Image forming apparatus

Abstract

To prevent an image forming section from being excited.SOLUTION: An image forming apparatus comprises: a rotating transfer barrel; a rotary member that is provided coaxially with the transfer barrel and rotates integrally with the transfer barrel; circulating members that are provided with a holding section that holds a leading end of a recording medium, are wound around the rotary member, and circulate in association with the rotation of the rotary member to convey the recording medium; an image forming section that forms an image; and a transfer unit having a transfer belt that is transferred with the image from the image forming section at a contact position with the image forming section and sandwiches the recording medium conveyed by the circulating members with the transfer barrel at a sandwiching position to transfer the image. The product of the mass of the transfer barrel and the distance from the mass gravity point of the transfer unit to the sandwiching position is smaller than the product of the mass of the image forming section and the distance from the mass gravity point to the contact position.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a transfer device including a belt-shaped image carrier that carries an image, a drive roller that winds around and moves the image carrier carrying the image, a first tension roller that winds around the image carrier moved by the drive roller and applies tension to the image carrier, a first elastic member that generates the tension, a first elastic support portion that supports one end of the rotation axis of the first tension roller, a second elastic member that generates the tension, a second elastic support portion that supports the other end of the rotation axis of the first tension roller, a backup roller that winds around the image carrier wound around the tension roller, a transfer roller that has a concave portion on its circumferential surface and forms a transfer nip by contacting the image carrier wound around the backup roller, and a second tension roller that winds around the image carrier wound around the backup roller and applies tension to the image carrier.

[0003] Patent Document 2 discloses an image forming apparatus having a toner image carrier, provided with a plurality of toner image forming means for forming toner images of corresponding colors on the toner image carrier, and including an intermediate transfer belt onto which the toner images of respective colors formed on the respective toner image carriers are transferred. In the image forming apparatus, the intermediate transfer belt is stretched in a shape having two or more flat portions where the toner image carriers provided in the toner image forming means are opposed to each other, and is provided with a plurality of stretching rollers, and a displacement means for changing the stretching state of the intermediate transfer belt by changing the position of at least one of the plurality of stretching rollers. At least one of the toner image carriers and the intermediate transfer belt are provided so as to be separated and contacted by the change in the stretching state of the intermediate transfer belt.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As an image forming apparatus, an image forming apparatus including a rotating transfer cylinder, a rotating member such as a sprocket that rotates integrally with the transfer cylinder, and a circulating member such as a chain that is wound around the rotating member and circulates as the rotating member rotates can be considered. As the image forming apparatus, further, an image forming unit that forms an image, and a transfer unit that has a transfer belt that transfers the image from the image forming unit at the contact position with the image forming unit and sandwiches the recording medium conveyed by the circulating member between the transfer cylinder at the sandwiching position to transfer the image can be considered.

[0006] In the image forming apparatus, vibrations generated in the circulating member and the rotating member are propagated to the transfer unit having the transfer belt through the sandwiching position between the transfer cylinder and the transfer belt, and further propagated to the image forming unit through the contact position between the transfer belt and the image forming unit, and the image forming unit may be vibrated.

[0007] An object of the present invention is to suppress the vibration of the image forming unit as compared with a configuration in which the product of the mass of the transfer cylinder and the distance from the mass center point of the transfer unit to the sandwiching position is larger than the product of the mass of the image forming unit and the distance from the mass center point to the contact position.

Means for Solving the Problems

[0008] The first aspect includes a rotating transfer cylinder, a rotating member provided coaxially with the transfer cylinder and rotating integrally with the transfer cylinder, a holding portion for holding the leading end portion of the recording medium, a circulating member wound around the rotating member and circulating as the rotating member rotates to convey the recording medium, an image forming portion for forming an image, and a transfer unit having a transfer belt that sandwiches the recording medium conveyed by the circulating member between the transfer belt and the transfer cylinder at a sandwiching position where the image is transferred from the image forming portion at a contact position with the image forming portion. The product of the mass of the transfer cylinder and the distance from the center of mass of the transfer unit to the sandwiching position is smaller than the product of the mass of the image forming portion and the distance from the center of mass to the contact position.

[0009] The second aspect includes a first image forming portion as the image forming portion, and a second image forming portion disposed downstream of the first image forming portion in the circumferential direction of the transfer belt and upstream of the sandwiching position. The product of the mass of the second image forming portion and the distance from the center of mass to the contact position is larger than the product of the mass of the first image forming portion and the distance from the center of mass to the contact position.

[0010] The third aspect further includes a third image forming portion as the image forming portion disposed downstream of the second image forming portion in the circumferential direction of the transfer belt and upstream of the sandwiching position. The product of the mass of the third image forming portion and the distance from the center of mass to the contact position is larger than the product of the mass of the second image forming portion and the distance from the center of mass to the contact position.

[0011] In the fourth aspect, the transfer cylinder has a recess formed on the outer peripheral surface, and the transfer unit has an opposing roll disposed to face the transfer cylinder and pressed against the outer peripheral surface of the transfer cylinder via the transfer belt.

[0012] In the fifth aspect, the recess is a recess in which the holding portion is accommodated.

[0013] In the sixth aspect, the mass of the conveyance unit including the transfer cylinder, the rotating member, the holding unit, and the orbiting member is two times or more the mass of the transfer unit.

[0014] The seventh aspect includes an image forming unit that forms an image to be transferred onto the transfer belt, and the mass of the image forming unit is 100 kg or more.

Advantages of the Invention

[0015] According to the configuration of the first aspect, compared with a configuration in which the product of the mass of the transfer cylinder and the distance from the mass center of gravity point of the transfer unit to the clamping position is larger than the product of the mass of the image forming unit and the distance from the mass center of gravity point to the contact position, the image forming unit is suppressed from being vibrated.

[0016] According to the configuration of the second aspect, compared with a configuration in which the product of the mass in the second image forming unit and the distance from the mass center of gravity point to the contact position is smaller than the product of the mass in the first image forming unit and the distance from the mass center of gravity point to the contact position, image distortion occurring in the image transferred onto the recording medium is less noticeable.

[0017] According to the configuration of the third aspect, compared with a configuration in which the product of the mass in the third image forming unit and the distance from the mass center of gravity point to the contact position is smaller than the product of the mass in the second image forming unit and the distance from the mass center of gravity point to the contact position, image distortion occurring in the image transferred onto the recording medium is less noticeable.

