Image forming apparatus

Abstract

To prevent a transfer unit 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; and a transfer unit having a transfer belt that sandwiches the recording medium conveyed by the circulating members with the transfer barrel at a sandwiching position to transfer an image, wherein when seen in an axial direction of the rotary member, the sandwiching position is located on one side with respect to the center in a horizontal direction of the transfer unit, and the mass gravity point of the transfer unit is located on the sandwiching position side with respect to the center in the horizontal direction.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 driving 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 driving roller and applies tension to the image carrier; a first elastic member that generates the tension, and 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, and 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 having a concave portion on its peripheral surface and forming 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, and further transferring the toner images of respective colors transferred onto the intermediate transfer belt onto a recording medium. The intermediate transfer belt is stretched by a plurality of stretching rollers into 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 displacement means is provided 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, there is considered an image forming apparatus including a rotating transfer cylinder, a rotating member such as a sprocket provided coaxially with the transfer cylinder and rotating integrally with the transfer cylinder, a holding portion for holding a leading end portion of a recording medium, a circulating member such as a chain that is wound around the rotating member and circulates as the rotating member rotates to convey the recording medium, 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 to transfer an image.

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

[0007] An object of the present invention is to suppress the transfer unit from being vibrated as compared with a configuration in which, when viewed in the axial direction of the rotating member, the center of mass point of the transfer unit is located on the side opposite to the sandwiching position side with respect to the center in the horizontal direction of the transfer unit.

Means for Solving the Problems

[0008] The first aspect is a transfer unit having 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 a leading end portion of a recording medium, a circulating member wound around the rotating member and circulating as the rotating member rotates to convey the recording medium, and a transfer belt for transferring an image by sandwiching the recording medium conveyed by the circulating member between the transfer cylinder at a sandwiching position, wherein when viewed in the axial direction of the rotating member, the sandwiching position is located on one side with respect to the center in its horizontal direction, and the center of mass point of itself is located on the sandwiching position side with respect to the center in the horizontal direction.

[0009] The second aspect is a transfer unit having 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 a leading end portion of a recording medium, a circulating member wound around the rotating member and circulating as the rotating member rotates to convey the recording medium, and a transfer belt for transferring an image by sandwiching the recording medium conveyed by the circulating member between the transfer cylinder at a sandwiching position, wherein when viewed in the axial direction of the rotating member, the center of mass point of itself is located on the sandwiching position side with respect to the geometric center of itself.

[0010] In the third aspect, the transfer unit has a cleaning portion for cleaning the transfer belt, and the cleaning portion is located on the sandwiching position side with respect to the center in the horizontal direction when viewed in the axial direction of the rotating member.

[0011] In the fourth aspect, the transfer unit has a solid support roll for supporting the transfer belt, and the support roll is located on the sandwiching position side with respect to the center in the horizontal direction when viewed in the axial direction of the rotating member.

[0012] In the fifth aspect, the support roll is a drive roll for transmitting a driving force to the transfer belt.

[0013] The sixth aspect includes a plurality of image forming units that form an image transferred from the transfer belt to the recording medium, and the center of mass is closer to the image forming unit disposed immediately downstream in the circumferential direction of the transfer belt among the plurality of image forming units than to the image forming unit disposed downstream in the circumferential direction with respect to the image forming unit.

[0014] In the seventh aspect, the transfer cylinder has a recess formed on its outer peripheral surface, and the transfer unit has a counter roll disposed opposite to the transfer cylinder and pressed against the outer peripheral surface of the transfer cylinder via the transfer belt.

[0015] In the eighth aspect, the recess is a recess in which the holding portion is accommodated.

[0016] In the ninth aspect, the mass of the transfer cylinder, the rotating member, the holding portion, and the conveying unit including the circumferential member is at least twice the mass of the transfer unit.

[0017] The tenth aspect includes an image forming unit that forms an image transferred from the transfer belt to the recording medium, and the mass of the image forming unit is 100 kg or more.

Advantages of the Invention

[0018] According to the configuration of the first aspect, when viewed in the axial direction of the rotating member, the transfer unit is less likely to be vibrated compared to a configuration in which the center of mass of the transfer unit is located on the side opposite to the clamping position side with respect to the center in the horizontal direction of the transfer unit.

[0019] According to the configuration of the second aspect, when viewed in the axial direction of the rotating member, the transfer unit is less likely to be vibrated compared to a configuration in which the center of mass of the transfer unit is located on the side opposite to the clamping position side with respect to the geometric center of the transfer unit.

[0020] According to the configuration of the third aspect, compared with the configuration in which the cleaning unit is located on the side opposite to the clamping position side with respect to the center in the horizontal direction when viewed in the axial direction of the rotating member, it is easier to position the mass center point of the transfer unit on the clamping position side with respect to the center in the horizontal direction.

[0021] According to the configuration of the fourth aspect, compared with the configuration in which the solid support roll is located on the side opposite to the clamping position side with respect to the center in the horizontal direction when viewed in the axial direction of the rotating member, it is easier to position the mass center point of the transfer unit on the clamping position side with respect to the center in the horizontal direction.

