Image forming apparatus

Abstract

To suppress increase in a positional deviation amount between images formed on a formation object body by a plurality of second image formation bodies located on the downstream side with respect to a change roll in comparison to a case where a second distance being the distance between the plurality of second formation object bodies located on the downstream side in the conveyance direction of the formation object body with respect to the change roll is equal to or greater than a first distance being the distance between a plurality of first image formation bodies located on the upstream side in the conveyance direction with respect to the change roll.SOLUTION: An image formation apparatus comprises: a formation object body 52; a change roll 45 which is in contact with an inner peripheral surface of the formation object body in a manner of being rotatable around a rotational axis 45X and can rotate around a rotation central axis intersecting the rotational axis; a plurality of first image formation bodies 22 which are arranged so as to be apart from each other by a first distance 20B on the upstream side of the formation object body with respect to the change roll and form images on the formation object body; and a plurality of second image formation bodies 32 which are arranged so as to be apart from each other by a second distance 30B shorter than the first distance on the downstream side with respect to the change roll and form images on the formation object body.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] The writing device of Patent Document 1 includes a writing unit in which writing elements are linearly arranged in a number equal to or greater than the number of output dots at the same width as the output width, a first reference position setting means for setting the same number of first reference lines as the number of output dots perpendicular to the arrangement direction of the writing elements, and driving means for selectively driving the writing elements closest to each of the plurality of first reference lines among the writing elements.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to suppress an increase in the amount of misalignment between images formed on a formation object by a plurality of second image forming bodies located on the downstream side in the conveyance direction of the formation object from a change roll, compared with a case where a second distance, which is the distance between the plurality of second image forming bodies located on the downstream side in the conveyance direction from the change roll, is equal to or greater than a first distance, which is the distance between the plurality of first image forming bodies located on the upstream side in the conveyance direction from the change roll.

Means for Solving the Problems

[0005] To achieve the above object, an image forming apparatus according to a first aspect of the present invention includes an annular formation object to be conveyed, A drive roll that rotatably contacts the inner peripheral surface of the object to be formed and conveys the object to be formed in a predetermined conveyance direction, and at a position separated from the drive roll in the conveyance direction a change roll that is rotatably in contact with the inner peripheral surface of the formation object around a rotation axis and can change an angle of the rotation axis with respect to the width direction of the formation object, and upstream of the change roll in the conveyance direction of the formation object and on the downstream side in the conveyance direction from the drive roll In this case, a plurality of first image forming bodies that form images on the object to be formed and are arranged at a first distance from each other along the object to be formed, and downstream of the changing roll in the conveyance direction of the object to be formed and on the upstream side in the conveyance direction from the drive roll In this case, it includes a plurality of second image forming bodies that form images on the object to be formed and are arranged at a second distance shorter than the first distance from each other along the object to be formed.

[0006] The image forming apparatus according to the second aspect of the present invention is the image forming apparatus according to the first aspect, and is located between the first image forming body located on the most downstream side among the plurality of first image forming bodies and the changing roll, and is rotatably in contact with the inner peripheral surface of the object to be formed. A first roll, and a second roll that is located between the second image forming body located on the most upstream side among the plurality of second image forming bodies and the changing roll and is rotatably in contact with the inner peripheral surface of the object to be formed. The changing roll changes the angle of the rotation axis with respect to the width direction of the object to be formed by rotating around a rotation center axis that intersects the rotation axis. When viewed along the rotation axes of the first roll and the second roll, the rotation direction of the changing roll around the rotation center axis is along the direction of the tangent line of the ellipse focused on the rotation axes of the first roll and the second roll.

[0007] Further, the image forming apparatus according to the third aspect of the present invention is the image forming apparatus according to the first or second aspect, and the object to be formed has a first linear portion that is linear when viewed along the rotation axis and is located upstream of the changing roll, and a second linear portion that is linear when viewed along the rotation axis and is located downstream of the changing roll. The angle formed by the second linear portion and the horizontal direction is larger than the angle formed by the first linear portion and the horizontal direction, which is an acute angle or 0°.

[0009] Also, the Fourth aspect image forming apparatus according to the present invention is First to third the image forming apparatus according to any one of the aspects, and the second distance is an integer multiple of the outer peripheral length of the changing roll.

Advantages of the Invention

[0010] According to the first aspect, when the second distance is equal to or greater than the first distance, an amount of displacement between images formed on the object to be formed by a plurality of second image forming members located downstream of the change roll is suppressed from increasing. Furthermore, according to the first aspect, when the second distance, which is the distance between a plurality of second image forming members located downstream of the change roll located downstream of the drive roll, is greater than or equal to the first distance, the amount of misalignment between the images formed on the object to be formed by the plurality of second image forming members is suppressed from increasing.

