JP6579060B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a transport unit that opens and closes a transport path.

  An image forming apparatus such as a copying machine or a printer includes an apparatus main body and a conveyance unit rotatably provided on the apparatus main body, and conveys a sheet on which image formation is performed between the apparatus main body and the conveyance unit. A configuration in which a path is formed is common. In this configuration, a paper jam generated in the transport path can be handled by rotating the transport unit.

  In order to lock the transport unit to the apparatus main body in a state where the transport path is formed, the transport unit is provided with a hook, and the apparatus main body is provided with a boss for locking the hook. An image forming apparatus is described. The hook is biased in a direction to be locked to the boss by a biasing member such as a torsion coil spring. When the transport unit is rotated in the direction to form the transport path, the hook interferes with the boss and rotates in a direction against the urging force of the urging member, and then engages with the boss by the return force of the urging member. It is like that.

JP 2004-240329 A

  However, in the image forming apparatus described in Patent Document 1, when the return force of the urging member is not sufficient, a member that presses the conveyance unit from the outside to forcibly rotate or presses from the outside is provided. It was necessary to do. In addition, when an external force is applied to the transport unit, the hook and boss may become unstable, and the transport unit may not completely rotate to the transport path formation position, and the transport path may not be formed correctly. is there.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of reliably locking the transport unit to the apparatus main body with the restoring force of the urging member without applying a force from the outside.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a conveyance unit that is rotatably provided in an apparatus main body and forms or opens a sheet conveyance path between the apparatus main body and the apparatus main body. The transport unit includes an image carrier and a transfer member that are in pressure contact with each other when the transport unit rotates to the transport path forming position, and the transport unit has a rotation trajectory in the transport path forming direction. The peak position of the reaction force that the transfer member receives from the image carrier is provided in front of the transport path forming position, and the transport path is formed between the apparatus main body and the transport unit. Each of the engaging portions is engaged with each other in a state where one of the engaging portions is a boss, and the other engaging portion is rotatably provided and engages with the boss. And the foot A biasing member that biases the member in a direction to engage with the boss, and the hook member abuts the boss during the rotation of the transport unit in the transport path forming direction. After rotating in a direction against the urging force, the urging member is rotated by a restoring force to be engaged with the boss until the transport unit is rotated to the peak position of the reaction force. The return force of the urging member is maintained.

  By adopting such a configuration, the hook member is engaged with the boss by the restoring force of the urging member maintained at the maximum value at the same time as the reaction force received by the transport unit passes the peak. It can be automatically engaged with the boss. Therefore, there is no need to forcibly push the carrier unit into rotation. Furthermore, since a member necessary for pressing from the outside becomes unnecessary, the number of parts can be reduced and the cost can be reduced.

  In the image forming apparatus according to the aspect of the invention, the hook member includes a guided surface that is guided while being in contact with the boss and sliding with the boss when the transport unit rotates in the transport path forming direction. An engaging portion that is provided closer to the pivot fulcrum of the hook member than the guided surface and engages with the boss at the transfer path forming position. The guide surface may be formed along a circumferential direction of a circle centered on a moving fulcrum, and the guided surface may be formed to intersect at an acute angle with respect to the engagement surface.

  By adopting such a configuration, the return force of the urging member can be maintained until the transport unit rotates to the peak position of the reaction force.

  According to the present invention, the hook member is automatically engaged with the boss by the return force of the urging member maintained at the maximum value at the same time as the reaction force received by the transport unit passes the peak. Can be engaged.

1 is a front view schematically showing an overall configuration of a color printer according to an embodiment of the present invention. FIG. 2 is a perspective view illustrating a transport unit of a color printer according to an embodiment of the present invention. In the color printer which concerns on one Embodiment of this invention, it is a front view which shows the hook member of a conveyance unit. In the color printer which concerns on one Embodiment of this invention, it is a sectional side view which shows the conveyance unit rotated to the conveyance path | route formation position. FIG. 3 is a perspective view showing an engaging portion of the apparatus main body in the color printer according to the embodiment of the present invention. In the color printer which concerns on one Embodiment of this invention, it is a sectional side view which shows the guide part of a secondary transfer roller and a registration roller, FIG. 6 (A) is a guide part of a secondary transfer roller, FIG.6 (B) is FIG. The guide part of a registration roller is shown. In the color printer which concerns on one Embodiment of this invention, it is a graph which shows the relationship between the rotation position of a conveyance unit, the reaction force which a conveyance unit receives, and the reset force of a torsion coil spring. In the color printer which concerns on one Embodiment of this invention, it is a side view which shows the engagement process of a hook member and a boss | hub, FIG. 8 (A) shows the hook member of a comparative example, FIG. 8 (B) is this embodiment. The hook member is shown.

  Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings.

  First, the overall configuration of a color printer 1 as an image forming apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing the internal structure of the color printer 1. In the following description, the front side in FIG. 1 is the front side (front side) of the color printer, and the horizontal direction is based on the direction of the color printer as viewed from the front side.

  The apparatus main body 2 of the color printer 1 includes a paper feed cassette 4 that stores paper S, a paper feed device 5 that feeds the paper S from the paper feed cassette 4, and an image forming unit that forms an image on the fed paper S 6, a fixing device 7 that fixes the image formed on the paper S to the paper, and a discharge device 9 that discharges the paper S on which the image is fixed to the paper discharge tray 8.

  The image forming unit 6 includes four image forming units 11 and an intermediate transfer unit 12. Each image forming unit 11 includes a photosensitive drum 14 that is rotatably provided, a charging device 15 that is sequentially arranged around the photosensitive drum 14 along the rotation direction of the photosensitive drum, a developing device 16, and a cleaning device. 17.

  The intermediate transfer unit 12 includes an intermediate transfer belt 20 that circulates between the drive roller 19a and the driven roller 19b, and four primary transfer rollers 21 that are arranged in the front-rear direction in the hollow portion of the intermediate transfer belt 20. ,have. The primary transfer roller 21 is opposed to the photosensitive drum 14 via the intermediate transfer belt 20, and forms a primary transfer portion 22 between the photosensitive drum 14 and the intermediate transfer belt 20. A secondary transfer roller 24 as a transfer member faces the right end portion of the intermediate transfer belt 20 to form a secondary transfer portion 25 between the intermediate transfer belt 20 and the secondary transfer roller 24. .

  An outer cover 27 is supported on the right side surface of the apparatus main body 2 so as to be rotatable about the lower end. Further, a transport unit 28 is supported inside the outer cover 27 so as to be rotatable about the lower end. A transport path 31 for the paper S is formed between the transport unit 28 and the apparatus main body 2. The conveyance path 31 is formed so as to extend upward from the paper feeding device 5 and to the paper discharge device 9 through the secondary transfer unit 25 and the fixing device 7. The secondary transfer roller 24 forming the secondary transfer unit 25 is rotatably supported by the transport unit 28. Further, a registration roller pair 33 is provided in the transport path 31 between the paper feeding device 5 and the secondary transfer unit 25. One registration roller 34 of the registration roller pair 33 is supported by the apparatus main body 2, and the other registration roller 35 is supported by the transport unit 28. A duplex conveyance path 37 for duplex printing is formed between the conveyance unit 28 and the outer cover 27.

  Next, an image forming operation will be described. In each image forming unit 11, after the surface of the photosensitive drum 14 is charged by the charging device 15, exposure corresponding to the image data is performed on the photosensitive drum 14, and electrostatic latent images are formed on the surface of the photosensitive drum 14. An image is formed. The electrostatic latent image is developed into a corresponding color toner image by the developing device 16, and the toner image is primarily transferred onto the surface of the intermediate transfer belt 20 in the primary transfer unit 22. Each image forming unit 11 sequentially repeats the above operation, whereby a full-color toner image is formed on the intermediate transfer belt 20. The toner remaining on the photosensitive drum 14 is removed by the cleaning device 17.

  On the other hand, the sheet S sent from the sheet feeding cassette 4 to the conveyance path 31 by the sheet feeding device 5 is conveyed to the secondary transfer unit 25 by the registration roller pair 33 in synchronization with the above-described image forming operation, and is subjected to secondary transfer. In the section 25, the full color toner image on the intermediate transfer belt 20 is secondarily transferred to the paper S. The sheet S on which the toner image is secondarily transferred is conveyed through the conveyance path 31 and the toner image is fixed on the sheet by the fixing device 7. The paper S on which the toner image is fixed is discharged from the paper discharge device 9 to the paper discharge tray 8.

  Next, the transport unit 28 will be described with reference to FIG. FIG. 2 is a perspective view showing the transport unit. The transport unit 28 includes an inner guide part 41 that forms one guide surface of the transport path 31, an outer guide part 42 that forms one guide surface of the duplex printing path 37, and a pair of side plates 43 that face each other in the front-rear direction. It is equipped with.

  The inner guide portion 41 is formed so as to be convex inwardly, and a plurality of ribs are formed along the transport direction. The other registration roller 35 of the registration roller pair 33 is rotatably supported slightly below the top of the inner guide portion 41, and the secondary transfer roller 24 is rotatably supported slightly above the top. Yes. Both ends of the rotation shaft 35a of the other registration roller 35 and both ends of the rotation shaft 24a of the secondary transfer roller 24 protrude outward from the side plate 43, respectively. The outer guide part 42 is formed so as to be convexly convex outward, and a plurality of ribs are formed along the transport direction. Further, a roller (not shown) that rotates along the transport direction is supported on the outer guide portion 42 at a predetermined interval along the transport direction.