[0018] According to the configuration of the fourth aspect, in a configuration having a step due to the concave portion, compared with a configuration in which the product of the mass of the transfer cylinder and the distance from the mass center of gravity point of the transfer unit to the clamping position is larger than the product of the mass of the image forming unit and the distance from the mass center of gravity point to the contact position, the image forming unit is suppressed from being vibrated.

[0019] According to the configuration of the fifth aspect, in a configuration having a step formed by a concave portion in which the holding portion is accommodated, compared to a configuration in which the product of the mass of the transfer cylinder and the distance from the mass center of gravity point of the transfer unit to the clamping position is larger than the product of the mass of the image forming unit and the distance from the mass center of gravity point to the contact position, the image forming unit is suppressed from being vibrated.

[0020] According to the configuration of the sixth aspect, in a configuration in which the mass of the conveyance unit is two times or more the mass of the transfer unit, compared to a configuration in which the product of the mass of the transfer cylinder and the distance from the mass center of gravity point of the transfer unit to the clamping position is larger than the product of the mass of the image forming unit and the distance from the mass center of gravity point to the contact position, the image forming unit is suppressed from being vibrated.

[0021] According to the configuration of the seventh aspect, in a configuration in which the mass of the image forming unit is 100 kg or more, compared to a configuration in which the product of the mass of the transfer cylinder and the distance from the mass center of gravity point of the transfer unit to the clamping position is larger than the product of the mass of the image forming unit and the distance from the mass center of gravity point to the contact position, the image forming unit is suppressed from being vibrated.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0023] Hereinafter, an example of an embodiment according to the present invention will be described with reference to the drawings. (Image Forming Apparatus 10) First, the configuration of the image forming apparatus 10 according to the present embodiment will be described. FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus 10 according to the present embodiment.

[0024] Note that the arrow UP shown in the figure indicates the upper side (vertically upward) of the apparatus, and the arrow DO indicates the lower side (vertically downward) of the apparatus. Also, the arrow LH shown in the figure indicates the left side of the apparatus, and the arrow RH indicates the right side of the apparatus. Further, the arrow FR shown in the figure indicates the front of the apparatus, and the arrow RR indicates the rear of the apparatus. Since these directions are defined for convenience of explanation, the apparatus configuration is not limited to these directions. Note that in each direction of the apparatus, the term "apparatus" may be omitted. That is, for example, "the upper side of the apparatus" may be simply indicated as "the upper side".

[0025] Also, in the following description, the "vertical direction" may be used in the sense of "both the upper and lower sides" or "either the upper or lower side". The "left-right direction" may be used in the sense of "both the right and left sides" or "either the right or left side". The "left-right direction" can also be referred to as the lateral direction or the horizontal direction. The "front-rear direction" may be used in the sense of "both the front and rear sides" or "either the front or rear side". The front-rear direction corresponds to the axial direction of the sprocket 25 described later, and can also be referred to as the lateral direction or the horizontal direction. Also, the vertical direction, the left-right direction, and the front-rear direction are directions that intersect each other (specifically, orthogonal directions).

[0026] Also, the symbol with "×" described in the "○" in the figure means an arrow from the front to the back of the paper surface. Also, the symbol with "·" described in the "○" in the figure means an arrow from the back to the front of the paper surface.

[0027] The image forming apparatus 10 shown in FIG. 1 is an electrophotographic image forming apparatus that forms a toner image (an example of an image) on a recording medium P. Specifically, the image forming apparatus 10 includes an image forming apparatus main body 11, a medium storage unit 12, a conveyance unit 16, and an image forming mechanism 214. Hereinafter, each part of the image forming apparatus 10 (the image forming apparatus main body 11, the medium storage unit 12, the conveyance unit 16, and the image forming mechanism 214) will be described.

[0028] (Image forming apparatus main body 11) As shown in FIG. 1, the image forming apparatus main body 11 is a part where each component of the image forming apparatus 10 is provided. Specifically, as shown in FIG. 1, the image forming apparatus main body 11 has a housing 11A formed in a box shape and legs 11B provided at the lower end of the housing 11A.

[0029] In the present embodiment, as shown in FIG. 1, for example, the medium storage unit 12, the image forming mechanism 214, and the conveyance unit 16 are provided inside the housing 11A. A plurality of legs 11B are provided on the bottom surface of the housing 11A. The bottom surface 11C of each of the plurality of legs 11B is grounded to the floor surface 100 on which the image forming apparatus 10 is installed. And the housing 11A is supported by the plurality of legs 11B. Note that the image forming apparatus main body 11 may have a configuration without the legs 11B.

[0030] (Medium storage unit 12) The medium storage unit 12 is a part that stores the recording medium P in the image forming apparatus 10. The recording medium P stored in the medium storage unit 12 is supplied to the conveyance unit 16. Specifically, the recording medium P stored in the medium storage unit 12 is sent out toward the conveyance unit 16 by a conveyance member 12A such as a conveyance roll.

[0031] For example, paper is used as the recording medium P. Note that the recording medium P is not limited to paper, and may be, for example, a film or the like, as long as it is a medium on which an image can be formed.

[0032] (Conveyance unit 16) The conveyance unit 16 shown in FIG. 1 is a unit that conveys the recording medium P. Here, the unit refers to a constituent unit in the image forming apparatus 10. Therefore, the unit is a constituent part that is handled as a single, integrated unit in the image forming apparatus 10. In the present embodiment, the unit is configured to be detachable from the image forming apparatus main body 11. In other words, the unit is a unit that moves integrally with the image forming apparatus main body 11.

[0033] Specifically, as shown in FIGS. 1 and 2, the conveyance unit 16 includes a transfer cylinder 50, a pair of sprockets 25, a pair of chains 22, and a gripper 24. Further, as shown in FIG. 1, the conveyance unit 16 includes a pair of sprockets 37 and a pair of sprockets 45. The pair of sprockets 25 is an example of a "rotating member". The pair of chains 22 is an example of a "circumferential member". The gripper 24 is an example of a "holding part".

[0034] In FIG. 1, one of the pair of chains 22 is shown, and one of the pair of sprockets 25, 37, and 45 is shown. Also, in FIG. 1, the sprockets 25, 37, 45, the chain 22, the gripper 24, etc. are shown in a simplified manner. Further, in FIG. 2, the gripper 24 is shown in a simplified manner.

