Unit positioning mechanism and image forming apparatus

Abstract

To determine a location of a unit, while preventing an increase in the size of an apparatus.SOLUTION: A cover rotates in a closing direction to cause a first pressing part to start pressing a unit side receiving part. Contact of a hook part with a boss part displaces a positioning member toward the other side in a circumferential direction. After a contact point of the hook part with the boss part passes through the lowest point of the boss part, a second pressing part is caused to start pressing a hook side receiving part, and the positioning member is displaced toward one side in the circumferential direction and engaged with the boss part. The unit side receiving part is separated from the first pressing part by the time the cover reaches a closed position. Continuation of the rotation of the cover in the closing direction elastically deforms one of the second pressing part and the hook side receiving part in a direction to move away from the other, the second pressing part gets over the hook side receiving part, and pressing against the hook side receiving part performed by the second pressing part is released.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a unit positioning mechanism and an image forming apparatus. [Background technology]

[0002] A conventional image forming apparatus includes a rear cover and a transport unit that rotates in conjunction with the opening and closing of the rear cover. When the rear cover is closed, the transport unit rotates in one direction in conjunction with the closing of the rear cover, and reaches a position where it is positioned relative to the main body unit. Such an image forming apparatus is disclosed in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-43464 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, the transport unit is held in a state of being pressed against the main body unit. As a result, the transport unit receives a reaction force from the main body unit, and the reaction force may be applied to the rear cover. In this case, in order to suppress deformation of the rear cover caused by the reaction force from the main body unit, it is necessary to increase the rigidity of the rear cover by adding ribs to the rear cover or by making the rear cover itself thicker. As a result, the image forming apparatus becomes larger in size, which is an inconvenience.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a unit positioning mechanism and an image forming apparatus that are capable of positioning a unit while preventing the device in which the unit is installed from becoming larger, in a configuration in which the unit is positioned by rotating the unit in conjunction with the opening and closing of a cover. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, a unit positioning mechanism according to a first aspect of the present invention includes a cover that is displaceable between a closed position that covers the inside of the main frame from one side in a second direction that is perpendicular to the first direction and an open position that is a position other than the closed position by rotating about the axis of a first rotating shaft extending in a first direction perpendicular to the up-down direction; a first unit that is attached to the inside of the main frame and has a boss portion; a second unit that is arranged downstream in the closing direction, which is the direction from the open position to the closed position, with respect to the cover, and that is displaceable between a first position where the first unit is positioned and a second position that is a position other than the first position by rotating about the axis of a second rotating shaft that extends parallel to the first rotating shaft at a position above the first rotating shaft and on the other side opposite to the one side in the second direction from the first rotating shaft; a positioning member attached to the second unit and holding the second unit in the first position; and a torsion coil spring attached to the positioning member. The positioning member has a cylindrical portion with the first direction as its cylindrical axis direction, and a hook portion disposed radially outward of the cylindrical portion as viewed from the first direction, engageable with the boss portion so as to embrace the boss portion from one side in the circumferential direction centered on the cylindrical axis of the cylindrical portion, and regulating rotation of the second unit from the first position to the second position by engaging with the boss portion when the second unit is in the first position. The second unit has a support shaft into which the cylindrical portion is fitted and which supports the positioning member so as to be displaceable in the circumferential direction. The torsion coil spring biases the positioning member toward one side in the circumferential direction, which is the direction in which the hook portion engages with the boss portion. The cover has a first pressing portion and a second pressing portion. The second unit has a unit side receiving portion that receives a pressing force from the first pressing portion. The positioning member has a hook side receiving portion that receives a pressing force from the second pressing portion. When the cover rotates from the open position to the closed position, the first pressing portion starts pressing the unit side receiving portion so that the second unit rotates toward the first position. After the first pressing portion begins to press against the unit side receiving portion, the tip of the hook portion comes into contact with the boss portion, causing the positioning member to displace to the other circumferential side, which is the direction against the biasing force of the torsion coil spring.After the contact point of the tip of the hook portion with the boss portion passes the lowest point of the boss portion as viewed from the first direction, the second pressing portion contacts the hook side receiving portion from one side in the circumferential direction, and the second pressing portion starts pressing the hook side receiving portion so that the positioning member is displaced to one side in the circumferential direction, and the positioning member is displaced to one side in the circumferential direction and the hook portion engages with the boss portion. After the rotation of the cover starts in the closing direction, the positions of the first rotation shaft and the second rotation shaft differ from each other as viewed from the first direction until the cover reaches the closed position, and the unit side receiving portion moves away from the first pressing portion. After the displacement of the positioning member to one side in the circumferential direction stops as the hook portion engages with the boss portion, the rotation of the cover continues in the closing direction, and one of the second pressing portion and the hook side receiving portion elastically deforms in a direction away from the other, and the second pressing portion overcomes the hook side receiving portion, and the pressing of the hook side receiving portion by the second pressing portion is released.

[0007] An image forming apparatus according to a second aspect of the present invention includes the unit positioning mechanism. The first unit is a unit having an image carrier that carries an image. The second unit is a unit having a transfer roller. When the second unit is held at the first position, the image carrier and the transfer roller are pressed against each other to form a transfer nip between the image carrier and the transfer roller. The image forming apparatus transports a sheet to the transfer nip and transfers the image onto the sheet. Effect of the Invention

[0008] In the present invention, in a configuration in which the unit is positioned by rotating the unit in conjunction with the opening and closing of the cover, it is possible to position the unit while preventing an increase in size of an apparatus including the unit. [Brief description of the drawings]

