Image formation apparatus

Abstract

To provide a compact and low-cost image formation apparatus that has an intermediate transfer body that can be easily inserted to and removed from an apparatus body, suppresses image density variation, and achieves long service life.SOLUTION: An image formation apparatus 100 comprises: a plurality of frame members 49 that hold image carriers 1; an intermediate transfer body 3 that performs secondary transfer of toner images onto a recording medium P; a plurality of primary transfer members 11 that perform primary transfer of toner images onto the intermediate transfer body at a primary transfer unit; holding members 51, 81 that hold the primary transfer members; a plurality of pressure members 50, 80 that apply pressure to the holding members; and a pressing member 57 or 58 that presses the image carrier against the intermediate transfer frame 37 or a body structure side plate 55. The image formation apparatus positions the primary transfer members by abutting the holding members against the frame or frame members. One end side of the image carrier is positioned by being pressed against the frame by the pressing member 57, and the primary transfer member on the one end is positioned by abutting the holding member 81 against the frame 37 with the pressure member 80.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In a color printer, for the purpose of extending the life of the photoreceptor, it is common to separate the primary transfer rollers of colors other than black from the photoreceptor in monochrome mode. Patent Document 1 discloses providing holding members for each of the primary transfer roller and the backup roller, and separating the primary transfer roller and the backup roller from the photoreceptor by the rotation of a cam. The backup roller is a roller for determining the shape of the belt in order to aim at the transfer nip of the most upstream primary transfer roller.

[0003] However, in Patent Document 1, since holding members are provided for each of the primary transfer roller and the backup roller, the distance between the primary transfer roller and the backup roller becomes long, the apparatus becomes large, and as a result, the manufacturing cost of the apparatus increases.

[0004] In Patent Document 2, the primary transfer rollers and backup rollers for colors (cyan, magenta, yellow) are held by the same holding member, and when switching between monochrome mode and full-color mode, the entire holding member is moved to bring the primary transfer roller into contact with and separate from the photoreceptor. However, since the front and rear (left and right) end portions of the primary transfer rollers and backup rollers for colors must be held by the same holding member, the components become large, and the manufacturing cost of the apparatus increases.

[0005] In Patent Document 3, in order to reduce the size and cost of the transfer unit, a mechanism for holding the primary transfer roller and the backup roller with the same holding member and a configuration for positioning the holding member by abutting it against the transfer frame are disclosed. However, since the photosensitive member is not positioned with respect to the transfer frame, when the holding member is abutted against the transfer frame, the position of the primary transfer roller with respect to the photosensitive member is likely to vary due to the accumulation of component tolerances. Therefore, image density deviation is likely to occur on the left and right. In addition, since a mechanism for suppressing belt meandering is not provided, there is a problem that it is necessary to use an expensive belt or the belt life is short.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, an object of the present invention is to provide a small and low-cost image forming apparatus including an intermediate transfer member that can be easily inserted and removed from the apparatus main body, in which image density deviation is less likely to occur and the life is long.

Means for Solving the Problems

[0007] This problem is solved in an image forming apparatus including a plurality of image carriers that carry a toner image, a plurality of frame members that hold the image carriers, an intermediate transfer member that is movable to secondarily transfer the toner image primarily transferred from the image carrier to a recording medium, a plurality of primary transfer members that primarily transfer the toner image from the image carrier to the intermediate transfer member at a primary transfer portion where the outer peripheral surface of the image carrier and the intermediate transfer member are in contact, a holding member that holds the primary transfer members, an intermediate transfer frame that holds the intermediate transfer member and rotatably holds the holding member, a plurality of pressing members that press the holding member, and a pressing member that presses the image carrier against the intermediate transfer frame or a side plate of the main body structure. In the image forming apparatus that positions the primary transfer members by abutting the holding member against the intermediate transfer frame or the frame members, one end side of the image carrier is positioned by being pressed against the intermediate transfer frame by the pressing member, and the primary transfer member on the one end side is positioned by abutting the holding member against the intermediate transfer frame by the pressing member.

Advantages of the Invention

[0008] An image forming apparatus that is small and low-cost, has an intermediate transfer member that is easy to insert and remove from the apparatus main body, is less likely to exhibit image density deviation, and has a long service life can be obtained.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus 100 configured as a printer. The image forming apparatus 100 shown here includes a plurality of photoreceptors (an example of an image carrier) arranged in its main body housing. In the illustrated example, four photoreceptors 1a, 1b, 1c, and 1d (hereinafter, appropriately referred to as "photoreceptor 1" when not distinguishing colors) from the first to the fourth are provided. Toner images of different colors are respectively formed on each photoreceptor. In the example shown in FIG. 1, a black toner image, a magenta toner image, a cyan toner image, and a yellow toner image are respectively formed on these photoreceptors 1a, 1b, 1c, and 1d. Each of the photoreceptors 1a, 1b, 1c, and 1d shown in FIG. 1 is formed in a drum shape, but an endless belt-shaped photoreceptor wound around a plurality of rollers and rotationally driven can also be used.