[0011] According to the second aspect, when a rotation direction around a rotation center axis of the change roll is different from a direction of a tangent line of an ellipse focused on a rotation axis of the first roll and a rotation axis of the second roll, an amount of displacement between images formed on the object to be formed by a plurality of second image forming members is suppressed from increasing.

[0012] According to the third aspect, when an angle that is an acute angle formed between the second straight portion and the horizontal direction is equal to or less than an acute angle formed between the first straight portion and the horizontal direction or an angle of 0°, it becomes easier to make a horizontal distance between a plurality of second image forming members shorter than a horizontal distance between a plurality of first image forming members.

[0014] Fourth aspect According to, when the second distance is different from an integral multiple of an outer peripheral length of the change roll, an amount of displacement between images formed on the object to be formed by a plurality of second image forming members is suppressed from increasing.

Brief Description of the Drawings

[0015] [Fig. 1] It is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. [Fig. 2] It is a schematic side view showing a transfer belt, a first photoreceptor drum, a second photoreceptor drum, a primary transfer roll, and a rotating member according to the present embodiment. [Fig. 3] It is a schematic cross-sectional view of a steering roll, a retract roll, and a transfer belt of the present embodiment

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, the upstream side in the conveyance direction of the recording paper P as an example of the recording medium may be simply referred to as the "upstream side", and the downstream side in the conveyance direction may be simply referred to as the "downstream side". Similarly, the upstream side in the circumferential direction (conveyance direction) of the transfer belt (belt) (object to be formed) 52 may be simply referred to as the "upstream side", and the downstream side in the circumferential direction (conveyance direction) may be simply referred to as the "downstream side". Note that the reference positions of the "upstream side" and "downstream side" of the transfer belt in the following description are the secondary transfer position T2 (nip region Np) described later. That is, the direction from the secondary transfer position T2 through the drive roll 44 and then toward the push roll 49 is the "downstream side" of the transfer belt, and the direction from the secondary transfer position T2 through the retract roll 47 and then toward the second photoreceptor unit 30K is the "upstream side" of the transfer belt.

[0017] As shown in FIG. 1, the image forming apparatus 10 of the present embodiment is an electrophotographic system that forms a toner image (an example of an image) on the recording paper P. The image forming apparatus 10 includes an image forming unit 12, a housing unit 14, a conveyance unit 16, and a fixing device 18 in the apparatus main body (not shown). Hereinafter, each part of the image forming apparatus 10 will be described.

[0018] In the following description, the width direction (horizontal direction) of the apparatus main body is defined as the X direction, the vertical direction (vertical direction) of the apparatus main body is defined as the Y direction, and the front-rear direction (direction orthogonal to the paper surface) orthogonal to the X direction and the Y direction is defined as the Z direction. In FIG. 1, the front side of the paper surface is the front, and the back side of the paper surface is the back.

[0019] <Image forming unit> The image forming unit 12 has a function of forming a toner image on the recording paper P. The image forming unit 12 includes a first photoreceptor unit 20, a second photoreceptor unit 30, and a transfer device 50.

[0020] [Photoreceptor unit] As shown in FIG. 1, two first photoreceptor units 20 and two second photoreceptor units 30 are provided. Each first photoreceptor unit 20 and each second photoreceptor unit 30 are detachable from the apparatus main body. The image forming apparatus 10 has first photoreceptor units 20Y, 20M for yellow (Y) and magenta (M), and second photoreceptor units 30C, 30K for cyan (C) and black (K).

[0021] In the following description, when it is necessary to distinguish each color of yellow (Y), magenta (M), cyan (C), and black (K), English letters Y, M, C, and K are appended after the reference numerals of each member, and when it is not necessary to distinguish each color, the English letters Y, M, C, and K may be omitted.

[0022] The transfer belt 52 formed of an elastic material of the transfer device 50 described later has two straight portions that form a straight line when viewed from the Z direction. These two straight portions are an upper portion 52A and a lower portion 52B. When viewed from the Z direction, the upper portion 52A is along 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 by the lower portion 52B and the X direction is an acute angle, and the angle θB is larger than the angle θA (not shown) formed by the upper portion 52A and the X direction. Note that 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 arranged side by side in the Y direction. Note that the "straight portion" in this specification and the claims is not limited to a completely straight shape. For example, the upper portion 52A located between the retract roll (first roll) 39 and the retract roll 48 described later is slightly recessed at the portion pressed by the two first photoreceptor drums 22 and the primary transfer roll 41, but the upper portion 52A corresponds to the "straight portion (first straight portion)". Similarly, the lower portion 52B located between the retract roll (second roll) 40 and the retract roll 47 is slightly recessed at the portion pressed by the two second photoreceptor drums 32 and the primary transfer roll 41, but the lower portion 52B corresponds to the "straight portion (second straight portion)". The width direction of the transfer belt 52 is along the Z direction.