[0009] [Figure 1] 1 is a perspective view of an image forming apparatus according to an embodiment. [Diagram 2] 2 is a perspective view of the image forming apparatus shown in FIG. 1 with a rear cover removed. [Diagram 3] 1 is a schematic diagram illustrating an internal configuration of an image forming apparatus according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a configuration of an image forming unit of an image forming apparatus according to an embodiment. [Diagram 5] 1 is a side view of an image forming apparatus according to an embodiment in a state where a transport unit is separated from a main unit. [Figure 6] 2 is a side view of a transport unit and a positioning member attached to the transport unit of the image forming apparatus according to the embodiment. FIG. [Figure 7] 2 is a front perspective view of a transport unit and a positioning member attached to the transport unit of the image forming apparatus according to the embodiment; FIG. [Figure 8] 2 is a rear perspective view of a transport unit and a positioning member attached to the transport unit of the image forming apparatus according to the embodiment; FIG. [Figure 9] FIG. 2 is an enlarged perspective view of the periphery of a side portion of a transport unit of the image forming apparatus according to the embodiment. [Figure 10] 4 is a side view of a positioning member of the image forming apparatus according to the embodiment and a torsion coil spring temporarily fixed thereto. FIG. [Figure 11] 11A and 11B are perspective views for explaining a mounting step of the positioning member according to the embodiment. [Figure 12] 12 is a perspective view of the positioning member shown in FIG. 11 in a state where it has been rotated to one side in the circumferential direction. [Figure 13] 3A and 3B are diagrams illustrating the positional relationship between a first rotation shaft and a second rotation shaft of the image forming apparatus according to the embodiment. [Figure 14] 5A and 5B are diagrams illustrating a positional relationship between a boss portion and a hook portion of the image forming apparatus according to the embodiment. [Figure 15] 13A and 13B are diagrams illustrating a state when the second pressing portion of the image forming apparatus according to the embodiment starts to press the hook-side receiving portion. [Figure 16] 5A to 5C are diagrams illustrating respective shapes of a second pressing portion and a hook-side receiving portion of the image forming apparatus according to the embodiment. [Figure 17]11A and 11B are diagrams illustrating a state in which the pressure applied by the first pressing portion to the unit side receiving portion of the image forming apparatus according to the embodiment is released. [Figure 18] 10A to 10C are diagrams illustrating state transitions when the pressure applied by the second pressing portion to the hook-side receiving portion of the image forming apparatus according to the embodiment is released. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An image forming apparatus 100 according to an embodiment of the present invention will be described below with reference to Figures 1 to 18. In the following description, a color laser printer capable of executing a job to print an image on a sheet S is taken as an example, but the present invention is not limited to printers and can also be applied to multifunction machines having functions such as a copy machine.

[0011] In the following description, a direction perpendicular to a flat floor surface on which the image forming apparatus 100 is installed is defined as an up-down direction and is denoted by the symbol D. In addition, of horizontal directions perpendicular to the up-down direction D, one direction is denoted by the symbol D1, and the other direction perpendicular to the direction D1 is denoted by the symbol D2.

[0012] For example, one direction D1 is the width direction (left-right direction) of image forming device 100. In the following description, one direction D1 will be referred to as width direction D1. Width direction D1 corresponds to the "first direction." The other direction D2 is the front-rear direction of image forming device 100. In the following description, the other direction D2 will be referred to as front-rear direction D2. The front-rear direction corresponds to the "second direction."

[0013] <Overall configuration of image forming apparatus> Image forming apparatus 100 of this embodiment has an external appearance as shown in Figures 1 and 2. Image forming apparatus 100 includes a main body frame FR. Image forming apparatus 100 also includes a rear cover CV. The rear cover CV corresponds to a "cover." The main body frame FR is covered by an exterior cover including the rear cover CV (reference numbers for other covers are omitted). In Figure 2, the rear cover CV is omitted and the inside of the main body frame FR is illustrated.

[0014] The main body frame FR supports the exterior cover. The main body frame FR supports the rear cover CV rotatably around an axis extending in the width direction D1. Specifically, the main body frame FR has a first rotation axis RA1 (see FIG. 5) extending in the width direction D1. The first rotation axis RA1 supports a lower end of the rear cover CV. The rear cover CV rotates around the first rotation axis RA1 as a fulcrum so as to swing an end (i.e., an upper end) opposite to the side supported by the first rotation axis RA1. In other words, the rear cover CV is supported so as to be openable and closable with respect to the main body frame FR.

[0015] The rear cover CV can be displaced between a closed position in which the inside of the main body frame FR is covered from the rear (i.e., the outside), which is one side in the front-rear direction D2, and an open position which is a position other than the closed position, by rotating about the axis of a first rotation shaft RA1. When the rear cover CV is opened, the inside of the main body frame FR is exposed to the rear. When the rear cover CV is closed, the inside of the main body frame FR is covered from the rear. For example, when a sheet S jams during execution of a print job, the rear cover CV is opened to remove the sheet S.

[0016] The position of the rear cover CV shown in Fig. 1 is the closed position. At least a transport unit 2, which will be described later, is mounted inside the main body frame FR (see Fig. 2). When the rear cover CV is opened, the transport unit 2 is exposed to the rear.

[0017] As shown in Fig. 3, the image forming apparatus 100 includes a main transport path MP. The main transport path MP passes through a transfer nip, which will be described later. In Fig. 3, the main transport path MP is shown typically with a solid arrow. A double-sided printing transport path DP, which will be described later, is shown typically with a dashed arrow.

[0018] The image forming apparatus 100 also includes a sheet cassette CA. The sheet cassette CA stores sheets S to be used in a print job. The type of the sheets S is not particularly limited.

[0019] In a print job, the image forming apparatus 100 supplies a sheet S in a sheet cassette CA to a main transport path MP and transports the sheet S along the main transport path MP. Then, the image forming apparatus 100 prints an image on the sheet S being transported. In other words, the image forming apparatus 100 includes a printing unit 1000 that prints an image on the sheet S being transported.

[0020] The printing unit 1000 includes image forming units 110 for four colors: cyan, magenta, yellow, and black. Each image forming unit 110 forms a toner image of the corresponding color. The configuration of one image forming unit 110 will be described below. The basic configuration of each image forming unit 110 is the same. Therefore, the description of the configuration of the other image forming units 110 will be omitted, as the following description will be used as an example.

[0021] As shown in Fig. 4, the image forming unit 110 includes a developing cartridge 200. The developing cartridge 200 contains toner of a corresponding color and executes a developing process using the toner. The image forming unit 110 also includes a photoconductor drum 111 and a charging device 112. The image forming apparatus 100 also includes one exposure unit 113 for each of the image forming units 110 for four colors. The image forming unit 110 also includes a cleaning device 114.

[0022] When the image forming unit 110 forms an image, the photosensitive drum 111 rotates. The charging device 112 charges the outer peripheral surface of the photosensitive drum 111. The exposure unit 113 exposes the outer peripheral surface of the photosensitive drum 111 to light, and forms an electrostatic latent image on the outer peripheral surface of the photosensitive drum 111. The developing cartridge 200 then supplies toner to the outer peripheral surface of the photosensitive drum 111 as a developing process, and executes a process of developing the electrostatic latent image into a toner image. The toner image on the outer peripheral surface of the photosensitive drum 111 is primarily transferred to an intermediate transfer belt 121, which will be described later. The cleaning device 114 removes toner that has not been transferred to the intermediate transfer belt 121 and remains on the outer peripheral surface of the photosensitive drum 111.