[0022] According to the configuration of the fifth aspect, compared with the configuration in which the hollow support roll is a driving roll, while positioning the mass center point of the transfer unit on the clamping position side with respect to the center in the horizontal direction, the deflection deformation of the driving roll is suppressed.

[0023] According to the configuration of the sixth aspect, compared with the configuration in which the mass center point is located closer to the image forming unit arranged on the downstream side in the circumferential direction with respect to the image forming unit than the image forming unit arranged immediately downstream of the clamping position in the circumferential direction of the transfer belt among the plurality of image forming units, the image forming unit arranged immediately downstream of the clamping position in the circumferential direction of the transfer belt is suppressed from being vibrated.

[0024] According to the configuration of the seventh aspect, in the configuration having a step due to the concave portion, compared with the configuration in which the mass center point of the transfer unit is located on the side opposite to the clamping position side with respect to the center in the horizontal direction of the transfer unit when viewed in the axial direction of the rotating member, the transfer unit is suppressed from being vibrated.

[0025] According to the configuration of the eighth aspect, in the configuration having a step due to the concave portion in which the holding portion is accommodated, compared with the configuration in which the mass center point of the transfer unit is located on the side opposite to the clamping position side with respect to the center in the horizontal direction of the transfer unit when viewed in the axial direction of the rotating member, the transfer unit is suppressed from being vibrated.

[0026] According to the configuration of the ninth aspect, in a configuration where the mass of the conveyance unit is two times or more the mass of the transfer unit, when viewed in the axial direction of the rotating member, compared with a configuration where the center of mass point of the transfer unit is located on the side opposite to the clamping position side with respect to the center in the horizontal direction of the transfer unit, the transfer unit is suppressed from being vibrated.

[0027] According to the configuration of the tenth aspect, in a configuration where the mass of the image forming unit is 100 kg or more, when viewed in the axial direction of the rotating member, compared with a configuration where the center of mass point of the transfer unit is located on the side opposite to the clamping position side with respect to the center in the horizontal direction of the transfer unit, the transfer unit is suppressed from being vibrated.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0029] Hereinafter, an example of an embodiment according to the present invention will be described with reference to the drawings. <First Embodiment> (Image Forming Apparatus 10) First, the configuration of the image forming apparatus 10 according to the first embodiment will be described. FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus 10 according to the present embodiment.

[0030] Note that the arrow UP shown in the figure indicates the upper side (vertically upward) of the device, and the arrow DO indicates the lower side (vertically downward) of the device. Also, the arrow LH shown in the figure indicates the left side of the device, and the arrow RH indicates the right side of the device. Further, the arrow FR shown in the figure indicates the front side of the device, and the arrow RR indicates the rear side of the device. Since these directions are defined for the convenience of explanation, the device configuration is not limited to these directions. Note that in each direction of the device, the term "device" may be omitted for indication. That is, for example, "the upper side of the device" may be simply indicated as "the upper side".

[0031] 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).

[0032] Also, the symbol with "×" written in the "○" in the figure means an arrow pointing from the front to the back of the paper surface. Also, the symbol with "·" written in the "○" in the figure means an arrow pointing from the back to the front of the paper surface.

[0033] The image forming apparatus 10 shown in FIG. 1 is an ink - jet type image forming apparatus that forms an ink 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 14. 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 14) will be described.

[0034] (Image Forming Apparatus Main Body 11) As shown in FIG. 1, the main body 11 of the image forming apparatus is the part where each component of the image forming apparatus 10 is provided. Specifically, as shown in FIG. 1, the main body 11 of the image forming apparatus has a housing 11A formed in a box shape and legs 11B provided at the lower end of the housing 11A.

[0035] In the present embodiment, as shown in FIG. 1, for example, the medium storage unit 12, the image forming mechanism 14, 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 main body 11 of the image forming apparatus may have a configuration without the legs 11B.

[0036] (Medium storage unit 12) The medium storage unit 12 is the 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.

[0037] As the recording medium P, for example, paper is used. 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.

[0038] (Conveyance unit 16) The conveyance unit 16 shown in FIG. 1 is a unit that conveys the recording medium P. Note that 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 a unit that can be attached to and detached from the main body 11 of the image forming apparatus. In other words, the unit is a unit that moves integrally with respect to the main body 11 of the image forming apparatus.

[0039] Specifically, as shown in FIGS. 1 and 2, the conveying 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 conveying 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 portion".

[0040] 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.

[0041] (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.

[0042] Note that the rear view means the case where the object (here, the transfer cylinder 50) is viewed from the front to the rear. That is, the rear view means the case where it is viewed from the rear as one direction along the rotational axis direction of the pair of sprockets 25. Therefore, the rear view is an example of "the case where it is viewed in the axial direction of the rotating member".

[0043] As shown in FIGS. 1 and 2, a concave portion 54 is formed on the outer peripheral surface of the transfer cylinder 50. In the present embodiment, one concave portion 54 is provided in a part of the circumferential direction on the outer peripheral surface of the transfer cylinder 50. This concave portion 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 concave portion 54 is formed from one end to the other end in the axial direction of the transfer cylinder 50. That is, the concave portion 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.

[0044] 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 made 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 are provided may also be adopted.