  Support shafts 45 that protrude in opposite directions are formed at the lower ends of the pair of side plates 43. A hook member 47 and an urging member 48 as an engaging portion 46 that can be engaged with the apparatus main body 2 are supported on the upper side of each side plate 43.

  With reference to FIG. 3, the engaging portion 46 (the hook member 47 and the biasing member 48) will be described. FIG. 3 is a front view showing the hook member and the biasing member.

  The hook member 47 includes a shaft portion 51 that is rotatably supported by the side plate 43, and a main body portion 52 provided at one end of the shaft portion 51. The main body portion 52 has a substantially fan shape centered on the shaft portion 51. A hook portion 53 that protrudes in a circumferential direction of a circle centering on the shaft portion 51 (a forward direction of the rotation direction of the main body portion 52) is formed at the tip of one side edge of the main body portion 52. The hook portion 53 has a tapered shape toward the front end side in the circumferential direction, and has a guided surface 54 radially outside the shaft portion 51 and an engagement surface 55 on the inside. The guided surface 54 has a first inclined surface 54 a and a second inclined surface 54 b that bends at an obtuse angle with respect to the first inclined surface 54 a in order toward the tip of the hook portion 53. The engagement surface is formed along the circumferential direction of a circle centered on the shaft portion 51. With such a shape, the second inclined surface 54b of the guided surface 54 and the engagement surface 55 intersect at an acute angle. The angle between the first inclined surface 54a and the second inclined surface 54b and the angle between the second inclined surface 54b and the engaging surface 55 are formed in a curved shape. A torsion coil spring 48 as an urging member 48 is fitted on the shaft portion 51.

  As shown in FIG. 2, the hook member 47 is supported in such a posture that the shaft portion 51 is pivotally supported by the side plate 43 and the hook portion 53 faces upward by a torsion coil spring 48.

  In the transport unit 28 in which the hook member 47 is supported in this manner, the support shaft 45 formed at the lower ends of the pair of side plates 43 is supported by a shaft hole (not shown) provided in the apparatus main body 2. . As a result, the transport unit 28 can rotate between a transport path forming position where the transport path 31 is formed between the transport unit 28 and the transport path opening position where the transport path 31 is opened.

  As shown in FIG. 4, when the transport unit 28 rotates to the transport path formation position, a transport path 31 is formed between the transport unit 28 and the apparatus main body 2. FIG. 4 is a side view showing the transport unit rotated to the transport path forming position.

  Further, the other registration roller 35 is pressed against one registration roller 34. Further, the secondary transfer roller 24 is brought into pressure contact with the intermediate transfer belt 20 wound around the drive roller 19a, so that the secondary transfer portion 25 is formed. Here, the pressing force of one registration roller 34 and the reaction force generated on the other registration roller 35 are in opposite directions. Further, the pressing force of the intermediate transfer belt 20 and the reaction force generated in the secondary transfer roller 24 are in opposite directions.

  The apparatus main body 2 includes an engaging portion 61 that engages with the hook member 47 when the transport unit 28 is rotated to the transport path opening position, the rotation shaft 24 a of the secondary transfer roller 24, and the other registration roller 35. Guide portions 62 and 63 for guiding the rotation shaft 35a are formed.

  With reference to FIGS. 5 and 6, the engaging portion 61, the secondary transfer roller guide portion 62, and the registration roller guide portion 63 formed in the apparatus main body 2 will be described. FIG. 5 is a perspective view showing the periphery of the engaging portion, FIG. 6A is a side view showing the transfer roller guide portion, and FIG. 6B is a side view showing the registration roller guide portion. FIG. 5 also shows a hook member.

  As shown in FIG. 5, the engaging portion 61 is a boss 61 that can be engaged with a hook member 47 provided in the transport unit 28, and is erected below the secondary transfer portion 25 in the front-rear direction. Has been.

  The secondary transfer roller guide portion 62 is formed above the boss 61 as shown in FIG. As shown in FIG. 6 (A), the secondary transfer roller guide unit 62 sequentially enters the entrance unit 62a along the moving direction of the secondary transfer roller 24 when the transport unit 28 is rotated to the transport path formation position. And a recess 62b and a contact portion 62c. The inlet 62a is formed along the moving direction of the secondary transfer roller 24 when the transport unit 28 is rotated to the transport path forming position. The recess 62b is formed to be recessed in the direction toward the axis A1 of the drive roller 19a around which the intermediate transfer belt 20 is wound when the transport unit 28 is rotated to the transport path forming position. The contact portion 62c is formed along a direction that intersects the moving direction of the secondary transfer roller 24 when the transport unit 28 is rotated to the transport path forming position.