[0023] 3, the printing section 1000 includes a transfer belt unit 120. The printing section 1000 also includes a secondary transfer roller .

[0024] The transfer belt unit 120 is disposed below each image forming unit 110. The transfer belt unit 120 includes an intermediate transfer belt 121. The intermediate transfer belt 121 is an endless belt.

[0025] The intermediate transfer belt 121 is stretched and rotatably supported by multiple rollers including a drive roller 122 (reference numbers for the other rollers are omitted). The intermediate transfer belt 121 contacts the outer circumferential surface of the photoconductor drum 111 and rotates in this state. The drive roller 122 rotates by power transmitted from a belt motor (not shown). The intermediate transfer belt 121 rotates in response to the rotation of the drive roller 122. The intermediate transfer belt 121 corresponds to an "image carrier."

[0026] The transfer belt unit 120 includes primary transfer rollers 123. One primary transfer roller 123 is assigned to each of the colors cyan, magenta, yellow, and black. Each primary transfer roller 123 is disposed on the inner circumferential side of the intermediate transfer belt 121. Each primary transfer roller 123 is disposed opposite a photoconductor drum 111 carrying a toner image of the corresponding color, with the intermediate transfer belt 121 sandwiched therebetween.

[0027] The secondary transfer roller 130 is disposed to face the drive roller 122 with the intermediate transfer belt 121 in between. The secondary transfer roller 130 is in pressure contact with the intermediate transfer belt 121. The secondary transfer roller 130 forms a transfer nip between itself and the intermediate transfer belt 121. The secondary transfer roller 130 corresponds to a "transfer roller."

[0028] Each image forming unit 110 forms a toner image of a corresponding color. Then, each primary transfer roller 123 primarily transfers the toner image onto the outer circumferential surface of the intermediate transfer belt 121. The intermediate transfer belt 121 rotates while carrying the toner image primarily transferred from each photoconductor drum 111 on its outer circumferential surface. While the sheet S is passing through the transfer nip, the sheet S comes into contact with the outer circumferential surface of the intermediate transfer belt 121. The secondary transfer roller 130 forms a transfer electric field between itself and the intermediate transfer belt 121, thereby secondary transferring the toner image onto the sheet S passing through the transfer nip.

[0029] The printing unit 1000 includes a fixing roller pair 140. The fixing roller pair 140 includes a heating roller and a pressure roller. The heating roller has a built-in heater. The pressure roller is in pressure contact with the heating roller to form a fixing nip between the heating roller and the fixing roller pair 140. The fixing roller pair 140 nips the sheet S conveyed from the transfer nip and rotates. That is, the fixing roller pair 140 applies heat and pressure to the sheet S passing through the fixing nip. As a result, the fixing roller pair 140 fixes the toner image transferred to the sheet S to the sheet S. The sheet S is then discharged to the discharge tray ET.

[0030] The image forming apparatus 100 is capable of executing, as a print job, a single-sided print job in which a toner image is printed on only one side of a sheet S, as well as a double-sided print job in which a toner image is printed on both sides of a sheet S. To execute a double-sided print job, the image forming apparatus 100 is provided with a double-sided printing transport path DP.

[0031] The double-sided printing transport path DP branches off from the main transport path MP downstream of the fixing nip in the sheet transport direction, and merges with the main transport path MP upstream of the transfer nip in the sheet transport direction.

[0032] When the job to be executed is a single-sided print job, the sheet S passes through the transfer nip only once, and a single transfer process is performed on the sheet S while it is passing through the transfer nip. After the first transfer process, the sheet S is discharged directly onto the discharge tray ET.

[0033] When the job to be executed is a double-sided printing job, the sheet S passes through the transfer nip twice in order to perform the transfer process once on each of the front and back sides of the sheet S. Specifically, when the sheet S passes through the transfer nip for the first time, the transfer process is performed on one side of the sheet S. After the first transfer process, the sheet S is switched back after the rear end of the sheet S has passed through the fixing nip and before the sheet S is completely discharged onto the discharge tray ET. As a result, the rear end of the sheet S is drawn into the double-sided printing transport path DP.

[0034] Thereafter, the sheet S is transported along the double-sided printing transport path DP. The sheet S is then returned to the main transport path MP from the upstream side of the transfer nip in the sheet transport direction. The sheet S returned to the main transport path MP passes through the transfer nip again. At this time, the orientation of the front and back surfaces of the sheet S is inverted to the opposite orientation from when it passed through the transfer nip the previous time. As a result, when the sheet S passes through the transfer nip for the second time, a transfer process is performed on the other side of the sheet S that is opposite to the one side.

[0035] <Units inside the device> The image forming apparatus 100 includes a plurality of units. Some of the units will be described below.

[0036] As shown in Fig. 5, the image forming apparatus 100 includes a main body unit 1 and a transport unit 2. The main body unit 1 corresponds to a "first unit," and the transport unit 2 corresponds to a "second unit." Fig. 5 illustrates a state in which the rear cover CV is slightly open (a state in which the transport unit 2 is separated from the main body unit 1).

[0037] The main body side unit 1 is mounted inside the main body frame FR. The main body side unit 1 is a unit that has a transfer belt unit 120. That is, the main body side unit 1 has an intermediate transfer belt 121.

[0038] The transport unit 2 is a unit that is mainly responsible for transporting the sheet S. Hereinafter, the transport unit 2 will be described with reference to FIGS.

[0039] The conveying unit 2 has unit side portions 20. The unit side portions 20 are disposed on one side and the other side in the width direction D1. The pair of unit side portions 20 face each other in the width direction D1.

[0040] The transport unit 2 has a transport guide G1 that defines a part of the main transport path MP. The transport guide G1 is located between the pair of unit side portions 20 in the width direction D1. The transport guide G1 defines a part of the main transport path MP together with a transport guide (not shown) of another unit.

[0041] The transport unit 2 also has a transport guide G2 that defines a portion of the double-sided printing transport path DP. The transport guide G2 is located between the pair of unit side parts 20 in the width direction D1. The transport guide G2 defines a portion of the double-sided printing transport path DP together with a transport guide (reference number omitted) provided on the rear cover CV.