[0045] (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 axial ends 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).

[0046] 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.

[0047] A pair of sprockets 37 are arranged below the pair of sprockets 25 and the pair of sprockets 45 and on the left side (i.e., the side of the pair of sprockets 45) with respect to the pair of sprockets 25. This pair of sprockets 37 are arranged at intervals in the front-rear direction.

[0048] As shown in FIG. 1, a pair of chains 22 are formed in a ring shape. As shown in FIG. 2, this pair of chains 22 are 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.

[0049] Then, 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), so that while the pair of sprockets 37 and 45 rotate, the pair of chains 22 circulate in the circumferential direction C (the direction of arrow C in FIGS. 1 and 2). That is, as the pair of sprockets 25, 37, and 45 rotate, the pair of chains 22 circulate.

[0050] (Gripper 24) As shown in FIG. 3, the gripper 24 functions as a holding portion that holds the leading end portion of the recording medium P. As shown in FIG. 2, the gripper 24 is attached to an attachment 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 attachment member 23.

[0051] A plurality of attachment 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 attachment member 23 is attached to each of the pair of chains 22.

[0052] 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. In the gripper 24, the leading end portion of the recording medium P is sandwiched between the claw 24A and the claw base 24B to hold the recording medium P. Note that, for example, in the gripper 24, 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.

[0053] In the present embodiment, the gripper 24 as an example of the holding portion 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 portion, for example, a holding portion 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.

[0054] In the conveying unit 16, the leading end of the recording medium P supplied from the medium accommodating portion 12 that houses 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 rotates in the circumferential direction C to convey the recording medium P and pass it through the transfer position TA described later. At this time, the gripper 24 passes through the transfer position TA (that is, between the transfer cylinder 50 and the opposing roll 65) described later while being housed in the recess 54 of the transfer cylinder 50.

[0055] (Image forming mechanism 14) The image forming mechanism 14 shown in FIG. 1 has a function of forming an image on the recording medium P. Specifically, the image forming mechanism 14 forms an image on the recording medium P conveyed by the conveying unit 16 using ink. More specifically, as shown in FIG. 1, the image forming mechanism 14 includes ejection units 15A, 15B, 15C, 15D, 15E, 15F (hereinafter referred to as 15A to 15F) and a transfer unit 60 having a transfer belt 62.

[0056] (Ejection units 15A to 15F) Each of the ejection units 15A to 15F has a function of forming an image to be transferred from the transfer belt 62 to the recording medium P. Specifically, each of the ejection units 15A to 15F is a unit that ejects ink droplets of a predetermined color onto the transfer belt 62 to form an image of each color on the outer peripheral surface of the transfer belt 62. The predetermined colors include yellow (Y), magenta (M), cyan (C), and black (K). Note that each of the ejection units 15A to 15F is an example of an "image forming portion".

[0057] (Transfer unit 60) As described above, the transfer unit 60 is a unit having a transfer belt 62 for transferring an image to the recording medium P. Specifically, the transfer unit 60 includes a transfer belt 62, an opposing roll 65, a plurality of support rolls 64, and a cleaning unit 70.

[0058] 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 opposing roll 65, the plurality of support rolls 64, the cleaning unit 70, etc.). The support has support frames (not shown) arranged on the front side and the rear side with respect to the transfer belt 62, respectively.

[0059] (The transfer belt 62, the opposing roll 65, and the 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 arranged to face the transfer drum 50 with the transfer belt 62 disposed therebetween. Specifically, the opposing roll 65 is arranged on the upper right side with respect to the transfer drum 50. This opposing roll 65 is pressed against the outer peripheral surface of the transfer drum 50 via the transfer belt 62 by the elastic force of, for example, an elastic member (not shown).

[0061] In the present embodiment, the opposing position where the opposing roll 65 faces the transfer drum 50 is defined as the transfer position TA where an image is transferred onto 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 onto 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] Specifically, as indicated by reference numerals (A), (B), (C), and (D) in the drawing, four support rolls 64 are provided on the inner peripheral side of the transfer belt 62. 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 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 roll 64(C) and the support roll 64(D). The second surface 92 of the transfer belt 62 is the surface facing diagonally downward to the right between the support roll 64(B) and the support roll 64(C). The third surface 93 of the transfer belt 62 is the surface facing diagonally downward to the left between the opposing roll 65 and the support roll 64(D).

[0065] The ejection units 15A, 15B, and 15C face the first surface 91 of the transfer belt 62 and eject ink droplets onto the first surface 91 of the transfer belt 62 to form an image. The ejection units 15D, 15E, and 15F face the second surface 92 of the transfer belt 62 and eject ink droplets onto the second surface 92 of the transfer belt 62 to form an image.

[0066] Among 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 the shaft. As an example, the support roll 64 has a roll having a shaft and a rubber layer provided on the outer periphery of the shaft.

[0067] 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. The rotating transfer belt 62 sandwiches the recording medium P conveyed by the conveying unit 16 with the transfer cylinder 50 at the transfer position TA, and transfers the image formed on its outer peripheral surface to the recording medium P. Thereby, an image is formed on the recording medium P.