[0023] The two first photoreceptor units 20 face the outer peripheral surface (upper surface) of the upper part 52A and are arranged in the X direction along the upper part 52A. Each first photoreceptor unit 20 has a first photoreceptor drum 22 that rotates in one direction (for example, the counterclockwise direction in FIG. 1). Each first photoreceptor drum 22 is rotatable about a rotation axis 20X extending in the Z direction. Also, each first photoreceptor unit 20 has, in order from the upstream side in the rotation direction of the first photoreceptor drum 22, a first charging unit 24, a first exposure unit 25, a first developing unit 26, and a first removing unit 27. Further, each first photoreceptor unit 20 has a pair of support plates 28 spaced apart from each other in the Z direction. Note that in FIG. 1, the illustration of one of the support plates 28 is omitted. The first charging unit 24, the first exposure unit 25, the first developing unit 26, and the first removing unit 27 are members extending in the Z direction. Both end portions in the Z direction of the first charging unit 24, the first exposure unit 25, the first developing unit 26, and the first removing unit 27 are respectively supported by the pair of support plates 28. Further, the relative movement of the pair of support plates 28 is restricted. As shown in FIG. 1, the dimension of each first photoreceptor unit 20 in the X direction is the horizontal dimension 20L.

[0024] The two second photoreceptor units 30 face the outer peripheral surface (lower surface) of the lower part 52B and are arranged along the lower part 52B. Each second photoreceptor unit 30 has a second photoreceptor drum 32 that rotates in one direction (for example, the counterclockwise direction in FIG. 1). Each second photoreceptor drum 32 is rotatable about a rotation axis 30X extending in the Z direction. Also, each second photoreceptor unit 30 has, in order from the upstream side in the rotation direction of the second photoreceptor drum 32, a second charging unit 34, a second exposure unit 35, a second developing unit 36, and a second removing unit 37. Further, each second photoreceptor unit 30 has a pair of second support plates 38 spaced apart from each other in the Z direction. Note that in FIG. 1, the illustration of one of the second support plates 38 is omitted. The second charging unit 34, the second exposure unit 35, the second developing unit 36, and the second removing unit 37 are members extending in the Z direction. Both end portions in the Z direction of the second charging unit 34, the second exposure unit 35, the second developing unit 36, and the second removing unit 37 are respectively supported by the pair of second support plates 38. Further, the relative movement of the pair of second support plates 38 is restricted. As shown in FIG. 1, the dimension of each second photoreceptor unit 30 in the X direction is the horizontal dimension 30L.

[0025] In this specification and the claims, the "image forming body" refers to a component that attaches toner or ink to the object to be formed (e.g., the transfer belt 52). That is, the first photosensitive drum 22 of the first photosensitive unit 20 corresponds to the "first image forming body", and the second photosensitive drum 32 of the second photosensitive unit 30 corresponds to the "second image forming body". That is, the first charging unit 24, the first exposure unit 25, the first developing unit 26, and the first cleaning unit 27 do not correspond to the "first image forming body". Similarly, the second charging unit 34, the second exposure unit 35, the second developing unit 36, and the second cleaning unit 37 do not correspond to the "second image forming body". As will be described later, when the image forming apparatus 10 is an inkjet type, the inkjet head corresponds to the "image forming body (first image forming body, second image forming body)".

[0026] The distance in the Z direction between two sites where images are formed by two first photosensitive drums 22 or two inkjet heads on the outer peripheral surface of the upper portion 52A is the first distance 20B. When the first photosensitive drum 22 corresponds to the "first 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 the outer peripheral surface of the upper portion 52A at two intersecting sites on the outer peripheral surface. When the first photosensitive drum 22 corresponds to the "first image forming body", the distance between the two intersecting sites as viewed in the Z direction is the first distance 20B. When the image forming apparatus 10 is an inkjet type, the distance between the centers of the inkjet heads (first image forming body) corresponding to the first photosensitive unit 20 is the first distance 20B.

[0027] Furthermore, the distance in the Z direction between two sites where images are formed by two second photoreceptor units 30 or two inkjet heads on the outer peripheral surface of the lower part 52B is the second distance 30B. When the second photoreceptor drum 32 corresponds to the "second image forming body", two line segments connecting each second photoreceptor drum 32 and each primary transfer roll 41 corresponding to each second photoreceptor drum 32 intersect the outer peripheral surface of the lower part 52B at two intersecting sites on the outer peripheral surface. When the second photoreceptor drum 32 corresponds to the "second image forming body", the distance between the two intersecting sites when viewed in the Z direction is the second distance 30B. When the image forming apparatus 10 is of the inkjet type, the distance between the central portions of the inkjet heads (second image forming bodies) corresponding to the second photoreceptor units 30 is the second distance 30B.

