Image forming device

Abstract

To improve the positioning accuracy of a transfer roller without impairing workability during replacement. [Solution] An image forming apparatus comprising an apparatus main body having an image carrier and a detachable unit detachable from the apparatus main body, wherein the detachable unit has a transfer roller and a bearing member rotatable between a first position and a second position, and the apparatus main body has a holding member with a recess, wherein, when the detachable bearing member is viewed in the direction of the rotation axis, the width of the outer surface of the support portion in a second direction perpendicular to the first direction when the bearing member is in the first position and the support portion is engaged with the recess is defined as a first length, and the width of the outer surface in the second direction when the bearing member is rotated from the first position to the second position with the support portion engaged with the recess is defined as a second length, and the first length is shorter than the second length.

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a recording material. [Background technology]

[0002] Electrophotographic image forming apparatuses may be equipped with a transfer roller for transferring a toner image formed on an image carrier such as a photosensitive drum onto a recording material. Patent Document 1 describes a configuration in which the transfer roller and a bearing that supports the transfer roller shaft on a rotating member are configured as a unit that can be replaced integrally with the printer body. According to this document, the transfer roller bearing is attached to and detached from a bearing holding hook provided on the printer body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-072395 Summary of the Invention [Problem to be solved by the invention]

[0004] If there is backlash between the bearing member of the transfer roller provided in a unit that is detachable from the main body of the image forming apparatus and the holding member that is arranged in the main body of the apparatus to hold this bearing member, the positioning accuracy of the transfer roller may decrease. On the other hand, if the bearing member is configured to be press-fitted into the holding member when the unit is installed, for example, the workability of replacement may decrease.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that is capable of improving the positioning accuracy of a transfer roller without impairing the workability during replacement. [Means for solving the problem]

[0006] One aspect of the present invention is an image forming apparatus comprising an apparatus main body having an image carrier, and a detachable unit detachable from the apparatus main body, wherein the detachable unit comprises a transfer roller that, together with the image carrier, forms a transfer section for transferring an image from the image carrier to a recording material when the detachable unit is attached to the apparatus main body, and a bearing member having a shaft support portion for rotatably supporting a rotation shaft of the transfer roller and rotatable around the rotation axis of the transfer roller at a first position and a second position, and the apparatus main body comprises a holding member that holds the bearing member when the detachable unit is attached to the apparatus main body, the holding member having a recess recessed in a first direction intersecting the rotation axis, and when the detachable unit is attached to the apparatus main body, the bearing member is configured to be moved in the first direction so that the support portion engages with the recess, and then the bearing member is rotated from the first position to the second position and the support portion is held in a state where the outer surface of the support portion is in pressure contact with the inner surface of the recess, and when the bearing member is viewed in the direction of the rotation axis, the width of the outer surface of the support portion in a second direction perpendicular to the first direction when the support portion is engaged with the recess with the bearing member at the first position is defined as a first length, and the width of the outer surface in the second direction when the bearing member is rotated from the first position to the second position with the support portion engaged with the recess is defined as a second length, the first length is shorter than the second length. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an image forming apparatus that can improve the positioning accuracy of the transfer roller without impairing the workability during replacement. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2] 1A is a perspective view of a transfer roller unit and a photosensitive drum according to a first embodiment, and FIG. 1B is a cross-sectional view thereof. [Figure 3] FIG. 3 is an explanatory diagram regarding attachment and detachment of a transfer roller unit according to the first embodiment. [Figure 4] FIG. 2 is a perspective view of a transfer roller unit according to the first embodiment. [Figure 5] 1A and 1B are a side view and a perspective view of a bearing member according to a first embodiment of the present invention; [Figure 6] 1A is a side view and FIG. 1B is a perspective view of a holding member according to a first embodiment. [Figure 7] 4A to 4C are explanatory views (a to c) showing how the bearing member according to the first embodiment is attached to the holding member. [Figure 8] FIG. 2 is an explanatory view of a bearing member and a holding member according to the first embodiment. [Figure 9] FIG. 10 is an explanatory diagram regarding attachment and detachment of a transfer roller unit according to a second embodiment. [Figure 10] FIG. 10 is a perspective view of a transfer roller unit according to a second embodiment. [Figure 11] FIG. 10 is a side view of a bearing member according to a third embodiment. [Figure 12] FIG. 11 is a side view of a holding member according to a third embodiment. [Figure 13] 10A to 10C are explanatory views (a to c) showing how a bearing member according to a third embodiment is attached to a holding member. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] Example 1 FIG. 1 is a schematic diagram showing a cross section of a printer 1, which is an image forming apparatus according to an embodiment (first embodiment) of the present disclosure.

[0011] In the following description and drawings, the vertical direction (direction of gravity) when the printer 1 is placed on a horizontal surface is referred to as the Z-axis direction. The direction of the rotation axis of the photosensitive drum 51 (image carrier) provided in the printer 1 is referred to as the Y-axis direction. The direction intersecting both the Z-axis direction and the X-axis direction is referred to as the X-axis direction. The X-axis direction, Y-axis direction, and Z-axis direction are preferably perpendicular to each other.

[0012] First, we will explain the overview of the printer 1. The printer 1 is an electrophotographic laser beam printer that forms monochrome images. As shown in Figure 1, the printer 1 has a sheet feeding section 10, a pair of conveying rollers 2, a pair of registration rollers 3, an image forming section 40, a fixing device 60, a double-sided conveying section 70, a pair of discharge rollers 81, and a discharge tray 82.

[0013] The image forming section 40 includes a process unit 50, an exposure device 7, and a transfer roller 41. The process unit 50 has a photosensitive drum 51 as an image carrier that carries a toner image and a latent image, a charging roller 52 as a charger, a developing unit including a developing roller 53, and a cleaning unit. The photosensitive drum 51 is a cylindrical (drum-shaped) member with a photosensitive layer formed on the surface of a metal base using an organic photosensitive material or the like. The developing unit contains toner as a developer. The process unit 50 is configured as a cartridge that is detachable (replaceable) from the device main body 1A of the printer 1.

[0014] The transfer roller 41 forms a transfer nip N1 as a transfer portion between itself and the photosensitive drum 51. As will be described in detail later, the transfer roller 41 in this embodiment is detachable (replaceable) from the apparatus main body 1A as part of the transfer roller unit 410. The apparatus main body 1A in this embodiment refers to the portion of the printer 1 excluding the process unit 50 and the transfer roller unit 410.

[0015] In this embodiment, the transfer roller 41 is disposed below the photosensitive drum 51. The exposure device 7 is disposed above the process unit 50, and the duplex conveying section 70 is configured to pass further below the transfer roller 41. The exposure device 7 includes a laser light source and an exposure optical system that guides light emitted by the laser light source to the photosensitive drum 51. The exposure device 7 may also be an LED exposure device having multiple LED light sources aligned in the rotational axis direction of the photosensitive drum 51.

[0016] The fixing device 60 is a thermal fixing unit that has a pair of rotors that form a fixing nip and heats the toner image on the sheet S at the fixing nip. The fixing device 60 has a fixing member, a heat source that heats the fixing member, and a pressure member that forms the fixing nip together with the fixing member. The fixing member may be a cylindrical roller, a cylindrical flexible film, or a belt stretched over multiple rollers. The heat source may be, for example, a halogen lamp that emits radiant heat, a heater substrate with a resistive heating element pattern printed on a ceramic substrate, or a coil unit that heats a conductive layer in the fixing member by induction heating.

[0017] The sheet feeding section 10 includes a cassette 11 in which sheets S are stacked and stored, and a feeding unit that feeds sheets S from the cassette 11. As the sheets S, which are recording materials (recording media), a variety of sheet materials of different sizes and materials can be used, including paper such as plain paper and cardboard, surface-treated sheet materials such as coated paper, specially shaped sheet materials such as envelopes and index paper, plastic film, cloth, and the like.