[0068] (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 the foreign matter include paper dust generated from the paper as an example of the recording medium P, and ink.

[0069] 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.

[0070] 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 to remove the foreign matter from the transfer belt 62.

[0071] The housing 74 has an opening 74A on the third surface 93 side of the transfer belt 62 (that is, the support roll 64(D) side), and accommodates the foreign matter removed by the blade 72 through the opening 74A.

[0072] 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 that faces the blade 72 is arranged with the transfer belt 62 disposed therebetween and the blade 72.

[0073] (Positional relationship of each part in the transfer unit 60) In the transfer unit 60, when viewed from the rear, the transfer position TA is located on the left side with respect to the center 60T in the left-right direction of the transfer unit 60. The center 60T is the position at the center between the right end 60R and the left end 60L of the transfer unit 60 in the left-right direction. Therefore, the length along the left-right direction from the center 60T to the right end 60R (length LA in FIG. 1) and the length along the left-right direction from the center 60T to the left end 60L (length LB in FIG. 1) are made equal.

[0074] "Located on the left side with respect to the center 60T" means located on the left side with reference to the center 60T, and the vertical position is not considered. Note that the left-right direction is an example of the "horizontal direction". The left side is an example of the "one side".

[0075] In the transfer unit 60, the cleaning unit 70 is located on the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear. Also, in the transfer unit 60, the support roll 64(D) which is a driving roll is located on the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear. "Located on the transfer position TA side with respect to the center 60T" means located on the transfer position TA side (i.e., the left side) with reference to the center 60T, and the vertical position is not considered.

[0076] Then, when viewed from the rear, the center of mass point 60G of the transfer unit 60 is located on the transfer position TA side with respect to the center 60T in the left-right direction. The center of mass point 60G of the transfer unit 60 refers to the point at which the resultant force of the gravitational forces acting on each part of the transfer unit 60 is considered to act.

[0077] Also, in this embodiment, it can also be said that when viewed from the rear, the center of mass point 60G of the transfer unit 60 is located on the transfer position TA side with respect to the geometric center 60S of the transfer unit 60. The geometric center 60S refers to the point at the arithmetic mean position taken over all the points belonging to the outer shape of the transfer unit 60 when viewed from the rear. Note that if it is assumed that the transfer unit 60 is an object with a uniform density, the center of mass point 60G and the geometric center 60S coincide. In other words, the geometric center 60S can also be said to be the center of mass point 60G when it is assumed that the transfer unit 60 is an object with a uniform density.

[0078] Also, "the center of mass point 60G is located on the transfer position TA side with respect to the geometric center 60S of the transfer unit 60" means, in other words, that the distance between the center of mass point 60G and the transfer position TA (the distance of the broken line LX in FIG. 1) is shorter than the distance between the geometric center 60S and the transfer position TA (the distance of the broken line LY in FIG. 1), and the center of mass point 60G is in a state of being located at such a position. Note that the "distance from the transfer position TA" is the distance to the center in the circumferential direction of the transfer position TA when the transfer position TA has a width in the circumferential direction of the transfer belt 62.

[0079] (Mass of each part of the image forming apparatus 10) The mass of the transfer drum 50, the pair of sprockets 25, 37, 45, the pair of chains 22, and the gripper 24 included in the conveyance unit 16 is more than twice the mass of the transfer unit 60. Specifically, the mass of the transfer unit 60 is set to 300 kg, and the mass of the conveyance unit 16 is set to, for example, 600 kg.

[0080] Also, the mass of each of the ejection units 15A to 15F is 100 kg or more. Specifically, the mass of each of the ejection units 15A to 15F is in the range of 120 kg or more and 130 kg or less. Note that the mass of each of the ejection units 15A to 15F includes the mass of the ink filled in each of the ejection units 15A to 15F.

[0081] (Operation according to the first embodiment) Next, the operation according to the first embodiment will be described.

[0082] 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 rotates 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 cylinder 50 and the opposing roll 65 while being accommodated in the recess 54 of the transfer cylinder 50.

[0083] Then, the transfer belt 62 sandwiches the recording medium P with the transfer cylinder 50 at the transfer position TA and transfers the image formed on its outer peripheral surface to the recording medium P. Thereby, an image is formed on the recording medium P.

[0084] 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 through the transfer position TA to the transfer unit 60 having the transfer belt 62 from the transfer cylinder 50, and the transfer unit 60 may be vibrated.

[0085] In particular, in this embodiment, since the opposing roll 65 is pressed against the outer peripheral surface of the transfer cylinder 50 via the transfer belt 62, when the recess 54 of the transfer cylinder 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).

[0086] Further, 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 vibration generated in the conveyance unit 16 (hereinafter referred to as factor B).

[0087] Furthermore, in the present embodiment, since the mass of each of the ejection units 15A to 15F is 100 kg or more, the image forming apparatus 10 becomes large-sized, and the transfer unit 60 is likely to be excited (hereinafter referred to as factor C). When the transfer unit 60 is excited, image distortion such as banding occurs in the image transferred from the transfer belt 62 to the recording medium P. Note that banding is image distortion in which striped shading appears in the image.