[0028] As shown in FIG. 1, inside the first developing unit 26, a developing roll 26A, a recovery auger 26B, a supply auger 26C, and a stirring auger 26D are provided. Similarly, inside the second developing unit 36, a developing roll 36A, a recovery auger 36B, a supply auger 36C, and a stirring auger 36D are provided. The supply auger 26C and the stirring auger 26D are arranged in the X direction. On the other hand, the supply auger 36C and the stirring auger 36D are arranged 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. For this reason, the horizontal dimension 30L is shorter than the horizontal dimension 20L.

[0029] As shown in FIG. 1, when viewed in the Z direction, the two first photoreceptor units 20 are arranged in the X direction. That is, the two first photoreceptor units 20 are not arranged in the Y direction. On the other hand, when viewed in the Z direction, a part of the two second photoreceptor units 30 are arranged in the Y direction. The horizontal dimension 30V shown in FIG. 1 is the X direction dimension of the said part of the two second photoreceptor units 30. The 30E shown in FIG. 1 is the horizontal dimension of the part composed of the two second photoreceptor units 30. The 30G shown in FIG. 1 is the horizontal dimension of the part composed of the lower part 52B and the two second photoreceptor units 30.

[0030] The first charging unit 24 of each first photoreceptor unit 20 charges the outer peripheral surface of the first photoreceptor drum 22. Then, the first exposure unit 25 exposes the outer peripheral surface of the first photoreceptor drum 22 charged by the first charging unit 24 to form an electrostatic latent image on the outer peripheral surface of the first photoreceptor drum 22. Further, the first developing unit 26 develops the electrostatic latent image formed on the outer peripheral surface of the first photoreceptor drum 22 by the first exposure unit 25 to form a toner image. And after the transfer of the toner image to the transfer belt 52, the first cleaning unit 27 removes the toner remaining on the outer peripheral surface of the first photoreceptor drum 22.

[0031] The second charging unit 34 of each second photoreceptor unit 30 charges the outer peripheral surface of the second photoreceptor drum 32. Then, the second exposure unit 35 exposes the outer peripheral surface of the second photoreceptor drum 32 charged by the second charging unit 34 to form an electrostatic latent image on the outer peripheral surface of the second photoreceptor drum 32. Further, the second developing unit 36 develops the electrostatic latent image formed on the outer peripheral surface of the second photoreceptor drum 32 by the second exposure unit 35 to form a toner image. And after the transfer of the toner image to the transfer belt 52, the second cleaning unit 37 removes the toner remaining on the outer peripheral surface of the second photoreceptor drum 32.

[0032] [Transfer device] As shown in FIG. 1, the transfer device 50 includes four primary transfer rolls 41 as primary transfer members, a transfer belt 52 as a transfer member, and a transfer cylinder 85 as a secondary transfer member. That is, the transfer device 50 superposes and primary transfers the toner image formed on the outer peripheral surface of each first photoreceptor drum 22 onto the transfer belt 52, and secondary transfers the superposed toner image onto the recording paper P.

[0033] (Primary transfer roll) As shown in FIG. 1, each primary transfer roll 41 facing the upper portion 52A transfers the toner image formed on the outer peripheral surface of each first photoreceptor drum 22 to the outer peripheral surface of the transfer belt 52 at the primary transfer position T1 between the first photoreceptor 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 peripheral surface of each second photoreceptor drum 32 to the outer peripheral surface of the transfer belt 52 at the primary transfer position T1 between the second photoreceptor drum 32 and the primary transfer roll 41. In the present embodiment, a primary transfer voltage is applied between the primary transfer roll 41 and the first photoreceptor drum 22, whereby the toner image formed on the outer peripheral surface of the first photoreceptor drum 22 is transferred to the outer peripheral surface of the transfer belt 52 at the primary transfer position T1. Similarly, a primary transfer voltage is applied between the primary transfer roll 41 and the second photoreceptor drum 32, whereby the toner image formed on the outer peripheral surface of the second photoreceptor drum 32 is transferred to the outer peripheral surface of the transfer belt 52 at the primary transfer position T1.

[0034] Furthermore, each primary transfer roll 41 is movable in the thickness direction TD of the transfer belt 52 (see the arrow in FIG. 1). Note that the thickness direction TD of the transfer belt 52 in this specification refers to the thickness direction of the transfer belt 52 when each of the retract rolls 39, 40, 47, 48 described later is in the pressing position. Further, the rotation axis of the primary transfer roll 41 is biased in a direction approaching the inner peripheral surface of the transfer belt 52 by a biasing member (not shown).