[0018] The cassette 11 is provided with a lift plate (middle plate) that can move up and down while supporting the sheet S. The feeding unit of this embodiment includes a pickup roller 13, a feed roller 12, and a retard roller 14. The retard roller 14 is a roller to which a driving force (retard drive) in a direction opposite to the sheet feeding direction is input via a torque limiter. The retard roller 14 is an example of a separating member that forms a separation nip between itself and the feed roller 12 and separates the sheet S by frictional force. For example, a pad-shaped elastic member (separation pad) may be used as the separating member.

[0019] The following describes a series of operations (image forming operations) in which the printer 1 forms an image on the sheet S while conveying the sheet S one by one. The control unit of the printer 1 starts the image forming operation when an execution command for image formation (print instruction) is input from an external computer or the like connected to the printer 1.

[0020] The control unit starts the electrophotographic process by the image forming unit 40 based on image information input from an external computer or the like. Specifically, the charging roller 52 uniformly charges the surface of the rotating photosensitive drum 51. The exposure device 7 irradiates the photosensitive drum 51 with laser light based on the input image information. This exposes the photosensitive drum 51, and an electrostatic latent image is formed on the surface of the photosensitive drum 51. The development unit causes the development roller 53 to carry toner and supplies it to the photosensitive drum 51, developing the electrostatic latent image into a toner image.

[0021] In parallel with the operation of the image forming unit 40 described above, the sheets S stored in the cassette 11 of the sheet feeding unit 10 are fed by the pickup roller 13. The sheets S fed by the pickup roller 13 are separated one by one by the feed roller 12 and the retard roller 14, and are conveyed to the registration roller pair 3 via the conveying roller pair 2. The registration roller pair 3 corrects skew of the sheet S, and then conveys the sheet S to the transfer nip N1 in synchronization with the toner image formed on the photosensitive drum 51 in the image forming unit 40.

[0022] A transfer bias (transfer voltage) is applied to the transfer roller 41, and the toner image is transferred from the photosensitive drum 51 to the sheet S when the sheet S passes through the transfer nip N1. Residual toner that is not transferred to the sheet S and remains on the photosensitive drum 51 is collected by a cleaning unit of the process unit 50.

[0023] The sheet S that has passed through the transfer nip N1 is subjected to a fixing process of the image by heat and pressure by the fixing device 60. The sheet S that has passed through the fixing device 60 is discharged to the outside of the apparatus main body by a pair of discharge rollers 81 (discharge section) and stacked on a discharge tray 82. In the case of double-sided printing in which images are formed on both sides of the sheet S, the sheet S, on which an image has been formed on the first side by passing through the transfer nip N1 and the fixing device 60, is reversed by the pair of discharge rollers 81 (reversal section) and conveyed again toward the transfer nip N1 via the double-sided conveying section 70. Then, the sheet S, on which an image has been formed on the second side by passing through the transfer nip N1 and the fixing device 60 again, is discharged to the outside of the apparatus main body by the pair of discharge rollers 81 and stacked on a discharge tray 82.

[0024] [Transfer roller unit] The transfer roller unit 410 will be described using Figures 2(a) and 2(b). Figure 2(a) is a perspective view of the photosensitive drum 51 and the transfer roller unit 410. Figure 2(b) is a cross-sectional view of the photosensitive drum 51 and the transfer roller unit 410 taken along a plane passing through the rotation axis of the photosensitive drum 51 and the rotation axis Ax1 of the transfer roller 41. Figures 2(a) and 2(b) show a state in which the process unit 50 and the transfer roller unit 410 are both mounted in the apparatus main body 1A.

[0025] 2(a) and 2(b), the transfer roller unit 410 has a transfer roller 41 and a bearing member 101. The transfer roller unit 410 is a detachable unit (replaceable unit) that is detachable (replaceable) from the apparatus main body 1A.

[0026] The transfer roller 41 has a roller body 41a having an outer circumferential surface that can come into contact with the outer circumferential surface of the photosensitive drum 51, and a rotation shaft 41b (shaft portion) that supports the roller body 41a. The transfer roller 41 is rotatable around a rotation axis Ax1 that passes through the center of the rotation shaft 41b. When both the process unit 50 and the transfer roller unit 410 are mounted in the apparatus main body 1A, the rotation axis Ax1 is parallel to the rotation axis of the photosensitive drum 51. Hereinafter, the direction of the rotation axis Ax1 of the transfer roller 41 may be referred to as the "roller axis direction."

[0027] One end of the rotation shaft 41b of the transfer roller 41 is rotatably supported (held) by a bearing member 101 which is a first bearing member. The other end of the rotation shaft 41b of the transfer roller 41 is rotatably supported (held) by a bearing member 103 which is a second bearing member.

[0028] In this embodiment, the bearing member 103 is disposed in the apparatus main body 1A. In other words, even when the transfer roller unit 410 is removed from the apparatus main body 1A when replacing the transfer roller 41, the bearing member 103 remains in the apparatus main body 1A. However, it is also possible for the bearing member 103 to be part of the transfer roller unit 410.

[0029] The device main body 1A is provided with a holding member 102 and a nip pressure spring 105 corresponding to the bearing member 101, and a holding member 104 and a nip pressure spring 106 corresponding to the bearing member 103. The holding members 102 and 104 (support members) engage with the bearing members 101 and 103, respectively, and hold (support) the bearing members 101 and 103.

[0030] Each of the holding members 102, 104 is configured to be slidable (linearly movable and reciprocating) in the vertical direction (Z-axis direction) in FIG. 2(b) relative to the frame of the apparatus main body 1A. Nip pressure springs 105, 106 are biasing members that bias the holding members 102, 104 upward in FIG. 2(b). The biasing forces of the nip pressure springs 105, 106 are transmitted to the transfer roller 41 via the holding members 102, 104 and bearing members 101, 103. The direction of the biasing forces applied by the nip pressure springs 105, 106 to the holding members 102, 104 is from the rotational axis Ax1 of the transfer roller 41 toward the rotational axis of the photosensitive drum 51. Therefore, when both the process unit 50 and the transfer roller unit 410 are mounted in the apparatus main body 1A, the transfer roller 41 is pressed against the photosensitive drum 51 by the biasing forces of the nip pressure springs 105 and 106, forming a transfer nip N1.

[0031] Transfer roller 41 is electrically connected to a high-voltage board arranged in apparatus main body 1A, and configured so that a transfer voltage is applied from a voltage application circuit on the high-voltage board. At least one of the nip pressure springs and bearing members (nip pressure spring 106 and bearing member 103 in this embodiment) is made of conductive material, and forms a path for applying a transfer voltage to transfer roller 41.

[0032] The bearing member 103 and the holding member 104 of this embodiment can also be made into an integrated member. In that case, this integrated member rotatably supports the rotation shaft 41b of the transfer roller 41 and receives the biasing force of the nip pressure spring 106. This integrated member may be disposed in the apparatus main body 1A in the same way as the holding member 104 and the bearing member 103 of this embodiment, or may be disposed in the transfer roller unit 410.

[0033] [Transfer roller replacement work] The replacement work of the transfer roller 41 will be described. Fig. 3 is a perspective view showing the transfer roller unit 410 in the middle of being removed from the apparatus main body 1A. Fig. 4 is a perspective view showing the transfer roller unit 410 in the state removed from the apparatus main body 1A.

[0034] 3, when replacing the transfer roller 41 in this embodiment, the transfer roller 41 and one of the bearing members 101 are removed integrally as a transfer roller unit 410 from the apparatus main body 1A. The bearing member 101 is removed from the holding member 102 of the apparatus main body 1A in a removal direction Dd. The removal direction Dd is a direction intersecting (preferably a direction perpendicular to) the roller axial direction (Y-axis direction) of the transfer roller 41 when the transfer roller unit 410 is attached to the apparatus main body 1A.

