Image forming apparatus

Abstract

To solve the problem in which: in an image forming apparatus that allows attachment and detachment of a transfer unit in a direction intersecting with a surface on which a toner image is transferred to a transfer material, it is demanded that the transfer unit is accurately located during image formation.SOLUTION: A transfer unit 8 has a boss 33 that is provided on the same axis as a drive roller 30, and a frame 18 has a contact surface 41a and a contact surface 41b that are brought into contact with the boss 33 to locate the transfer unit 8. When seen from a rotation axis direction of the drive roller 30, the second contact surface 41b is arranged on the upstream side of the contact surface 41a with respect to a conveyance direction of a transfer material P. The contact surface 41a and the contact surface 41b are surfaces that extend in a direction intersecting with the conveyance direction of the transfer material P, and the interval between the surfaces is increased toward the upstream side with respect to a mounting direction of the transfer unit 8.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, such as a printer or copying machine, that utilizes an electrophotographic system and is equipped with a belt conveying device having an endless belt. [Background technology]

[0002] In the past, color image forming apparatuses equipped with an intermediate transfer belt have been known among image forming apparatuses using electrophotography, such as printers and copiers. In such image forming apparatuses, the entire transfer unit equipped with the intermediate transfer belt is detachably installed and replaced from the main body of the image forming apparatus, so that maintenance of the transfer unit can be easily performed.

[0003] Patent Document 1 discloses a configuration in which a transfer unit is attached and detached in a direction perpendicular to the axial direction of the image carriers and in the direction in which multiple image carriers are arranged. More specifically, a guide pin provided on the transfer unit is guided along a guide rail provided on the frame of the device main body, and the transfer unit is positioned by abutting the guide pin against the end face of the guide rail. Patent Document 1 also discloses a configuration in which a fit tolerance, i.e., a predetermined gap, is provided between the height width of the guide rail and the diameter of the guide pin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-275987 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the configuration of Patent Document 1, a fit tolerance is provided between the guide rail and the guide pin in the vertical direction (the direction intersecting the surface where the toner image is transferred onto the transfer material) that is perpendicular to the attachment / detachment direction of the transfer unit, which can lead to the following problem: When forming an image, a vertical force is applied from the transfer material being transported in the vertical direction, which can cause the positioning part of the transfer unit to shift by the amount of the fit tolerance, which can result in image defects.

[0006] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to accurately position a transfer unit during image formation in an image forming apparatus in which the transfer unit can be attached and detached in a direction intersecting the surface on which a toner image is transferred onto a transfer material. [Means for solving the problem]

[0007] The present invention relates to a toner image forming apparatus including: an image carrier that carries a toner image; a transfer unit including an endless belt that can come into contact with the image carrier and rotates, a plurality of rotatable tension members that tension the belt, and a primary transfer member that is disposed on an inner peripheral surface of the belt and that transfers a toner image carried on the image carrier to the belt; a positioning section that positions the transfer unit; a secondary transfer member that comes into contact with the belt to form a secondary transfer section and that transfers the toner image transferred from the image carrier to the belt, from the belt to a transfer material in the secondary transfer section; and a biasing member that biases the secondary transfer member via the belt toward an opposing member of the plurality of tension members that is disposed at a position opposing the secondary transfer member, wherein a transport direction of the transfer material in the secondary transfer section is a direction perpendicular to a straight line connecting a rotation center of the secondary transfer member and a rotation center of the opposing member when viewed from a rotation axis direction of the opposing member, and a mounting and removing direction of the transfer unit is a direction perpendicular to the secondary transfer member. In an image forming device in which the direction intersects with the surface of a transfer material to which a toner image is transferred in a transfer section, the transfer unit has an abutment portion that is arranged so as to overlap at least a portion with the opposing member when viewed from the direction of the rotation axis of the opposing member, and the positioning portion has a first abutment surface that positions the transfer unit in the conveying direction by abutting with the abutment portion when the transfer unit receives a biasing force from the biasing member via the secondary transfer member, and a second abutment surface that positions the transfer unit in the direction opposite to the conveying direction by abutting with the abutment portion, when viewed from the direction of the rotation axis of the opposing member, the second abutment surface is arranged upstream of the first abutment surface in the conveying direction, and the first abutment surface and the second abutment surface are surfaces that extend in a direction intersecting with the conveying direction and are configured so that the distance between them increases toward the upstream side in the installation direction of the transfer unit. [Effects of the Invention]

[0008] According to the present invention, in an image forming apparatus in which a transfer unit can be attached and detached in a direction intersecting the surface on which a toner image is transferred onto a transfer material, the transfer unit can be positioned with high precision during image formation. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus in a first embodiment. [Figure 2] FIG. 2 is a schematic perspective view illustrating the configuration of a transfer unit in the first embodiment. [Figure 3] FIG. 2 is a schematic top view illustrating the configuration of a transfer unit in the first embodiment. [Figure 4] 2 is a simplified schematic top view of a transfer unit attached to an apparatus main body in the first embodiment. FIG. [Figure 5] 4 is a schematic cross-sectional view illustrating attachment and detachment of a transfer unit in the first embodiment. FIG. [Figure 6] 5A and 5B are schematic diagrams illustrating the relationship between the guide portion and the guide rail when the attachment of the transfer unit is completed in the first embodiment. [Figure 7] 1 is a partial perspective view of a positioning portion of a transfer unit and a frame attached thereto in the first embodiment. FIG. [Figure 8] FIG. 2 is a schematic perspective view illustrating attachment of a transfer unit in the first embodiment. [Figure 9] 5A and 5B are schematic diagrams illustrating the relationship between the guide portion and the guide rail when the transfer unit starts to be attached in the first embodiment. [Figure 10] FIG. 2 is a schematic perspective view illustrating a state in the middle of attaching a transfer unit in the first embodiment. [Figure 11] 10 is a schematic diagram illustrating the relationship between the guide portion and the guide rail when the transfer unit is in the middle of being attached in the first embodiment. FIG. [Figure 12] 10A and 10B are schematic diagrams illustrating the state of the transfer unit immediately before the attachment of the transfer unit is completed in the first embodiment. [Figure 13] 5A and 5B are schematic diagrams illustrating the relationship between a positioning portion and a contact portion when the transfer unit is attached in the first embodiment. [Figure 14]FIG. 10 is a schematic perspective view illustrating the configuration of a spacing means in the second embodiment. [Figure 15] FIG. 10 is a schematic diagram illustrating a separation configuration of a primary transfer roller in the second embodiment. [Figure 16] 10 is a schematic diagram illustrating the configuration of a rotating part of a separating means in Example 2. FIG. [Figure 17] 10A and 10B are schematic diagrams illustrating the states of the primary transfer roller and the secondary transfer roller during standby or when the power is off in the second embodiment. [Figure 18] 10A and 10B are schematic diagrams illustrating the state of the primary transfer roller and the secondary transfer roller during monochrome image formation in the second embodiment. [Figure 19] 10A and 10B are schematic diagrams illustrating the state of a primary transfer roller and a secondary transfer roller during full-color image formation in the second embodiment. [Figure 20] FIG. 10 is a schematic cross-sectional view illustrating the configuration of an image forming apparatus according to a third embodiment. [Figure 21] 2 is a schematic cross-sectional view of the periphery of a secondary transfer unit of the image forming apparatus according to the first embodiment. [Figure 22] FIG. 22 is an enlarged view of a main part of the schematic cross-sectional view shown in FIG. 21. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will now be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions. Therefore, unless otherwise specified, they are not intended to limit the scope of the present invention.