[0035] (Transfer cylinder 50) As shown in FIG. 2, the transfer cylinder 50 is formed in a substantially cylindrical shape with the front-rear direction as the axial direction. In other words, the transfer cylinder 50 is formed in a substantially circular shape when viewed from the rear.

[0036] Here, the rear view means the case where the object (here, the transfer cylinder 50) is viewed from the front toward the rear. That is, the rear view means the case where the object is viewed rearward as one direction along the axial direction of the pair of sprockets 25.

[0037] As shown in FIGS. 1 and 2, a recess 54 is formed on the outer peripheral surface of the transfer cylinder 50. In the present embodiment, one recess 54 is provided in a part of the circumferential direction on the outer peripheral surface of the transfer cylinder 50. This recess 54 is elongated along the axial direction of the transfer cylinder 50 and has a depth along the radial direction of the transfer cylinder 50. Specifically, the recess 54 is formed from one end to the other end in the axial direction of the transfer cylinder 50. That is, the recess 54 opens at one end and the other end in the axial direction of the transfer cylinder 50 and penetrates the transfer cylinder 50 in the axial direction.

[0038] Furthermore, as shown in FIG. 2, the recess 54 is a recess for accommodating the gripper 24. Therefore, the depth of the recess 54 along the radial direction of the transfer cylinder 50 and the width along the circumferential direction of the transfer cylinder 50 are larger than the size of the gripper 24. Thus, the recess 54 in the present embodiment is different from the recess microscopically formed on the outer peripheral surface of the transfer cylinder 50. In the present embodiment, one recess 54 is provided in a part of the circumferential direction on the outer peripheral surface of the transfer cylinder 50, but a configuration in which a plurality of recesses 54 are provided may also be adopted.

[0039] (A pair of sprockets 25, 37, 45, and a pair of chains 22) As shown in FIG. 2, a pair of sprockets 25 are provided on both ends in the axial direction of the transfer cylinder 50. This pair of sprockets 25 are provided coaxially with the transfer cylinder 50 and are configured to rotate integrally with the transfer cylinder 50. The transfer cylinder 50 and the pair of sprockets 25 are rotationally driven by a drive unit (not shown).

[0040] As shown in FIG. 1, a pair of sprockets 45 are arranged on the left side (i.e., the downstream side in the conveying direction) with respect to the pair of sprockets 25. This pair of sprockets 45 are arranged at intervals in the front-rear direction.

[0041] A pair of sprockets 37 is located below the pair of sprockets 25 and the pair of sprockets 45, and is arranged on the left side with respect to the pair of sprockets 25 (i.e., on the side of the pair of sprockets 45). This pair of sprockets 37 is arranged at intervals in the front-rear direction.

[0042] As shown in FIG. 1, a pair of chains 22 is formed in a ring shape. As shown in FIG. 2, this pair of chains 22 is arranged at intervals in the front-rear direction. Each of this pair of chains 22 is wound around each of the pair of sprockets 25, 37, 45. That is, each of the pair of chains 22 meshes with each of the pair of sprockets 25, 37, 45.

[0043] When the transfer cylinder 50 and the pair of sprockets 25 are integrally rotationally driven in the rotational direction B (the direction of arrow B in FIGS. 1 and 2), while the pair of sprockets 37, 45 rotate, the pair of chains 22 circulates in the circumferential direction C (the direction of arrow C in FIGS. 1 and 2). That is, as the pair of sprockets 25, 37, 45 rotate, the pair of chains 22 circulates.

[0044] (Gripper 24) As shown in FIG. 3, the gripper 24 functions as a holding portion for holding the leading end portion of the recording medium P. As shown in FIG. 2, the gripper 24 is attached to a mounting member 23 provided along the front-rear direction between the pair of chains 22. That is, the gripper 24 is provided on the pair of chains 22 via the mounting member 23.

[0045] A plurality of mounting members 23 are arranged at predetermined intervals along the circumferential direction C of the chain 22. Each of one end portion and the other end portion in the longitudinal direction of the mounting member 23 is attached to each of the pair of chains 22.

[0046] As shown in FIG. 2, a plurality of grippers 24 are attached to the attachment member 23 at predetermined intervals along the front-rear direction. As shown in FIG. 3, the gripper 24 has a claw 24A and a claw base 24B. The gripper 24 is configured to hold the recording medium P by sandwiching the leading end portion of the recording medium P between the claw 24A and the claw base 24B. Note that, for example, the claw 24A is pressed against the claw base 24B by a spring or the like, and the claw 24A is opened and closed with respect to the claw base 24B by the action of a cam or the like.

[0047] In the present embodiment, the gripper 24, which is an example of the holding unit, holds the leading end portion of the recording medium P from the downstream side in the conveyance direction with respect to the recording medium P, but is not limited thereto. As an example of the holding unit, for example, a holding unit that holds the leading end portion of the recording medium P from the lateral sides on both sides of the recording medium P may be used, as long as it holds the leading end portion of the recording medium P.

[0048] In the conveyance unit 16, the leading end portion of the recording medium P supplied from the medium storage portion 12 in which the recording medium P is stored is held by the gripper 24 as shown in FIG. 3. With the gripper 24 holding the leading end portion of the recording medium P, the chain 22 circulates in the circumferential direction C to convey the recording medium P and pass through a transfer position TA (to be described later) and a fixing position NP (to be described later). The gripper 24 passes through a transfer position TA (that is, between the transfer cylinder 50 and the opposing roll 65), which will be described later, while being accommodated in the recess 54 of the transfer cylinder 50. Further, the gripper 24 passes through a fixing position NP, which will be described later, while being accommodated in the recess 284 of the pressure roll 281, which will be described later.

[0049] (Image forming mechanism 214) The image forming mechanism 214 shown in FIG. 1 has a function of forming an image on a recording medium P. Specifically, the image forming mechanism 214 forms an image on the recording medium P conveyed by the conveying unit 16 using toner. More specifically, as shown in FIG. 1, the image forming mechanism 214 includes toner image forming units 222A, 222B, 222C, 222D, 222E, 222F (hereinafter referred to as 222A to 222F), a transfer unit 60 having a transfer belt 62, and a fixing device 280.