[0088] Here, in the present embodiment, when viewed from the rear, the mass center point 60G of the transfer unit 60 is located on the transfer position TA side with respect to the center 60T in the left-right direction.

[0089] Therefore, even when it is propagated from the transfer cylinder 50 to the transfer unit 60 having the transfer belt 62 via the transfer position TA, when viewed from the rear, the mass center point 60G of the transfer unit 60 is located on the side opposite to the transfer position TA side with respect to the center 60T in the left-right direction (hereinafter referred to as configuration A). Compared with the configuration, the transfer unit 60 is less likely to be excited.

[0090] As a result, according to the present embodiment, in a configuration in which the transfer unit 60 is likely to be excited due to the above-described factors A, B, and C, compared with configuration A, the excitation of the transfer belt 62 is suppressed, and image distortion of the image formed on the recording medium P is suppressed.

[0091] Also, it can be said that in the present embodiment, when viewed from the rear, the mass center point 60G of the transfer unit 60 is located on the transfer position TA side with respect to the geometric center 60S of the transfer unit 60.

[0092] Therefore, even when it is propagated from the transfer cylinder 50 to the transfer unit 60 having the transfer belt 62 via the transfer position TA, when viewed from the rear, the mass center point 60G of the transfer unit 60 is located on the side opposite to the transfer position TA side with respect to the geometric center 60S of the transfer unit 60 (hereinafter referred to as configuration B). Compared to this, the transfer unit 60 is less likely to be vibrated.

[0093] As a result, according to the present embodiment, in a configuration in which the transfer unit 60 is likely to be vibrated due to the above-described factors A, B, and C, compared to configuration B, the vibration of the transfer belt 62 is suppressed, and image blurring of the image formed on the recording medium P is suppressed.

[0094] Further, in the present embodiment, the cleaning unit 70 is located on the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear.

[0095] Therefore, compared to a configuration in which the cleaning unit 70 is located on the side opposite to the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear, it is easier to position the mass center point 60G of the transfer unit 60 on the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear.

[0096] Further, in the present embodiment, the solid support roll 64(D) is located on the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear.

[0097] Therefore, compared to a configuration in which the solid support roll 64(D) is located on the side opposite to the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear, it is easier to position the mass center point 60G of the transfer unit 60 on the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear.

[0098] Also, in the present embodiment, the solid support roll 64(D) is used as a drive roll for transmitting a driving force to the transfer belt 62. Therefore, compared with a configuration in which a hollow support roll is a drive roll, while positioning the mass center point 60G of the transfer unit 60 on the transfer position TA side with respect to the center 60T in the left - right direction in a rear view, the deflection deformation of the support roll 64(D) is suppressed.

[0099] <Second Embodiment> (Image forming apparatus 200) In the first embodiment, the image forming apparatus 10 was an ink - jet type image forming apparatus that forms an image on the recording medium P using ink. However, the image forming apparatus is not limited to this. As an example of the image forming apparatus, for example, an electrophotographic image forming apparatus may be used, as long as it is an apparatus that forms an image. In the second embodiment, an electrophotographic image forming apparatus 200 will be described. FIG. 4 is a schematic diagram showing the configuration of the image forming apparatus 200 according to the present embodiment. Note that parts having the same functions as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0100] (Image forming mechanism 214) The image forming apparatus 200 has an image forming mechanism 214 instead of the image forming mechanism 14. The image forming mechanism 214 has a function of forming a toner image (an example of an image) on the recording medium P by an electrophotographic method. More specifically, as shown in FIG. 4, the image forming mechanism 214 includes toner image forming units 222A, 222B, 222C, 222D, 222E, 222F (hereinafter referred to as 222A to 222F) that form a toner image, and a transfer unit 60 having a transfer belt 62.

[0101] (Toner image forming units 222A - 222F) Each of the toner image forming units 222A to 222F shown in FIG. 4 has a function of forming an image transferred from the transfer belt 62 to the recording medium P. Specifically, each of the toner image forming units 222A to 222F is a unit that 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). Note that each of the toner image forming units 222A to 222F is an example of an "image forming unit".

[0102] In the present embodiment, since each of the toner image forming units 222A to 222F is configured in the same manner except for the toner used, reference numerals are attached to each part of the toner image forming unit 222C in FIG. 4 to represent the toner image forming units 222A to 222F.

[0103] 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. 4). Each of the toner image forming units 222A to 222F also has a charger 223, an exposure device 240, and a developing device 238.

[0104] In each of the toner image forming units 222A to 222F, the charger 223 charges the photoreceptor 224. Further, the exposure device 240 exposes the photoreceptor 224 charged by the charger 223 to form an electrostatic latent image on the photoreceptor 224. Also, the developing device 238 develops the electrostatic latent image formed on the photoreceptor 224 by the exposure device 240 to form a toner image.

[0105] 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.

[0106] In this embodiment, 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.

[0107] Also, the mass of each of the toner image forming units 222A to 222F is 100 kg or more. Specifically, the mass of each of the toner image forming units 222A to 222F is in the range of 120 kg or more and 130 kg or less.