[0011] Example 1 [Configuration of image forming device] FIG. 1 is a schematic diagram of an image forming apparatus 1 according to this embodiment. As shown in FIG. 1, the image forming apparatus 1 according to this embodiment is an electrophotographic, intermediate transfer color image forming apparatus having first, second, third, and fourth image forming units SY, SM, SC, and SK as multiple image forming units. The first, second, third, and fourth image forming units SY, SM, SC, and SK are used to form images of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. These four image forming units SY, SM, SC, and SK are arranged in a line at regular intervals. Furthermore, in this embodiment, each image forming unit SY, SM, SC, and SK is located below the intermediate transfer belt 26 in the direction of gravity. In this embodiment, the first to fourth image forming units SY, SM, SC, and SK have substantially the same configuration, except for the toner colors they use. Therefore, unless a particular distinction is made, the subscripts Y, M, C, and K given to the reference numerals to indicate which color an element is provided for will be omitted and the elements will be generally described.

[0012] Each image forming apparatus 1 is provided with a rotatable drum-shaped electrophotographic photosensitive member 6 (hereinafter referred to as photosensitive drum 6) as an image carrier on which a toner image is formed. A charging roller 61 as a charging member that charges the photosensitive drum 6, a developing means, and a cleaning means are provided around the photosensitive drum 6. In addition, an exposure unit that is irradiated with laser light from an exposure means 7 (laser scanner) is provided downstream of the charging roller 61 and upstream of the developing means in terms of the rotation direction of the photosensitive drum 6.

[0013] The developing means has a developing roller 63 as a developing member and toner as a developer. The developing roller 63 is rotatable by receiving a driving force from a driving source (not shown). The cleaning means has a cleaning blade 65 as a cleaning member that contacts the photosensitive drum 6, and collects the toner collected by the cleaning blade 65.

[0014] Next, the overall configuration of the image forming apparatus 1 will be described. As shown in Fig. 1, an intermediate transfer belt 26, which is an endless intermediate transfer body, is disposed opposite the photosensitive drum 6 of the image forming unit S. The intermediate transfer belt 26 is stretched over a plurality of tension members, and more specifically, stretched over three tension rollers: a drive roller 30 (opposing member), a driven roller 28, and a tension roller 22. The intermediate transfer belt 26 can rotate in the direction of arrow AA in the drawing by the rotation of the drive roller 30, which rotates by receiving a driving force from a drive source (not shown).

[0015] A primary transfer roller 16 serving as a primary transfer member (transfer member) is disposed on the inner peripheral surface side of the intermediate transfer belt 26 at a position facing the photosensitive drum 6. The primary transfer roller 16 is urged with a predetermined pressure against the photosensitive drum 6 via the intermediate transfer belt 26, forming a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 26 and the photosensitive drum 6 come into contact. A primary transfer power supply (not shown) is connected to the primary transfer roller 16, and the primary transfer power supply can apply a voltage of positive or negative polarity to the primary transfer roller 16.

[0016] A secondary transfer roller 10 serving as a secondary transfer member is disposed on the outer peripheral surface side of the intermediate transfer belt 26 at a position facing the drive roller 30. The secondary transfer roller 10 is urged with a predetermined pressure against the drive roller 30 via the intermediate transfer belt 26 by a spring 38 serving as an urging member, and forms a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 26 and the secondary transfer roller 10 come into contact. A secondary transfer power supply (not shown) is connected to the secondary transfer roller 10, and the secondary transfer power supply can apply a voltage of positive or negative polarity to the secondary transfer roller 10.

[0017] In terms of the movement direction of the intermediate transfer belt 26, a cleaning unit 20 is provided upstream of each photosensitive drum 6 and downstream of the secondary transfer portion N2 to collect toner remaining on the intermediate transfer belt 26 after secondary transfer (hereinafter referred to as residual toner). The cleaning unit 20 has a cleaning blade 20a that comes into contact with the intermediate transfer belt 26.

[0018] Provided upstream of the secondary transfer section N2 in the transport direction of the transfer material P are a paper feed cassette 2 that stores the transfer material P, a feed roller 3 for feeding the transfer material P, and transport rollers 4 and 5 for transporting the transfer material P to the secondary transfer section N2. Also provided downstream of the secondary transfer section N2 in the transport direction of the transfer material P are a fixing means 9 equipped with a heat source, a paper discharge roller 12 for discharging the transfer material P from the image forming apparatus 1, and a paper discharge tray 15 for stacking the discharged transfer material P.

[0019] [Image formation operation] When an operation start command and an image signal are sent from a host device (not shown) to a controller (not shown) as control means, the controller controls various means to start the image forming operation of the image forming apparatus 1. When the image forming operation starts, each photosensitive drum 6, intermediate transfer belt 26, and developing roller 63 receives driving force from a driving source (not shown) and begins to rotate at a predetermined rotational speed. The surface of the rotating photosensitive drum 6 is charged approximately uniformly to a predetermined polarity (negative polarity in this embodiment) by the charging roller 61. At this time, a predetermined charging voltage is applied to the charging roller 61 from a charging power source. Thereafter, the photosensitive drum 6 is exposed by the exposure means 7 based on image information corresponding to each image forming station S, and an electrostatic latent image according to the image information is formed on the surface of the photosensitive drum 6.

[0020] The developing roller 63 carries toner charged to the normal charging polarity of the toner (negative polarity in this embodiment), and a predetermined developing voltage is applied from a developing power supply. As a result, the latent image formed on the photosensitive drum 6 is visualized by negative toner at the opposing portion (developing portion) between the photosensitive drum 6 and the developing roller 63, and a toner image is formed on the photosensitive drum 6.

[0021] Next, the toner image formed on the photosensitive drum 6 is transferred (primary transfer) to the intermediate transfer belt 26, which is being rotated, at the primary transfer portion N1 by a current (hereinafter referred to as the primary transfer current) flowing from the primary transfer roller 16 to the photosensitive drum 6. At this time, a voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the primary transfer roller 16 from the primary transfer power supply. That is, in the configuration of this embodiment, the toner image is primarily transferred from the photosensitive drum 6 to the intermediate transfer belt 26 by constant current control, which controls the output of the primary transfer power supply so that a predetermined primary transfer current flows from the primary transfer roller 16 to the photosensitive drum 6.

[0022] When a full-color image is formed, an electrostatic latent image is formed on each photosensitive drum 6 in each image forming station S, and this is developed into a toner image of each color. The toner images of each color formed on each photosensitive drum 6 in each image forming station S are then transferred to the intermediate transfer belt 26 in each primary transfer station N1Y, N1M, N1C, and N1K so as to be sequentially superimposed on each other, and four-color toner images are formed on the intermediate transfer belt 26.

[0023] Furthermore, a transfer material P loaded in a paper feed cassette 2 serving as a storage section is fed to a conveyance roller 4 by a feed roller 3, and then conveyed to a secondary transfer section N2 by conveyance rollers 4 and 5. The four-color multiple toner image carried on the intermediate transfer belt 26 is transferred (secondarily transferred) to the conveyed transfer material P at the secondary transfer section N2 by a current (hereinafter referred to as the "secondary transfer current") flowing from a secondary transfer roller 10 to the intermediate transfer belt 26. At this time, a secondary transfer voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the secondary transfer roller 10 from a secondary transfer power source. That is, in this embodiment, the toner image is secondarily transferred from the intermediate transfer belt 26 to the transfer material P by constant current control, which controls the output of the secondary transfer power source so that a predetermined secondary transfer current flows from the secondary transfer roller 10 to the intermediate transfer belt 26.

[0024] The transfer material P onto which the toner image has been transferred is then transported to the fixing means 9, and after the toner image has been fixed onto the surface of the transfer material P, it is discharged outside the main body of the image forming apparatus 1 and loaded onto the paper output tray 15.

[0025] Note that the toner remaining on the photosensitive drum 6 after the primary transfer is removed from the surface of the photosensitive drum 6 by a cleaning blade 65. Furthermore, the untransferred toner remaining on the intermediate transfer belt 26 after passing through the secondary transfer portion N2 is removed from the surface of the intermediate transfer belt 26 by a cleaning blade 20a. Thereafter, the removed toner passes through the toner transport path 23 and is stored in the toner recovery container 24.