[0042] Here, the transport unit 2 has a secondary transfer roller 130. However, the transport unit 2 is a separate unit from the main body side unit 1. In this configuration, the transport unit 2 is positioned relative to the main body side unit 1 in order to form a transfer nip between the intermediate transfer belt 121 and the secondary transfer roller 130.

[0043] The transport unit 2 is rotatable around an axis extending in the width direction D1. Specifically, the main frame FR has a second rotation axis RA2 extending in the width direction D1. The second rotation axis RA2 extends parallel to the first rotation axis RA1. The second rotation axis RA2 supports a lower end of the transport unit 2. The transport unit 2 rotates around the second rotation axis RA2 as a fulcrum so as to swing an end (i.e., an upper end) opposite to the side supported by the second rotation axis RA2. The transport unit 2 is displaceable between a first position and a second position by rotating around the axis of the second rotation axis RA2.

[0044] The first position is a position where the transport unit 2 is positioned relative to the main body side unit 1 inside the main body frame FR. The position of the transport unit 2 shown in FIG. 6 is the first position. When the transport unit 2 is held at the first position (i.e., the transport unit 2 is positioned relative to the main body side unit 1), the secondary transfer roller 130 is pressed against the intermediate transfer belt 121. As a result, a transfer nip is formed between the intermediate transfer belt 121 and the secondary transfer roller 130.

[0045] The second position is a position other than the first position, and is a position where the transport unit 2 is not positioned relative to the body side unit 1. When the transport unit 2 is in the second position, the transport unit 2 cannot be positioned relative to the body side unit 1.

[0046] When the transport unit 2 is held in the first position, a part of the main transport path MP is formed by the transport guide G1 of the transport unit 2 and the transport guides of the other units. Also, when the transport unit 2 is held in the first position and the rear cover CV is closed, a part of the double-sided printing transport path DP is formed by the transport guide G2 of the transport unit 2 and the transport guide of the rear cover CV.

[0047] For example, when a sheet S jams during execution of a print job, the rear cover CV is opened and the transport unit 2 is rotated to the second position to clear the jam. By opening the rear cover CV, the double-sided printing transport path DP is exposed, making it possible to remove the jammed sheet S on the double-sided printing transport path DP. By rotating the transport unit 2 to the second position, the main transport path MP is exposed, making it possible to remove the jammed sheet S on the main transport path MP.

[0048] After the jam clearing operation, the rear cover CV is closed. By closing the rear cover CV, the rear cover CV pushes the transport unit 2. As a result, the transport unit 2 is returned to the first position in synchronization with the closing of the rear cover CV.

[0049] In this configuration, it is necessary to reliably hold the transport unit 2 at the first position during normal times (such as while a print job is being executed). If the transport unit 2 is displaced from the first position while a print job is being executed, the image quality may deteriorate or a jam may occur.

[0050] Therefore, the image forming apparatus 100 includes a positioning member 3. The positioning member 3 positions the transport unit 2 with respect to the main body unit 1. In other words, the positioning member 3 holds the transport unit 2 at a first position. In further other words, the positioning member 3 restricts the rotation of the transport unit 2 from the first position to the second position.

[0051] <Unit positioning> Hereinafter, the structure of the positioning member 3 and its mounting structure to the transport unit 2 will be described with reference to FIGS.

[0052] The positioning member 3 is a hook that can engage with another member. One positioning member 3 is attached to each of a pair of unit side parts 20 of the transport unit 2. The structure of the positioning member 3 and the attachment structure to the transport unit 2 are the same on both sides. For this reason, only one side will be described below, and the other will be omitted as the following description is incorporated herein.

[0053] The positioning member 3 is disposed outward in the width direction D1 of the unit side part 20. The secondary transfer roller 130 and the like are disposed inward in the width direction D1 of the unit side part 20. Note that the outward direction in the width direction D1 refers to a direction from the center of the width direction D1 of the transport unit 2 toward one side or the other side in the width direction D1. The inward direction in the width direction D1 refers to a direction from one side or the other side in the width direction D1 of the transport unit 2 toward the center in the width direction D1.

[0054] The unit side part 20 has a support shaft 21 that supports the positioning member 3 outward in the width direction D1. The support shaft 21 protrudes outward from the unit side part 20 in a columnar or cylindrical shape. The support shaft 21 has a circular outer shape when viewed in the width direction D1. For example, the unit side part 20 is made of resin. The support shaft 21 is molded integrally with the unit side part 20.

[0055] The positioning member 3 has a cylindrical portion 30. When the positioning member 3 is attached to the unit side portion 20, the width direction D1 corresponds to the cylindrical axis direction of the cylindrical portion 30. The positioning member 3 is attached to the unit side portion 20 by inserting the support shaft 21 into the cylindrical portion 30. The cylindrical portion 30 is fitted into the support shaft 21 from the outside in the width direction D1. In the following description, the circumferential direction centered on the cylindrical axis of the cylindrical portion 30 fitted into the support shaft 21 (i.e., the support shaft 21) as viewed from the width direction D1 will be simply referred to as the circumferential direction.

[0056] The cylindrical portion 30 is slidable in the circumferential direction relative to the outer circumferential surface of the support shaft 21. That is, the support shaft 21 supports the positioning member 3 so as to be displaceable in the circumferential direction. Note that the cylindrical portion 30 is also slidable in the width direction D1 relative to the outer circumferential surface of the support shaft 21.

[0057] The positioning member 3 has a hook portion 31. The hook portion 31 is disposed radially outward of the cylindrical portion 30 as viewed in the width direction D1. The hook portion 31 is a portion that extends radially outward (i.e., in a direction away from the cylindrical portion 30) as viewed in the width direction D1 from the cylindrical portion 30, and is a hook-shaped portion that can engage with a boss portion 10 (described later) from one side in the circumferential direction. The hook portion 31 rotates about the cylinder axis of the cylindrical portion 30 as a result of the cylindrical portion 30 being displaced in the circumferential direction.

[0058] In order to hold the conveying unit 2 at the first position using the positioning member 3, the main body side unit 1 has a boss portion 10 (see Figs. 5 and 6) that protrudes in the width direction D1. When viewed from the width direction D1, the boss portion 10 is disposed on a rotation trajectory of the hook portion 31 when the hook portion 31 is rotated around the cylindrical axis of the cylindrical portion 30 (i.e., when the hook portion 31 is rotated in the circumferential direction).