[0035] After the bearing member 101 has been detached from the holding member 102, the transfer roller unit 410 is moved along the rotation axis Ax1, whereby the rotation shaft 41b is pulled out from the bearing member 103 that remains in the apparatus main body 1A. This completes the removal of the transfer roller unit 410 from the apparatus main body 1A. The removed transfer roller unit 410 may be replaced with a new transfer roller unit 410, or the removed transfer roller unit 410 may be further disassembled and only the transfer roller 41 replaced.

[0036] When the transfer roller unit 410 is to be mounted in the apparatus main body 1A, the rotation shaft 41b is engaged with the bearing member 103, and then the bearing member 101 is moved in the mounting direction D1 opposite to the removal direction Dd and mounted on the holding member 102. The mounting of the bearing member 101 will be described in detail later.

[0037] By configuring the bearing member 101 and the transfer roller 41 as an integrated unit that can be attached and detached to the device main body 1A, it is possible to prevent the fingers of an operator from touching the surface of the transfer roller 41 when replacing the transfer roller 41.

[0038] Furthermore, according to the configuration of this embodiment, even when the transfer roller unit 410 is removed from the apparatus main body 1A, at least the holding members 102 and 104 and the nip pressure springs 105 and 106 remain in the apparatus main body 1A. Therefore, when replacing the transfer roller 41, the transfer roller unit 410 is less likely to be subjected to the biasing force of the nip pressure springs 105 and 106, improving workability.

[0039] Furthermore, some printers 1 are equipped with a separation mechanism that can separate the transfer roller 41 from the photosensitive drum 51 when the transfer roller unit 410 is attached to the device main body 1A. The separation mechanism is, for example, a mechanism that moves the holding members 102 and 104 against the biasing forces of the nip pressure springs 105 and 106. Even in the case of a printer 1 equipped with a separation mechanism, the configuration of this embodiment makes it possible to remove the transfer roller unit 410 from the device main body 1A while leaving the holding members 102 and 104 in the device main body 1A. In other words, the transfer roller 41 can be replaced while the separation mechanism and the holding members 102 and 104 are in the state in which they separate the transfer roller 41 from the photosensitive drum 51.

[0040] [Bearing component mounting configuration] Next, the configuration for mounting the bearing member 101 and the holding member 102 will be described. Fig. 5(a) is a side view of the bearing member 101 as viewed in the direction of the rotation axis Ax1 of the transfer roller 41 (Y-axis direction). Fig. 5(b) is a perspective view of the bearing member 101. Fig. 6(a) is a side view of the holding member 102 as viewed in the Y-axis direction. Fig. 6(b) is a perspective view of the holding member 102 as viewed from above. Note that Figs. 5(a) and (b) show the bearing member 101 in a state in which it is in a second position, which will be described later.

[0041] 5(a) and 5(b), the bearing member 101 has a support portion 101A, an operating portion 103e, a retaining rib 101f, a claw portion 101g, and an arm portion 101h. The bearing member 101 may be an integrated part in which the above-mentioned portions are continuously formed using a resin material.

[0042] The shaft support portion 101A is a cylindrical portion having a bearing surface 101a provided on the inner periphery side for rotatably supporting the rotation shaft 41b of the transfer roller 41. The shaft support portion 101A is engaged with a recess 102A of a holding member 102 described below.

[0043] The outer peripheral surface of the bearing portion 101A has an arc portion 101b (cylindrical portion) formed in an arc shape (cylindrical surface shape) when viewed in the roller axial direction, and protruding portions 101c and 101d that protrude outward in a radial direction perpendicular to the rotation axis Ax1 compared to the arc portion 101b. In this embodiment, the protruding portions 101c and 101d are provided at two locations on opposite sides of the rotation axis Ax1, but the protruding portion 101c or 101d may be provided only on one side of the rotation axis Ax1.

[0044] The bearing member 101 is rotatable (movable) around the rotation axis Ax1 between a first position (FIGS. 7(a) and (b)) and a second position (FIGS. 5(a) and 7(c)). Rotation of the bearing member 101 changes the orientation of the protrusions 101c and 101d, changing the width of the support portion 101A in the width direction D2 of the recess 102A. The width direction D2 (second direction) of the recess 102A is perpendicular to the mounting direction D1 (first direction) of the bearing member 101 relative to the holding member 102 when viewed in the roller axial direction.

[0045] The width of the outer peripheral surface of the pivot support portion 101A in the width direction D2 when the bearing member 101 is in the first position (first phase, first angle, attached / detached posture) is defined as L1 (first length). The width of the outer peripheral surface of the pivot support portion 101A in the width direction D2 when the bearing member 101 is rotated from the first position to the second position (second phase, second angle, attached posture) is defined as L2 (second length).

[0046] In this embodiment, L2 is longer than L1 (L2>L1). In other words, the width of the outer peripheral surface of the pivotal support portion 101A in the width direction D2 (second direction) when the pivotal support portion 101A is engaged with the recessed portion 102A with the bearing member 101 in the first position is defined as the first length (L1). The width of the outer peripheral surface of the pivotal support portion 101A in the width direction D2 (second direction) when the bearing member 101 is rotated from the first position to the second position (second phase, second angle, mounting posture) with the pivotal support portion 101A engaged with the recessed portion 102A is defined as the second length (L2). In this case, the first length is shorter than the second length.

[0047] Specifically, in this embodiment, the protrusions 101c and 101d are arranged so that the arc portion 101b faces the width direction D2 when the bearing member 101 is in the first position, and the protrusions 101c and 101d face the width direction D2 when the bearing member 101 is in the second position. Therefore, L1 in this embodiment is the diameter of the arc portion 101b. L2 in this embodiment is equal to the sum of the diameter of the arc portion 101b and the protrusion amounts of the protrusions 101c and 101d relative to the arc portion 101b. In other words, the width L2 of the support portion 101A when the bearing member 101 is in the second position is greater than the width L1 of the support portion 101A when the bearing member 101 is in the first position by the protrusion amounts of the protrusions 101c and 101d.

[0048] The operating portion 103e (grip portion) is a lever-shaped portion that is operated (grip) to move the bearing member 101 between the first position and the second position. When viewed in the roller axial direction, the operating portion 103e protrudes outward from the pivot support portion 101A and is connected to the pivot support portion 101A via the arm portion 101h.

[0049] In this embodiment, the operating unit 103e is disposed as a part of the bearing member 101, but the operating unit 103e may be a separate member from the bearing member 101. In that case, the operating unit 103e and the bearing member 101 are connected using a link, a cam, or the like so that the bearing member 101 moves in conjunction with the operating unit 103e when the operating unit 103e is operated.

[0050] The claw portion 101g is formed to protrude from the arm portion 101h (FIGS. 5(a) and 5(b)). At least a part of the arm portion 101h is formed as a thin portion that can be elastically deformed (flexed) to allow movement of the operating portion 103e and the claw portion 101g.

[0051] The retaining rib 101f protrudes outward from the outer peripheral surface of the bearing portion 101A when viewed in the roller axial direction (FIGS. 5(a) and 5(b)).

[0052] 6(a) and 6(b), the holding member 102 has a recess 102A, abutting portion 102f, a locking portion 102g, and a spring receiving portion 102s. The holding member 102 may be an integrated part in which the above-mentioned portions are continuously formed using a resin material.

[0053] The recess 102A has a recessed shape (groove shape) recessed toward the mounting direction D1. In this embodiment, the recess 102A is formed by side surfaces 102b and 102c facing each other in the width direction D2 and a bottom surface 102d connecting the downstream ends (lower ends) of the side surfaces 102b and 102c in the mounting direction D1. In this embodiment, the side surfaces 102b and 102c are each formed by a rib extending in the mounting direction D1, and the bottom surface 102d is formed by a rib extending in the width direction D2 (FIG. 6(b)). The upstream portion of the recess 102A in the mounting direction D1 is defined as an opening 102e.