[0026] [Calibration operation] The toner images are transferred onto the intermediate transfer belt 26 in a sequentially overlapping manner, forming a four-color toner image on the intermediate transfer belt 26. However, due to factors such as component variations in the image forming apparatus 1, changes in the resistance of the intermediate transfer belt 26 due to changes in the installation environment, and abrasion of the photosensitive drum 6, the overlapping position of the toner images on the intermediate transfer belt 26 and the density of the toner images of each color may deviate from the expected values. To correct this deviation, a controller (not shown) transfers a toner image of a predetermined pattern onto the intermediate transfer belt 26 and reads the transferred pattern with a sensor 13, thereby performing adjustment control to adjust the transferred position and density of the toner image. When adjustment control is performed, the pattern data read by the sensor 13 is sent to the controller (not shown) and then processed, and the timing and exposure time of the exposure of the photosensitive drum 6 by the exposure means 7 are adjusted based on the results.

[0027] [Intermediate transfer unit] Next, the configuration of the transfer unit 8 (belt conveying device) and its surroundings in the image forming apparatus will be described with reference to Figures 2, 3, 4, 5, 6, and 7. Figure 2 is a schematic perspective view illustrating the configuration of the transfer unit 8, and Figure 3 is a schematic top view illustrating the configuration of the transfer unit 8.

[0028] 2 and 3, the transfer unit 8 has a transfer frame 17F and a transfer frame 17R on either side of the width direction of the intermediate transfer belt 26 (hereinafter simply referred to as the belt width direction), which is perpendicular to the movement direction (the direction of the arrow AA in the figure) of the intermediate transfer belt 26. The transfer frames 17F and 17R face each other in the belt width direction (i.e., the direction of the rotation axis of the drive roller 30). The intermediate transfer belt 26 is disposed inside the two transfer frames 17F and 17R and is tensioned by three tension rollers: the drive roller 30, the driven roller 28, and the tension roller 22.

[0029] As will be explained in detail later, the transfer unit 8 can be removed from the image forming apparatus 1 by moving it in a direction from the cleaning means 20 toward the secondary transfer roller 10 in FIG. 1 . The transfer unit 8 can be attached to the image forming apparatus 1 by moving it in a direction from the secondary transfer roller 10 toward the cleaning means 20 in FIG. 1 . The attachment / detachment direction of the transfer unit 8 in this embodiment is a direction intersecting the surface of the transfer material P onto which the toner image is secondarily transferred at the secondary transfer portion N2 shown in FIG. 1 . In other words, it is a direction intersecting the vertical direction, which is the transport direction of the transfer material P at the secondary transfer portion N2. The transport direction of the transfer material P at the secondary transfer portion N2 is defined as a direction perpendicular to a line connecting the rotation center of the drive roller 30 and the rotation center of the secondary transfer roller 10 when viewed from the axial direction of the drive roller 30. The vertical direction in this embodiment is substantially the same as the direction of gravity.

[0030] 2 and 3, bosses 32F and 32R are provided downstream in the mounting direction of transfer unit 8. Furthermore, bosses 33F and 33R are provided as abutment portions coaxially (on the same axis) with drive roller 30 upstream in the mounting direction of transfer unit 8.

[0031] The bosses 32F and 33F are provided to protrude from the transfer frame 17F at one end in the belt width direction. Specifically, the bosses 32F and 33F protrude in a direction away from the intermediate transfer belt 26 (i.e., toward the opposite side from the intermediate transfer belt) in the belt width direction (i.e., the direction of the rotation axis of the drive roller).

[0032] Furthermore, bosses 32R and 33R are provided to protrude from the transfer frame 17R on the other end side in the belt width direction. Specifically, bosses 32R and 33R protrude in a direction away from the intermediate transfer belt 26 (i.e., toward the opposite side from the intermediate transfer belt) in the belt width direction (i.e., the direction of the rotation axis of the drive roller).

[0033] In this embodiment, the boss 33F and the boss 33R (contact portion) are described as being "coaxially (same axis) arranged" with the drive roller 30, but they do not have to be "coaxially arranged." That is, they may be arranged so that at least a portion of the boss 33F and the boss 33R (contact portion) overlaps with the drive roller 30 when viewed from the direction of the rotation axis of the drive roller 30.

[0034] For example, when viewed from the direction of the rotation axis of the drive roller 30, the boss 33F and the boss 33R (contact portion) can be disposed inside the area occupied by the drive roller 30. It is also desirable to dispose the centers (axial cores) of the boss 33F and the boss 33R (contact portion) inside the area occupied by the drive roller 30.

[0035] Furthermore, the transfer unit 8 has covers 35F and 35R on the upstream side in the removal direction, which hold the tension roller 22 with a vertical play of about 0.5 mm so that the tension roller 22 can move independently of the transfer frames 17F and 17R. The covers 35F and 35R are provided with bosses 34F and 34R, respectively, at positions coaxial with (on the same axis as) the tension roller 22.

[0036] As will be described in detail later, these bosses 32F, 32R, 34F, and 34R function as guides when the transfer unit 8 is attached to the main body of the image forming apparatus 1. The reason why bosses 34F, 34R, 33F, and 33R protruding from the tension roller 22 and the drive roller 30 are provided at positions coaxial with each other is to accurately position the various rollers, which are important when attaching the transfer unit 8, relative to the main body of the image forming apparatus 1. In this embodiment, bosses 32F and 32R provided near the tension roller 22 and bosses 33F and 33R provided at a position coaxial with the drive roller 30 are spaced apart. This allows the orientation of transfer frames 17F and 17R to be accurately positioned when the transfer unit 8 is attached to the image forming apparatus 1, thereby reducing misalignment of the transfer unit 8 relative to the main body.

[0037] 2, the upstream end of the transfer unit 8 in the installation direction is provided with holding portions 21F and 21R that can be held by a user when installing the transfer unit 8 in the image forming apparatus 1. The transfer unit 8 is also provided with holding portions 11F and 11R that can be held by a user when installing the transfer unit 8 in the image forming apparatus 1. The holding portions 11F and 11R are provided downstream of the holding portions 21F and 21R in the installation direction of the transfer unit 8. The holding portions 11F and 21F are provided on the frame 17F side, which is one end side in the belt width direction, and the holding portions 11R and 21R are provided on the frame 17R side, which is the other end side in the belt width direction.

[0038] Fig. 4 is a simplified schematic top view of the transfer unit 8 when attached to the main body of the image forming apparatus 1. As shown in Fig. 4, the image forming apparatus 1 has a frame 18 on one end side of the transfer unit 8 in the belt width direction, and a frame 19 on the other end side of the transfer unit 8 in the belt width direction. The frames 18 and 19 are disposed opposite each other in the belt width direction, and the transfer unit 8 is disposed between the frames 18 and 19 in the belt width direction when attached to the image forming apparatus 1.

[0039] As shown in FIG. 4, the frame 18 is provided with a guide rail 36 having a rail groove for guiding the bosses 32F and 34F provided on the transfer unit 8 on the side where the transfer unit 8 is provided in the belt width direction. The frame 19 is also provided with a guide rail 37 as a guide member having a rail groove for guiding the bosses 32R and 34R provided on the transfer unit 8 on the side where the transfer unit 8 is provided in the belt width direction. The rail grooves of the guide rails 36 and 37 are formed in the shapes indicated by the dashed lines in FIG. 4. In the following description, the bosses 32F and 34F provided downstream in the installation direction of the transfer unit 8 are collectively referred to as the leading boss 31F, and the bosses 32R and 34R are collectively referred to as the leading boss 31R. The leading bosses 31F and 31F form a guide portion that guides the transfer unit 8 along the guide rails 36 and 37 when the transfer unit 8 is installed or removed.