[0108] (Transfer Unit 60) The transfer unit 60 shown in FIG. 4 has a function of transferring the toner images formed by each of the toner image forming units 222A to 222F to the recording medium P. Specifically, the transfer unit 60 superimposes and primarily transfers the toner images of the photoreceptors 224 of each color onto the transfer belt 62 as an intermediate transfer member, and secondarily transfers the superimposed toner images to the recording medium P. As shown in FIG. 4, the transfer unit 60 has a primary transfer roll 226 in addition to the transfer belt 62, the opposing roll 65, the plurality of support rolls 64, and the cleaning unit 70.

[0109] The primary transfer roll 226 is a roll that transfers the toner images of the photoreceptors 224 of each 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.

[0110] 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. Further, the toner image transferred to the transfer belt 62 is transferred to the recording medium P sandwiched between the transfer belt 62 and the transfer cylinder 50 at the transfer position TA by applying a secondary transfer electric field between the opposing roll 65 and the transfer cylinder 50.

[0111] (Fixing device 280) The image forming apparatus 200 further includes a fixing device 280 that fixes the toner image transferred to the recording medium P to the recording medium P. As shown in FIG. 4, the fixing device 280 has a pressure roll 281 and a heating roll 282.

[0112] In this embodiment, a pair of sprockets 45 are provided on both axial ends of the pressure roll 281. This pair of sprockets 45 are arranged coaxially with the pressure roll 281 and are 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.

[0113] In the fixing device 280, the heating roll 282 is arranged above the pressure roll 281. This heating roll 282 has a heating source 282A such as a halogen lamp inside the roll.

[0114] Then, in the fixing device 280, while conveying the recording medium P in a state of being 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 to the recording medium P to the recording medium P.

[0115] In the image forming apparatus 200, the conveyance unit 16 passes the recording medium P through the transfer position TA and the fixing position NP between the pressure roll 281 and the heating roll 282 by the chain 22 rotating in the circumferential direction C while the gripper 24 holds the leading end portion of the recording medium P. Then, the toner image primarily transferred onto the transfer belt 62 at each primary transfer position T1 of the toner image forming units 222A to 222F is secondarily transferred onto the recording medium P at the transfer position TA. The toner image secondarily transferred onto the recording medium P is fixed onto the recording medium P at the fixing position NP.

[0116] The transfer unit 60 in the present embodiment is configured in the same manner as the transfer unit 60 in the first embodiment, except that it has the primary transfer roll 226, and the present embodiment exhibits the same operation as the first embodiment.

[0117] In the transfer unit 60 in the present embodiment, further, the mass center point 60G is closer to the toner image forming unit 222A disposed immediately downstream of the transfer position TA in the circumferential direction A of the transfer belt 62 among the toner image forming units 222A to 222F than to the toner image forming units 222B, 222C, 222D, 222E, and 222F disposed downstream of the toner image forming unit 222A in the circumferential direction A with respect to the toner image forming unit 222A.

[0118] "Disposed immediately downstream of the transfer position TA in the circumferential direction A of the transfer belt 62" means that it is disposed at a position downstream of the transfer position TA in the circumferential direction A and at the position where the distance seen from the transfer position TA downstream in the circumferential direction A is the closest.

[0119] Also, "being located at a close position" means being located at a position where the distance (the distance indicated by the broken line in FIG. 4) between the primary transfer position T1 (i.e., the contact position between the photoreceptor 224 and the transfer belt 62) and the mass center point 60G is short. Note that the "distance between the primary transfer position T1 and the mass center point 60G" is the distance to the center in the circumferential direction of the primary transfer position T1 when the primary transfer position T1 has a width in the circumferential direction of the transfer belt 62.

[0120] Here, in the transfer unit 60, when viewed with respect to the transfer position TA, on the downstream side in the circumferential direction with respect to the transfer position TA, the transfer belt 62 is the side to be pulled, and on the upstream side in the circumferential direction with respect to the transfer position TA, it is the pulling side. For this reason, the transfer belt 62 is in a state where tension is applied on the downstream side in the circumferential direction with respect to the transfer position TA rather than on the upstream side in the circumferential direction with respect to the transfer position TA, and the vibration propagated from the transfer drum 50 to the transfer belt 62 via the transfer position TA is likely to propagate to the downstream side in the circumferential direction with respect to the transfer position TA. As a result, the toner image forming unit 222A is more likely to be vibrated than the toner image forming units 222B, 222C, 222D, 222E, and 222F.

[0121] And in the present embodiment, as described above, the mass center point 60G is located closer to the toner image forming unit 222A than to the toner image forming units 222B, 222C, 222D, 222E, and 222F among the toner image forming units 222A to 222F.

[0122] For this reason, compared to a configuration in which the mass center point 60G is located closer to any one of the toner image forming units 222B, 222C, 222D, 222E, and 222F than to the toner image forming unit 222A among the toner image forming units 222A to 222F, the vibration of the toner image forming unit 222A is suppressed.

[0123] (Evaluation) In the evaluation, in the configuration of the second embodiment, the position of the mass center point 60G of the transfer unit 60 was changed in the left - right direction of the transfer unit 60, an image was formed on the recording medium P, and the presence or absence of banding occurring in the image was evaluated.