[0054] When the bearing member 101 is not engaged with the holding member 102, the distance between the side surfaces 102b and 102c of the recess 102A at the reference position z0 in the mounting direction D1 is defined as the width L3 of the recess 102A. The reference position z0 is the position within the recess 102A where the rotation axis Ax1 of the transfer roller 41 is located when the bearing member 101 is engaged with the holding member 102 (FIG. 7(c)). In this embodiment, the reference position z0 is the position of the rotation axis Ax1 when the outer circumferential surface of the support portion 101A abuts against the bottom surface 102d of the recess 102A. In the following description, the position of the support portion 101A when the rotation axis Ax1 is at the reference position z0 may also be referred to as the reference position z0 of the support portion 101A.

[0055] Furthermore, when the bearing member 101 is not engaged with the holding member 102, the minimum value of the distance between the side surfaces 102b and 102c of the recess 102A upstream of the reference position z0 in the mounting direction D1 is defined as the opening width Lw of the recess 102A. In this embodiment, the ridges of the ribs forming the side surfaces 102b and 102c are all linear and parallel to each other. Therefore, the opening width Lw of the recess 102A in this embodiment is equal to the width L3 of the recess 102A at the reference position z0.

[0056] The width L3 of the recess 102A of the holding member 102 at the reference position z0 is greater than the width L1 of the pivotal support portion 101A when the bearing member 101 is in the first position, and is smaller than the width L2 of the pivotal support portion 101A when the bearing member 101 is in the second position. In other words, L2 > L3 > L1. The advantages of this configuration will be described later.

[0057] Spring receiving portion 102s is a portion that supports nip pressure spring 105 (see FIG. 7(c)) and receives the biasing force of nip pressure spring 105. Spring receiving portion 102s is provided on the back side of bottom surface 102d of recess 102A in mounting direction D1.

[0058] The locking portion 102g is disposed at a position where it can engage with the operating portion 103e and the claw portion 101g of the bearing member 101. The abutting portion 102f is disposed at a position where it can engage with the retaining rib 101f of the bearing member 101.

[0059] Attachment of the bearing member 101 to the holding member 102 will be described using Figures 7(a) to (c) and Figure 8. Figures 7(a) to (c) are views of the bearing member 101 and the holding member 102 as viewed from the inside of the device (the center side of the transfer roller 41) in the roller axial direction. Figure 7(a) shows the state before the bearing member 101 is attached to the holding member 102. Figure 7(b) shows the state when the bearing member 101 is in the first position and the support portion 101A is engaged with the recess 102A of the holding member 102. Figure 7(c) shows the state when the bearing member 101 has been further rotated from the first position to the second position.

[0060] 7(a), when the transfer roller unit 410 is mounted to the apparatus main body 1A, the bearing member 101 is moved in the mounting direction D1 while the bearing member 101 is in the first position, whereby the support portion 101A of the bearing member 101 passes through the opening 102e of the holding member 102, which opens upstream in the mounting direction D1, and engages with the recess 102A.

[0061] As described above, the width L1 of the shaft support portion 101A when the bearing member 101 is in the first position is smaller than the opening width Lw of the concave portion 102A of the holding member 102 (L1 < Lw). In other words, in a state where the transfer roller unit 410 (detachable unit) is not attached to the apparatus main body 1A, the minimum value of the width of the concave portion 102A in the width direction D2 (second direction) upstream of the reference position z0 with respect to the mounting direction D1 (first direction) is defined as the opening width Lw of the concave portion 102A. In this case, the first length (L1) is shorter than the opening width (Lw) of the concave portion 102A.

[0062] Therefore, the shaft support portion 101A is received in the concave portion 102A without receiving frictional resistance due to sliding friction with the inner surface of the concave portion 102A. Specifically, the shaft support portion 101A passes through the opening portion 102e of the concave portion 102A with a gap between the arc portion 101b of the shaft support portion 101A and the side surfaces 102b, 102c of the concave portion 102A. Then, when the outer surface of the shaft support portion 101A abuts against the bottom surface 102d of the concave portion 102A, the shaft support portion 101A reaches the reference position z0.

[0063] As shown in FIG. 7(b), in a state where the shaft support portion 101A has reached the reference position z0, the operator operates the operation portion 101e to rotate the bearing member 101 in the rotation direction R2 from the first position toward the second position. Then, the protruding portions 101c, 101d on the outer peripheral surface of the shaft support portion 101A face the side surfaces 102c, 102b of the concave portion 102A, respectively. When the bearing member 101 is rotated from the first position to the second position in a state where the shaft support portion 101A is at the reference position z0, the attachment of the bearing member 101 to the holding member 102 is completed.

[0064] As described above, the width L2 of the shaft support portion 101A when the bearing member 101 is in the second position is larger than the width L3 of the concave portion 102A of the holding member 102 (L2 > L3). Therefore, by rotating the bearing member 101 to the second position, a part (the protruding portions 101c, 101d) of the outer peripheral surface of the shaft support portion 101A is in a state of being in pressure contact with the inner surface of the concave portion 102A (press-fitting state). As a result, the movement of the shaft support portion 101A in the width direction D2 is restricted, and the rotation axis of the transfer roller 41 is positioned in the width direction D2.

[0065] In this way, by the outer peripheral surface of the support portion 101A being in pressure contact with the inner surface of the recess 102A, rattle of the bearing member 101 can be suppressed, and a decrease in the positioning accuracy of the transfer roller 41 can be suppressed. For example, even if there is variation in the dimensions of the support portion 101A or the dimensions of the recess 102A due to manufacturing tolerances of the bearing member 101 or the holding member 102, this is less likely to manifest as a decrease in the positioning accuracy of the transfer roller 41. Furthermore, because a decrease in the positioning accuracy of the transfer roller 41 is suppressed, an image can be transferred under favorable conditions in the transfer nip N1, contributing to improved image quality.

[0066] In this embodiment, when the bearing member 101 is in the second position, at least a portion of the protrusions 101c and 101d of the support portion 101A faces the recording material conveyance direction in the transfer nip N1. In other words, when the bearing member 101 is in the second position and viewed in the roller axial direction, the contact area of ​​the outer surface of the support portion 101A that comes into contact with the inner surface of the recess 102A intersects with an imaginary line that passes through the rotation axis Ax1 and extends in the recording material conveyance direction. In this case, the pressure force generated between the outer surface of the support portion 101A and the inner surface of the recess 102A is in the recording material conveyance direction (preferably parallel to the recording material conveyance direction). Therefore, even when a force directed upstream or downstream in the recording material conveyance direction is applied to the transfer roller 41 from the sheet S passing through the transfer nip N1, the positional fluctuation of the support portion 101A in the recording material conveyance direction can be suppressed, thereby minimizing the influence on transfer.

[0067] In this embodiment, recess 102A of holding member 102 is open toward the biasing direction of nip pressure spring 105. This prevents the biasing force of nip pressure spring 105 from causing deformation of holding member 102 that would affect the positioning accuracy of pivot support portion 101A (for example, deformation that widens width L3 of recess 102A).

[0068] In this embodiment, when viewed in the roller axial direction, the recess 102A of the holding member 102 is formed in a U-shape, and the support portion 101A of the bearing member 101 is formed in a substantially cylindrical shape. Therefore, the recess 102A of the holding member 102 has a shape that is more easily elastically deformed than the support portion 101A. Furthermore, the holding member 102 is preferably formed of an elastically deformable material so that the amount of deformation of the inner surface of the recess 102A due to engagement with the support portion 101A is greater than the amount of deformation of the outer surface of the support portion 101A due to engagement with the recess 102A. This can suppress deformation of the support portion 101A due to engagement with the recess 102A, thereby suppressing deterioration in sliding properties between the rotation shaft 41b of the transfer roller 41 and the support portion 101A.