[0059] When the transport unit 2 is in the first position, the hook portion 31 engages with the boss portion 10 so as to embrace the boss portion 10 from one side in the circumferential direction. This causes the hook portion 31 to restrict the rotation of the transport unit 2 from the first position to the second position. As a result, the transport unit 2 is held in the first position. In other words, the transport unit 2 is positioned relative to the main unit 1.

[0060] However, the positioning member 3 is not fixed to the unit side part 20 (i.e., the transport unit 2) and is detachable from the unit side part 20. In this configuration, unless some measure is taken, the cylindrical part 30 may come off the support shaft 21 and the positioning member 3 may fall off the unit side part 20.

[0061] If the positioning member 3 falls off from the unit side portion 20, the hook portion 31 is disengaged from the boss portion 10, causing the transport unit 2 to rotate from the first position to the second position. In other words, the transport unit 2 is displaced relative to the main body side unit 1.

[0062] In order to prevent such inconvenience, the unit side portion 20 has a restricting portion 23. The positioning member 3 also has a restricted portion 32.

[0063] The regulated portion 32 is disposed radially outward from the cylindrical portion 30 and at a different position in the circumferential direction from the hook portion 31, as viewed in the width direction D1. For example, the positioning member 3 has a portion 32a extending radially outward from the cylindrical portion 30, as viewed in the width direction D1, and has a protruding piece protruding from the portion 32a to one side in the circumferential direction as the regulated portion 32. Note that the cylindrical portion 30 is displaceable in the circumferential direction. Therefore, the regulated portion 32 disposed radially outward from the cylindrical portion 30 is rotatable around the cylinder axis of the cylindrical portion 30.

[0064] When viewed from the width direction D1, the restricting portion 23 is disposed at a predetermined position (hereinafter, the predetermined position is referred to as the restricting position) on a rotation trajectory of the restricted portion 32 that rotates around the cylinder axis of the cylindrical portion 30. The restricted portion 32 is disposed at the restricting position by engaging the hook portion 31 with the boss portion 10 from one side in the circumferential direction. As a result, in a state in which the hook portion 31 is engaged with the boss portion 10 from one side in the circumferential direction, the restricting portion 23 overlaps the restricted portion 32 from the outside in the width direction D1.

[0065] In a state in which the restricting portion 23 overlaps the restricted portion 32 from the outside in the width direction D1, even if the restricted portion 32 (i.e., the positioning member 3) tries to move outward in the width direction D1, the restricted portion 32 collides with the restricting portion 23. That is, the restricting portion 23 restricts the outward movement of the positioning member 3 in the width direction D1. As a result, it is possible to prevent the positioning member 3 from falling off the unit side portion 20.

[0066] However, when the positioning member 3 is displaced to the other side in the circumferential direction, the restricting portion 23 and the restricted portion 32 do not overlap in the width direction D1. In this case, the positioning member 3 may fall off the unit side portion 20.

[0067] Therefore, image forming apparatus 100 further includes a torsion coil spring 4. Torsion coil spring 4 is attached to positioning member 3. Torsion coil spring 4 restricts, by its biasing force, displacement of positioning member 3 to the other side in the circumferential direction.

[0068] The torsion coil spring 4 has a wound spring portion 40 (in other words, a coil-shaped portion). The wound spring portion 40 is fitted into the cylindrical portion 30, and thereby disposed on the outer periphery of the cylindrical portion 30. In other words, the cylindrical portion 30 is inserted into the wound spring portion 40. The wound spring portion 40 is fitted into the cylindrical portion 30, and thereby the torsion coil spring 4 is attached to the positioning member 3.

[0069] The torsion coil spring 4 has a first arm 41 extending from one end of the wound spring portion 40 and a second arm 42 extending from the other end of the wound spring portion 40. The first arm 41 and the second arm 42 each extend in a tangential direction of the wound spring portion 40 when viewed from the width direction D1.

[0070] The first arm portion 41 engages with the positioning member 3. Specifically, the positioning member 3 has a first engagement portion 33. The first engagement portion 33 is disposed radially outward of the cylindrical portion 30 when viewed from the width direction D1. The first arm portion 41 engages with the first engagement portion 33.

[0071] The second arm portion 42 engages with the transport unit 2. Specifically, a second engagement portion 22 is provided on the unit side portion 20. An edge portion of an opening 20a penetrating the unit side portion 20 in the width direction D1 functions as the second engagement portion 22. The second arm portion 42 engages with the second engagement portion 22.

[0072] The torsion coil spring 4 generates a force that biases the positioning member 3 to one side in the circumferential direction by engaging the first arm portion 41 with the first engagement portion 33 (i.e., the positioning member 3) and the second arm portion 42 with the second engagement portion 22 (i.e., the unit side portion 20). In other words, the torsion coil spring 4 biases the positioning member 3 in a direction in which the hook portion 31 engages with the boss portion 10 (i.e., to one side in the circumferential direction). In yet other words, the torsion coil spring 4 restricts the displacement of the positioning member 3 to the other side in the circumferential direction.

[0073] This can prevent the positioning member 3 from being displaced to the other side in the circumferential direction. If the positioning member 3 does not displace to the other side in the circumferential direction, the overlap between the regulating portion 23 and the regulated portion 32 in the width direction D1 is maintained, thereby preventing the positioning member 3 from falling off from the unit side portion 20. As a result, the rotation of the transport unit 2 from the first position to the second position can be prevented. In other words, the transport unit 2 can be prevented from being misaligned with respect to the main body side unit 1.

[0074] When the positioning member 3 is attached to the unit side portion 20, the second arm portion 42 is engaged with the temporary fastening portion 34 (see FIG. 10). Then, as shown in FIG. 11, the cylindrical portion 30 is fitted onto the support shaft 21 in a state in which the restricting portion 23 and the restricted portion 32 do not overlap in the width direction D1. Thereafter, as shown in FIG. 12, the positioning member 3 is displaced to one side in the circumferential direction. Also, although not shown in FIG. 12, the second arm portion 42 is hooked from the temporary fastening portion 34 to the second engaging portion 22.

[0075] <Rotation of the transport unit to the first position> When the rear cover CV is opened or closed, the transport unit 2 rotates in sync with the opening and closing of the rear cover CV, and the transport unit 2 is displaced between the first position and the second position. Specific explanations will be given below.