[0040] [Transfer unit installation / removal operation] Next, the attachment / detachment operation of transfer unit 8 and various configurations of transfer unit 8 related to the attachment / detachment operation will be described with reference to Figures 5 to 13. Here, the configurations on one end side and the other end side in the belt width direction have many common parts with some exceptions, and transfer unit 8 has a substantially symmetrical configuration in the belt width direction. Therefore, in the following description, unless a special distinction is required, the configuration on the frame 18 side, which is one end side in the belt width direction, will be described, and a description of the configuration on the frame 19 side, which is the other end side in the belt width direction, will be omitted.

[0041] Fig. 5 is a schematic diagram illustrating the drawing (removal) of the transfer unit 8 from the main body of the image forming apparatus 1. As shown in Fig. 5, the image forming apparatus 1 has a door 14 as an openable / closable part. Furthermore, the secondary transfer roller 10, together with a member that holds the secondary transfer roller 10, can be opened and closed in the same direction as the door 14, as shown in Fig. 5.

[0042] 5, when attaching or detaching the transfer unit 8, the door 14 and the secondary transfer roller 10 are rotated in the direction of the arrow Rc in the drawing to open the interior of the image forming apparatus 1. In the configuration of this embodiment, a mechanism (not shown) is provided that links the opening and closing operations of the door 14 and the secondary transfer roller 10, and when a user rotates the door 14 in the direction of the arrow Rc in the drawing, the secondary transfer roller 10 also rotates in the direction of the arrow Rc in the drawing, thereby opening the interior of the image forming apparatus 1. Note that in this embodiment, the door 14 and the secondary transfer roller 10 are configured to open and close in a linked manner, but the present invention is not limited to this, and the door 14 and the secondary transfer roller 10 may be configured to open and close separately.

[0043] 5, that is, with the interior of the image forming apparatus 1 open, by pulling out the transfer unit 8 in the direction in which the secondary transfer roller 10 is retracted (the direction of the arrow in the figure), it is possible to remove the transfer unit 8 from the main body of the image forming apparatus 1. When attaching the transfer unit 8 to the main body of the image forming apparatus 1, after inserting the transfer unit 8 in the direction opposite to the direction of the arrow in the figure, the secondary transfer roller 10 and door 14 are closed to release the open state of the interior of the image forming apparatus 1.

[0044] When the transfer unit 8 is attached, the secondary transfer roller 10 is rotated to move it to a position where an image forming operation can be performed, and the transfer unit 8 receives a biasing force from the spring 38 that biases the secondary transfer roller 10 toward the drive roller 30. As will be described in detail later, in this embodiment, the biasing force from the secondary transfer roller 10 causes the bosses 33F and 33R of the transfer unit 8 to come into contact with and bias against the frames 18 and 19 that serve as positioning portions, thereby positioning the transfer unit 8.

[0045] Fig. 6(a) is a schematic cross-sectional view illustrating the relationship between the tip boss 31F and the guide rail 36 before the attachment of the transfer unit 8 is completed, as viewed from the rotational axis direction of the drive roller 30. Fig. 6(b) is a schematic cross-sectional view illustrating the relationship between the tip boss 31F and the guide rail 36 after the attachment of the transfer unit 8 is completed, as viewed from the rotational axis direction of the drive roller 30.

[0046] As shown in FIG. 6(a), before the installation of the transfer unit 8 is complete, a gap is provided between the tip boss 31F and the guide rail 36 in the vertical direction perpendicular to the installation direction of the transfer unit 8. This allows the transfer unit 8 to be installed smoothly without generating excessive friction between the tip boss 31F and the guide rail 36. On the other hand, as shown in FIG. 6(b), when the installation of the transfer unit 8 is complete, the tip boss 31F is sandwiched in the vertical direction by the guide shape of the guide rail 36. This positions the downstream side (tip side) of the transfer unit 8 in the installation direction relative to the device body of the image forming apparatus 1 in the vertical direction.

[0047] 7 is a schematic perspective view showing the configuration of the vicinity of the upstream end of the transfer unit 8 in the installation direction when the transfer unit 8 is installed in the image forming apparatus 1. As shown in FIG. 7, a boss 33F provided on the transfer unit 8 has an abutment portion 33a that can abut against abutment surface 41a (first abutment surface) provided on the frame 18 as a positioning portion, and an abutment portion 33b that can abut against abutment surface 41b (second abutment surface). The abutment surface 41a and the abutment surface 41b are provided in a cutout portion 41F formed by cutting out the frame 18, and are opposed to each other in the vertical direction, which is the conveyance direction of the transfer material P, and the abutment surface 41b is provided below the abutment surface 41a in the vertical direction. In addition, the abutment surface 41a and the abutment surface 41b have a sloped shape that extends in a direction intersecting the conveyance direction of the transfer material P, and the respective sloped shapes are configured so that the distance between them increases toward the upstream side in the installation direction of the transfer unit 8.

[0048] When the transfer unit 8 is attached to the image forming apparatus 1, the contact surface 41a comes into contact with the contact portion 33a, and the contact surface 41b comes into contact with the contact portion 33b. Then, due to the biasing force of the secondary transfer roller 10 that is biased toward the drive roller 30, the contact portions 33a and 33b, which are provided coaxially with the drive roller 30, are biased toward the contact surfaces 41a and 41b, respectively. This positions the transfer unit 8 in the attachment / detachment direction of the transfer unit 8.

[0049] In this embodiment, as shown in FIG. 7, the holding portion 21F is provided so that the notch 41F of the frame 18 and the holding portion 21F at least partially overlap with each other in the belt width direction (i.e., the direction of the rotation axis of the drive roller 30 constituting the opposing member). This allows for effective use of the space inside the image forming apparatus 1. Furthermore, since the user holds the holding portion 21F and pushes the transfer unit 8 toward the device body when installing the transfer unit 8, this configuration allows for the position where the user applies force in the installation direction and the position where the boss 33F abuts against the frame 18 to be located close to each other. This makes it easier for the user's force to be directly transmitted to the transfer unit 8 when installing the transfer unit 8, improving user operability when installing the transfer unit 8.

[0050] Next, an operation for mounting a new replacement transfer unit 8 to the main body of the image forming apparatus 1 and a positioning configuration for the transfer unit 8 will be described with reference to FIGS.

[0051] FIG. 8 is a schematic perspective view of the image forming apparatus 1 at the beginning of installation of the transfer unit 8. When installing the transfer unit 8, the user first grasps the holders 11F and 11R of the transfer unit 8 and begins inserting the transfer unit 8 toward the device body. As shown in the enlarged view of the dotted line in FIG. 8, as the transfer unit 8 begins to be inserted, the cover 35F provided on the leading end of the transfer unit 8 in the installation direction comes into contact with the guide 25 provided on the device body. This allows the leading boss 31F of the transfer unit 8 to be guided into the rail groove of the guide rail 36, preventing the transfer unit 8 from contacting the photosensitive drum 6. In this embodiment, the guide 25 is configured as a cover member that covers the sensor 13 used during calibration and is shaped to contact the transfer unit 8 at the end of the transfer unit 8 in the belt width direction.

[0052] 9 is a schematic cross-sectional view showing the state when the transfer unit 8 is attached and the tip boss 31F has begun to be guided by the guide rail 36. When the transfer unit 8 is further inserted into the device body from the state shown in FIG. 8, the tip boss 31F is guided by the guide rail 36, as shown in FIG.

[0053] Figure 10 is a schematic perspective view showing a state in which the transfer unit 8 has been inserted further from the state in Figure 8. As shown in Figure 10, when the transfer unit 8 is inserted to the point where the holding portions 11F and 11R are inserted into the device main body, it becomes difficult for the user to hold the holding portions 11F and 11R. At this time, the user can continue to hold the transfer unit 8 and proceed with the installation operation by switching from holding the holding portions 11F and 11R to holding the holding portions 21F and 21R.