[0011] An intermediate transfer belt 3 configured as an intermediate transfer member is disposed opposite to the first to fourth photoreceptors 1a, 1b, 1c, and 1d, and each photoreceptor 1a, 1b, 1c, 1d is in contact with the surface of the intermediate transfer belt 3. The intermediate transfer belt 3 secondarily transfers the toner image primarily transferred to itself from the photoreceptors 1a, 1b, 1c, 1d to the recording medium P. The intermediate transfer belt 3 shown here is wound around a driving roller 4, a tension roller 5, and an entrance roller 7, and one of these support rollers, for example, the support roller 4, is a driving roller driven by a driving source (not shown), and the intermediate transfer belt 3 is rotationally driven in the direction of arrow A by driving of the roller. The intermediate transfer belt 3 may have a multilayer structure or a single-layer structure. If it has a multilayer structure, it is preferably formed with a base layer made of, for example, a fluororesin with little elongation, a PVDF sheet, or a polyimide-based resin, and the surface is covered with a coating layer having good smoothness such as a fluororesin. If it is a single layer, materials such as PVDF, PC, or polyimide are preferably used.

[0012] The configuration for forming a toner image on the photoreceptors 1a, 1b, 1c, 1d and the configuration for transferring each toner image onto the intermediate transfer belt 3 are substantially all the same, and only the colors of the formed toner images are different. Therefore, only the configuration and operation for forming a black toner image on the first photoreceptor 1a and transferring the toner image onto the intermediate transfer belt 3 will be described. This photoreceptor 1a is rotationally driven counterclockwise as shown by the arrow in FIG. 1. At this time, the surface of the photoreceptor is irradiated with light from a charge removal device (not shown), and the surface potential of the photoreceptor 1a is initialized. The initialized surface of the photoreceptor is uniformly charged to a predetermined polarity, in this example, a negative polarity, by a charging device 8. The charged surface is irradiated with a laser beam L whose light is modulated and emitted from an exposure device 9, and an electrostatic latent image corresponding to the writing information is formed on the surface of the photoreceptor 1a. In the image forming apparatus 100 shown in FIG. 1, an exposure device 9 composed of a laser writing device that emits a laser beam is used, but an exposure device having an LED array and an imaging means or the like can also be used.

[0013] When the electrostatic latent image formed on the photoreceptor 1a passes through the developing device 10, it is visualized as a visible black toner image. On the other hand, inside the intermediate transfer belt 3, primary transfer rollers 11a, 11b, 11c, 11d (hereinafter, appropriately referred to as "primary transfer roller 11" when not distinguishing colors), which are primary transfer members positioned substantially opposite to the photoreceptor 1a with the belt interposed therebetween, are arranged. This primary transfer roller 11 abuts against the back surface of the intermediate transfer belt 3, ensuring an appropriate transfer nip between the photoreceptor 1a and the intermediate transfer belt 3. Since this primary transfer roller 11 is made of metal, it is arranged slightly offset with respect to the photoreceptor 1 (indirect transfer method). In this embodiment, the belt distance (offset amount) that does not contact either the photoreceptor 1 or the primary transfer roller 11 is set to 4 to 5 mm.

[0014] A transfer voltage of the opposite polarity to the toner charging polarity of the toner image formed on the photoreceptor 1a, in this example, a positive polarity, is applied to the above-mentioned primary transfer roller 11. Thereby, a transfer electric field is formed between the photoreceptor 1a and the intermediate transfer belt 3, and at the primary transfer portion where the photoreceptor 1a and the outer peripheral surface of the intermediate transfer belt 3 come into contact, the toner image on the photoreceptor 1a is electrostatically transferred onto the intermediate transfer belt 3 that is rotationally driven in synchronization with the photoreceptor 1a (primary transfer). The transfer residual toner adhering to the surface of the photoreceptor 1a after transferring the toner image to the intermediate transfer belt 3 is removed by the cleaning device 12, and the surface of the photoreceptor 1a is cleaned.

[0015] In exactly the same manner, magenta, cyan, and yellow toner images are respectively formed on the second to fourth photoreceptors 1b, 1c, and 1d, and the toner images of each color are sequentially superimposed and electrostatically transferred onto the intermediate transfer belt 3 onto which the black toner image has been transferred.