[0050] (Toner image forming units 222A to 222F) Each of the toner image forming units 222A to 222F shown in FIG. 1 has a function of forming an image to be transferred from the transfer belt 62 to the recording medium P. Specifically, each of the toner image forming units 222A to 222F forms an image of each color using toner of a predetermined color. The predetermined colors include yellow (Y), magenta (M), cyan (C), and black (K). Each of the toner image forming units 222A to 222F is an example of an "image forming section".

[0051] In the present embodiment, since each of the toner image forming units 222A to 222F has the same configuration except for the toner used, reference numerals are assigned to each part of the toner image forming unit 222C in FIG. 1 to represent the toner image forming units 222A to 222F.

[0052] Specifically, each of the toner image forming units 222A to 222F has a photoreceptor 224 that rotates in one direction (for example, the counterclockwise direction in FIG. 1). Each of the toner image forming units 222A to 222F also includes a charger 223, an exposure device 240, and a developing device 238.

[0053] In each of the toner image forming units 222A to 222F, a charger 223 charges a photoreceptor 224. Further, an exposure device 240 exposes the photoreceptor 224 charged by the charger 223 to form an electrostatic latent image on the photoreceptor 224. Also, a developing device 238 develops the electrostatic latent image formed on the photoreceptor 224 by the exposure device 240 to form a toner image.

[0054] Note that each of the toner image forming units 222A to 222F further has a support (not shown) that supports each part of the toner image forming units 222A to 222F (specifically, the photoreceptor 224, the charger 223, the exposure device 240, the developing device 238, etc.). The support has support frames (not shown) disposed on each of the front side and the rear side with respect to the photoreceptor 224. Also, as the toner image forming units 222A to 222F, at least a unit having the photoreceptor 224 may be sufficient.

[0055] (Transfer Unit 60) As described above, the transfer unit 60 is a unit having a transfer belt 62 that transfers an image to a recording medium P. Specifically, the transfer unit 60 superposes and primarily transfers the toner image of each color photoreceptor 224 onto the transfer belt 62 as an intermediate transfer body, and secondarily transfers the superposed toner image to the recording medium P. More specifically, the transfer unit 60 has a primary transfer roll 226, a transfer belt 62, a counter roll 65, a plurality of support rolls 64, and a cleaning unit 70.

[0056] Note that the transfer unit 60 further has a support (not shown) that supports each part of the transfer unit 60 (specifically, the transfer belt 62, the counter roll 65, the plurality of support rolls 64, the cleaning unit 70, etc.). The support has support frames (not shown) disposed on each of the front side and the rear side with respect to the transfer belt 62.

[0057] (Primary Transfer Roll 226) The primary transfer roll 226 is a roll that transfers the toner image on each photoreceptor 224 of the toner image forming units 222A to 222F to the transfer belt 62 at the primary transfer position T1 between the photoreceptor 224 and the primary transfer roll 226. Specifically, each of the primary transfer rolls 226 sandwiches the transfer belt 62 at the primary transfer position T1 with each of the photoreceptors 224. Therefore, each of the photoreceptors 224 of the toner image forming units 222A to 222F and the transfer belt 62 are in contact at the primary transfer position T1. The primary transfer position T1 is an example of a "contact position".

[0058] In this embodiment, a primary transfer electric field is applied between the primary transfer roll 226 and the photoreceptor 224, so that the toner image formed on the photoreceptor 224 is transferred to the transfer belt 62 at the primary transfer position T1.

[0059] (Transfer belt 62, opposing roll 65, and plurality of support rolls 64) The transfer belt 62 is formed in an annular shape (specifically, endless), and is supported by the opposing roll 65 and the plurality of support rolls 64 by being wound around the opposing roll 65 and the plurality of support rolls 64.

[0060] The opposing roll 65 is disposed opposite to the transfer cylinder 50 with the transfer belt 62 disposed therebetween. Specifically, the opposing roll 65 is disposed on the upper right side with respect to the transfer cylinder 50. This opposing roll 65 is pressed against the outer peripheral surface of the transfer cylinder 50 via the transfer belt 62 by the elastic force of an elastic member (not shown), for example.

[0061] In this embodiment, the opposing position where the opposing roll 65 opposes the transfer cylinder 50 is set as the transfer position TA where an image is transferred to the recording medium P. The transfer position TA is an example of a "pinching position". Also, at the transfer position TA, since an image is transferred to the recording medium P and an image is formed on the recording medium P, it can also be said to be an image forming position.

[0062] A plurality of support rolls 64 are specifically provided in four on the inner peripheral side of the transfer belt 62 as indicated by the reference signs (A), (B), (C), and (D) in the figure. The support rolls 64(A) and 64(B) are arranged side by side along the left - right direction on the lower right side with respect to the transfer position TA. The support roll 64(C) is arranged on the upper right side with respect to the transfer position TA. The support roll 64(D) is arranged on the upper left side with respect to the transfer position TA. The support rolls 64(C) and 64(D) are arranged side by side along the left - right direction.

[0063] The transfer belt 62 is wound around the opposing roll 65 and the four support rolls 64, and thus forms a substantially pentagonal shape including five surfaces, namely, a first surface 91, a second surface 92, and a third surface 93, when viewed from the rear.

[0064] The first surface 91 of the transfer belt 62 is the surface facing upward between the support rolls 64(C) and 64(D). The second surface 92 of the transfer belt 62 is the surface facing obliquely downward to the right between the support rolls 64(B) and 64(C). The third surface 93 of the transfer belt 62 is the surface facing obliquely downward to the left between the opposing roll 65 and the support roll 64(D). Also, the first surface 91 is arranged on the downstream side with respect to the third surface 93 and on the upstream side with respect to the second surface 92 in the circumferential direction A of the transfer belt 62. Also, the second surface 92 is arranged on the downstream side with respect to the first surface 91 and on the upstream side with respect to the transfer position TA in the circumferential direction A of the transfer belt 62.

[0065] The toner image forming units 222A, 222B, and 222C face the first surface 91 of the transfer belt 62, and the photoreceptors 224 of each of the toner image forming units 222A, 222B, and 222C are in contact with the first surface 91 of the transfer belt 62. Also, the toner image forming units 222D, 222E, and 222F face the second surface 92 of the transfer belt 62, and the photoreceptors 224 of each of the toner image forming units 222D, 222E, and 222F are in contact with the second surface 92 of the transfer belt 62.