[0076] In the following description, the rotation direction of the rear cover CV when the rear cover CV is rotated from the open position to the closed position is simply referred to as the closing direction, and the rotation direction of the rear cover CV when the rear cover CV is rotated from the closed position to the open position is simply referred to as the opening direction.

[0077] The rear cover CV and the transport unit 2 are disposed so as to have the positional relationship shown in Fig. 5. The position of the rear cover CV shown in Fig. 5 is the open position. In Fig. 5, the counterclockwise direction around the first rotation axis RA1 is the closing direction, and the clockwise direction is the opening direction. The position of the transport unit 2 shown in Fig. 5 is the second position.

[0078] The conveying unit 2 is disposed downstream of the rear cover CV in the closing direction. The second rotation shaft RA2 supporting the conveying unit 2 is located above the first rotation shaft RA1 supporting the rear cover CV when viewed from the width direction D1. The second rotation shaft RA2 is located forward of the first rotation shaft RA1 when viewed from the width direction D1 (i.e., on the other side opposite to one side in the front-rear direction D2).

[0079] As a result, when the rear cover CV rotates from the open position to the closed position while the transport unit 2 is in the second position, the transport unit 2 is pressed by the rear cover CV so as to rotate from the second position to the first position. In other words, the displacement of the transport unit 2 between the first position and the second position can be synchronized with the opening and closing of the rear cover CV.

[0080] The rear cover CV has a first pressing portion 101 that presses the transport unit 2, and also has a second pressing portion 102 that presses the positioning member 3. The transport unit 2 has a unit-side receiving portion 24 that is pressed by the first pressing portion 101. The positioning member 3 has a hook-side receiving portion 35 that is pressed by the second pressing portion 102.

[0081] The first pressing portion 101 is disposed at a position closer to the first rotation axis RA1 than the second pressing portion 102 when viewed from the width direction D1. In other words, the second pressing portion 102 is disposed at a position farther from the first rotation axis RA1 than the first pressing portion 101 when viewed from the width direction D1.

[0082] When the rear cover CV is in the open position and the transport unit 2 is in the second position, the first pressing portion 101 is in contact with the unit-side receiving portion 24, as shown in Fig. 13. As a result, when the rear cover CV is in the open position and the transport unit 2 is in the second position, the rear cover CV rotates from the open position in the closing direction, causing the first pressing portion 101 to start pressing the unit-side receiving portion 24 so that the transport unit 2 rotates from the second position to the first position. Note that in Fig. 13, the positioning member 3 is omitted for ease of viewing.

[0083] After the first pressing portion 101 starts pressing the unit side receiving portion 24 (i.e., while the transport unit 2 is rotating from the second position to the first position), the tip 31a of the hook portion 31 contacts the boss portion 10, as shown in Fig. 14, and the positioning member 3 is displaced in the circumferential direction. In the initial stage, of the tip 31a of the hook portion 31, the outer portion opposite to the inner portion that engages with the boss portion 10 contacts the boss portion 10. Therefore, in the initial stage, the hook portion 31 does not engage with the boss portion 10 (see the upper diagram in Fig. 14).

[0084] As the rear cover CV rotates from the open position in the closing direction (i.e., the conveying unit 2 rotates from the second position to the first position) from a state in which the outer portion of the tip 31a of the hook portion 31 is in contact with the boss portion 10, the positioning member 3 is displaced to the other side in the circumferential direction, which is the direction against the biasing force of the torsion coil spring 4, while keeping the outer portion of the tip 31a of the hook portion 31 in contact with the boss portion 10. Thereafter, the positioning member 3 is displaced to one side in the circumferential direction.

[0085] Specifically, as shown in the upper diagram of FIG. 14, first, an outer portion of the tip 31a of the hook portion 31 comes into contact with a portion of the boss portion 10 on one side in the front-rear direction D2 (hereinafter simply referred to as the one side portion of the boss portion 10). Thereafter, the tip 31a of the hook portion 31 moves from the one side portion of the boss portion 10 and gets over the lowest point P. Then, as shown in the lower diagram of FIG. 14, the tip 31a of the hook portion 31 reaches a portion of the boss portion 10 on the other side opposite to the one side in the front-rear direction D2 (hereinafter simply referred to as the other side portion of the boss portion 10). At this time, an inner portion of the tip 31a of the hook portion 31 comes into contact with the other side portion of the boss portion 10. This causes the hook portion 31 to engage with the boss portion 10.

[0086] The boss portion 10 has a first portion 10a which is an upper portion of the boss portion 10, and a second portion 10b which is a portion located below the first portion 10a. The first portion 10a has an arc-shaped periphery that is convex upward when viewed from the width direction D1. The second portion 10b has a tapered shape (i.e., a substantially triangular shape) that tapers downward from the first portion 10a when viewed from the width direction D1. The second portion 10b protrudes sharply downward from the first portion 10a. In other words, the second portion 10b is a V-shaped portion in a side view that protrudes downward from the first portion 10a. In this configuration, the lowest point P of the boss portion 10 is the tip position on the lower side of the second portion 10b.

[0087] After the contact point of the tip 31a of the hook portion 31 with the boss portion 10 passes the lowest point P of the boss portion 10, the second pressing portion 102 comes into contact with the hook side receiving portion 35 from one side in the circumferential direction, as shown in Fig. 15, and thus the second pressing portion 102 starts to press the hook side receiving portion 35 so as to displace the positioning member 3 to one side in the circumferential direction. Note that in Fig. 15, the transport unit 2 is shown by a dashed line to make the drawing easier to see.

[0088] The second pressing portion 102 and the hook side receiving portion 35 each have a shape as shown in Fig. 16. The second pressing portion 102 has a cover side arm 1021 and a cover side protrusion 1022 protruding from the cover side arm 1021 in the width direction D1. The hook side receiving portion 35 has a hook side arm 351 and a hook side protrusion 352 protruding from the hook side arm 351 in the width direction D1.