[0016] At this time, there are two modes: a full-color mode that uses toner images of each of the four colors and a black single-color mode that uses only black. In the full-color mode, the intermediate transfer belt 3 and the four-color photoreceptor 1 are in contact, and toner of all four colors is transferred onto the intermediate transfer belt 3. On the other hand, in the black single-color mode, only the black photoreceptor 1a is in contact with the intermediate transfer belt 3, and only black toner is transferred onto the intermediate transfer belt 3. At this time, the intermediate transfer belt 3 and the magenta, cyan, and yellow photoreceptors 1b, 1c, and 1d are not in contact, and the primary transfer rollers 11b, 11c, and 11d are separated from the photoreceptors 1b, 1c, and 1d by the contact and separation mechanism 90 provided in the image forming apparatus 100.

[0017] On the other hand, as shown in FIG. 1, a paper feeding device 14 is disposed at the lower part inside the apparatus main body. The paper feeding device 14 feeds out a recording medium P made of, for example, transfer paper in the direction of arrow B by the rotation of a paper feeding roller 15. The fed recording medium P is fed between a portion of the intermediate transfer belt 3 wound around a support roller 4 at a predetermined timing by a registration roller pair 16 and a secondary transfer roller 17 opposed thereto. At this time, a predetermined transfer voltage is applied to the secondary transfer roller 17, whereby the composite toner image on the intermediate transfer belt 3 is secondarily transferred onto the recording medium P.

[0018] The recording medium P onto which the composite toner image has been secondarily transferred is further conveyed upward and passes through a fixing device 18. At this time, the toner image on the recording medium P is fixed by the action of heat and pressure. The recording medium P that has passed through the fixing device 18 is discharged outside the image forming apparatus via a paper discharging roller pair 19 provided in the paper discharging portion.

[0019] Further, the transfer residual toner adhering to the intermediate transfer belt 3 after the toner image transfer is removed by the belt cleaning device 20. In the belt cleaning device 20 in this embodiment, a blade-shaped cleaning blade 21 made of urethane or the like is used, and the cleaning blade 21 is brought into contact with the intermediate transfer belt 3 in a counter direction to the rotation direction of the intermediate transfer belt 3. However, as is apparent to those skilled in the art, various types of cleaning devices 20 can be appropriately used. For example, the cleaning device may be a capacitance type.

[0020] The transfer residual toner removed from the intermediate transfer belt 3 by the cleaning blade 21 is sent rearward in the longitudinal direction by the waste toner coil in the cleaning case, and is conveyed to the waste toner container through the waste toner path provided in the apparatus main body.

[0021] FIG. 1 shows an example of a schematic diagram of the power supply applied in this embodiment. A primary transfer bias power supply 27BK, which is a primary transfer power supply for applying a voltage to the primary transfer roller 11a, is connected to the detection unit 28 and the control unit 30. The detection unit 28 is connected to the primary transfer bias power supply 27BK, the primary transfer roller 11a, and the control unit 30. Here, the detection unit 28 is connected only to the primary transfer roller 11a corresponding to the photosensitive member 1a of one color (black in this embodiment) among the full-color photosensitive members 1a, 1b, 1c, 1d.

[0022] When the output of the primary transfer bias power supply 27BK is under constant voltage control, the detection unit 28 is a primary transfer current detection unit that detects the amount of current flowing through the primary transfer roller 11a when a bias is applied to the primary transfer roller 11a. When the output of the primary transfer bias power supply 27BK is under constant current control, the detection unit 28 detects the output bias of the primary transfer bias power supply 27BK.

[0023] The other primary transfer rollers 11b, 11c, 11d are applied by another primary transfer power supply 29FC. Therefore, the image forming apparatus 100 includes a plurality of primary transfer power supplies 27BK and 29FC, one of which is connected to the primary transfer roller 11a corresponding to the photoreceptor 1a for the black toner image, and the detection unit 28 is also connected only to the primary transfer roller 11a corresponding to the photoreceptor 1a for the black toner image. As a result, the image forming apparatus 100 only needs to have one detection unit 28, so that the cost of the configuration of the intermediate transfer unit 60 and the resistance detection configuration can be reduced. In addition, over time and every time the environment changes, control for changing the target value of the transfer bias becomes unnecessary, and there is no need to drive the intermediate transfer device or the image carrier each time, so that the intermediate transfer body and the image carrier can have a longer lifespan.