[0035] (Transfer Belt) The annular 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, and its posture is determined.

[0036] Each of the retract rollers 39, 40, 47, 48 which is the moving mechanism of the present embodiment is rotatably in contact with the inner peripheral surface of the transfer belt 52 and is movable in a predetermined forward and backward direction RD. Each of the retract rollers 39, 40, 47, 48 is movable in the forward and backward direction RD between a pressing position and a retracted position which is a position on the inner peripheral side of the transfer belt 52 from the pressing position. The retract roller 39 is located downstream of the first photoreceptor unit 20Y and upstream of the steering roller 45. The retract roller 40 is located upstream of the second photoreceptor unit 30C and downstream of the steering roller 45. The retract roller 47 is located downstream of the second photoreceptor unit 30K and upstream of the backup roller 46. The retract roller 48 is located upstream of the first photoreceptor unit 20Y and downstream of the drive roller 44.

[0037] The upper portion 52A and the lower portion 52B of the transfer belt 52 are movable in the 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 roller 41 moves in the thickness direction TD following the transfer belt 52.

[0038] For example, when the retract rollers 40 and 47 are in the pressed position, the lower part 52B is located at the first conveyance position PM1 shown by the solid line in FIG. 2. At this time, the second photoreceptor units 30C and 30K can transfer the toner image to the transfer belt 52. When the retract rollers 40 and 47 are in the retracted position, the lower part 52B is located at the second conveyance position PM2 shown by the phantom line in FIG. 2. At this time, the second photoreceptor units 30C and 30K cannot transfer the toner image to the transfer belt 52. Although not shown, when the retract roller 39 and the retract roller 48 are in the pressed position, the upper part 52A is located at the first conveyance position PM1 corresponding to the first conveyance position PM1 in FIG. 2. At this time, the first photoreceptor units 20Y and 20M can transfer the toner image to the transfer belt 52. When the retract roller 39 and the retract roller 48 are in the retracted position, the upper part 52A is located at the second conveyance position PM2 corresponding to the second conveyance position PM2 in FIG. 2. At this time, the first photoreceptor units 20Y and 20M cannot transfer the toner image to the transfer belt 52. By individually controlling the positions of the retract rollers 39, 40, 47, and 48, it is possible to make only any one to three of the second photoreceptor units 30 capable of transferring to the transfer belt 52.

[0039] The moving direction MD, which is the 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. The inclination angle formed by the moving direction MD and the thickness direction TD when viewed along the Z direction when the moving direction MD is inclined with respect to the thickness direction TD is an arbitrary magnitude of 10° or less.

[0040] The drive roller 44 having a circular cross section is configured to be rotationally driven about an axis 44X extending in the Z direction by a drive unit (not shown), and to circulate the transfer belt 52 in the circulation direction indicated by the arrow A at a predetermined speed.

[0041] The diameter of the steering roll 45 with a circular cross-section shown in FIGS. 1 and 3 is the same as that of the drive roll 44 within the tolerance range. In other words, the outer peripheral length 45C of the steering roll 45 and the outer peripheral length 44C of the drive roll 44 are the same within the tolerance range. The steering roll 45 is rotatable about a rotation axis 45X extending along one direction. The steering roll 45 is an example of a changing roll. Further, the steering roll 45 includes a rotation center axis 45AX intersecting the rotation axis 45X, provided at the central portion in the direction of the rotation axis 45X of the steering roll 45. The rotation center axis 45AX is rotatably supported by a rotation support portion (not shown) provided in the image forming apparatus 10. Therefore, the steering roll 45 is rotatable about the rotation center axis 45AX. The position of the rotation direction SD about the rotation center axis 45AX of the steering roll 45 when the rotation axis 45X is parallel to the Z direction is the neutral position of the steering roll 45. Further, the transfer device 50 includes a drive mechanism (not shown) that rotates the steering roll 45 about the rotation center axis 45AX by applying a driving force to the steering roll 45. When a movement detection device (not shown) detects the amount of movement (meandering amount) of the transfer belt 52 in the width direction when the transfer belt 52 moves (meanders) in the width direction, the drive mechanism applies a driving force corresponding to the detected amount of movement to the steering roll 45. As a result, the angle of the rotation axis 45X of the steering roll 45 rotating about the rotation center axis 45AX with respect to the width direction (Z direction) of the transfer belt 52 changes. As a result, the meandering of the transfer belt 52 is suppressed by the steering roll 45.