[0069] The relationship between the bearing member 101 and the holding member 102 when the bearing member 101 is attached to the holding member 102 will be further described using Figure 8. Figure 8 is a view of the bearing member 101 and the holding member 102 in Figure 7(c) as viewed from outside the device (the opposite side to Figure 7(c)) in the roller axial direction.

[0070] 8, the operating portion 101e of the bearing member 101 is provided at a position further outward than the protruding portions 101c and 101d of the journal support portion 101A in a radial direction perpendicular to the rotation axis Ax1 of the transfer roller 41. This makes it possible to reduce the operating force applied to the operating portion 101e when rotating the bearing member 101 from the first position to the second position against the resistance caused by the pressure contact between the protruding portions 101c and 101d and the inner surface of the recess 102A.

[0071] In this embodiment, the protruding direction of the operating part 101e relative to the journal part 101A is the same as the protruding direction of the protruding parts 101c and 101d. Therefore, when an operator grips the operating part 101e before attaching the bearing member 101 to the holding member 102, the weight of the transfer roller unit 410 naturally positions the bearing member 101 at the first position (FIG. 7(a)), allowing the attachment work to be carried out smoothly.

[0072] 8, when the bearing member 101 is rotated to the second position with the pivotal support portion 101A having reached the reference position z0, the retaining rib 101f of the bearing member 101 comes into contact with the abutment portion 102f of the holding member 102. In this case, the retaining rib 101f is located downstream of the abutment portion 102f in the mounting direction D1, and the abutment portion 102f prevents the pivotal support portion 101A from separating from the recess 102A. Note that when the bearing member 101 is in the first position, the retaining rib 101f and the abutment portion 102f do not interfere with each other, allowing the pivotal support portion 101A to engage with the recess 102A.

[0073] On the other hand, if the bearing member 101 is rotated to the second position before the pivotal support portion 101A reaches the reference position z0, interference between the retaining rib 101f and the abutting portion 102f prevents the pivotal support portion 101A from engaging with the recessed portion 102A. In this case, the retaining rib 101f and the abutting portion 102f function to prevent the bearing member 101 from engaging with the holding member 102 when the bearing member 101 is in an incorrect position, and to prevent the pivotal support portion 101A from coming into pressure contact with the recessed portion 102A by any means other than rotating the bearing member 101.

[0074] In other words, when the bearing member 101 is in the first position, the abutment portion 102f functions as a restricting portion that restricts engagement and disengagement of the pivotal support portion 101A with the recessed portion 102A without coming into contact with the bearing member 101. When the bearing member 101 is in the first position, the abutment portion 102f does not come into contact with the bearing member 101 but allows engagement and disengagement of the pivotal support portion 101A with the recessed portion 102A.

[0075] 8, when the bearing member 101 is rotated to the second position with the journal portion 101A reaching the reference position z0, the operating portion 101e of the bearing member 101 comes into contact with the locking portion 102g of the holding member 102, restricting rotation of the bearing member 101 in the rotation direction R2. The locking portion 102g functions as a stopper that restricts the bearing member 101 from rotating beyond the second position in the rotation direction R2 of the bearing member 101 from the first position toward the second position. Note that the abutting portion 102f described above can also be given the function of a stopper.

[0076] Furthermore, when the bearing member 101 is rotated from the first position to the second position after the pivot support portion 101A reaches the reference position z0, the claw portion 101g of the bearing member 101 comes into contact with the locking portion 102g, which serves as a contact portion, provided on the holding member 104. Pressed by the locking portion 102g, the claw portion 101g temporarily retreats to the left in FIG. 8 due to the elastic deformation of the arm portion 101h, and then releases from the locking portion 102g and moves to the right in FIG. 8 before the bearing member 101 reaches the second position. The contact and release of the claw portion 101g with the locking portion 102g provides the operator with a clicking sensation via the operating portion 101e. This allows the operator to easily recognize that the bearing member 101 has been rotated to the correct position, further improving operability.

[0077] Furthermore, by locking the claw portion 101g with the locking portion 102g, it is possible to prevent the bearing member 101 from inadvertently moving from the second position to the first position, for example, if the operator's finger comes into contact with the bearing member 101 after the bearing member 101 has been rotated from the first position to the second position. When removing the transfer roller unit 410 from the apparatus main body 1A, the operator can rotate the bearing member 101 from the second position to the first position while pressing the operating portion 101e to disengage the claw portion 101g from the locking portion 102g.

[0078] As described above, according to this embodiment, the width of the outer peripheral surface of the pivot support portion 101A varies depending on the circumferential position relative to the rotation axis Ax1, and L2 (second length) is longer than L1 (first length). Furthermore, by rotating the bearing member 101 after the pivot support portion 101A engages with the recess 102A, the outer peripheral surface of the pivot support portion 101A is brought into pressure contact with the inner surface of the recess 102A. In other words, when the transfer roller unit 410 (attachment / detachment unit) is attached to the apparatus main body 1A, the bearing member 101, which is in the first position, is moved toward the attachment direction D1 (first direction), thereby engaging the pivot support portion 101A with the recess 102A. Thereafter, the bearing member 101 is rotated from the first position to the second position, and the bearing member 101 is held by the holding member 102 with the outer peripheral surface of the pivot support portion 101A in pressure contact with the inner surface of the recess 102A.

[0079] This configuration makes it possible to provide an image forming apparatus that can improve the positioning accuracy of the transfer roller without impairing the workability during replacement.

[0080] (Variation) In the first embodiment, a configuration has been described in which the width L1 of the journal portion 101A when the bearing member 101 is in the first position is narrower than the opening width Lw of the recessed portion 102A. In this configuration, when the journal portion 101A is engaged with the recessed portion 102A, the journal portion 101A passes through the opening 102e with a gap between the journal portion 101A and the inner surface of the recessed portion 102A. However, the present invention is not limited to this, and a configuration may also be adopted in which, when the journal portion 101A is engaged with the recessed portion 102A, the journal portion 101A passes through the opening 102e while rubbing against the inner surface of the recessed portion 102A.

[0081] That is, the width L1 (first length) of the support portion 101A in the width direction D2 (second direction) when the bearing member 101 is in the first position may be set to be equal to or greater than the opening width Lw of the recess 102A (L1≧Lw). In this case, similar to the first embodiment, the width L2 (second length) of the support portion 101A in the width direction D2 (second direction) when the bearing member 101 is in the second position is set to be greater than the width L3 (third length) of the recess 102A at the reference position z0. In addition, the difference between L2 (second length) and L3 (third length) is set to be greater than the difference between L1 (first length) and Lw (opening width of the recess) (L2-L3>L1-Lw). With this configuration, the pressure acting between the journal support portion 101A and the recessed portion 102A when the bearing member 101 is rotated to the second position after the journal support portion 101A engages with the recessed portion 102A is greater than the force acting between the journal support portion 101A and the recessed portion 102A when the bearing member 101 passes through the opening 102e. Therefore, as in the first embodiment, it is possible to provide an image forming apparatus that can improve the positioning accuracy of the transfer roller without impairing the workability during replacement.

[0082] Example 2 Another embodiment (Example 2) of the present disclosure will be described. Below, elements with the same reference numerals as Example 1 will have basically the same configurations and functions as those described in Example 1 unless otherwise specified, and differences from Example 1 will be mainly described.

[0083] Fig. 9 is a perspective view of the transfer roller unit 410 in the second embodiment. Fig. 10 is a perspective view showing a state in the middle of the replacement work of the transfer roller unit 410 in the second embodiment.