[0024] The control unit 30 is connected to the primary transfer bias power supply 27BK, the primary transfer power supply 29FC, and the detection unit 28, and determines the primary transfer voltage of the primary transfer roller 11a corresponding to all colors based on the detection result by the detection unit 28, that is, the current value X detected by the detection unit 28.

[0025] FIG. 2 shows a schematic diagram of an image forming apparatus according to an embodiment of the present invention. In the image forming apparatus 100, the photoreceptors 1a, 1b, 1c, and 1d are held by photoreceptor frames 49a, 49b, 49c, and 49d (an example of frame members). FIG. 2 shows, by way of example, the photoreceptor 1d and the photoreceptor frame 49d on the front side of the apparatus. At both longitudinal ends of the photoreceptors 1a, 1b, 1c, and 1d, abutting members are provided respectively. Specifically, in FIG. 2, an abutting member 48d is provided on the front side in the insertion / removal direction of the photoreceptor 1d, and an abutting member 53d is provided on the rear side in the insertion / removal direction of the photoreceptor 1d. Further, a photoreceptor frame 49d (an example of a frame member) for holding the photoreceptor 1d is provided. A photoreceptor pressing member 57d (an example of a pressing member) is provided on the front side in the insertion / removal direction of the photoreceptor frame 49d, and a photoreceptor pressing member 58d (an example of a pressing member) is provided on the rear side in the insertion / removal direction of the photoreceptor frame 49d. The pressing members 57d and 58d press the abutting members 48d and 53d against the members to be abutted, thereby positioning the photoreceptors 1a, 1b, 1c, and 1d. However, the members to be abutted against which the abutting members 48d and 53d abut are different. That is, the abutting member 48d on the front side in the insertion / removal direction is abutted against and positioned by the intermediate transfer frame 37 or a separate member provided on the intermediate transfer frame 37, and the abutting member 53d on the rear side in the insertion / removal direction is abutted against and positioned by the main body structure side plate 55 or the main body side plate holder 54d provided on the main body structure side plate 55.

[0026] FIG. 3 is a schematic view showing the insertion / removal direction of the intermediate transfer unit and the photoreceptor unit into the image forming apparatus. In this embodiment, the intermediate transfer unit 60 and the photoreceptor units 70a, 70b, 70c, and 70d can be easily inserted into and removed from the image forming apparatus 100 from the right side to the left side or from the left side to the right side as viewed from the front of the apparatus. The insertion / removal direction of the intermediate transfer unit 60 is parallel to the insertion / removal direction of the photoreceptor units 70a, 70b, 70c, and 70d. When the opening / closing door of the image forming apparatus 100 is opened, a large opening 61 is opened, so that the insertion and removal of the intermediate transfer unit 60 and the photoreceptor units 70a, 70b, 70c, and 70d are easy. The intermediate transfer unit 60 has an intermediate transfer belt 3, a driving roller 4, a tension roller 5, an entrance roller 7, a belt cleaning device 20, four primary transfer rollers 11, etc. (FIG. 1). The photoreceptor unit 70 has four photoreceptors 1, four charging devices 8, etc. (FIG. 1).

[0027] FIG. 4 is a schematic view showing the intermediate transfer unit and the photoreceptor units on the back side in the insertion / removal direction, and FIG. 5 is a schematic view showing the intermediate transfer unit and the photoreceptor units on the front side in the insertion / removal direction. As shown in FIG. 4, on the back side in the insertion / removal direction, the photoreceptors 1a, 1b, 1c, and 1d are respectively positioned by abutting the photoreceptor abutting members 53a, 53b, 53c, and 53d against the main body side plate holders 54a, 54b, 54c, and 54d provided on the main body structure side plate 55 by the photoreceptor pressing members 58a, 58b, 58c, and 58d which are the first pressing members. Also, as shown in FIG. 5, on the front side in the insertion / removal direction, the photoreceptors 1a, 1b, 1c, and 1d are respectively positioned by abutting the photoreceptor abutting members 48a, 48b, 48c, and 48d against the intermediate transfer frame 37 or a separate member provided on the intermediate transfer frame 37 by the photoreceptor pressing members 57a, 57b, 57c, and 57d which are the second pressing members.