[0042] As shown in FIG. 3 here, assume an ellipse EL (refer to the chain line in FIG. 3) with the rotation axes 39X and 40X of the retract rollers 39 and 40 located at the pressing position (the position shown by the solid line) as two foci. When looking at the transfer device 50 along the rotation axes 39X and 40X of the retract rollers 39 and 40, the rotation direction SD of the steering roll 45 is along the tangent line TL (refer to the virtual line in FIG. 3) that contacts the ellipse EL at the position passing through the rotation axis 45X of the steering roll 45 in the neutral position. Whether the retract rollers 39 and 40 are located at the pressing position or the retracted position, the rotation direction SD is along the direction of the tangent line TL. Further, when the retract rollers 39 and 40 are located at the pressing position, the angle formed by the rotation direction SD and the tangent line TL is minimized. In other words, the angle formed by the rotation direction SD and the tangent line TL when the retract rollers 39 and 40 are located at the pressing position is smaller than the angle formed by the rotation direction SD and the tangent line TL when at least one of the retract rollers 39 and 40 is located at the retracted position. Further, when looking at the transfer device 50 along the rotation axes 39X and 40X of the retract rollers 39 and 40, the extension line 45EL of the rotation center axis 45AX passes through the midpoint of the line segment LS connecting the retract roller 39 located at the pressing position and the retract roller 40 located at the pressing position, and the line segment LS and the extension line 45EL are perpendicular to each other.

[0043] Here, "the rotation direction SD is along the direction of the tangent line TL" includes that the rotation direction SD and the direction of the tangent line TL are completely parallel, and that the rotation direction SD is slightly inclined with respect to the direction of the tangent line TL. The inclination angle formed by the rotation direction SD and the tangent line TL when looking along the Z direction when the rotation direction SD is inclined with respect to the direction of the tangent line TL is any magnitude of 10° or less.

[0044] Note that in this embodiment, the positions of the rotation axes 39X and 40X are set so that the retract rollers 39 and 40 are symmetric with respect to the extension line 45EL. However, as long as the inclination angle formed by the rotation direction SD and the tangent line TL is any magnitude of 10° or less, one of the retract roller 39 and the retract roller 40 may be provided at a position slightly deviated from these positions.

[0045] The first distances 20B between the two first photoreceptor drums 22 and the second distances 30B between the two second photoreceptor drums 32 are set to be integer multiples of the outer peripheral length 44C of the drive roll 44 and the outer peripheral 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 4 times the outer peripheral length 44C and the outer peripheral length 45C, and the second distance 30B is set to be 3 times the outer peripheral length 44C and the outer peripheral length 45C.

[0046] The distance along the transfer belt 52 between the primary transfer position T1 of the downstream first photoreceptor drum 22 and the primary transfer position T1 of the upstream second photoreceptor drum 32 is a distance different from the first distance 20B and the second distance 30B. That is, the distance along the transfer belt 52 between the primary transfer position T1 of the downstream first photoreceptor drum 22 and the primary transfer position T1 of the upstream second photoreceptor drum 32 does not correspond to the "adjacent distance (first distance, second distance)" in the claims. The distance along the transfer belt 52 between the primary transfer position T1 of the downstream first photoreceptor drum 22 and the primary transfer position T1 of the upstream second photoreceptor drum 32 is also set to be an integer multiple of the outer peripheral length 44C of the drive roll 44 and the outer peripheral length 45C of the steering roll 45.

[0047] The backup roll 46 faces the transfer cylinder 85 with the transfer belt 52 interposed therebetween. The region where the transfer cylinder 85 and the transfer belt 52 are in contact is the nip region Np (see FIG. 1). The nip region Np is the secondary transfer position T2 where the toner image is transferred from the transfer belt 52 to the recording paper P.

[0048] Furthermore, the push-in roll 49, which is located upstream of the retract roll 48 and downstream of the drive roll 44, rotatably contacts the outer peripheral surface of the transfer belt 52 and presses the transfer belt 52 toward the inner peripheral side.

[0049] <Conveying unit> As shown in FIG. 1, the conveying unit 16 has a conveying device (not shown) that conveys the recording paper P sent out from the storage unit 14 in the direction of arrow B. By the conveying device, the recording paper P sent out from the storage unit 14 is conveyed to the transfer cylinder 85. The recording paper P on which the toner image has been secondarily transferred by passing through the transfer cylinder 85 (secondary transfer position T2) is conveyed to the fixing device 18 by the conveying device.

[0050] <Fixing device> As shown in FIG. 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 onto the recording paper P by the transfer cylinder 85 to the recording paper P by heating and pressing the recording paper P with the heating roll 42 and the pressure roll 43.

[0051] Next, the operation and effects of the image forming apparatus 10 having the above configuration will be described in detail.