[0066] In this embodiment, the toner image forming units 222A to 222F are arranged in this order along the circumferential direction A of the transfer belt 62. Therefore, it can be said that the toner image forming units 222A to 222F are arranged as follows. That is, each of the toner image forming units 222B, 222C, 222D, 222E, and 222F is arranged on the downstream side of the toner image forming unit 222A and on the upstream side of the transfer position TA in the circumferential direction A of the transfer belt 62. Also, each of the toner image forming units 222C, 222D, 222E, and 222F is arranged on the downstream side of the toner image forming unit 222B and on the upstream side of the transfer position TA in the circumferential direction A of the transfer belt 62. Also, each of the toner image forming units 222D, 222E, and 222F is arranged on the downstream side of the toner image forming unit 222C and on the upstream side of the transfer position TA in the circumferential direction A of the transfer belt 62. Also, each of the toner image forming units 222E and 222F is arranged on the downstream side of the toner image forming unit 222D and on the upstream side of the transfer position TA in the circumferential direction A of the transfer belt 62. Also, the toner image forming unit 222F is arranged on the downstream side of the toner image forming unit 222E and on the upstream side of the transfer position TA in the circumferential direction A of the transfer belt 62.

[0067] Of the four support rolls 64, the support roll 64(D) is a drive roll that transmits a driving force to the transfer belt 62. The support roll 64(D) is rotationally driven by a drive motor (not shown). Also, the support roll 64(D) is a solid support roll. On the other hand, the support rolls 64(A), 64(B), and 64(C) are hollow support rolls and are used as driven rolls. For this reason, the mass of the support roll 64(D) is larger than the mass of each of the support rolls 64(A), 64(B), and 64(C). Note that a hollow support roll means a support roll having a cavity inside, and a solid support roll means a support roll having no cavity inside.

[0068] Then, the transfer belt 62 rotates in the circumferential direction A (the direction of arrow A in FIG. 1) when the support roll 64(D) is rotationally driven. This rotating transfer belt 62 sandwiches the recording medium P conveyed by the conveying unit 16 between itself and the transfer cylinder 50 at the transfer position TA, and a secondary transfer electric field is applied between the opposing roll 65 and the transfer cylinder 50, thereby transferring the image formed on its outer peripheral surface to the recording medium P. As a result, an image is formed on the recording medium P.

[0069] (Cleaning unit 70) The cleaning unit 70 has a function of cleaning the transfer belt 62. Specifically, the cleaning unit 70 has a function of removing foreign matter adhering to the transfer belt 62. Examples of foreign matter include paper dust generated from paper as an example of the recording medium P, and toner.

[0070] As shown in FIG. 1, the cleaning unit 70 is disposed to face the third surface 93 of the transfer belt 62. The cleaning unit 70 includes a blade 72 and a housing 74 in which the blade 72 is disposed inside.

[0071] The blade 72 has a function as an example of a contact portion that contacts the transfer belt 62 and removes foreign matter from the transfer belt 62. Specifically, the blade 72 contacts a portion of the transfer belt 62 wound around the support roll 64(D). That is, the blade 72 is disposed to face the support roll 64(D) with the transfer belt 62 disposed therebetween. In the present embodiment, the blade 72 contacts a portion of the transfer belt 62 wound around the support roll 64(D), and scrapes off the foreign matter adhering to the transfer belt 62, thereby removing the foreign matter from the transfer belt 62.

[0072] The housing 74 has an opening 74A on the third surface 93 side of the transfer belt 62 (i.e., the support roll 64(D) side), and accommodates the foreign matter removed by the blade 72 through the opening 74A.

[0073] Note that an example of the contact portion that contacts the transfer belt 62 is not limited to the blade 72. As an example of the contact portion, a brush or the like may be used, as long as it can remove foreign matter from the transfer belt 62. Further, the blade 72 as an example of the contact portion may be configured to contact a portion of the transfer belt 62 that is not wound around the support roll 64. In this case, a member such as a roll facing the blade 72 is disposed with the transfer belt 62 disposed therebetween.

[0074] (Fixing device 280) The fixing device 280 has a function of fixing the toner image transferred to the recording medium P to the recording medium P. Specifically, as shown in FIG. 1, the fixing device 280 includes a pressure roll 281 and a heating roll 282.

[0075] In the present embodiment, the pair of sprockets 45 are provided on both axial ends of the pressure roll 281. The pair of sprockets 45 are arranged coaxially with the pressure roll 281 and configured to rotate integrally with the pressure roll 281. Further, a recess 284 for accommodating the gripper 24 and the mounting member 23 is formed on the outer periphery of the pressure roll 281.

[0076] In the fixing device 280, the heating roll 282 is disposed above the pressure roll 281. The heating roll 282 has a heating source 282A such as a halogen lamp inside the roll.

[0077] Then, in the fixing device 280, while conveying the recording medium P in a state where the recording medium P is sandwiched between the heating roll 282 and the pressure roll 281, the recording medium P is heated and pressurized, so that the toner image transferred to the recording medium P at the fixing position NP is fixed to the recording medium P.

[0078] (Relationship between mass, distance, and product in each part of the image forming apparatus 10) In this embodiment, the product of the mass of the transfer cylinder 50 and the distance LA from the mass center point 60G of the transfer unit 60 to the transfer position TA is smaller than the product of the mass of each of the toner image forming units 222A to 222F and the respective distances L1, L2, L3, L4, L5, L6 (hereinafter referred to as L1 to L6) from the mass center point 60G to each primary transfer position T1.

[0079] The mass of the transfer cylinder 50 is at least reduced to be smaller than the mass of each of the toner image forming units 222A to 222F. Specifically, the mass of the transfer cylinder 50 is in the range of, for example, 50 kg or more and 60 kg or less.

[0080] The mass of each of the toner image forming units 222A to 222F is at least increased to be larger than the mass of the transfer cylinder 50. The mass of each of the toner image forming units 222A to 222F is, for example, set to be 2 times or more the mass of the transfer cylinder 50. The mass of each of the toner image forming units 222A to 222F is, for example, 100 kg or more. Specifically, the mass of each of the toner image forming units 222A to 222F is in the range of, for example, 100 kg or more and 150 kg or less.

[0081] The mass center point 60G of the transfer unit 60 refers to a point where the resultant force of the gravitational forces acting on each part of the transfer unit 60 is considered to act.

[0082] The distance LA and the distances L1 to L6 are distances in a rear view. Also, the "distance to the transfer position TA" means, when the transfer position TA has a width in the circumferential direction A of the transfer belt 62, the distance to the center in the circumferential direction A at the transfer position TA.

