment has moved most upward in FIG. 9. The second position 52P2 is the position of the transfer belt 52 when the transfer belt 52 of this embodiment has moved most downward in FIG. 9. In this way, by utilizing the biasing forces of coil spring 59 and coil spring 77, the contact state between contact portion 57C3 of rotating member 57 and side surface 52G of transfer belt 52 is maintained, and the contact state between pressing portion 57D and interlocking member 72 (pressed portion 74) is also maintained, so that rotating member 57 and interlocking member 72 can be rotated in conjunction with the widthwise movement of belt 52.

[0081] <Transportation section> 1, conveying section 16 has a conveying device (not shown) that conveys recording paper P sent out from storage section 14 in the direction of arrow B. The conveying device conveys recording paper P sent out from storage section 14 to transfer cylinder 85. Recording paper P onto which the toner image has been secondarily transferred by passing through transfer cylinder 85 (secondary transfer position T2) is then conveyed to fixing device 18 by the conveying device.

[0082] <Fixing device> 1, the fixing device 18 has a heating roll 42 as an example of a heating member and a pressure roll 43 as an example of a pressure member. The fixing device 18 fixes the toner image transferred to the recording paper P by the transfer cylinder 85 onto the recording paper P by sandwiching the recording paper P between the heating roll 42 and the pressure roll 43 and applying heat and pressure thereto.

[0083] Next, the operation and effects of the image forming apparatus 10 configured as above will be described in detail.

[0084] In the image forming apparatus 10 of this embodiment, the transfer belt 52, which is rotated in the direction of arrow A by the driving force generated by the drive roll 44, may meander in the width direction. Specifically, the transfer belt 52 may move from the reference position 52SP toward the first position P1 and the second position SP2, causing the rotating member 57 (rotating portion 57C) to rotate from the reference rotation position 57SP to the first rotation position 57P1 and the second rotation position 57P2. In other words, the interlocking member 72 may rotate from the reference rotation position 72SP to the first rotation position 72P1 and the second rotation position 72P2. As a result, the position of the detection target portion 75 in the rotational direction changes as shown in FIG. 5 . Therefore, the amount of inspection light (physical quantity) received by the light receiving element 69 changes. Specifically, the amount of inspection light received by the light receiving element 69 changes due to the rotation of the rotating portion 57C around the rotation axis 58. That is, the amount of inspection light received by the light receiving element 69 changes depending on the amount of movement of the transfer belt 52 in the width direction from the reference position 52SP.

[0085] Information regarding the amount of inspection light received by the light receiving element 69 is transmitted from the light receiving element 69 to the control device 80. The control device 80 receives this information and calculates the amount of movement of the transfer belt 52 in the width direction from the reference position 52SP based on the information, and controls the drive mechanism.

[0086] In the image forming apparatus 10 of this embodiment, the upper and lower portions 52A and 52B of the transfer belt 52 are movable in the movement direction MD between the first conveying position PM1 and the second conveying position PM2. As described above, regardless of the positions of the retract rolls 39, 40, 47, and 48 in the movement direction MD, the contact state between the contact portion 57C3 of the movement amount detection device 17A and the side surface 52G of the upper portion 52A is maintained, and the contact state between the contact portion 57C3 of the movement amount detection device 17B and the side surface 52G of the lower portion 52B is maintained. Furthermore, the linear contact portion 57C3 of the rotating portion 57C extends in the direction along the rotation shaft 58. Therefore, even if the position of the transfer belt 52 in the thickness direction TD changes, the magnitude of the rotation angle of the rotating member 57 (rotating portion 57C) per unit movement amount in the width direction of the transfer belt 52 is constant. Therefore, the movement amount detection devices 17A and 17B (optical sensor 67) of this embodiment can acquire the physical amount (light amount) more accurately than when acquiring a physical amount (light amount) that changes due to rotation of a rotating part that is rotatable around a rotation axis along the transport direction of the transfer belt 52. Therefore, the image forming apparatus 10 of this embodiment can detect the movement amount in the width direction of the transfer belt 52, whose position in the thickness direction TD changes, more accurately than when acquiring a physical amount (light amount) that changes due to rotation of a rotating part that is rotatable around a rotation axis along the transport direction of the transfer belt 52.