[0054] Figure 11 is a schematic cross-sectional view of the state in which the transfer unit 8 has been further inserted from the state in Figure 10, as viewed from the direction of the rotation axis of the drive roller 30. As shown in Figure 11, at this time, on the downstream side (leading end side) of the transfer unit 8 in the installation direction, the leading end boss 31F is guided by the guide rail 36, thereby maintaining the posture of the leading end side of the transfer unit 8. Also, on the upstream side (rear end side) of the transfer unit 8 in the installation direction, the lower surface of the frame 17F of the transfer unit 8 in the vertical direction comes into contact with a guide portion 25 provided on the device main body, thereby maintaining the posture of the rear end side of the transfer unit 8.

[0055] 12 is a schematic cross-sectional view of the transfer unit 8 just before completion of installation, as viewed from the direction of the rotation axis of the drive roller 30, showing a state in which the transfer unit 8 has been further inserted from the state shown in FIG. 11. At this time, the downstream side (leading end side) of the transfer unit 8 in the installation direction is guided by the guide rail 36, as in the state shown in FIG. 11, so that the orientation of the leading end side of the transfer unit 8 is maintained. Meanwhile, the upstream side (rear end side) of the transfer unit 8 in the installation direction is such that the lower surface of the frame 17F of the transfer unit 8 is separated from the guide portion 25 on the device main body side. At this time, the rear end side boss 33F of the transfer unit 8 comes into contact with the wall surface of the notch 41F provided in the frame 18, so that the orientation of the rear end side of the transfer unit 8 is maintained.

[0056] 6(a) to 6(b), when the attachment of the transfer unit 8 is completed, the tip side in the attachment direction of the transfer unit 8 has the tip boss 31F sandwiched between the guide rails 36. As a result, the tip side of the transfer unit 8 is positioned in the vertical direction by the guide rails 36, and that posture is maintained.

[0057] 13(a) to 13(c) are schematic diagrams illustrating the positioning of the rear end side in the installation direction of the transfer unit 8. As shown in Fig. 13(a), when the transfer unit 8 is inserted in the direction of the arrow, the boss 33F first comes into contact with the wall surface of the cutout portion 41F, thereby maintaining the posture of the rear end side of the transfer unit 8. Then, as the insertion operation continues, the boss 33F is guided by the shape of the cutout portion 41F and moves diagonally downward at 45 degrees (angle EE) from the horizontal direction, which was the insertion direction up to that point, as shown in Fig. 13(b).

[0058] More specifically, boss 33F is provided with facing portion 33c in addition to contact portions 33a and 33b that come into contact with contact surfaces 41a and 41b when attachment of transfer unit 8 to the device body is complete. When attachment of transfer unit 8 to the device body is complete, facing portion 33c faces inclined surface 41c provided in cutout portion 41F of frame 18 with a minute gap of about 0.1 mm between them. When transfer unit 8 is inserted, facing portion 33c moves along the shape of inclined surface 41c (inclined portion) while making contact with inclined surface 41c, and moves diagonally downward in the vertical direction as shown in FIG. 13(b).

[0059] When the boss 33F drops vertically downward along the inclined surface 41c, the state shown in FIG. 13(c) is reached. In the state shown in FIG. 13(c), the installation of the transfer unit 8 is almost complete, and the user releases the holding portions 21F and 21R of the transfer unit 8 in the state shown in FIG. 13(c) and closes the secondary transfer roller 10 and the door 14. As a result, the drive roller 30 receives a biasing force from the secondary transfer roller 10, and the contact portions 33a and 33b of the boss 33F, which are provided coaxially with the drive roller 30, are biased toward the contact surfaces 41a and 41b of the notch portion 41F, respectively. As a result, the transfer unit 8 is positioned in the correct position for image formation, and the installation of the transfer unit 8 is complete.

[0060] In the configuration of this embodiment, the contact surfaces 41a and 41b provided on the frame 18 are shaped as slopes that intersect with the installation direction of the transfer unit 8, and the slopes are shaped so that the distance between them increases toward the upstream side in the installation direction. With this configuration, when the transfer unit 8 is positioned in the normal position (the position during image formation), it is possible to accurately position the transfer material P in the transport direction (vertical direction). That is, the biasing force of the secondary transfer roller 10 presses the contact portion 33a against the sloped contact surface 41a, and presses the contact portion 33b against the sloped contact surface 41b, thereby suppressing shaking of the transfer unit 8 in the vertical direction when the transfer material P is transported.

[0061] For example, in a conventional configuration (such as that described in the prior art), in which the transfer unit is positioned using horizontal guide rails installed above and below in the vertical direction, a vertical fit tolerance is required to reduce friction when the transfer unit is inserted. This can lead to the risk of the transfer unit being displaced vertically by the fit tolerance when a vertical force is generated by the transport of the transfer material in the secondary transfer section during image formation. In contrast, in the configuration of this embodiment, the abutment surfaces 41a and 41b that position the transfer unit vertically are configured as shown in FIG. 13, thereby enabling more accurate positioning in the vertical direction, which is the transport direction of the transfer material, while maintaining the mountability of the transfer unit 8.

[0062] Furthermore, as in the configuration of this embodiment, by using the slope 41c to drop the transfer unit 8 diagonally downward just before the installation of the transfer unit 8 is complete, the user can determine that the transfer unit 8 has been inserted into the correct position. In other words, the dropping action of the transfer unit 8 allows the user to recognize the completed installation position of the transfer unit 8, and prevents the user from abandoning the insertion of the transfer unit 8 midway through the installation action. Furthermore, by making the insertion trajectory of the transfer unit 8 horizontal before the dropping action by the slope 41c, it is possible to reduce the load during the insertion of the transfer unit 8.

[0063] In this embodiment, the shape of the inclined surface of the contact surface 41a is set to be approximately parallel to 45 degrees, which is the angle of diagonal movement of the transfer unit 8 immediately before it is attached to the correct position. That is, the shape of the inclined surface of the contact surface 41a is set to be approximately parallel to the shape of the inclined surface 41c. This ensures that the boss 33F does not bite into the shape of the notch 41F when attaching or detaching the transfer unit 8.

[0064] 21 is a schematic cross-sectional view of the periphery of the secondary transfer unit of the image forming apparatus in Example 1. FIG. 22 is an enlarged view of the main part of FIG.

[0065] As shown in Figure 21, the transfer material P transported by the transport roller 5 passes through the secondary transfer section N2 (secondary transfer roller 10) and the fixing section (fixing means 9) in sequence, and the toner image on the intermediate transfer belt 26 is secondarily transferred onto the transfer material P and then fixed onto the transfer material P.

[0066] At the secondary transfer portion N2, the secondary transfer roller 10 is biased in a predetermined direction (F10) by the biasing force F1 of the (biasing) spring 38. Figure 22 shows an enlarged view of the direction F10 in which the biasing force F1 of the spring 38 acts (biases).

[0067] As shown in FIG. 22, the biasing direction F10 of the biasing force F1 is a direction along the direction L10 in which the imaginary line L1 connecting the rotation center 30c1 of the drive roller 30 and the rotation center 10c1 of the secondary transfer roller 10 extends.

[0068] In this embodiment, the fact that the biasing direction F10 is "along" the direction L10 means that the biasing direction F10 and the direction L10 are "the same" direction, or that the "intersection angle between the two directions is within 20 degrees."

[0069] 22, in this embodiment, in the posture during use, the biasing direction F10 is arranged along the direction L10 so as to pass through the position of the center 10c1 of the secondary transfer roller 10 and a position P1 that is slightly below the center 30c1 of the drive roller 30. In this embodiment, the crossing angle between the biasing direction F10 and the direction L10 can be set to, for example, 3 degrees.

[0070] In this embodiment, the biasing direction F10 passes through the position P1 below the center 30c1 of the drive roller 30. However, for example, when viewed from the rotational axis direction of the drive roller 30, the biasing direction F10 of the biasing force F1 of the spring 38 may pass through the area occupied by the drive roller 30. This allows the biasing force F1 of the spring 38 to efficiently bias (position) the transfer unit 8 (boss 33) toward the positioning portion (first contact surface 41a, second contact surface 41b).