[0028] Next, the positioning of the primary transfer roller will be described with reference to FIGS. 6 and 7. FIG. 6 is a schematic view showing the position of the primary transfer roller on the back side in the insertion / removal direction of the intermediate transfer unit, and FIG. 7 is a schematic view showing the position of the primary transfer roller on the front side in the insertion / removal direction of the intermediate transfer unit. In the image forming apparatus 100 shown in FIG. 6, the primary transfer rollers 11a, 11b, 11c, and 11d for each color are respectively held by primary transfer roller holding members 51a, 51b, 51c, and 51d (an example of holding members), and first pressing members 50a, 50b, 50c, and 50d for pressing the primary transfer rollers 11a, 11b, 11c, and 11d are respectively installed on the primary transfer roller holding members 51a, 51b, 51c, and 51d. The primary transfer roller holding members 51a, 51b, 51c, and 51d can rotate around the rotation shafts 52a, 52b, 52c, and 52d by the pressing force of the first pressing members 50a, 50b, 50c, and 50d, and abutting portions 56a, 56b, 56c, and 56d formed at the lower portions of the primary transfer roller holding members 51a, 51b, 51c, and 51d abut against the photoreceptor frames 49a, 49b, 49c, and 49d. Therefore, by abutting the primary transfer roller holding members 51a, 51b, 51c, and 51d against the photoreceptor frames 49a, 49b, 49c, and 49d respectively, the primary transfer rollers 11a, 11b, 11c, and 11d are positioned. As a result, variations in the positional relationship between the primary transfer rollers 11a, 11b, 11c, and 11d with respect to the photoreceptors 1a, 1b, 1c, and 1d are minimized, and variations in image density are suppressed. Also, the insertion and removal of the intermediate transfer unit 60 into and from the apparatus main body are facilitated, and downsizing and cost reduction of the apparatus are achieved. Note that the intermediate transfer frame 37 holds the intermediate transfer belt 3 and rotatably holds the primary transfer roller holding members 51a, 51b, 51c, and 51d.

[0029] Next, the positioning of the primary transfer roller on the front side in the insertion / removal direction will be described. In the image forming apparatus 100 shown in FIG. 7, on the front side in the insertion and extraction direction, the primary transfer rollers 11a, 11b, 11c, and 11d of each color are respectively held by primary transfer roller holding members 81a, 81b, 81c, and 81d (an example of a holding member), and second pressing members 80a, 80b, 80c, and 80d for pressing the primary transfer rollers 11a, 11b, 11c, and 11d are respectively installed on the primary transfer roller holding members 81a, 81b, 81c, and 81d. The primary transfer roller holding members 81a, 81b, 81c, and 81d can rotate around the rotation shafts 52a, 52b, 52c, and 52d by the pressing force of the second pressing members 80a, 80b, 80c, and 80d, and abutting portions 86a, 86b, 86c, and 86d formed at the lower portions of the primary transfer roller holding members 81a, 81b, 81c, and 81d abut against the intermediate transfer body frame 37. Therefore, by abutting the primary transfer roller holding members 81a, 81b, 81c, and 81d against the intermediate transfer body frame 37 by the second pressing members 80a, 80b, 80c, and 80d respectively, the primary transfer rollers 11a, 11b, 11c, and 11d are positioned. The intermediate transfer body frame 37 holds the intermediate transfer belt 3 and rotatably holds the primary transfer roller holding members 81a, 81b, 81c, and 81d.

[0030] As described above, since the positions of the photoconductors 1a, 1b, 1c, and 1d on the front side in the insertion and extraction direction are determined by abutting the photoconductor abutting members 48a, 48b, 48c, and 48d against the intermediate transfer body frame 37, even if the primary transfer rollers 11a, 11b, 11c, and 11d are positioned by abutting against the intermediate transfer body frame 37, the positional variation of the primary transfer rollers 11a, 11b, 11c, and 11d with respect to the photoconductors 1a, 1b, 1c, and 1d will not increase significantly. The smaller the positional variation of the primary transfer rollers 11a, 11b, 11c, and 11d with respect to the photoconductors 1a, 1b, 1c, and 1d, the smaller the variation in image density on the back side and the front side in the insertion and extraction direction, and a good image can be provided.

[0031] In summary, in the image forming apparatus 100, after positioning the photoreceptors 1a, 1b, 1c, and 1d by abutting one end side of the photoreceptors 1a, 1b, 1c, and 1d against one end side of the intermediate transfer frame 37 (Fig. 5), by abutting the primary transfer roller holding members 81a, 81b, 81c, and 81d against the intermediate transfer frame 37 (Fig. 7), the primary transfer rollers 11a, 11b, 11c, and 11d on this one end side can be accurately positioned. Moreover, since the intermediate transfer unit 60 can be attached to and detached from the main scanning direction, it is easy to attach and detach the intermediate transfer unit 60 to and from the apparatus main body.