[0052] In the image forming apparatus 10 of the present embodiment, the second distance 30B between the two second photoreceptor drums 32 located downstream of the first photoreceptor drum 22 is shorter than the first distance 20B. By the way, in the case of a comparative example (not shown) in which the second distance 30B is set to a length 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 photoreceptor unit 30K is shorter in the present embodiment than in the comparative example. The longer this distance is, the greater the speed variation of the transfer belt 52 and the cumulative amount of errors in the adjacent distances become. Therefore, in the comparative example, the amount of registration deviation of the toner image between the second photoreceptor unit 30C and the second photoreceptor unit 30K is likely to be larger than the amount of registration deviation of the toner image between the first photoreceptor unit 20Y and the first photoreceptor unit 20M. On the other hand, in the embodiment, since the distance (second distance 30B) between the second photoreceptor unit 30C and the second photoreceptor unit 30K is shorter than in the comparative example, the cumulative amount of speed variation and errors in the adjacent distances is smaller than in the comparative example. Therefore, in the present embodiment, compared with the case where the second distance 30B is set to a length equal to or longer than the first distance 20B, it is suppressed that the amount of registration deviation of the toner image increases as the position of the photoreceptor drum is located downstream of the transfer belt 52.

[0053] Furthermore, in the image forming apparatus 10 of the present embodiment, when viewing the transfer device 50 along the rotation axes 39X and 40X of the retract rolls 39 and 40, the rotation direction SD of the steering roll 45 in the neutral position is along the tangent line TL of the ellipse EL at the position passing through the steering roll 45. Therefore, compared with the case where the rotation direction SD of the steering roll 45 in the neutral position is different from the direction of the tangent line TL, the difference in the circumferential length of both side edges of the transfer belt 52 when the steering roll 45 rotates is smaller. Therefore, compared with the case where the rotation direction SD of the steering roll 45 in the neutral position is different from the direction of the tangent line TL, it is suppressed that the amount of registration deviation of the toner image formed on the transfer belt (formed body) 52 by the two second photoreceptor drums 32 located downstream of the steering roll 45 increases.

[0054] Furthermore, when viewed from the Z direction, the acute angle θB formed between the linear lower part 52B and the horizontal direction (X direction) is larger than the angle θA formed between the linear upper part 52A and the horizontal direction. And two second photoreceptor units 30 are provided along the lower part 52B. Further, the second distance 30B, which is the distance (adjacent distance) between the two rotation axes 30X when viewed from the Z direction, is shorter than the first distance 20B, which is the distance (adjacent distance) between the two rotation axes 20X. Therefore, compared with the case where the intervals between adjacent image forming bodies (the first photoreceptor drum 22 and the second photoreceptor drum 32) respectively arranged in plurality on the upper part 52A and the lower part 52B are all the same, the horizontal dimension 30G of the part composed of the lower part 52B and the two second photoreceptor units 30 is smaller. Further, the horizontal distance 30BH (see FIG. 1), which is the horizontal distance when viewed from the Z direction between two parts on the transfer belt 52 on which an image is formed by the second photoreceptor unit 30, is shorter than the first distance 20B. Therefore, compared with the case where the intervals between adjacent image forming bodies respectively arranged in plurality on the upper part 52A and the lower part 52B are all the same, the horizontal dimension of the image forming apparatus 10 when viewed from the Z direction is smaller.

[0055] The second distance (adjacent distance) 30B, which is the distance between the rotation axes 30X of the two second photoreceptor drums 32 located downstream of the steering roll 45 and upstream of the transfer position to the recording paper P, is an integral multiple of the outer peripheral length 45C of the steering roll 45. Therefore, compared with the case where the second distance 30B is a length different from an integral multiple of the outer peripheral length 45C, an increase in the amount of deviation of the registration of the toner image formed on the transfer belt (formed body) 52 by the two second photoreceptor drums 32 located downstream of the steering roll 45 is suppressed.

[0056] Furthermore, in the image forming apparatus 10, the first distance 20B between the two first photoreceptor drums 22 and the second distance 30B between the two second photoreceptor drums 32 are set to be integer multiples of the outer peripheral length 44C of the driving roll 44. Therefore, compared with the case where the first distance 20B and the second distance 30B are set to lengths different from integer multiples of the outer peripheral length 44C, the amount of deviation in the registration of the toner image formed on the transfer belt (object to be formed) 52 by the two second photoreceptor drums 32 located downstream of the steering roll 45 is suppressed from increasing.

[0057] As described above, the image forming apparatus 10 according to the present embodiment has been described with reference to the drawings. However, the image forming apparatus 10 according to the present embodiment is not limited to that shown in the drawings, and can be appropriately designed and changed within a range not departing from the gist of the present invention.