[0087] FIG. 10 also shows a rotating member 90 according to a comparative example of the present invention. The rotating portion 91 of the rotating member 90 is a plate-like member with a rectangular cross section. The outer peripheral surface of the rotating portion 91 is composed of four flat surfaces. A first corner 93 is formed between a first surface 92, one of the four surfaces, and a second surface 95 adjacent to the first surface 92. Similarly, a second corner 94 is formed between the first surface 92 and a third surface 96 adjacent to the first surface 92. The rotating member 90 extends in a direction parallel to the rotation axis 58. As shown by the solid line in FIG. 10, when the transfer belt 52 is located at the second position 52P2, the first corner 93 of the rotating portion 91 contacts the side surface 52G of the transfer belt 52. When the transfer belt 52 is located at the first position 52P1, the second corner 94 of the rotating portion 91 contacts the side surface 52G.

[0088] In FIG. 10, Dm1 is a line segment connecting the rotation shaft 58 and the first corner 93, and Dm2 is a line segment connecting the rotation shaft 58 and the second corner 94. The line segment Dm1 is longer than the line segment Dm2. That is, the length of the line segment Dm1 is different from the length of the line segment Dm2. Therefore, the rotation angle of the rotation unit 91 around the rotation shaft 58 when the transfer belt 52 moves a unit amount of movement in the width direction from the second position 52P2 is different from the rotation angle of the rotation unit 91 around the rotation shaft 58 when the transfer belt 52 moves a unit amount of movement in the width direction from the first position 52P1. Therefore, the optical sensor 67 of this comparative example may not accurately acquire the amount of received light (physical quantity) that changes due to the rotation of the rotating member 90. Therefore, the accuracy of the calculation amount (the amount of movement of the transfer device 50 in the width direction) calculated by the control device 80 based on the amount of received light may be reduced.

[0089] In contrast, contact portion 57C3 of rotating portion 57C of image forming apparatus 10 of this embodiment is linear (rounded) extending in the direction along rotation shaft 58. Therefore, even if the rotation position of rotating portion 57C changes, the length of the line segment connecting the contact position between contact portion 57C3 and side surface 52G of transfer belt 52 and rotation shaft 58 does not change. Therefore, image forming apparatus 10 of this embodiment can more accurately detect the amount of movement of transfer belt 52 in the width direction compared to when a part of planar first surface 92 is brought into contact with side surface 52G of transfer belt 52.

[0090] 10 are formed by corners of a plate-like member. Therefore, when the first corner 93 and the second corner 94 come into contact with the side surface 52G of the transfer belt 52, the transfer belt 52 is likely to be damaged. In contrast, the contact portion 57C3 of the rotating portion 57C of the rotating member 57 of this embodiment has a rounded surface shape. Therefore, the rotating portion 57C of the rotating member 57 of this embodiment is less likely to damage the transfer belt 52 than when the first corner 93 and the second corner 94, which are formed by corners of a plate-like member, come into contact with the side surface 52G of the transfer belt 52.