[0032] Also, the other end sides of the photoreceptors 1a, 1b, 1c, and 1d are pressed against the main body structure side plate 55 and positioned in consideration of the ease of attachment and detachment of the intermediate transfer unit 60 (Fig. 4). At this time, in order to determine the positions of the primary transfer roller holding members 81a, 81b, 81c, and 81d on this other end side, the primary transfer roller holding members 81a, 81b, 81c, and 81d are abutted against the photoreceptor frames 49a, 49b, 49c, and 49d (Fig. 6). Thereby, the positions of the primary transfer rollers 11a, 11b, 11c, and 11d with respect to the photoreceptors 1a, 1b, 1c, and 1d can be accurately determined, and the image density deviation is reduced.

[0033] Also, as shown in FIGS. 6 and 7, a backup roller 47 that rotates in contact with the inner circumference of the intermediate transfer belt 3 is disposed upstream of the primary transfer rollers 11a, 11b, 11c, 11d of each color. Thereby, the shape of the transfer nip located most upstream, which is formed between the photoreceptor 1d and the intermediate transfer belt 3, can be made as desired. Further, this backup roller 47 is held at both ends (in FIGS. 6 and 7) by the primary transfer roller holding members 51d, 81d located at the most upstream in the rotation direction of the intermediate transfer belt 3 (yellow in this embodiment). The primary transfer roller holding members 51d, 81d are second holding members that hold the backup roller 47. That is, the holding member that holds the most upstream primary transfer roller 11d among the plurality of primary transfer rollers 11a, 11b, 11c, 11d and the second holding member that holds the backup roller 47 are the same member. Also, the backup roller pressing member 72 (see FIG. 10) as the third pressing member, the first pressing member 50 (FIG. 6), and the second pressing member 80 (FIG. 7) are the same member. Further, the other primary transfer rollers 11a, 11b, 11c are held at both ends (in FIGS. 6 and 7) by the respective primary transfer roller holding members 51a, 51b, 51c and 81a, 81b, 81c. Also, a contact / separation mechanism 90 for contacting and separating the primary transfer roller 11 to contact and separate the intermediate transfer belt 3 from the photoreceptor 1 is provided (see FIG. 10). With these configurations, it is possible to reduce the size of the image forming apparatus 100 compared to separately arranging the backup roller 47, and thus to reduce the manufacturing cost and simplify the apparatus structure.

[0034] Also, in order to position the primary transfer roller 11 and the backup roller 47, the second holding member that holds the backup roller is positioned on the photoreceptor frames 49a, 49b, 49c, 49d (FIG. 6) or the intermediate transfer member frame 37 (FIG. 7).

[0035] Also, in the image forming apparatus 100, a tension roller 5, which is a rotatable body that is located upstream of the backup roller 47 and supports the intermediate transfer belt 3 and can be tilted, is provided with a belt deviation correction mechanism 150 that corrects the deviation of the belt by tilting the tension roller 5. By providing the belt deviation correction mechanism 150, the durability against cracks in the intermediate transfer belt 3 can be enhanced, and the life of the belt can be extended.

[0036] FIG. 8 is a schematic diagram showing a belt deviation correction mechanism for correcting the deviation of the belt. The belt deviation correction mechanism 150 is a correction mechanism that corrects the deviation of the belt by tilting the tension roller 5. The belt deviation correction mechanism 150 is installed at an axial end portion of the tension roller 5 and includes a belt end detection member 130, a belt position correction portion 140, and the like. The belt end detection member 130 has a cylindrical shape and is provided so as to be movable in the roller axis direction on the roller shaft 5a of the tension roller 5. The belt end detection member 130 has a flat portion 130a that extends substantially perpendicular to the roller axis direction. The periphery of the flat portion 130a is formed in a circular shape, and the center of the circle is on the axis of the tension roller 5. The flat portion 130a functions as a belt contact portion that contacts the end portion of the intermediate transfer belt 3 (referred to as the belt end 3a) when the intermediate transfer belt 3 moves outward in the roller axis direction.

[0037] As shown in FIG. 8, the roller shaft 5a is arranged coaxially with the axis of the tension roller 5. The roller shaft 5a has a cylindrical shape with a smaller diameter than the tension roller 5, is provided integrally with the tension roller 5, and passes through the belt end detection member 130, the axis inclination member 128 of the belt position correction portion 140, and the tension roller support member 133.

[0038] When the belt end 3a abuts against the flat portion 130a of the belt end detection member 130, the belt end detection member 130, which is movably provided in the direction of the roller shaft 5a, moves in the direction of the axis of the tension roller 5 (referred to as the roller shaft 5a direction).