[0058] For example, the image forming apparatus 10 may be configured such that each first photoreceptor unit 20 and each second photoreceptor unit 30 form a toner image on a recording paper P (object to be formed) conveyed by a conveyance belt (not shown) provided in place of the transfer belt 52.

[0059] Also, in the present embodiment, a toner image is given as an example of an image, and here it is a toner image formed by a dry electrophotographic method. However, 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 may be an image formed by an inkjet method.

[0060] Furthermore, an image by ink or a toner image may be formed on a long and non-circular continuous paper (object to be formed) that is wound around a plurality of rotating bodies including the driving roll 44 and is conveyed by these rotating bodies while having at least one straight portion when viewed along the Z direction, and the image forming apparatus 10 may be configured such that the steering roll (changing roll) 45 rotatably contacts the inner peripheral surface of the continuous paper.

[0061] When the image forming apparatus 10 includes the first photoreceptor unit 20 and the second photoreceptor unit 30, each adjacent distance may be the same within the tolerance range. Similarly, when the image forming apparatus 10 includes an inkjet, each adjacent distance may be the same within the tolerance range.

[0062] When the image forming apparatus 10 includes either the first photoreceptor unit 20 and the second photoreceptor unit 30 or an inkjet, each adjacent distance may not be an integer multiple of the outer peripheral length 44C and the outer peripheral length 45C.

[0063] The diameter of the steering roll 45 and the diameter of the drive roll 44 may be different from each other. However, also in this case, it is preferable to set the diameter of the steering roll 45 and the diameter of the drive roll 44 so that each adjacent distance becomes an integer multiple of the outer peripheral length 45C and the outer peripheral length 44C.

[0064] The number of types of colors of the images (toner images, ink images) formed on the object to be formed (transfer belt 52, recording medium P) may not be four. For example, the number of types of colors of the images may be six.

[0065] For example, three or more image forming members may be arranged along the upper portion 52A. Similarly, three or more image forming members may be arranged along the lower portion 52B.

Description of Reference Numerals

[0066] 10 Image forming apparatus 20B First distance (adjacent distance) 22 First photoreceptor drum (first image forming member) 30B Second distance (adjacent distance) 32 Second photoreceptor drum (second image forming member) 39 Retract roll (first roll) 40 Retract roll (second roll) 44 Drive roll 45 Steering roll (changing roll) 45X Rotation axis 45AX Rotation center axis 52 Transfer belt (belt) (object to be formed) 52A Upper part (first straight part) 52B Lower part (second straight part) P Recording paper (recording medium) (object to be formed) SD Rotation direction EL Ellipse TL Tangent line

Claims

1. An annular object to be formed to be conveyed, A drive roll that rotatably contacts the inner peripheral surface of the object to be formed and conveys the object to be formed in a predetermined conveyance direction, A change roll that rotatably contacts the inner peripheral surface of the object to be formed at a position away from the drive roll in the conveyance direction, and can change the angle of the rotation axis with respect to the width direction of the object to be formed, A plurality of first image forming members that form images on the object to be formed, arranged at a first distance from each other along the object to be formed, upstream of the change roll in the conveyance direction of the object to be formed and downstream of the drive roll in the conveyance direction, A plurality of second image forming members that form images on the object to be formed, arranged at a second distance shorter than the first distance from each other along the object to be formed, downstream of the change roll in the conveyance direction of the object to be formed and upstream of the drive roll in the conveyance direction, An image forming apparatus comprising the above.

2. A first roll that is located between the first image forming member located on the most downstream side among the plurality of first image forming members and the change roll and rotatably contacts the inner peripheral surface of the object to be formed, A second roll that is located between the second image forming member located on the most upstream side among the plurality of second image forming members and the change roll and rotatably contacts the inner peripheral surface of the object to be formed, Comprising, The change roll changes the angle of the rotation axis with respect to the width direction of the object to be formed by rotating around a rotation center axis that intersects the rotation axis, When viewed along the rotation axes of the first roll and the second roll, the rotation direction of the change roll around the rotation center axis is along the direction of the tangent to the ellipse with the rotation axes of the first roll and the second roll as the foci, The image forming apparatus according to Claim 1.

3. The object to be formed has a first straight portion that is linear when viewed along the rotation axis and is located upstream of the change roll, and a second straight portion that is linear when viewed along the rotation axis and is located downstream of the change roll, The acute angle formed by the second straight portion and the horizontal direction is larger than the acute angle or 0° formed by the first straight portion and the horizontal direction, The image forming apparatus according to Claim 1 or Claim 2.

4. The second distance is an integer multiple of the outer peripheral length of the change roll, The image forming apparatus according to any one of Claims 1 to 3.

Images