[0071] Example 2 This embodiment includes a separation unit 27 that controls the contact / separation state between the intermediate transfer belt 26 and the photosensitive drum 6 by moving the primary transfer roller 16, and that causes the secondary transfer roller 10 to contact or separate from the intermediate transfer belt 26. Except for the presence of the separation unit 27, the other configurations and operations of this embodiment are substantially the same as those of the first embodiment. Therefore, in the following description, the same reference numerals are used for the configurations and operations common to the first embodiment, and their description will be omitted. The cross-sectional view illustrating the overall configuration of the image forming apparatus of this embodiment is substantially the same as FIG. 1 in the first embodiment.

[0072] In the image forming apparatus of this embodiment, only the black image forming station SK is used when forming a monochrome image. In this case, a black toner image is formed on the photosensitive drum 6K and then transferred to the transfer material P via the intermediate transfer belt 26, thereby obtaining a monochrome image. On the other hand, when forming a full-color image, all four image forming stations SY, SM, SC, and SK are used. In this case, yellow, magenta, cyan, and black toner images are formed sequentially on the photosensitive drums 6Y, 6M, 6C, and 6K, and then transferred to the transfer material P via the intermediate transfer belt 26, thereby obtaining a full-color image.

[0073] In addition, in the configuration of this embodiment, when forming a monochrome image, the rotation of the photosensitive drums 6Y, 6M, and 6C is stopped to suppress wear on the surfaces of the photosensitive drums not used in image formation. At this time, to prevent the rotating intermediate transfer belt 26 from rubbing against the photosensitive drums 6Y, 6M, and 6C, the primary transfer rollers 16Y, 16M, and 16C are moved in a direction away from the photosensitive drums 6Y, 6M, and 6C by a spacing means 27, which will be described later. This separates the intermediate transfer belt 26 from the photosensitive drums 6Y, 6M, and 6C.

[0074] Furthermore, if the primary transfer portion N1 is maintained while the image forming apparatus is on standby or powered off, there is a risk that the primary transfer rollers 16, which are biased toward the photosensitive drums 6, will undergo plastic deformation. If the primary transfer rollers 16 undergo plastic deformation, the adhesion between the photosensitive drums 6 and the intermediate transfer belt 26 at the primary transfer portion N1 will be impaired, resulting in abnormal images such as uneven transfer. In this embodiment, to prevent such deformation of the primary transfer rollers 16, a separating unit 27 (described later) moves all of the primary transfer rollers 16 away from the photosensitive drums 6 while the image forming apparatus is on standby or powered off. This separates the intermediate transfer belt 26 from all of the photosensitive drums 6.

[0075] FIG. 14 is a schematic diagram illustrating the configuration of the transfer unit 108 in this embodiment. In FIG. 14, the transfer frame and intermediate transfer belt of the transfer unit 108 are not shown in order to illustrate the internal configuration of the transfer unit 108. Although the transfer frame and intermediate transfer belt are not shown, the configuration of the transfer frame is substantially the same as frames 17F and 17R in the first embodiment, and the configuration of the intermediate transfer belt is substantially the same as intermediate transfer belt 26 in the first embodiment. As shown in FIG. 14, the contact and separation of the photosensitive drum 6 and the intermediate transfer belt 26 by moving the primary transfer roller 16 is achieved by rotating a rotating unit 52 provided between primary transfer roller 16C and primary transfer roller 16K. A detailed description of the rotating unit 52 and the separation unit 27 will be given later.

[0076] The secondary transfer of the toner image onto the transfer material P is performed at a secondary transfer portion N2 (shown in FIG. 1) formed by a drive roller 30 and a secondary transfer roller 10 that face each other via the intermediate transfer belt 26. As shown in FIG. 14, the secondary transfer roller 10 is rotatably supported at both ends of its rotation shaft by bearings 29. The bearings 29 are biased by springs 38 that serve as biasing members, and the biasing force of the springs 38 presses the secondary transfer roller 10 toward the drive roller 30 via the intermediate transfer belt 26, thereby forming the secondary transfer portion N2.

[0077] If there is a gap at the secondary transfer portion N2, abnormal discharge will occur, so the biasing force of the spring 38, which is the biasing member for the secondary transfer roller 10, is set to a relatively strong force in order to improve the adhesion between the intermediate transfer belt 26 and the secondary transfer roller 10. In this embodiment, the biasing force of the spring 38 is set to 50 N on both sides combined.

[0078] If the secondary transfer roller 10 is left urged toward the drive roller 30 by the spring 38, which has a relatively strong urging force, for a long period of time, the urging force of the secondary transfer roller 10 may cause the intermediate transfer belt 26 to curl at the secondary transfer portion N2. If the intermediate transfer belt 26 curls, the adhesion between the photosensitive drum 6 and the intermediate transfer belt 26 at the primary transfer portion N1 and the adhesion between the intermediate transfer belt 26 and the secondary transfer roller 10 at the secondary transfer portion N2 will be impaired, resulting in image defects such as uneven transfer. For these reasons, the configuration of this embodiment is provided with a separation unit 27 that brings the secondary transfer roller 10 into or out of contact with the intermediate transfer belt 26 to prevent the intermediate transfer belt 26 from curling. The separation unit 27 will be described in detail later.

[0079] [Separation means] Next, the spacing means 27 of this embodiment will be described with reference to Figures 14 to 16. Figure 15 is a schematic diagram illustrating the configuration of a primary transfer bearing 39Y that supports the end of the primary transfer roller 16Y. Figure 16 is a schematic exploded perspective view of the components that make up the rotating unit 52 when removed from the spacing shaft 42.

[0080] As shown in FIG. 14, the primary transfer rollers 16 (16Y, 16M, 16C, 16K) are rotatably supported at both ends of their shafts by primary transfer bearings 39 (39Y, 39M, 39C, 39K). The primary transfer rollers 16 press the photosensitive drums 6 via the intermediate transfer belt 26 by springs 40 serving as urging members, forming a primary transfer portion N1. To explain the configuration for supporting the primary transfer rollers 16, the primary transfer roller 16Y will be used as an example. As shown in FIG. 15, the bearing 39Y supporting the primary transfer roller 16Y has a rotation fulcrum 39a and a hook 39b. The rotation fulcrum 39a is rotatably supported by the transfer frame.

[0081] In this embodiment, the bearings 39Y and 39M that support the primary transfer rollers 16Y and 16M have the same bearing configuration, and the bearings 39C and 39K that support the primary transfer rollers 16C and 16K have the same bearing configuration. By using some common parts in this way, the number of different parts is reduced. Bearings 39C and 39K are essentially the same as bearings 39Y and 39M except for their shapes, and have the same rotation starting points and hooks as bearings 39Y and 39M.

[0082] The spacing means 27 in this embodiment has a rotating part 52, a slider 46, and a slider 47. As shown in Fig. 16, the rotating part 52 has a spacing shaft 42, a spacing cam 43, a coupling 44, and a damper 45. The spacing shaft 42 is made of a metal plate bent into a U shape, and the spacing cam 43, the damper 45, and the coupling 44 are fixed to the spacing shaft 42. The spacing cam 43 is provided on both ends of the spacing shaft 42 in the axial direction. The rotating part 52 is rotatably held with respect to the transfer unit 108 by fitting a boss 43a provided on the spacing cam 43 into a hole (not shown) provided in the transfer frame and by fitting the outer circumferential surface of the coupling 44 into a hole (not shown) provided in the transfer frame.

[0083] Rotating portion 52 rotates when power is transmitted to coupling 44 from a drive source (not shown) provided in the main body of the image forming apparatus. Damper 45 comes into contact with the transfer frame at a certain rotation phase of rotating portion 52 and elastically deforms, thereby acting as a brake to prevent rotating portion 52 from rotating too forcefully. As shown in Figure 16, separating cam 43 is integrally formed with cam portion 43b (first cam) and cam portion 43c (second cam) that are in different phases.