[0039] The belt position correcting unit 140 includes a shaft tilting member 128, a guide member 135, a rotation support member 134, a tension roller support member 133, and a roller shaft support spring 145. The shaft tilting member 128 is provided on the roller shaft 5a so as to be in contact with the belt end detecting member 130 inside in the direction of the roller shaft 5a. When the belt end 3a abuts against the belt end detecting member 130 and the belt end detecting member 130 moves outward in the axial direction, the shaft tilting member 128 is pushed by the belt end detecting member 130 and moves outward in the direction of the roller shaft 5a. Further, the shaft tilting member 128 has an inclined surface 128a which is a plane inclined with respect to the surface of the belt 3 on the outer side in the direction of the roller shaft 5a. As the shaft tilting member 128 moves in the direction of the roller shaft 5a, the inclined surface 128a also moves in the direction of the roller shaft 5a.

[0040] Furthermore, as shown in FIG. 8, the guide member 135 is provided in contact with the inclined surface 128a of the shaft tilting member 128. The guide member 135 is in contact with the inclined surface 128a of the shaft tilting member 128 at a shaft displacement portion contact portion 135a which is a part thereof. The guide member 135 is fixed so as not to move even when the roller shaft 5a and the shaft tilting member 128 move. With such a configuration, when the shaft tilting member 128 moves outward in the direction of the roller shaft 5a, as shown in FIG. 9, the contact position between the shaft displacement portion contact portion 135a and the inclined surface 128a is shifted upward from the state of FIG. 8, whereby the shaft tilting member 128 and the roller shaft 5a passing through the shaft tilting member 128 are inclined.

[0041] FIG. 10 is a schematic view showing the position of the tension roller 5 (solid line) corresponding to FIG. 8 and the position of the tension roller 5 (broken line) corresponding to FIG. 9. FIG. 10 is a schematic view showing the position of the primary transfer roller on the back side in the insertion and extraction direction of the intermediate transfer unit. However, the front side in the insertion and extraction direction of the intermediate transfer unit is similarly configured, and a backup roller holding member, a backup roller pressing member, and the like are provided. The primary transfer roller 11d and the backup roller 47 are held by a backup roller holding member 71 as a second holding member, and the backup roller holding member 71 is pressurized by a backup roller pressurizing member 72 as a third pressurizing member. As shown by the solid line and the broken line in FIG. 10, when the tension roller 5 and the roller shaft 5a are inclined, the angle at which the intermediate transfer belt 3 is wound around the backup roller 47 changes. Then, since the force received by the backup roller holding member 71 also changes, in some cases, the position of the most upstream primary transfer roller 11d becomes unstable. Therefore, the pressing force of the backup roller pressurizing member 72 is set such that when the intermediate transfer belt 3 is brought into contact with all the photoreceptors 1, the backup roller holding member 71 located most upstream abuts against the intermediate transfer member frame 37 (see FIG. 7) or the photoreceptor frame 49d (see FIG. 6) on the front side in the insertion and extraction direction regardless of the position of the inclined tension roller 5. Thereby, regardless of the position of the tension roller 5 and the roller shaft 5a, the primary transfer roller 11d held by the backup roller holding member 71 is always maintained at the same position, and a good image with less density deviation can be obtained.

[0042] Aspects of the present invention are as follows, for example. (Aspect 1) A plurality of image carriers that carry toner images, A plurality of frame members that hold the image carriers, An intermediate transfer body that is movable for secondary-transferring the toner image primary-transferred from the image carrier to a recording medium, A plurality of primary transfer members that primary-transfer the toner image from the image carrier to the intermediate transfer body at a primary transfer portion where the outer peripheral surface of the image carrier and the intermediate transfer body are in contact, A holding member that holds the primary transfer member, An intermediate transfer body frame that holds the intermediate transfer body and rotatably holds the holding member, A plurality of pressurizing members that pressurize the holding member, A pressing member that presses the image carrier against the intermediate transfer body frame or the main body structure side plate, In an image forming apparatus that positions the primary transfer member by abutting the holding member against the intermediate transfer member frame or the frame member, One end side of the image carrier is positioned by being pressed against the intermediate transfer member frame by the pressing member, The primary transfer member on the one end side is positioned by abutting the holding member against the intermediate transfer member frame by the pressing member. The image forming apparatus is characterized by this. (Aspect 2) The other end side of the image carrier is positioned by being pressed against the main body structure side plate, The primary transfer member on the other end side of the image carrier is positioned by abutting the holding member against the frame member. The image forming apparatus according to Aspect 1 is characterized by this. (Aspect 3) A backup roller that is disposed upstream of the plurality of primary transfer members and rotates in contact with the inner circumference of the intermediate transfer member, A second holding member that holds the backup roller, A third pressing member that presses the second holding member, A contact / separation mechanism that separates / approaches the primary transfer member in order to separate / approach the intermediate transfer member from the image carrier. The image forming apparatus includes this, The holding member that holds the most upstream primary transfer member among the plurality of primary transfer members and the second holding member are the same member, The third pressing member and the pressing member are the same member, The other primary transfer members are each held by their respective holding members. The image forming apparatus according to Aspect 1 or 2 is characterized by this. (Aspect 4) A rotatable body that is located upstream of the backup roller and supports the intermediate transfer member, A correction mechanism that corrects the approach of the intermediate transfer member by tilting the rotatable body. The image forming apparatus according to Aspect 3 is characterized by this. (Aspect 5) The pressing force of the uppermost third pressing member is set such that when the intermediate transfer member and all the image carriers are in contact, the uppermost second holding member abuts against the frame member or the intermediate transfer member frame regardless of the position of the inclined belt support rotating body. The image forming apparatus according to aspect 3 or 4, characterized by this.