[0124] In this evaluation, a single - color halftone image (image density: 20%) was formed on the recording medium P using each of the toner image forming units 222A to 222F, and the occurrence of banding was visually confirmed.

[0125] (Evaluation Criteria) A: Banding generation cannot be confirmed B: Banding generation can be confirmed

[0126] (Example 1) The position of the center of mass point 60G was set to a position where the distance along the left - right direction from the right end 60R of the transfer unit 60 (distance L1 in Fig. 4) was 1000 mm, and the distance along the left - right direction from the left end 60L of the transfer unit 60 (distance L2 in Fig. 4) was 600 mm.

[0127] In Example 1, when viewed from the rear, the center of mass point 60G of the transfer unit 60 is located on the transfer position TA side with respect to the center 60T in the left - right direction. Also, in Example 1, when viewed from the rear, the center of mass point 60G of the transfer unit 60 is also located on the transfer position TA side with respect to the geometric center 60S of the transfer unit 60.

[0128] (Comparative Example 1) The position of the center of mass point 60G was set to a position where the distance along the left - right direction from the right end 60R of the transfer unit 60 (distance L1 in Fig. 4) was 800 mm, and the distance along the left - right direction from the left end 60L of the transfer unit 60 (distance L2 in Fig. 4) was 800 mm.

[0129] In Comparative Example 1, when viewed from the rear, the center of mass point 60G is set to a position that coincides with the center 60T in the left - right direction. Also, in Comparative Example 1, when viewed from the rear, the center of mass point 60G of the transfer unit 60 is set to a position on the side opposite to the transfer position TA side with respect to the geometric center 60S of the transfer unit 60.

[0130] (Comparative Example 2) The position of the center of mass point 60G was set to a position where the distance along the left - right direction from the right end 60R of the transfer unit 60 (distance L1 in Fig. 4) was 600 mm, and the distance along the left - right direction from the left end 60L of the transfer unit 60 (distance L2 in Fig. 4) was 1000 mm.

[0131] In Comparative Example 2, in a rear view, the mass center of gravity point 60G is set at a position on the side opposite to the transfer position TA side with respect to the center 60T in the left-right direction. Further, in Comparative Example 2, in a rear view, the mass center of gravity point 60G of the transfer unit 60 is set at a position on the side opposite to the transfer position TA side with respect to the geometric center 60S of the transfer unit 60.

[0132] (Evaluation Results) As shown in FIG. 5, in Comparative Examples 1 and 2, the occurrence of banding was confirmed. On the other hand, in Example 1, the occurrence of banding was not confirmed. It is considered that the banding is generated when the transfer unit 60 is vibrated. Therefore, from the results shown in FIG. 5, it is considered that the transfer unit 60 is less likely to be vibrated in Example 1 compared to Comparative Examples 1 and 2.

[0133] (Modification) In the first and second embodiments, as described above, in a rear view, the mass center of gravity point 60G of the transfer unit 60 is located on the transfer position TA side with respect to the center 60T in the left-right direction (hereinafter referred to as the first configuration), and in a rear view, the mass center of gravity point 60G of the transfer unit 60 is located on the transfer position TA side with respect to the geometric center 60S of the transfer unit 60 (hereinafter referred to as the second configuration). However, the present invention is not limited to this. The transfer unit 60 may have at least one of the first configuration and the second configuration.

[0134] Further, in the first and second embodiments, the cleaning unit 70 is located on the transfer position TA side with respect to the center 60T in the left-right direction in a rear view. However, the present invention is not limited to this. For example, the cleaning unit 70 may be configured to be located on the side opposite to the transfer position TA side with respect to the center 60T in the left-right direction in a rear view.

[0135] In the first and second embodiments, the solid support roll 64(D) was located on the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear. However, the present invention is not limited to this. For example, the solid support roll 64(D) may be configured to be located on the side opposite to the transfer position TA side with respect to the center 60T in the left-right direction when viewed from the rear.

[0136] In the first and second embodiments, the solid support roll 64(D) was used as the drive roll for transmitting the driving force to the transfer belt 62. However, the present invention is not limited to this. For example, a hollow support roll may be configured as the drive roll.

[0137] In the first and second embodiments, the concave portion 54 was formed on the outer peripheral surface of the transfer cylinder 50. However, the present invention is not limited to this. For example, the 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.

[0138] In the first and second embodiments, a chain 22 was used as an example of the circulating member, and a sprocket 25 was used as an example of the rotating member. However, the present invention is not limited to this. For example, a timing belt having irregularities on the inner periphery may be used as an example of the circulating member, and a timing pulley (that is, a pulley having irregularities on the outer periphery) may be used as an example of the rotating member. Further, a belt may be used as an example of the circulating member, and a pulley that circulates the belt by friction may be used as an example of the rotating member.

[0139] In the first and second embodiments, the mass of the transport unit 16 was set to be twice or more the mass of the transfer unit 60. However, the present invention is not limited to this. For example, the mass of the transport unit 16 may be configured to be less than twice the mass of the transfer unit 60.