[0084] As shown in FIG. 14, slider 46 (first slider) and slider 47 (second slider) are slidably mounted within the transfer frame near bearings 39Y, 39M, 39C, and 39K. Slider 46 engages with cam portion 43b and moves back and forth in the directions indicated by arrows BB and CC in response to the rotation of cam portion 43b. Slider 47 engages with cam portion 43c and moves back and forth in the directions indicated by arrows BB and CC in response to the rotation of cam portion 43c. A resin with good sliding properties is preferably used for the separation cam 43 and slider 46 and slider 47; in this embodiment, POM is used. Furthermore, slider 46 and slider 47 are positioned within the area defined by the inner circumferential surface of intermediate transfer belt 26, without extending beyond the upper and lower surfaces of intermediate transfer belt 26, which is stretched over three tension rollers, in the vertical direction.

[0085] The slider 47 is capable of moving the primary transfer rollers 16Y, 16M, and 16C against the biasing force of the spring 40 in conjunction with its reciprocating movement. More specifically, the slider 47 has contact surfaces 47Y, 47M, and 47C that can come into contact with the hooks 39b provided on the bearings 39Y, 39M, and 39C, respectively. The slider 47 is capable of moving the primary transfer rollers 16Y, 16M, and 16C by changing the contact state between the hooks 39b and the contact surfaces 47Y, 47M, and 47C through reciprocating movement in response to rotation of the rotating part 52.

[0086] The slider 46 is capable of moving the primary transfer roller 16K against the biasing force of the spring 40 in conjunction with its reciprocating movement. More specifically, the slider 46 has an abutment surface 46K that can abut against a hook 39b provided on a bearing 39K. The slider 46 changes the contact state between the hook 39b and the abutment surface 47K by reciprocating movement in response to the rotation of the rotating part 52, thereby moving the primary transfer roller 16K.

[0087] Furthermore, the slider 46 has an arm 46a for moving the slider 46 to separate the secondary transfer roller 10 from the intermediate transfer belt 26 against the biasing force of the spring 38. As shown in Fig. 14, the arm 46a is disposed between the core of the drive roller 30 and the core of the driven roller 28 in the vertical direction, and is disposed so as to protrude toward the secondary transfer roller 10 in the movement direction of the slider 46.

[0088] Fig. 17 is a schematic diagram illustrating the state of the primary transfer roller 16 and the secondary transfer roller 10 (fully separated state) when the image forming apparatus is on standby or while the power is off. Fig. 18 is a schematic diagram illustrating the state of the primary transfer roller 16 and the secondary transfer roller 10 (mono-contact state) when forming a monochrome image. Fig. 19 is a schematic diagram illustrating the state of the primary transfer roller 16 and the secondary transfer roller 10 (full contact state) when forming a full-color image.

[0089] As shown in FIG. 17, when the image forming apparatus is on standby or powered off, the hooks 39b of the bearings 39 of each primary transfer roller 16 abut against the contact surfaces 47Y, 47M, 47C, and 46K of the slider 47 and slider 46, respectively. That is, the hooks 39b abut against the contact surfaces 47Y, 47M, 47C, and 46K for each color, respectively. As a result, each primary transfer roller 16 resists the biasing force of each spring 40 and is positioned at a distance from each photosensitive drum 6, as shown in FIG. 17. As a result, the intermediate transfer belt 26 and each photosensitive drum 6 are spaced apart from each other.

[0090] 17, the arm 46a of the slider 46 abuts against the pressing surface 29a of the bearing 29 and presses the bearing 29 of the secondary transfer roller 10 against the biasing force of the spring 38. This causes the secondary transfer roller 10 to be separated from the intermediate transfer belt 26. In this way, when the image forming apparatus is on standby or powered off, each photosensitive drum 6 and the secondary transfer roller 10 are separated from the intermediate transfer belt 26, and this state is referred to as a fully separated state.

[0091] Here, the spring 38 presses the area of ​​the bearing 29 where the core metal of the secondary transfer roller 10 is fitted, and in this embodiment, as shown in Fig. 17, the spring 38, bearing 29, arm 46a, and separation cam portion 43b are arranged on approximately the same straight line. In other words, the spring 38, bearing 29, arm 46a, and cam portion 43b, which are provided at both ends in the belt width direction, are arranged to be aligned on approximately a straight line in the movement direction of the slider 46. Therefore, a moment force from the spring 38 is unlikely to be applied to the slider 46 and arm 46a.

[0092] When the image forming apparatus receives a print signal for forming a monochrome image, as shown in Fig. 18, rotating unit 52 rotates 120° in the direction of the arrow DD from the fully separated state shown in Fig. 17. This rotation causes slider 46 to move in the direction of the arrow CC by cam portion 43b. At this time, cam portion 43c and slider 47 remain engaged even when rotating unit 52 is rotated 120°, so slider 47 does not move in the direction of the arrow CC.

[0093] When the slider 46 moves in the direction of the arrow CC in the drawing, the hook 39b provided on the bearing 39K of the primary transfer roller 16K and the abutment surface 46K move from a contact state to a separated state. As a result, the primary transfer roller 16K moves to a position where it urges the intermediate transfer belt 26 toward the photosensitive drum 6K by the urging force of the spring 40, and the intermediate transfer belt 26 and the photosensitive drum 6K come into contact with each other, forming a primary transfer portion N1K. Furthermore, when the slider 46 moves in the direction of the arrow CC in the drawing, the arm 46a and the pressing surface 29a move from a contact state to a separated state. As a result, the secondary transfer roller 10 moves to a position where it abuts the intermediate transfer belt 26 by the urging force of the spring 38, and presses the drive roller 30 via the intermediate transfer belt 26, forming a secondary transfer portion N2.

[0094] Thus, during monochrome image formation, the photosensitive drum 6K and the intermediate transfer belt 26 are in contact with each other, and the secondary transfer roller 10 and the intermediate transfer belt 26 are in contact with each other; this state is referred to as a "mono-contact state." After the primary and secondary transfers are completed during monochrome image formation, the slider 46 can be moved in the direction of arrow BB by rotating the rotating part 52 240° in the direction of arrow DD at a predetermined timing. This movement brings the hook 39b of the bearing 39K into contact with the contact surface 46K, and also brings the arm 46a into contact with the pressing surface 29a, thereby achieving the fully separated state shown in FIG. 17.

[0095] When the image forming apparatus receives a print signal for forming a full-color image, as shown in Fig. 19, rotating portion 52 rotates 240° in the direction of the arrow DD from the fully separated state shown in Fig. 17. This rotation moves slider 47 in the direction of the arrow CC by cam portion 43c, and slider 46 in the direction of the arrow CC by cam portion 43b.

[0096] When the slider 47 moves in the direction of arrow CC, the hooks 39b provided on the bearings 39Y, 39M, and 39C of the primary transfer rollers 16Y, 16M, and 16C move from a contact state to a separation state with the contact surfaces 47Y, 47M, and 47C. As a result, the primary transfer rollers 16Y, 16M, and 16C move to positions where they urge the intermediate transfer belt 26 toward the photosensitive drums 6Y, 6M, and 6C by the urging forces of the springs 40Y, 40M, and 40C. As a result, the intermediate transfer belt 26 and the photosensitive drums 6Y, 6M, and 6C come into contact with each other, forming primary transfer portions N1Y, N1M, and N1C.

[0097] Furthermore, when the slider 46 moves in the direction of the arrow CC, as described above, the photosensitive drum 6K and the intermediate transfer belt 26 come into contact with each other to form a temporary transfer portion N1K, and the secondary transfer roller 10 and the intermediate transfer belt 26 come into contact with each other to form a secondary transfer portion N2. In this way, during full-color image formation, each photosensitive drum 6 comes into contact with the intermediate transfer belt 26, and the secondary transfer roller 10 comes into contact with the intermediate transfer belt 26; this state is called a swinging contact state.