[0084] As shown in Fig. 9, the transfer roller unit 410 of this embodiment includes a transfer roller 41, a bearing member 101 (first bearing member) that holds one end of the rotating shaft 41b of the transfer roller 41, and a bearing member 107 (second bearing member) that holds the other end of the rotating shaft 41b. As shown in Fig. 10, the two bearing members 101 and 107 that hold both ends of the rotating shaft 41b of the transfer roller 41 are configured to be detachable (replaceable) from the device main body 1A together with the transfer roller 41. This configuration allows the replacement work to be performed while both ends of the transfer roller 41 are axially supported by the bearing members 101 and 107, further reducing the possibility of the worker accidentally touching the surface of the transfer roller 41.

[0085] The bearing member 101 is engaged with a holding member 102 of the apparatus main body 1A and is held (supported) by the holding member 102. The bearing member 107 is engaged with a holding member 108 of the apparatus main body 1A and is held (supported) by the holding member 108.

[0086] Each of the holding members 102, 108 is configured to be slidable (linearly and reciprocally movable) in the Z-axis direction relative to the frame of the apparatus main body 1A. Nip pressure springs 105, 106 urge the holding members 102, 107 upward, respectively. When the process unit 50 and the transfer roller unit 410 are both mounted in the apparatus main body 1A, the urging forces of the nip pressure springs 105, 106 press the transfer roller 41 against the photosensitive drum 51, forming a transfer nip N1.

[0087] The configurations of the bearing member 107 and the holding member 108 may be substantially the same as the configurations of the bearing member 101 and the holding member 102, except for differences such as the member shapes being inverted in the Y-axis direction. When the transfer roller unit 410 of this embodiment is mounted to the apparatus main body 1A, the left and right bearing members 101 and 107 are simultaneously moved in the mounting direction D1 to engage the support portions 101A and 107A with the recesses 102A and 108A of the holding members 102 and 108. Thereafter, the bearing members 101 and 107 are rotated from the first position to the second position, respectively, to complete the mounting of the bearing members 101 and 107 to the holding members 102 and 108.

[0088] With this configuration, similar to the first embodiment, it is possible to provide an image forming apparatus capable of improving the positioning accuracy of the transfer roller without impairing the workability at the time of replacement.

[0089] Example 3 Another embodiment (Example 3) of the present disclosure will be described. Below, elements with the same reference numerals as Example 1 will have basically the same configurations and functions as those described in Example 1 unless otherwise specified, and differences from Example 1 will be mainly described.

[0090] FIG. 11 is a side view of the bearing member 101 of this embodiment as viewed in the direction of the rotation axis Ax1 of the transfer roller 41 (Y-axis direction). FIG. 12 is a side view of the holding member 102 of this embodiment as viewed in the Y-axis direction. FIGS. 13(a) to 13(c) are views of the bearing member 101 and holding member 102 of this embodiment as viewed from the inside of the device (the center side of the transfer roller 41) in the roller axial direction. FIG. 13(a) shows the state before the bearing member 101 is attached to the holding member 102. FIG. 13(b) shows the state when the bearing member 101 is in the first position and the support portion 101A is engaged with the recess 102A of the holding member 102. FIG. 13(c) shows the state when the bearing member 101 has been further rotated from the first position to the second position.

[0091] 11, the outer peripheral surface of the support portion 101A of the bearing member 101 in this embodiment includes an arc portion 101k (cylindrical portion) and recessed portions 101i and 101j (flat portions). The arc portion 101k is formed in an arc shape (cylindrical surface shape) centered on the rotation axis Ax1 when viewed in the roller axial direction. The recessed portions 101i and 101j are recessed radially inward relative to an imaginary cylindrical surface that is in contact with the arc portion 101k, in a direction perpendicular to the rotation axis Ax1.

[0092] In this embodiment, the retraction portions 101i and 101j are provided at two locations on opposite sides of the rotation axis Ax1, but the retraction portions 101i and 101j may be provided only on one side of the rotation axis Ax1. In this embodiment, the retraction portions 101i and 101j are planar and parallel to the rotation axis Ax1 and to each other. In other words, when viewed in the roller axial direction, the support portion 101A in this embodiment has an I-cut shape obtained by cutting a part of a circle by two parallel straight lines.

[0093] The bearing member 101 is rotatable (movable) around the rotation axis Ax1 between a first position (FIGS. 13(a) and 13(b)) and a second position (FIGS. 5(a) and 13(c)). The rotation of the bearing member 101 changes the orientation of the retracted portions 101i and 101j, and the width of the bearing portion 101A in the width direction D2 of the recess 102A changes.

[0094] The width of the outer peripheral surface of the support portion 101A when the bearing member 101 is in the first position (first phase, first angle) is defined as L1 (first length). The width of the outer peripheral surface of the support portion 101A when the bearing member 101 is in the second position (second phase, second angle) is defined as L2 (second length).

[0095] In this embodiment, L2 is longer than L1 (L2>L1). In other words, the width of the outer peripheral surface of the pivotal support portion 101A in the width direction D2 (second direction) when the pivotal support portion 101A is engaged with the recess 102A with the bearing member 101 in the first position is defined as the first length (L1). The width of the outer peripheral surface of the pivotal support portion 101A in the width direction D2 (second direction) when the bearing member 101 is rotated from the first position to the second position (second phase, second angle, mounting posture) with the pivotal support portion 101A engaged with the recess 102A is defined as the second length (L2). In this case, the first length is shorter than the second length. In this case, the first length is shorter than the second length.

[0096] Specifically, in this embodiment, the retracted portions 101i and 101j are arranged so that when the bearing member 101 is in the first position, the retracted portions 101i and 101j face the width direction D2, and when the bearing member 101 is in the second position, the arc portion 101k faces the width direction D2. Therefore, L1 in this embodiment is equal to the distance between the retracted portions 101i and 101j. Furthermore, L2 in this embodiment is the diameter of the arc portion 101k.

[0097] The configuration of the bearing member 101 other than the pivot support portion 101A may be the same as that of the bearing member 101 of the first embodiment.

[0098] 12, the recess 102A of the holding member 102 in this embodiment is formed so that the width L3 (third length) of the recess 102A at the reference position z0 is wider than the opening width Lw of the recess 102A (L3>Lw). The recess 102A in this embodiment is formed in an arc shape. The width L3 of the recess 102A at the reference position z0 is the inner diameter of the arc-shaped recess 102A. The center of the arc of the recess 102A coincides with the rotation axis Ax1 of the transfer roller 41 when the bearing member 101 is attached to the holding member 102.

[0099] As shown in Fig. 13(a), when the transfer roller unit 410 is attached to the apparatus main body 1A, the bearing member 101 is moved in the attachment direction D1 with the bearing member 101 in the first position. As a result, the shaft support portion 101A of the bearing member 101 passes through the opening 102e of the holding member 102 that opens toward the upstream in the attachment direction D1 and engages with the recess 102A.

[0100] Here, the width L1 of the shaft support portion 101A when the bearing member 101 is in the first position is smaller than the opening width Lw of the recess 102A (L1 < Lw). In other words, in a state where the transfer roller unit 410 (detachable unit) is not attached to the apparatus main body 1A, the minimum value of the width of the recess 102A in the width direction D2 (second direction) on the upstream side of the reference position z0 with respect to the attachment direction D1 (first direction) is defined as the opening width Lw of the recess 102A. In this case, the first length (L1) is shorter than the opening width Lw of the recess 102A.

[0101] Therefore, the shaft support portion 101A can be received in the recess 102A without receiving frictional resistance from the inner surface of the recess 102A. Specifically, with a gap between the retreat portions 101i, 102j of the shaft support portion 101A and the side surfaces 102c, 102b of the recess 102A, the shaft support portion 101A passes through the opening 102e of the recess 102A and is inserted into the recess 102A. Then, when the outer peripheral surface of the shaft support portion 101A abuts against the bottom surface 102d of the recess 102A, the shaft support portion 101A reaches the reference position z0.