[0140] Also, in the first embodiment, the mass of each of the ejection units 15A to 15F was 100 kg or more, but it is not limited thereto. For example, the mass of each of the ejection units 15A to 15F may be less than 100 kg.

[0141] Also, in the second embodiment, the mass of each of the toner image forming units 222A to 222F was 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.

[0142] Also, in the second embodiment, the mass center point 60G was located closer to the toner image forming unit 222A than to the toner image forming units 222B, 222C, 222D, 222E, and 222F among the toner image forming units 222A to 222F, but it is not limited thereto.

[0143] For example, the mass center point 60G may be located closer to the toner image forming unit 222A than to any one or more of the toner image forming units 222B, 222C, 222D, 222E, and 222F among the toner image forming units 222A to 222F. Further, for example, the mass center point 60G may be configured to be located closer to any one of the toner image forming units 222B, 222C, 222D, 222E, and 222F than to the toner image forming unit 222A among the toner image forming units 222A to 222F.

[0144] The present invention is not limited to the above embodiments, and various modifications, changes, and improvements are possible without departing from the gist thereof. For example, the above-described modified examples may be configured by appropriately combining a plurality of them.

Explanation of Reference Numerals

[0145] 10, 200 Image forming apparatus 15A to 15F Ejection unit (an example of an image forming unit) 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 part 60 Transfer unit 60G Center of mass 60S Geometric center 60T Center 62 Transfer belt 64 Support roll 65 Opposing roll 70 Cleaning part 222A - 222F Toner image forming unit (an example of an image forming part) P Recording medium 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 circumferential member provided with a holding portion for holding the leading end portion of the recording medium, wound around the rotating member, and circulating as the rotating member rotates to convey the recording medium, A transfer unit having a transfer belt that sandwiches and transfers an image with the transfer cylinder at a sandwiching position of the recording medium conveyed by the circumferential member, wherein when viewed in the axial direction of the rotating member, the sandwiching position is located on one side with respect to the center in its horizontal direction, and the center of mass point of itself is located on the sandwiching position side with respect to the center in the horizontal direction, the transfer unit, A plurality of image forming units that form an image transferred from the transfer belt to the recording medium, comprising, The transfer unit, has a plurality of members including the transfer belt and rollers that support the transfer belt, supported by a common support, The center of mass point, among the plurality of image forming units, is located closer to the first image forming unit disposed immediately downstream of the sandwiching position in the circumferential direction of the transfer belt than to the image forming unit disposed downstream of the first image forming unit in the circumferential direction, Further, the center of mass point, is located at a position closer to the second image forming unit disposed immediately upstream of the sandwiching position in the circumferential direction of the transfer belt than to the first image forming unit among the plurality of image forming units, An image forming apparatus.

2. A rotating transfer cylinder, A rotating member provided coaxially with the transfer cylinder and rotating integrally with the transfer cylinder, A circumferential member provided with a holding portion for holding the leading end portion of the recording medium, wound around the rotating member, and circulating as the rotating member rotates to convey the recording medium, A transfer unit having a transfer belt that sandwiches and transfers an image with a transfer cylinder at a sandwiching position of a recording medium conveyed by the circumferential member, wherein when viewed in the axial direction of the rotating member, the center of mass point of the transfer unit is located on the sandwiching position side with respect to the geometric center of the transfer unit itself; A plurality of image forming units that form an image transferred from the transfer belt to the recording medium; Comprising; The transfer unit; Has a plurality of members including the transfer belt and a roller that supports the transfer belt, supported by a common support; The center of mass point; Among the plurality of image forming units, with respect to a first image forming unit arranged immediately downstream of the sandwiching position in the circumferential direction of the transfer belt, it is located closer to the first image forming unit than to an image forming unit arranged downstream of the first image forming unit in the circumferential direction; Furthermore, the center of mass point; Among the plurality of image forming units, with respect to a second image forming unit arranged immediately upstream of the sandwiching position in the circumferential direction of the transfer belt, it is located at a position next closest to the first image forming unit; An image forming apparatus.

3. The transfer unit has a cleaning unit for cleaning the transfer belt; When viewed in the axial direction of the rotating member, the cleaning unit is located on the sandwiching position side with respect to the center in the horizontal direction; The image forming apparatus according to claim 1.

4. The transfer unit has a solid support roll for supporting the transfer belt; When viewed in the axial direction of the rotating member, the support roll is located on the sandwiching position side with respect to the center in the horizontal direction; The image forming apparatus according to claim 1 or 3.

5. The support roll is a driving roll that transmits a driving force to the transfer belt; The image forming apparatus according to claim 4.

6. The transfer cylinder has a recess formed on its outer peripheral surface, the transfer unit is disposed opposite to the transfer cylinder and has a counter roll 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 5.

7. The recess is a recess in which the holding portion is accommodated The image forming apparatus according to claim 6.

8. The mass of the conveyance unit including the transfer cylinder, the rotating member, the holding portion, and the circulating member is not less than twice the mass of the transfer unit The image forming apparatus according to any one of claims 1 to 7.

9. An image forming unit that forms an image transferred from the transfer belt to the recording medium, the mass of the image forming unit is 100 kg or more The image forming apparatus according to any one of claims 1 to 8.

Images