[0089] The cover-side projection 1022 contacts the hook-side projection 352 from the other side opposite to the one side in the circumferential direction, and the cover-side projection 1022 presses the hook-side projection 352 from the other side in the circumferential direction to one side. That is, the pressing portion of the second pressing portion 102 that actually presses the hook-side receiving portion 35 is the cover-side projection 102. The pressed portion of the hook-side receiving portion 35 that is actually pressed by the second pressing portion 102 is the hook-side projection 352. In FIG. 16, the outside of the width direction D1 is indicated by "Out" and the inside of the width direction D1 is indicated by "In". In FIG. 16, the pressing direction of the second pressing portion 102 against the hook-side receiving portion 35 due to the rear cover CV rotating in the closing direction is indicated by an arrow D3. The same applies to FIG. 18, which will be referred to later.

[0090] When the tip 31a of the hook portion 31 passes the lowest point P of the boss portion 10, the second pressing portion 102 presses the hook side receiving portion 35, displacing the positioning member 3 to one side in the circumferential direction. As a result, the hook portion 31 engages with the boss portion 10, resulting in the state shown in the lower diagram of FIG. 14. After the hook portion 31 engages with the boss portion 10, the positioning member 3 is biased by the torsion coil spring 4 so as to displace to one side in the circumferential direction, so that the engagement of the hook portion 31 with the boss portion 10 is maintained. Note that, as the hook portion 31 engages with the boss portion 10, the displacement of the positioning member 3 to one side in the circumferential direction is stopped. After the hook portion 31 engages with the boss portion 10, even if the rear cover CV continues to rotate in the closing direction, i.e., even if the second pressing portion 102 continues to press the hook side receiving portion 35, the positioning member 3 does not displace to one side in the circumferential direction.

[0091] Here, the positions of the first rotation shaft RA1 and the second rotation shaft RA2 are different from each other when viewed from the width direction D1. That is, as shown in Fig. 13, when viewed from the width direction D1, the rotation trajectory T2 of the unit side receiving part 24 rotating around the axis of the second rotation shaft RA2 is shifted from the rotation trajectory T1 of the first pressing part 101 rotating around the axis of the first rotation shaft RA1.

[0092] As a result, after the rear cover CV starts to rotate in the closing direction, the pressure applied by the first pressing portion 101 to the unit side receiving portion 24 is released before the rear cover CV reaches the closed position, as shown in Fig. 17. The first pressing portion 101 and the unit side receiving portion 24 rotate while moving away from each other. Note that in Fig. 17, the positioning member 3 is omitted for ease of viewing.

[0093] In addition, after the hook portion 31 engages with the boss portion 10 and the displacement of the positioning member 3 toward one side in the circumferential direction stops, the rear cover CV continues to rotate in the closing direction, so that one of the second pressing portion 102 and the hook side receiving portion 35 elastically deforms in a direction away from the other, as shown in FIG. 18. For example, both the second pressing portion 102 and the hook side receiving portion 35 are made of an elastically deformable resin. For this reason, when one of the second pressing portion 102 and the hook side receiving portion 35 elastically deforms in a direction away from the other, the other may also elastically deform in a direction away from the one. In other words, both of the second pressing portion 102 and the hook side receiving portion 35 may elastically deform in a direction away from each other.

[0094] Before the hook portion 31 engages with the boss portion 10, the cover-side projection 1022 is located on the other side opposite to the one side in the circumferential direction with respect to the hook-side projection 352 (see FIG. 16). As a result, the positioning member 3 is pressed so as to be displaced to one side in the circumferential direction.

[0095] Then, after the hook portion 31 engages with the boss portion 10 and the displacement of the positioning member 3 toward one side in the circumferential direction stops, if the rear cover CV continues to rotate in the closing direction, one of the second pressing portion 102 and the hook side receiving portion 35 elastically deforms in a direction away from the other (see the upper diagram of FIG. 18). As a result, the second pressing portion 102 rides over the hook side receiving portion 35, and the second pressing portion 102 reaches one side in the circumferential direction relative to the hook side receiving portion 35 (see the lower diagram of FIG. 18). Specifically, the cover side projection 1022 rides over the hook side projection 352, and the cover side projection 1022 reaches one side in the circumferential direction relative to the hook side projection 352. As a result, the pressing of the second pressing portion 102 against the hook side receiving portion 35 is released.

[0096] In this embodiment, when the rear cover CV is rotated in the closing direction until the hook portion 31 and the boss portion 10 engage with each other, that is, until the secondary transfer roller 130 (i.e., the transport unit 2) is appropriately pressed against the intermediate transfer belt 121 (i.e., the main body side unit 1) on the drive roller 122, the pressure applied by the second pressing portion 102 against the hook side receiving portion 35 is released. At this point, the pressure applied by the first pressing portion 101 against the unit side receiving portion 24 has already been released. In other words, in a state in which the secondary transfer roller 130 is appropriately pressed against the intermediate transfer belt 121 on the drive roller 122, the rear cover CV is not pressing against the transport unit 2.

[0097] As a result, when the transport unit 2 is held in the first position and the rear cover CV is held in the closed position, no pressing force is applied from the transport unit 2 to the rear cover CV. Note that, even if the rear cover CV does not press the transport unit 2 when the transport unit 2 is held in the first position, the secondary transfer roller 130 is held in a state of being pressed against the intermediate transfer belt 121 on the drive roller 122 because the hook portion 31 is engaged with the boss portion 10.

[0098] If the transport unit 2 is held in the first position by continuously pressing the rear cover CV against the transport unit 2, the rear cover CV may be deformed due to the pressing force applied to the rear cover CV. To prevent this from happening, measures such as increasing the rigidity of the rear cover CV must be taken. For example, measures such as making the rear cover CV thicker or adding ribs to the rear cover CV are required. If such measures are taken, the image forming apparatus 100 will become larger.

[0099] On the other hand, in this embodiment, the transport unit 2 can be held in the first position without continuously pressing the rear cover CV against the transport unit 2. This eliminates the need to increase the rigidity of the rear cover CV. As a result, the transport unit 2 can be positioned without increasing the size of the image forming apparatus 100.

[0100] In this embodiment, the position of the lower tip of the second portion 10b of the boss portion 10 is offset toward one side (i.e., rearward) in the front-rear direction D2 from the center position of a circle including the outer periphery of the first portion 10a when viewed from the width direction D1. This allows the tip 31a of the hook portion 31 to quickly pass through the lowest point P during rotation of the conveying unit 2 caused by the rear cover CV pressing the conveying unit 2.

[0101] After the tip 31a of the hook portion 31 passes the lowest point P, the positioning member 3 tries to displace to one side in the circumferential direction due to the biasing force of the torsion coil spring 4. In other words, after the tip 31a of the hook portion 31 passes the lowest point P, a new force is generated to rotate the transport unit 2 toward the first position. This makes it possible to reduce the force for closing the rear cover CV.