[0102] As shown in Fig. 13(b), in a state where the shaft support portion 101A has reached the reference position z0, the operator operates the operation portion 101e to rotate the bearing member 101 in the rotational direction R2 from the first position toward the second position. Then, the arc portions 101k on the outer peripheral surface of the shaft support portion 101A face the side surfaces 102c, 102b of the recess 102A, respectively. When the bearing member 101 is rotated from the first position to the second position with the shaft support portion 101A in the reference position z0, the attachment of the bearing member 101 to the holding member 102 is completed. [[ID=,14]]

[0103] Here, the width L2 of the support portion 101A when the bearing member 101 is in the second position is greater than the width L3 of the recessed portion 102A at the reference position z0 (L2>L3). Therefore, when the bearing member 101 is rotated to the second position, a part of the outer circumferential surface of the support portion 101A (the arc portion 101k) is brought into pressure contact with the inner surface of the recessed portion 102A (press-fit state). This restricts movement of the support portion 101A in the width direction D2, and positions the rotation axis of the transfer roller 41 in the width direction D2.

[0104] In this way, the outer peripheral surface of the bearing portion 101A is in pressure contact with the inner surface of the recess 102A, so that rattle of the bearing member 101 can be suppressed, and deterioration in the positioning accuracy of the transfer roller 41 can be suppressed.

[0105] That is, even with the configuration of this embodiment, it is possible to provide an image forming apparatus that can improve the positioning accuracy of the transfer roller without impairing the workability during replacement.

[0106] In this embodiment, the opening width Lw of the recess 102A is narrower than the width L3 (third length) of the recess 102A at the reference position z0 (L3>Lw), which has the advantage of reducing the possibility that the support portion 101A will come off the recess 102A when the bearing member 101 is in the second position.

[0107] (Variation) In Example 3, a configuration where L1 < Lw was described. However, not limited to this, similar to the modification of Example 1, when the bearing member 101 is in the first position, the width L1 (first length) of the shaft support portion 101A in the width direction D2 (second direction) may be set to be equal to or greater than the opening width Lw of the concave portion 102A (L1 ≧ Lw). In this case, the width L2 (second length) of the shaft support portion 101A in the width direction D2 (second direction) when the bearing member 101 is in the second position shall be greater than the width L3 (third length) of the concave portion 102A at the reference position z0. Also, the difference between L2 (second length) and L3 (third length) shall be greater than the difference between L1 (first length) and Lw (opening width of the concave portion) (L2 - L3 > L1 - Lw). According to this configuration, the pressing contact force acting between the shaft support portion 101A and the concave portion 102A in the state where the bearing member 101 is rotated to the second position after the shaft support portion 101A engages with the concave portion 102A is greater than the force acting between the shaft support portion 101A and the concave portion 102A when passing through the opening portion 102e. Therefore, similar to Example 3, it is possible to provide an image forming apparatus that can improve the positioning accuracy of the transfer roller without impairing the workability during replacement.

[0108] (Other Embodiments) The technology of the present disclosure is not limited to the forms of the above-described respective examples. For example, in Example 3, the shaft support portion 101A was of an I-cut shape, but it may be of a shape (D-cut shape) in which only one of the retreat portions 101i, 101j is left and the remaining outer peripheral surface of the shaft support portion 101A is an arc portion 101k.

[0109] Also, in Examples 1 to 3, a direct transfer type monochrome laser beam printer was exemplified as the image forming apparatus, but the image forming apparatus may be, for example, an intermediate transfer type color laser beam printer. The intermediate transfer method is a method in which a toner image formed on a photosensitive drum is first transferred to an intermediate transfer body such as an intermediate transfer belt, and then the toner image is transferred from the intermediate transfer body to a recording material. In this case, the "transfer roller" may be a secondary transfer roller that forms a transfer portion (secondary transfer nip) between the intermediate transfer body as an image carrier.

[0110] 《Summary of the Present Disclosure》 The present disclosure includes at least the following: (Configuration 1) an apparatus main body having an image carrier; a detachable unit that is detachable from the device body; An image forming apparatus comprising: The detachable unit includes: a transfer roller that, together with the image carrier, forms a transfer section for transferring an image from the image carrier to a recording material when the detachable unit is attached to the apparatus main body; a bearing member having a shaft support portion that rotatably supports a rotation shaft of the transfer roller, and that is rotatable around the rotation axis of the transfer roller between a first position and a second position; and the device main body includes a holding member that holds the bearing member when the detachable unit is attached to the device main body, the holding member having a recess that is recessed in a first direction intersecting with the rotation axis, When the detachable unit is attached to the device main body, the bearing member in the first position is moved in the first direction to engage the pivotal support portion with the recessed portion, and then the bearing member is rotated from the first position to the second position, and the pivotal support portion is held in a state where the outer peripheral surface of the pivotal support portion is in pressure contact with the inner surface of the recessed portion, When the bearing member is viewed in the direction of the rotation axis, a width of the outer circumferential surface of the journal support portion in a second direction perpendicular to the first direction when the journal support portion is engaged with the recessed portion in a state where the bearing member is at the first position is defined as a first length, and a width of the outer circumferential surface in the second direction when the bearing member is rotated from the first position to the second position in a state where the journal support portion is engaged with the recessed portion is defined as a second length, and the first length is shorter than the second length. An image forming apparatus characterized by: (Configuration 2) When a position in the recess where the rotation axis is located when the detachable unit is attached to the device body in the first direction is defined as a reference position, and when the detachable unit is not attached to the device body, the minimum value of the width of the recess in the second direction upstream of the reference position in the first direction is defined as an opening width of the recess, the first length is shorter than the opening width; 2. The image forming apparatus according to claim 1, (Configuration 3) a reference position in the recess where the rotation axis is located when the detachable unit is attached to the device body in the first direction; a third length is a width of the recess in the second direction at the reference position when the detachable unit is not attached to the device body; and a minimum value of the width of the recess in the second direction upstream of the reference position in the first direction is an opening width of the recess. the first length is equal to or greater than the opening width, the second length is greater than the third length; a difference between the second length and the third length is greater than a difference between the first length and the opening width; 2. The image forming apparatus according to claim 1, (Configuration 4) a reference position in the recess where the rotation axis is located when the detachable unit is attached to the device body in the first direction; a third length is a width of the recess in the second direction at the reference position when the detachable unit is not attached to the device body; and a minimum value of the width of the recess in the second direction upstream of the reference position in the first direction is an opening width of the recess. the opening width is smaller than the third length; 2. The image forming apparatus according to claim 1, (Configuration 5) the outer peripheral surface of the bearing portion has an arc portion formed in an arc shape centered on the rotation axis when viewed in the direction of the rotation axis, and a protruding portion protruding outward from the arc portion in a radial direction perpendicular to the rotation axis, When the bearing member is in the first position, the arc portion faces the second direction, When the bearing member is in the second position, the protrusion faces the second direction. 5. The image forming apparatus according to any one of configurations 1 to 4. (Configuration 6) The protrusions are provided at two locations opposite to each other across the rotation axis. 6. The image forming apparatus according to configuration 5. (Configuration 7) the outer peripheral surface of the bearing portion has an arc portion formed in an arc shape centered on the rotation axis when viewed in the direction of the rotation axis, and a retracted portion retracted inward in a radial direction perpendicular to the rotation axis with respect to the arc portion, When the bearing member is in the first position, the retracted portion faces the second direction, When the bearing member is in the second position, the arc portion faces the second direction. 5. The image forming apparatus according to any one of configurations 1 to 4. (Configuration 8) The retracting portions are provided at two locations opposite to each other across the rotation axis. 8. The image forming apparatus according to configuration 7. (Configuration 9) The retraction portion is formed in a plane parallel to the rotation axis. 9. The image forming apparatus according to configuration 7 or 8. (Configuration 10) the retaining member is elastically deformable so that the amount of deformation of the outer peripheral surface of the journal portion due to engagement with the recess is smaller than the amount of deformation of the inner surface of the recess due to engagement with the journal portion. 10. The image forming apparatus according to any one of configurations 1 to 9. (Configuration 11) The bearing member has an operating portion that is operated to rotate the bearing member from the first position to the second position. 11. The image forming apparatus according to any one of configurations 1 to 10. (Configuration 12) the bearing member has an elastically deformable arm portion and a claw portion supported by the arm portion, The holding member has a contact portion that comes into contact with the claw portion to elastically deform the arm portion and then releases the claw portion during the process of rotating the bearing member from the first position to the second position by operating the operating portion. 12. The image forming apparatus according to claim 11, (Configuration 13) the holding member has a stopper that restricts the bearing member from rotating beyond the second position in the rotation direction of the bearing member from the first position toward the second position. 13. The image forming apparatus according to any one of configurations 1 to 12. (Configuration 14) the retaining member has a restricting portion that allows the pivotal support portion to engage with and disengage from the recessed portion without coming into contact with the bearing member when the bearing member is in the first position, and that restricts the pivotal support portion to engage with and disengage from the recessed portion by coming into contact with the bearing member when the bearing member is in the second position. 14. The image forming apparatus according to any one of configurations 1 to 13. (Configuration 15) when viewed in the direction of the rotation axis in a state in which the bearing member is in the second position, a region of the outer circumferential surface of the bearing support portion that contacts the inner surface of the recess intersects with a virtual line that passes through the rotation axis and extends in a conveying direction of the recording material in the transfer portion; 15. The image forming apparatus according to any one of configurations 1 to 14. (Configuration 16) a biasing member for biasing the transfer roller toward the image carrier when the detachable unit is attached to the apparatus main body; The recess is open toward the biasing direction of the biasing member. 16. The image forming apparatus according to any one of configurations 1 to 15. (Configuration 17) a biasing member that biases the holding member when the detachable unit is attached to the device body, the holding member is movable in the first direction, and receives a biasing force from the biasing member and transmits the biasing force to the transfer roller, thereby causing the transfer roller to contact the image carrier. 17. The image forming apparatus according to any one of configurations 1 to 16. [Explanation of symbols]