[0083] Also, the "distance to the primary transfer position T1" means, when the primary transfer position T1 has a width in the circumferential direction A of the transfer belt 62, the distance to the center in the circumferential direction A at the primary transfer position T1.

[0084] The distances LA and L1 to L6 are, for example, in the order of distance L1, distance L2, distance L6, distance LA, distance L5, distance L3, and distance L4, and are getting longer. The distance L1 is, for example, 200 mm or more and less than 300 mm. The distance L2 is, for example, more than 300 mm and less than 400 mm. The distance L6 is, for example, more than 400 mm and less than 450 mm. The distance LA is, for example, more than 450 mm and less than 550 mm. The distance L5 is, for example, more than 550 mm and less than 650 mm. The distance L3 is, for example, more than 650 mm and less than 800 mm. The distance L4 is, for example, more than 800 mm and less than 900 mm.

[0085] Furthermore, in the present embodiment, the product of the mass of each of the toner image forming units 222A to 222F and each of the distances L1 to L6 is in the order of the product of the mass of the toner image forming unit 222A and the distance L1, the product of the mass of the toner image forming unit 222B and the distance L2, the product of the mass of the toner image forming unit 222F and the distance L6, the product of the mass of the toner image forming unit 222E and the distance L5, the product of the mass of the toner image forming unit 222C and the distance L3, and the product of the mass of the toner image forming unit 222D and the distance L4, and is getting larger.

[0086] The toner image forming unit 222A is an example of the "first image forming unit". The toner image forming unit 222B is an example of the "second image forming unit". The toner image forming unit 222C is an example of the "third image forming unit".

[0087] In addition, when each of the toner image forming unit 222A and the toner image forming unit 222B is regarded as an example of each of the "first image forming unit" and the "second image forming unit", any one of the toner image forming units 222D, 222E, and 222F may be regarded as an example of the "third image forming unit". Also, each of the toner image forming unit 222B, the toner image forming unit 222C, and the toner image forming unit 222D may be regarded as an example of each of the "first image forming unit", the "second image forming unit", and the "third image forming unit".

[0088] Furthermore, when the toner image forming unit 222A is regarded as an example of the "first image forming unit", any one of the toner image forming units 222C, 222D, 222E, and 222F may be regarded as an example of the "second image forming unit". Also, when the toner image forming unit 222B is regarded as an example of the "first image forming unit", any one of the toner image forming units 222C, 222D, 222E, and 222F may be regarded as an example of the "second image forming unit". Further, each of the toner image forming unit 222C and the toner image forming unit 222D may be regarded as an example of each of the "first image forming unit" and the "second image forming unit".

[0089] (Mass of the conveyance unit 16 and the transfer unit 60) The mass of the conveyance unit 16 including the transfer drum 50, the pair of sprockets 25, 37, 45, the pair of chains 22, and the gripper 24 is two times or more the mass of the transfer unit 60. Specifically, the mass of the transfer unit 60 is 300 kg, and the mass of the conveyance unit 16 is, for example, 600 kg.

[0090] (Operation according to this embodiment) Next, the operation according to this embodiment will be described.

[0091] In the image forming apparatus 10, the leading end of the recording medium P supplied from the medium storage unit 12 that stores the recording medium P is held by the gripper 24 as shown in FIG. 3. With the gripper 24 holding the leading end of the recording medium P, the chain 22 circulates in the circumferential direction C to convey the recording medium P and pass it through the transfer position TA. At this time, the gripper 24 passes between the transfer drum 50 and the counter roll 65 while being accommodated in the recess 54 of the transfer drum 50. Then, the transfer belt 62 sandwiches the recording medium P with the transfer drum 50 at the transfer position TA and transfers the image formed on its outer peripheral surface to the recording medium P.

[0092] Further, with the gripper 24 holding the leading end of the recording medium P, the chain 22 rotates in the circumferential direction C to convey the recording medium P and pass it through the fixing position NP. At this time, the gripper 24 passes between the heating roll 282 and the pressure roll 281 while being accommodated in the recess 284 of the pressure roll 281. Then, while conveying the recording medium P in a state where it is sandwiched between the heating roll 282 and the pressure roll 281, the recording medium P is heated and pressurized to fix the toner image transferred onto the recording medium P to the recording medium P. Thereby, an image is formed on the recording medium P.

[0093] Here, in the image forming apparatus 10, vibrations generated by the chain 22, the sprocket 25, etc. during the conveyance of the recording medium P are propagated to the transfer unit 60 having the transfer belt 62 from the transfer drum 50 via the transfer position TA. The vibrations propagated to the transfer unit 60 may further be propagated to each of the toner image forming units 222A to 222F via the primary transfer position T1, and each of the toner image forming units 222A to 222F may be vibrated.

[0094] In particular, in the present embodiment, since the opposing roll 65 is pressed against the outer peripheral surface of the transfer drum 50 via the transfer belt 62, when the recess 54 of the transfer drum 50 passes through the transfer position TA, vibrations are likely to occur at the transfer position TA due to the step of the recess 54 (hereinafter referred to as factor A).

[0095] Also, in the present embodiment, since the mass of the conveyance unit 16 is set to be twice or more the mass of the transfer unit 60, the transfer unit 60 is likely to vibrate due to the vibrations generated in the conveyance unit 16 (hereinafter referred to as factor B).

[0096] Furthermore, in the present embodiment, since the mass of each of the toner image forming units 222A to 222F is 100 kg or more, the image forming apparatus 10 becomes large-sized, and the transfer unit 60 is likely to be vibrated (hereinafter referred to as factor C). When the transfer unit 60 is vibrated, the toner image forming units 222A to 222F are also vibrated. Due to this, image disturbance such as banding occurs in the image transferred from the transfer belt 62 to the recording medium P. Note that banding is image disturbance in which striped shading appears in the image.

[0097] Here, in the present embodiment, the product of the mass of the transfer drum 50 and the distance LA from the mass center of gravity point 60G of the transfer unit 60 to the transfer position TA is smaller than the product of the mass of each of the toner image forming units 222A to 222F and each of the distances L1 to L6 from the mass center of gravity point 60G to each primary transfer position T1.