[0091] Furthermore, the area of a cross section of the rotating unit 57C of the image forming apparatus 10 of this embodiment, intersecting with the direction along the rotation axis 58, varies depending on the position of the rotating unit 57C in that direction. Specifically, the base end of the rotating unit 57C, which is the end connected to the connecting portion 57B, is defined as "one end," and the end of the rotating unit 57C where the narrow portion 57C2b is provided is defined as "the other end." In this case, as is clear from FIGS. 6 to 8 , the cross-sectional area of the portion of the rotating unit 57C excluding the other end is larger than the cross-sectional area of the other end of the rotating unit 57C. In other words, the cross-sectional area of the portion shown in FIGS. 7 and 8 is larger than the cross-sectional area of the portion shown in FIG. 6 . The mechanical strength of the rotating unit 57C configured in this manner is higher than when the cross-sectional area of the entire rotating unit 57C intersecting with the direction along the rotation axis 58 is the same as the cross-sectional area of the other end. Furthermore, the rotational movement of the rotating part 57C configured in this manner around the rotation axis 58 is more stable than when the cross-sectional area of the entire rotating part 57C intersecting the direction along the rotation axis 58 is the same as the cross-sectional area of the other end.

[0092] Furthermore, the rotating section 57C of the image forming apparatus 10 of this embodiment has a plate-like structure, which allows smoother rotation of the rotating section 57C of the image forming apparatus 10 compared to when the rotating section is a block body.

[0093] Furthermore, image forming apparatus 10 of this embodiment has coil spring 77 that applies force to interlocking member 72 in a direction that causes it to come into contact with rotating member 57. Therefore, the structure of image forming apparatus 10 of this embodiment is simpler than when rotating member 57 and interlocking member 72 are connected via a link member.

[0094] Furthermore, image forming apparatus 10 of this embodiment has coil spring 59 that applies force to rotating member 57 in a direction that brings contact portion 57C3 into contact with side surface 52G of transfer belt 52. Therefore, the structure of image forming apparatus 10 of this embodiment is simpler than when contact portion 57C3 (rotating member 57) and transfer belt 52 are connected by a mechanism that allows relative displacement between them.

[0095] Furthermore, the rotating member 57 of the image forming apparatus 10 of this embodiment has a pressing portion 57D that can come into contact with the pressed portion 74 of the detection unit 60. Therefore, the image forming apparatus 10 of this embodiment can detect the amount of movement in the width direction of the transfer belt 52, whose position in the thickness direction TD changes, by using the detection unit 60 that includes the interlocking member 72 and the optical sensor 67.

[0096] A second distance (adjacent distance) 30B, which is the distance between the rotation axes 30X of two second photosensitive drums 32 (image forming bodies) located downstream of the steering roll 45 and upstream of the transfer position onto the recording paper P, is an integer multiple of the outer circumferential length 45C of the steering roll 45. Therefore, compared to when the second distance 30B is a length other than an integer multiple of the outer circumferential length 45C, an increase in the amount of misregistration of the toner image formed on the transfer belt (formed body) 52 by the two second photosensitive drums 32 located downstream of the steering roll 45 is suppressed.

[0097] Furthermore, in the image forming apparatus 10, the first distance 20B between the two first photosensitive drums 22 and the second distance 30B between the two second photosensitive drums 32 are set to an integer multiple of the outer circumferential length 44C of the drive roll 44. Therefore, compared to when the first distance 20B and the second distance 30B are set to lengths other than an integer multiple of the outer circumferential length 44C, the amount of misregistration of the toner images formed on the transfer belt (image substrate) 52 by the two second photosensitive drums 32 located downstream of the steering roll 45 is prevented from increasing.

[0098] Furthermore, the second distance 30B between the two second photoconductor drums 32 located downstream of the first photoconductor drum 22 is shorter than the first distance 20B. In a comparative example (not shown) in which the second distance 30B is set to be equal to or longer than the first distance 20B, the second distance 30B is adjusted to match the first distance 20B. Therefore, the distance along the transfer belt 52 from the drive roll 44 to the second photoconductor unit 30K is shorter in this embodiment than in the comparative example. The longer this distance, the greater the cumulative amount of speed fluctuations in the transfer belt 52 and the error in the adjacent distance. Therefore, in the comparative example, the amount of misregistration of the toner images between the second photoconductor unit 30C and the second photoconductor unit 30K tends to be greater than the amount of misregistration of the toner images between the first photoconductor unit 20Y and the first photoconductor unit 20M. In contrast, in the embodiment, the distance between second photoconductor unit 30C and second photoconductor unit 30K (second distance 30B) is shorter than in the comparative example, and therefore the accumulated amount of speed fluctuation and adjacent distance error is smaller than in the comparative example. Therefore, in the present embodiment, the amount of toner image registration deviation is suppressed from increasing as the photoconductor drum is positioned downstream of transfer belt 52, compared to when second distance 30B is set to a length equal to or longer than first distance 20B.