[0111] 1A... device body / 41... transfer roller / 51... image carrier (photosensitive drum) / 101... bearing member / 101A... bearing support portion / 102... holding member / 102A... recess / 410... detachable unit (transfer roller unit) / D1... first direction (mounting direction) / D2... second direction (width direction) / L1... first length / L2... second length

Claims

1. an apparatus main body having an image carrier; a detachable unit that is detachable from the device body; An image forming apparatus comprising: The detachable unit includes: a transfer roller that, together with the image carrier, forms a transfer section for transferring an image from the image carrier to a recording material when the detachable unit is attached to the apparatus main body; a bearing member having a support portion for rotatably supporting a rotation shaft of the transfer roller, the bearing member being rotatable around the rotation axis of the transfer roller between a first position and a second position; and the device body includes a holding member that holds the bearing member when the detachable unit is attached to the device body, the holding member having a recess that is recessed in a first direction intersecting with the rotation axis, When the detachable unit is attached to the device main body, the bearing member in the first position is moved in the first direction to engage the pivotal support portion with the recess, and then the bearing member is rotated from the first position to the second position, and the pivotal support portion is held in a state where the outer peripheral surface of the pivotal support portion is in pressure contact with the inner surface of the recess, When the bearing member is viewed in the direction of the rotation axis, a width of the outer circumferential surface of the journal support portion in a second direction perpendicular to the first direction when the journal support portion is engaged with the recessed portion in a state where the bearing member is at the first position is defined as a first length, and a width of the outer circumferential surface in the second direction when the bearing member is rotated from the first position to the second position in a state where the journal support portion is engaged with the recessed portion is defined as a second length, and the first length is shorter than the second length. An image forming apparatus characterized by:

2. When a position in the recess where the rotation axis is located when the detachable unit is attached to the device body in the first direction is defined as a reference position, and when the detachable unit is not attached to the device body, a minimum value of the width of the recess in the second direction upstream of the reference position in the first direction is defined as an opening width of the recess, the first length is less than the opening width; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. When a position in the recess where the rotation axis is located when the detachable unit is attached to the device body in the first direction is defined as a reference position, a width of the recess in the second direction at the reference position when the detachable unit is not attached to the device body is defined as a third length, and a minimum value of the width of the recess in the second direction upstream of the reference position in the first direction is defined as an opening width of the recess, the first length is equal to or greater than the opening width; the second length is greater than the third length; a difference between the second length and the third length is greater than a difference between the first length and the opening width; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. When a position in the recess where the rotation axis is located when the detachable unit is attached to the device body in the first direction is defined as a reference position, a width of the recess in the second direction at the reference position when the detachable unit is not attached to the device body is defined as a third length, and a minimum value of the width of the recess in the second direction upstream of the reference position in the first direction is defined as an opening width of the recess, the opening width is smaller than the third length; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. the outer peripheral surface of the bearing portion has an arc portion formed in an arc shape centered on the rotation axis when viewed in the direction of the rotation axis, and a protruding portion protruding outward from the arc portion in a radial direction perpendicular to the rotation axis, When the bearing member is in the first position, the arc portion faces the second direction, When the bearing member is in the second position, the protrusion faces the second direction.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The protrusions are provided at two locations on opposite sides of the rotation axis.

6. The image forming apparatus according to claim 5,

7. the outer peripheral surface of the bearing portion has an arc portion formed in an arc shape centered on the rotation axis when viewed in the direction of the rotation axis, and a retracted portion retracted inward in a radial direction perpendicular to the rotation axis with respect to the arc portion, When the bearing member is in the first position, the retracted portion faces the second direction, When the bearing member is in the second position, the arc portion faces the second direction.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. The retraction sections are provided at two locations opposite to each other across the rotation axis.

8. The image forming apparatus according to claim 7,

9. The retraction portion is formed in a plane parallel to the rotation axis.

8. The image forming apparatus according to claim 7,

10. the retaining member is elastically deformable so that the amount of deformation of the outer peripheral surface of the journal portion due to engagement with the recess is smaller than the amount of deformation of the inner surface of the recess due to engagement with the journal portion.

10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

11. the bearing member has an operating portion that is operated to rotate the bearing member from the first position to the second position; 10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

12. the bearing member has an elastically deformable arm portion and a claw portion supported by the arm portion, the holding member has a contact portion that comes into contact with the claw portion to elastically deform the arm portion and then releases the claw portion during the process of rotating the bearing member from the first position to the second position by operating the operating portion.

12. The image forming apparatus according to claim 11.

13. the holding member has a stopper that restricts the bearing member from rotating beyond the second position in the rotation direction of the bearing member from the first position toward the second position.

10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

14. the retaining member has a restricting portion that allows the pivotal support portion to engage with and disengage from the recessed portion without coming into contact with the bearing member when the bearing member is in the first position, and that restricts the pivotal support portion from engaging with and disengaging from the recessed portion by coming into contact with the bearing member when the bearing member is in the second position.

10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

15. when viewed in the direction of the rotation axis in a state in which the bearing member is in the second position, a region of the outer circumferential surface of the bearing portion that contacts the inner surface of the recess intersects with a virtual line that passes through the rotation axis and extends in a conveying direction of the recording material in the transfer unit; 10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

16. a biasing member for biasing the transfer roller toward the image carrier when the detachable unit is attached to the apparatus main body; The recess is open toward the biasing direction of the biasing member.

10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

17. a biasing member that biases the holding member when the detachable unit is attached to the device body, the holding member is movable in the first direction, and receives a biasing force from the biasing member and transmits the biasing force to the transfer roller, thereby causing the transfer roller to contact the image carrier.

10. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images