[0098] The product can be regarded as vibration energy. In other words, the larger the product (specifically, the transfer position TA or the primary transfer position T1), the less likely it is to vibrate when vibration is propagated from the mass center of gravity point 60G, and when it becomes a vibration source, it outputs large vibration to the mass center of gravity point 60G.

[0099] Therefore, according to the present embodiment, it can be said that the vibration energy input from the transfer position TA to the mass center of gravity point 60G is smaller than the vibration energy input from each primary transfer position T1 to the mass center of gravity point 60G. On the other hand, when vibration is propagated from the mass center of gravity point 60G, it can be said that it is less likely to vibrate at each primary transfer position T1 than at the transfer position TA.

[0100] For this reason, according to the present embodiment, compared with a configuration (hereinafter referred to as configuration A) in which the product of the mass of the transfer drum 50 and the distance LA from the mass center of gravity point 60G of the transfer unit 60 to the transfer position TA is larger than the product of the mass of each of the toner image forming units 222A to 222F and each of the distances L1 to L6 from the mass center of gravity point 60G to each primary transfer position T1, vibration of each of the toner image forming units 222A to 222F is suppressed.

[0101] As a result, according to this embodiment, due to the aforementioned factors A, B, and C, in a configuration where the toner image forming units 222A to 222F are likely to be vibrated, compared with Configuration A, the vibration of the toner image forming units 222A to 222F is suppressed, and image distortion of the image formed on the recording medium P is suppressed.

[0102] Also, in this embodiment, the product of the mass of the toner image forming unit 222B and the distance L2 is made larger than the product of the mass of the toner image forming unit 222A and the distance L1.

[0103] Thereby, at the primary transfer position T1 where the order of transferring the image to the transfer belt 62 is later, since vibration is suppressed, in the image formed on the transfer belt 62, image distortion such as banding is less noticeable.

[0104] As a result, compared with a configuration where the product of the mass of the toner image forming unit 222B and the distance L2 is smaller than the product of the mass of the toner image forming unit 222A and the distance L1, image distortion such as banding occurring in the image transferred to the recording medium P is less noticeable.

[0105] Furthermore, in this embodiment, the product of the mass of the toner image forming unit 222C and the distance L3 is made larger than the product of the mass of the toner image forming unit 222B and the distance L2.

[0106] Thereby, at the primary transfer position T1 where the order of transferring the image to the transfer belt 62 is later, since vibration is suppressed, in the image formed on the transfer belt 62, image distortion such as banding is less noticeable.

[0107] As a result, compared with a configuration where the product of the mass of the toner image forming unit 222C and the distance L3 is smaller than the product of the mass of the toner image forming unit 222B and the distance L2, image distortion such as banding occurring in the image transferred to the recording medium P is less noticeable.

[0108] (Evaluation) In the evaluation, in the configuration of the present embodiment, in the toner image forming units 222A to 222F and the transfer cylinder 50, the relationship of the product of mass and distance was changed to form an image on the recording medium P, and the presence or absence of banding occurring in the image was evaluated.

[0109] In this evaluation, using each of the toner image forming units 222A to 222F, a halftone image (image density: 20%) of each color was formed on the recording medium P, and the occurrence of banding was visually confirmed.

[0110] (Evaluation Criteria) A: Banding cannot be confirmed. B: Banding can be slightly confirmed. C: Banding can be significantly confirmed.

[0111] (Example 1) As shown in the table of FIG. 4, the product of the mass of the transfer cylinder 50 and the distance LA from the mass center point 60G of the transfer unit 60 to the transfer position TA is set smaller than the product of the mass of each of the toner image forming units 222A to 222F and each of the distances L1 to L6 from the mass center point 60G to each primary transfer position T1.

[0112] (Example 2) As shown in the table of FIG. 4, the product of the mass of the transfer cylinder 50 and the distance LA from the mass center point 60G of the transfer unit 60 to the transfer position TA is larger than the product of the mass of each of the toner image forming units 222A, 222B, 222E, 222F and each of the distances L1, L2, L5, L6 from the mass center point 60G to each primary transfer position T1, and is set smaller than the product of the mass of each of the toner image forming units 222C, 222D and each of the distances L3, L4 from the mass center point 60G to each primary transfer position T1.

[0113] (Comparative Example 1) As shown in the table of FIG. 4, the product of the mass of the transfer cylinder 50 and the distance LA from the mass center of gravity point 60G of the transfer unit 60 to the transfer position TA is set to be larger than the product of the mass of each of the toner image forming units 222A to 222F and each of the distances L1 to L6 from the mass center of gravity point 60G to each primary transfer position T1.

[0114] (Evaluation result) As shown in FIG. 4, in Comparative Example 1, the occurrence of banding was significantly confirmed. In contrast, in Example 1, the occurrence of banding could not be confirmed. Also, in Example 2, the occurrence of banding was slightly confirmed. It is considered that the banding is caused by the transfer unit 60 being vibrated. Therefore, from the results shown in FIG. 4, it is considered that the transfer unit 60 is suppressed from being vibrated in Examples 1 and 2 as compared with Comparative Example 1.

[0115] (Modification example) In the present embodiment, the product of the mass of the toner image forming unit 222B and the distance L2 is larger than the product of the mass of the toner image forming unit 222A and the distance L1, but it is not limited thereto. A configuration in which the product of the mass of the toner image forming unit 222B and the distance L2 is smaller than the product of the mass of the toner image forming unit 222A and the distance L1 may also be used.

[0116] Also, the product of the mass of the toner image forming unit 222C and the distance L3 is larger than the product of the mass of the toner image forming unit 222B and the distance L2, but it is not limited thereto. For example, a configuration in which the product of the mass of the toner image forming unit 222C and the distance L3 is smaller than the product of the mass of the toner image forming unit 222B and the distance L2 may also be used. Thus, the magnitude relationship of the products among the toner image forming units 222A to 222F is not limited to the above-described relationship.