[0099] The image forming apparatus 10 and movement amount detection devices 17A and 17B according to this embodiment have been described above with reference to the drawings. However, the image forming apparatus 10 and movement amount detection devices 17A and 17B according to this embodiment are not limited to those shown in the drawings, and can be modified in design as appropriate within the scope of the gist of the present invention.

[0100] For example, the image forming device 10 may be configured so that each first photosensitive unit 20 and each second photosensitive unit 30 forms a toner image on a recording paper P (image substrate) transported by a conveying belt (not shown) provided in place of the transfer belt 52.

[0101] In addition, in the present embodiment, a toner image is given as an example of an image, and here, a toner image formed by a dry electrophotographic method is used, but the present invention is not limited to this. For example, the image of the present invention may be a toner image formed by a wet electrophotographic method or an image formed by an inkjet method.

[0102] In addition, the image forming device 10 may be configured so that an ink image or a toner image is formed on a long, non-circular continuous paper (substrate) that is wrapped around multiple rotating bodies including a drive roll 44 and transported by these rotating bodies while having a shape with at least one straight portion when viewed along the Z direction, and a steering roll (changing roll) 45 is in rotatable contact with the inner surface of the continuous paper.

[0103] The smaller the angle formed by the line (not shown) connecting the contact portion 57C3 and the rotation shaft 58 in a plan view when the transfer belt 52 is positioned at the reference position 52SP and the conveyance direction A of the transfer belt 52, the better. That is, when this angle is small, the difference between the amount of rotation of the rotation portion 57C about the rotation shaft 58 when the transfer belt 52 moves a unit amount of widthwise movement from the reference position 52SP and the amount of rotation of the rotation portion 57C about the rotation shaft 58 when the transfer belt 52 moves a unit amount of widthwise movement from the first position 52P1 or the second position 52P2 becomes smaller. That is, the smaller this angle, the more accurately a sensor (e.g., optical sensor 67) that acquires the physical quantity can acquire the physical quantity that changes due to the rotation of the rotation portion 57C. Therefore, the present invention may be implemented, for example, in the modified embodiment shown in FIG. 11. The planar shape of the connecting portion 57B in this modified embodiment is V-shaped. In the example shown in FIG. 11, a portion of the connecting portion 57B is located directly below the upper portion 52A. In the example shown in Figure 11, when the transfer belt 52 is located at the reference position 52SP, the angle formed by the straight line connecting the contact portion 57C3 and the rotation shaft 58 in a plan view and the conveying direction A of the transfer belt 52 is approximately 0°.

[0104] Either the movement amount detection device 17A or the movement amount detection device 17B may be omitted from the image forming apparatus 10.

[0105] In addition to the movement amount detection device 17A and the movement amount detection device 17B, the image forming apparatus 10 may be provided with another movement amount detection device.

[0106] The number of types of colors of the image (toner image, ink image) formed on the formation target (transfer belt 52, recording medium P) does not have to be four. For example, the number of types of colors of the image may be six.