Explanation of Signs

[0043] 1a, 1b, 1c, 1d Photoconductor (image carrier) 3 Intermediate transfer belt (intermediate transfer member) 5 Tension roller (rotating body) 5a Roller shaft 11a, 11b, 11c, 11d Primary transfer roller (primary transfer member) 21 Cleaning blade 47 Backup roller 49a, 49b, 49c, 49d Photoconductor frame (frame member) 50a, 50b, 50c, 50d First pressing member (pressing member) 51a, 51b, 51c, 51d Primary transfer roller holding member (holding member) 55 Main body structure side plate 57a, 57b, 57c, 57d Photoconductor pressing member (pressing member) 58a, 58b, 58c, 58d Photoconductor pressing member (pressing member) 71 Backup roller holding member (second holding member) 72 Backup roller pressing member (third pressing member) 80a, 80b, 80c, 80d Second pressing member (pressing member) 81a, 81b, 81c, 81d Primary transfer roller holding member (holding member) 90 Contact-separation mechanism 100 Image forming apparatus 150 Belt approximation correction mechanism (correction mechanism) P Recording medium

Prior Art Documents

Patent Documents

[0044] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-113907 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-122596 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-197774

Claims

1. A plurality of image carriers carrying toner images; A plurality of frame members for holding the image carriers; an intermediate transfer member that is movable for secondarily transferring the toner image that has been primarily transferred from the image carrier to a recording medium; a plurality of primary transfer members for primarily transferring a toner image from the image carrier to the intermediate transfer member at a primary transfer portion where the image carrier and the outer peripheral surface of the intermediate transfer member are in contact with each other; a holding member that holds the primary transfer member; an intermediate transfer body frame that holds the intermediate transfer body and rotatably holds the holding member; A plurality of pressure members for applying pressure to the holding member; a pressing member that presses the image carrier against the intermediate transfer body frame or a side plate of the main body structure, In an image forming apparatus in which the primary transfer member is positioned by abutting the holding member against the intermediate transfer body frame or the frame member, one end side of the image carrier is positioned by being pressed against the intermediate transfer body frame by the pressing member, 2. An image forming apparatus according to claim 1, wherein the primary transfer member at the one end side is positioned by abutting the holding member against the intermediate transfer body frame by the pressure member.

2. the other end of the image carrier is pressed against the side plate of the main body structure to be positioned; 2. The image forming apparatus according to claim 1, wherein the primary transfer member at the other end side of the image carrier is positioned by abutting the holding member against the frame member.

3. a backup roller disposed upstream of the plurality of primary transfer members and rotating in contact with an inner periphery of the intermediate transfer body; A second holding member that holds the backup roller; A third pressure member that presses the second holding member; a contact / separation mechanism for contacting and separating the primary transfer member so as to contact and separate the intermediate transfer member from the image carrier, the holding member that holds the most upstream primary transfer member among the plurality of primary transfer members and the second holding member are the same member, the third pressure member and the pressure member are the same member, 3. The image forming apparatus according to claim 1, wherein the other primary transfer members are held by the respective holding members.

4. a tiltable rotating body that is located upstream of the backup roller and supports the intermediate transfer body; 4. The image forming apparatus according to claim 3, further comprising a correction mechanism that corrects deviation of the intermediate transfer body by tilting the rotating body.

5. 4. The image forming apparatus according to claim 3, wherein the pressure of the third pressure member at the most upstream position is set so that, when the intermediate transfer body and all of the image carriers are brought into contact with each other, the second holding member at the most upstream position is abutted against the frame member or the intermediate transfer body frame regardless of the position of the inclined rotating body.

Images