[0117] Also, in this embodiment, the product of the mass of the transfer cylinder 50 and the distance LA from the mass center point 60 of the transfer unit 60 to the transfer position TA was made smaller than the products of the masses of the respective toner image forming units 222A to 222F and the respective distances L1 to L6 from the mass center point 60G to the respective primary transfer positions T1, but it is not limited to this. It is sufficient that the product of the mass of the transfer cylinder 50 and the distance LA from the mass center point 60 of the transfer unit 60 to the transfer position TA is made smaller than the product in at least one of the toner image forming units 222A to 222F. Therefore, for example, when the toner image forming units 222A to 222F are configured as toner image forming units that form six-color toner images of yellow (Y), magenta (M), cyan (C), black (K), and two special colors, the product in a part of the six-color toner image forming units may be made smaller than the product in the transfer cylinder 50. In this case, for example, among the six-color toner image forming units 222A to 222F, the product in the toner image forming unit of a color that has a small influence on image quality is smaller than the product in the transfer cylinder 50, and the product in the toner image forming unit of a color that has a large influence on image quality is larger than the product in the transfer cylinder 50 (hereinafter referred to as configuration X). Specifically, as configuration X, for example, the product in the transparent toner image forming unit as a special color is smaller than the product in the transfer cylinder 50, and the products in the toner image forming units of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are larger than the product in the transfer cylinder 50. Also, as configuration X, for example, the product in the black (K) toner image forming unit may be smaller than the product in the transfer cylinder 50, and the products in the toner image forming units of the respective colors of yellow (Y), magenta (M), and cyan (C) may be larger than the product in the transfer cylinder 50. Configuration X can be realized, for example, by arranging the toner image forming units of colors that have a small influence on image quality among the six-color toner image forming units 222A to 222F at the position closest to the mass center point 60G and arranging the toner image forming units of colors that have a large influence on image quality farther from the mass center point 60G.Note that examples of the special colors described above include, for example, transparent, white, gold, silver, violet, green, orange, light magenta, light cyan, and gray, etc.

[0118] Also, in this embodiment, although the concave portion 54 was formed on the outer peripheral surface of the transfer cylinder 50, it is not limited thereto. For example, a transfer cylinder 50 without the concave portion 54 may be used. In this case, for example, a holding portion disposed on both axial ends of the transfer cylinder 50 is configured to hold the leading end portion of the recording medium P from the lateral sides on both sides of the recording medium P. That is, a holding portion that does not require accommodation in the concave portion 54 is used. Further, the concave portion 54 formed on the outer peripheral surface of the transfer cylinder 50 may be a concave portion used for purposes other than accommodating the gripper 24 as an example of the holding portion.

[0119] In this embodiment, as an example of the circulating member, the chain 22 is used, and as an example of the rotating member, the sprocket 25 is used, but it is not limited thereto. For example, as an example of the circulating member, a timing belt having irregularities on the inner periphery may be used, and as an example of the rotating member, a timing pulley (that is, a pulley having irregularities on the outer periphery) may be used. Also, as an example of the circulating member, a belt may be used, and as an example of the rotating member, a pulley that circulates the belt by friction may be used.

[0120] Also, in this embodiment, the mass of the conveyance unit 16 is set to be twice or more the mass of the transfer unit 60, but it is not limited thereto. For example, a configuration in which the mass of the conveyance unit 16 is less than twice the mass of the transfer unit 60 may be used.

[0121] Also, in this embodiment, the mass of each of the toner image forming units 222A to 222F is set to be 100 kg or more, but it is not limited thereto. For example, the mass of each of the toner image forming units 222A to 222F may be less than 100 kg.

[0122] The present invention is not limited to the above-described embodiments, and various modifications, changes, and improvements are possible without departing from the gist thereof. For example, the above-described modification examples may be configured by appropriately combining a plurality of them.

Explanation of Signs

[0123] 10 Image forming apparatus 16 Conveying unit 22 Chain (an example of a circulating member) 24 Gripper (an example of a holding part) 25 Sprocket (an example of a rotating member) 50 Transfer cylinder 54 Concave portion 60 Transfer unit 60G Center of mass point 62 Transfer belt 222A~222F Toner image forming unit (an example of an image forming part) 222A Toner image forming unit (an example of a first image forming part) 222B Toner image forming unit (an example of a second image forming part) 222C Toner image forming unit (an example of a third image forming part) L1, L2, L3, L4, L5, L6 Distances LA Distance P Recording medium T1 Primary transfer position (an example of a contact position) TA Transfer position (an example of a clamping position)

Claims

1. A rotating transfer cylinder, A rotating member provided coaxially with the transfer cylinder and rotating integrally with the transfer cylinder, A holding portion for holding the leading end portion of the recording medium, a circulating member wound around the rotating member and circulating as the rotating member rotates to convey the recording medium, An image forming portion for forming an image, A transfer unit having a transfer belt that sandwiches the recording medium conveyed by the circulating member at a sandwiching position with the transfer cylinder at a contact position where the image is transferred from the image forming portion to the transfer belt and transfers the image, Comprising, The transfer unit, Has a plurality of members including the transfer belt and rollers supporting the transfer belt, supported by a common support, The product of the mass of the transfer cylinder and the distance from the mass center of gravity point of the transfer unit to the sandwiching position is smaller than the product of the mass of the image forming portion and the distance from the mass center of gravity point to the contact position An image forming apparatus.

2. A first image forming portion as the image forming portion, A second image forming portion disposed downstream of the first image forming portion in the circumferential direction of the transfer belt and upstream of the sandwiching position, Comprising, The product of the mass in the second image forming portion and the distance from the mass center of gravity point to the contact position is larger than the product of the mass in the first image forming portion and the distance from the mass center of gravity point to the contact position The image forming apparatus according to claim 1.

3. A third image forming portion as the image forming portion disposed downstream of the second image forming portion in the circumferential direction of the transfer belt and upstream of the sandwiching position, Further comprising, The product of the mass in the third image forming portion and the distance from the mass center of gravity point to the contact position is larger than the product of the mass in the second image forming portion and the distance from the mass center of gravity point to the contact position The image forming apparatus according to claim 2.

4. The transfer cylinder has a recess formed on the outer peripheral surface, The transfer unit has an opposing roll disposed opposite to the transfer cylinder and pressed against the outer peripheral surface of the transfer cylinder via the transfer belt The image forming apparatus according to any one of claims 1 to 3.

5. The recess is a recess in which the holding portion is accommodated The image forming apparatus according to claim 4.

6. The mass of the conveyance unit including the transfer cylinder, the rotating member, the holding portion, and the circulating member is twice or more the mass of the transfer unit The image forming apparatus according to any one of claims 1 to 5.

7. An image forming unit that forms an image to be transferred onto the transfer belt, wherein the mass of the image forming unit is 100 kg or more. The image forming apparatus according to any one of claims 1 to 6.

Images