[0107] For example, three or more image forming members may be arranged along the upper portion 52A, and similarly, three or more image forming members may be arranged along the lower portion 52B. [Explanation of symbols]

[0108] 10 Image forming device 22 First photosensitive drum (image forming body) 32 Second photosensitive drum (image forming body) 39 Retract roll (movement mechanism) 40 Retract roll (movement mechanism) 47 Retract roll (movement mechanism) 48 Retract roll (movement mechanism) 52 Transfer belt (belt) (subject to be formed) 52G side 57 Rotating members 57B Connection part 57C Rotating part 57C1 First plate-shaped part 57C2 Second plate-shaped part 57C3 Contact part 59 Coil spring (second biasing member) 67 Optical sensor (acquisition unit) 72 Interlocking member (interlocking part) 77 Coil spring (first biasing member) 80 control device (detection unit) P Recording paper (recording medium) (subject to be formed) TD thickness direction MD movement direction

Claims

1. A conveying belt; an image forming member that forms an image on the belt or a recording medium transported by the belt; a moving mechanism that moves the belt in a moving direction along a thickness direction of the belt; a rotating member having a rotation axis along the moving direction and a contact portion that is rotatable around the rotation axis and that comes into contact with a side surface of the belt regardless of a position of the belt in the moving direction; an acquisition unit that acquires a physical quantity that changes due to rotation of the contact portion about the rotation axis when the belt moves in the width direction; a detection unit that detects the amount of movement of the belt in the width direction based on the physical amount acquired by the acquisition unit; Equipped with The contact portion is a rounded surface portion, the rotating member has a rotating part that rotates around the rotation axis and extends in a direction along the rotation axis, The rotating part is A first plate-shaped portion; a second plate-shaped portion connected to the first plate-shaped portion so as to intersect with the first plate-shaped portion when viewed along the rotation axis; the contact portion being the rounded surface portion formed at a connection portion between the first plate-shaped portion and the second plate-shaped portion; An image forming apparatus having the same.

2. The contact portion is a linear portion extending in a direction along the rotation axis. The image forming apparatus according to claim 1 .

3. The rotating member is a rotating portion that rotates around the rotation axis and extends in a direction along the rotation axis; a connecting portion that connects the rotary shaft and one end of the rotary portion; and an area of a cross section of the rotating part intersecting a direction along the rotation axis is larger at a portion of the rotating part excluding the other end than at the other end; 3. The image forming apparatus according to claim 1.

4. an interlocking portion that rotates in conjunction with the rotation of the contact portion about the rotation axis and that is separate from the rotating member; the acquisition unit acquiring the physical quantity that changes due to rotation of the interlocking unit; Equipped with The image forming apparatus according to any one of claims 1 to 3.

5. a first biasing member that applies a force to the interlocking portion in a direction that causes the interlocking portion to contact the rotating member; The image forming apparatus according to claim 4 .

6. a second biasing member that applies a force to the contact portion in a direction that causes the contact portion to contact the side surface of the belt; The image forming apparatus according to any one of claims 1 to 5.

7. a rotating member having a rotation axis and a contact portion rotatable around the rotation axis and extending in a direction along the rotation axis; an acquiring unit that acquires a physical quantity that changes due to the rotation of the contact portion when the contact portion is transported in a direction intersecting an extension direction of the rotation axis and rotates around the rotation axis while contacting a side surface of a detection object that is movable in a width direction of the contact portion; Equipped with The contact portion is a rounded surface portion, the rotating member has a rotating part that rotates around the rotation axis and extends in a direction along the rotation axis, The rotating part is A first plate-shaped portion; a second plate-shaped portion connected to the first plate-shaped portion so as to intersect with the first plate-shaped portion when viewed along the rotation axis; the contact portion being the rounded surface portion formed at a connection portion between the first plate-shaped portion and the second plate-shaped portion; A movement amount detection device having the same.

8. The contact portion is a linear portion extending in a direction along the rotation axis. The movement amount detection device according to claim 7.

9. an interlocking portion that rotates in conjunction with the rotation of the contact portion about the rotation axis and that is separate from the rotating member; the acquisition unit acquiring a physical quantity that changes due to rotation of the interlocking unit; Equipped with The movement amount detection device according to claim 7 or 8.

Images