[0098] During full-color image formation, after the primary transfer and secondary transfer are completed, the sliders 46 and 47 can be moved in the direction of the arrow BB by rotating the rotating portion 52 120 degrees in the direction of the arrow DD at a predetermined timing. This movement brings the hooks 39b of the bearings 39Y, 39M, 39C, and 39K into contact with the contact surfaces 47Y, 47M, 47C, and 46K, and brings the arm 46a into contact with the pressing surface 29a, thereby achieving the fully separated state shown in FIG.

[0099] As described above, in the configuration of this embodiment, contact / separation control between the primary transfer roller 16 and the secondary transfer roller 10 is performed by the configuration of the separation means 27 provided inside the transfer unit 108. As a result, when the secondary transfer roller 10 is in contact with the intermediate transfer belt 26, a biasing force is applied to the drive roller 30 by the spring 38 via the secondary transfer roller 10, thereby applying a biasing force to the transfer unit 108. Furthermore, when the secondary transfer roller 10 is separated from the intermediate transfer belt 26, as shown in FIG. 17 , the slider 46 provided in the transfer unit 108 is biased by the spring 38 via the bearing 29, thereby applying the biasing force of the spring 38 to the transfer unit 108.

[0100] That is, by adopting the configuration of this embodiment, it is possible to apply the biasing force of the spring 38 to the transfer unit 108 when the transfer unit 108 is attached to the image forming apparatus, regardless of whether the secondary transfer roller 10 is in contact with or separated from the transfer roller 10. This not only provides the effect described in the first embodiment, but also allows the transfer unit 108 to be always positioned at the correct position by always applying the biasing force to the transfer unit 108, regardless of whether the secondary transfer roller 10 is in contact with or separated from the transfer roller 10.

[0101] Example 3 Fig. 20 is a schematic diagram of an image forming apparatus 100 of this embodiment. As shown in Fig. 19, the image forming apparatus 100 of this embodiment is an intermediate transfer type color image forming apparatus that uses an electrophotographic system. Hereinafter, a third embodiment will be described with reference to Fig. 20. In the following description, components common to the first embodiment will be assigned the same reference numerals as the first embodiment, and description thereof will be omitted.

[0102] Below the image forming unit, between the scanner unit 7 and cassette 2, toner supply containers 48Y, 48M, 48C, and 48K are disposed substantially horizontally. Toner supply container 48 is filled with replenishment toner corresponding to each color. Toner conveying devices 49Y, 49M, 49C, and 49K convey the toner received from toner supply container 48 upward in accordance with toner consumption in the image forming unit, and supply the toner to the developing device. Toner conveying device 48 is driven by toner conveyance driving devices 51Y, 51M, 51C, and 51K disposed below toner conveying device 48.

[0103] In this type of toner supply configuration, the toner supply container is located above the cassette 2, which means that the distance from the cassette 2 to the secondary transfer unit is long. Therefore, compared to a configuration that does not use a toner supply container, it is not possible to feed small-sized transfer materials without adding a transport roller 50. In this way, when there are more rollers transporting the transfer material, the effects of differences in transport speed between the rollers become more likely to be felt, and there is a higher possibility that a force pushing or pulling the transfer material P will occur at the secondary transfer unit N2.

[0104] Even in the configuration of the image forming apparatus 100 of this embodiment, the same effects as in Example 1 can be obtained by adopting the method for positioning the transfer unit 8 and the method for replacing the transfer unit 8 described in Example 1. [Explanation of symbols]

[0105] 8 Transfer Unit 10 Secondary transfer roller 17 Transfer Frame 26 Intermediate transfer belt 33 Boss 41 Notch

Claims

1. An image forming apparatus including a transfer unit and an apparatus main body that detachably supports the transfer unit in a first direction, The transfer unit comprises: An endless belt that rotates and moves; a tension roller that rotates together with the belt and tensions the belt; A positioned portion; and The device body includes: a photosensitive drum that transfers a toner image onto the belt; a guide member having a guide surface that guides the transfer unit to move in the first direction when the transfer unit is attached or detached, the guide surface extending linearly in the first direction; a positioning portion with which the positioned portion abuts so as to position the transfer unit relative to the apparatus main body; A biasing member; and the biasing member biases the positioned portion so as to contact the positioning portion, thereby positioning the transfer unit in a plane direction intersecting the rotation axis direction of the tension roller, The positioning unit is a first contact portion that is a part of a first surface that is a plane inclined with respect to the first direction and that contacts the positioned portion; a second abutment portion that is a part of a second surface that is a plane inclined with respect to the first direction and that extends in a direction intersecting the first plane, the second abutment portion abutting against the positioned portion; an inclined portion for guiding the transfer unit downward in the direction of gravity when the transfer unit is attached to the apparatus main body; and the first surface and the second surface are configured such that the distance between them narrows toward a downstream side in a direction in which the transfer unit is attached to the apparatus main body along the first direction, When viewed from the direction of the rotation axis, the inclined portion is disposed downstream of the guide surface and upstream of the first surface and the second surface in relation to the direction in which the transfer unit is attached to the apparatus body. An image forming apparatus characterized by:

2. 2. The image forming apparatus according to claim 1, wherein the tension roller is a drive roller for driving the belt to rotate.

3. The image forming apparatus according to claim 2, characterized in that the positioned portion is a boss provided on the rotation axis of the drive roller, and protrudes on the opposite side of the frame of the transfer unit from the side on which the belt is provided, in relation to the direction of the rotation axis of the drive roller.

4. a transfer roller that contacts the belt to form a transfer section, and transfers the toner image on the belt from the belt to a transfer material at the transfer section; 4. An image forming apparatus according to claim 1, further comprising an opening / closing section that can open the inside of the image forming apparatus, wherein the transfer roller can be retracted from a position in contact with the belt to a position separated from the belt in conjunction with the opening of the opening / closing section, and wherein the retraction of the transfer roller makes it possible to attach and detach the transfer unit in a direction intersecting the surface of the transfer material to which the toner image is transferred in the transfer section.

5. 5. The image forming apparatus according to claim 1, wherein the transfer unit has a boss that is guided in the first direction by the guide member and is provided downstream of the positioned portion in the mounting direction of the transfer unit.

6. the guide member has a rail groove for guiding the boss in the first direction, 6. The image forming apparatus according to claim 5, wherein the boss is provided at the end of the rotation shaft of the tension roller and protrudes from the frame of the transfer unit on the side opposite to the side on which the belt is provided.

7. the device main body further includes a photosensitive drum that carries an image; The transfer unit comprises: a primary transfer roller disposed on the inner circumferential surface of the belt and configured to transfer the toner image formed on the photosensitive drum onto the belt; a separating unit that separates the photosensitive drum and the belt by moving the primary transfer roller in a direction away from the photosensitive drum; and the transfer roller is a secondary transfer roller that secondarily transfers the toner image that has been primarily transferred onto the belt; the separating unit is configured to be able to separate the secondary transfer roller and the belt by moving the secondary transfer roller against the biasing force of the biasing member, 7. An image forming apparatus according to claim 1, wherein when the secondary transfer roller and the belt are in contact with each other, the transfer unit is positioned relative to the positioning portion by receiving a biasing force from the biasing member via the secondary transfer roller, and when the secondary transfer roller and the belt are separated from each other, the transfer unit is positioned relative to the positioning portion by receiving a biasing force from the biasing member via the separating means.

8. the transfer unit has a holding portion that can be held by a user when attaching or detaching the transfer unit; 8. The image forming apparatus according to claim 1, wherein the position where the holding portion is provided and the position where the positioning portion is provided at least partially overlap with each other in the direction of the rotation axis of the tension roller.

Images