[0102] <Rotation of the transport unit to the second position> When the rear cover CV is in the closed position and the transport unit 2 is held in the first position (i.e., when the hook portion 31 is engaged with the boss portion 10), the cover-side projection 1022 of the second pressing portion 102 is located on one circumferential side of the hook-side projection 352 of the hook-side receiving portion 35. In this state, when the rear cover CV rotates from the closed position in the opening direction, the cover-side projection 1022 engages with the hook-side projection 352 from one circumferential side.

[0103] Then, when the rear cover CV is further rotated in the opening direction, the cover-side projection 1022 of the second pressing portion 102 presses the hook-side projection 352 of the hook-side receiving portion 35 from one circumferential side. As a result, the positioning member 3 is displaced to the other circumferential side against the biasing force of the torsion coil spring 4.

[0104] As the positioning member 3 is displaced to the other side in the circumferential direction, the tip 31a of the hook portion 31 reaches the lowest point P and passes over the lowest point P. That is, the tip 31a of the hook portion 31 passes from the other side portion of the boss portion 10, passes the lowest point P, and reaches the one side portion of the boss portion 10. As a result, the engagement of the hook portion 31 with the boss portion 10 is released.

[0105] In this embodiment, by rotating the rear cover CV from the closed position to the open position, the positioning member 3 releases the positioning of the transport unit 2 relative to the main body unit 1, and the transport unit 2 can be rotated from the first position to the second position. From the worker's perspective, it is convenient because the transport unit 2 can be brought to the second position simply by opening the rear cover CV.

[0106] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0107] 1 Main unit (first unit) 2 Transport unit (second unit) 3 Positioning member 10 Boss part 10a Part 1 10b Part 2 21 Support shaft 24 Unit side receiving part 30 Cylindrical section 31 Hook part 31a Tip 35 Hook side receiving part 100 Image forming device 101 First pressing part 102 Second pressing part 121 Intermediate transfer belt (image carrier) 130 Secondary transfer roller (transfer roller) CV Rear Cover (Cover) FR Main frame P lowest point RA1 1st rotating shaft RA2 2nd rotating shaft S Seat

Claims

1. a cover that is movable between a closed position that covers an inside of the main body frame from one side in a second direction that is perpendicular to the horizontal direction and an open position that is a position other than the closed position by rotating about an axis of a first rotating shaft that extends in a first direction perpendicular to a vertical direction; a first unit that is attached to the inside of the main body frame and has a boss portion; a second unit that is disposed downstream of the cover in a closing direction, which is a direction from the open position toward the closed position, and that is displaceable between a first position that is positioned relative to the first unit and a second position that is a position other than the first position by rotating about an axis of a second rotation shaft that extends parallel to the first rotation shaft at a position above the first rotation shaft and on the other side opposite to the one side of the first rotation shaft in the second direction; a positioning member attached to the second unit and configured to hold the second unit in the first position; a torsion coil spring attached to the positioning member, The positioning member is a cylindrical portion whose cylindrical axis direction is the first direction; a hook portion that is disposed radially outward of the cylindrical portion when viewed from the first direction, is engageable with the boss portion so as to embrace the boss portion from one side in a circumferential direction about a cylindrical axis of the cylindrical portion, and restricts rotation of the second unit from the first position to the second position by engaging with the boss portion when the second unit is in the first position, the second unit has a support shaft into which the cylindrical portion is fitted and which supports the positioning member so as to be displaceable in the circumferential direction, the torsion coil spring biases the positioning member toward one side in the circumferential direction, which is a direction in which the hook portion engages with the boss portion, The cover has a first pressing portion and a second pressing portion, the second unit has a unit side receiving portion that receives a pressing force from the first pressing portion, the positioning member has a hook-side receiving portion that receives a pressing force from the second pressing portion, When the cover rotates from the open position in the closing direction, the first pressing portion starts to press the unit side receiving portion so that the second unit rotates toward the first position, after the first pressing portion starts to press the unit side receiving portion, the tip of the hook portion comes into contact with the boss portion, and the positioning member is displaced to the other side in the circumferential direction, which is a direction against the biasing force of the torsion coil spring, After the contact point of the tip of the hook portion with the boss portion passes through the lowest point of the boss portion when viewed from the first direction, the second pressing portion contacts the hook side receiving portion from one side in the circumferential direction, and thus the second pressing portion begins to press the hook side receiving portion so that the positioning member is displaced to one side in the circumferential direction, and the positioning member is displaced to one side in the circumferential direction so that the hook portion engages with the boss portion, after the cover starts to rotate in the closing direction, by the time the cover reaches the closed position, the positions of the first rotation shaft and the second rotation shaft differ from each other when viewed from the first direction, so that the unit side receiving portion is separated from the first pressing portion, After the displacement of the positioning member to one side in the circumferential direction stops as the hook portion engages with the boss portion, the cover continues to rotate in the closing direction, causing one of the second pressing portion and the hook side receiving portion to elastically deform in a direction away from the other, causing the second pressing portion to overcome the hook side receiving portion, and releasing the pressure applied by the second pressing portion to the hook side receiving portion.

2. When viewed from the first direction, the boss portion A first portion having an arcuate periphery; a second portion that is V-shaped in a side view and protrudes downward from the first portion, a tip end position of the second portion of the boss portion is the lowest point, 2 . The unit positioning mechanism according to claim 1 , wherein a tip position of the second portion is offset to one side in the second direction from a center position of a circle including an outer periphery of the first portion.

3. 2. The unit positioning mechanism according to claim 1, wherein when the cover rotates from the closed position to the open position, the second pressing portion presses the hook side receiving portion from one side in the circumferential direction so that the positioning member is displaced to the other side in the circumferential direction against the biasing force of the torsion coil spring, thereby releasing the engagement of the hook portion with the boss portion.

4. A unit positioning mechanism according to any one of claims 1 to 3, the first unit is a unit having an image carrier that carries an image, the second unit is a unit having a transfer roller, When the second unit is held at the first position, the image carrier and the transfer roller are brought into pressure contact with each other to form a transfer nip between the image carrier and the transfer roller; An image forming apparatus that conveys a sheet to the transfer nip and transfers the image onto the sheet.

Images