  The registration roller guide portion 63 is formed below the secondary transfer roller guide portion 62. As shown in FIG. 6B, the registration roller guide portion 63 is formed so as to be recessed in the direction toward the axis A2 of one of the registration rollers 34 when the conveyance unit 28 rotates to the conveyance path formation position. Has been.

  Next, when the transport unit 28 is rotated to the transport path forming position, the reaction force received by the secondary transfer roller 24 from the intermediate transfer belt 20 wound around the drive roller 19a and the one registration roller 34 to the other. The reaction force received by the registration roller 35 will be described with reference to FIGS. 6A and 6B and the upper graph of FIG. The upper graph in FIG. 7 is a graph showing the relationship between the position of the transport unit on the rotation trajectory of the transport unit to the transport path formation position and the reaction force received by the transport unit. The horizontal axis indicates the position of the transport unit in the rotation locus, and the vertical axis indicates the reaction force. The two-dot chain line in the graph is the reaction force received by the secondary transfer roller, the chain line is the reaction force received by the registration roller, and the solid line is the sum of the reaction force received by the secondary transfer roller and the reaction force received by the registration roller, that is, the transport unit. Indicates the reaction force received by.

  As the transport unit 28 is rotated from the transport path opening position toward the transport path forming position, the secondary transfer roller 24 comes into contact with the intermediate transfer belt 20 before long, as shown by the two-dot chain line in the graph. In addition, the reaction force received by the secondary transfer roller 24 gradually increases. Then, as shown in FIG. 6A, when the end portion of the rotation shaft 24a of the secondary transfer roller 24 starts to be guided along the inlet portion 62a of the secondary transfer roller guide portion 62 (see arrow B1). Since the secondary transfer roller 24 is also pressed against the tangential direction of the intermediate transfer belt 20, the degree of increase in the reaction force is increased. And when the rotating shaft 24a reaches the angle | corner of the entrance part 62a and the recessed part 62b, reaction force will become a peak. Thereafter, when the end of the rotating shaft 24a of the secondary transfer roller 24 comes into contact with the contact portion 62c, the pressure in the tangential direction of the intermediate transfer belt 20 is released and the reaction force is once reduced. By the subsequent rotation of the transport unit 28, the rotary shaft 24a is guided to the front end side in the recess 62b (see arrow B2), so that the reaction force gradually increases again.

  On the other hand, the end of the rotation shaft 35a of the other registration roller 35 is moved in the direction toward the axis A2 of one registration roller 34 by the registration roller guide 63 when the conveyance unit 28 is rotated in the conveyance path forming direction. (See arrow B3), the reaction force received by the other registration roller 35 increases linearly as the transport unit 28 rotates in the transport path forming direction, as indicated by the chain line in the graph. I will do it.

  The reaction force received by the transport unit 28 is the sum of the reaction force received by the secondary transfer roller 24 and the reaction force received by the other registration roller 35, and as shown by the solid line in the upper graph of FIG. In the rotation trajectory of 28 in the transport path forming direction, there is a peak before the transport path forming position.

  Next, with respect to the engagement process between the hook member 47 and the boss 61 and the restoring force of the torsion coil spring 48 when the transport unit 28 is rotated to the transport path forming position, the lower graph of FIG. 8 (A) and FIG. 8 (B) will be described. The lower graph of FIG. 7 is a graph showing the relationship between the position of the transport unit on the trajectory of the transport unit to the transport path formation position and the return force of the torsion coil spring 48. The horizontal axis indicates the position of the transport unit in the rotation locus, and the vertical axis indicates the return force. The chain line in the graph indicates the hook member of the conventional example, and the solid line indicates the hook member of the present embodiment. FIG. 8A shows the engagement process of the hook member of the comparative example, and FIG. 8B shows the engagement process of the hook member of this embodiment.

  A conventional hook member is used as a comparative example. When compared with the hook portion 53 of the hook member 47 of the present embodiment, the hook portion 53 of the hook member 47 ′ having the conventional shape has a second inclined surface 54 b of the guided surface 54 as shown in FIG. It has a shape curved in an arc shape toward the front end side in the circumferential direction.

  First, a process in which the hook member 47 ′ of the comparative example is engaged with the boss will be described with reference to FIG. When the transport unit 28 rotates in the transport path forming direction, first, the first inclined surface 54a of the hook portion 53 comes into contact with the outer peripheral surface of the boss 61 and is pressed by the boss 61 while sliding on the outer peripheral surface. . As a result, the main body 52 starts to rotate counterclockwise in FIG. 8A around the shaft 51 against the urging force of the torsion coil spring 48. When the transport unit 28 is further rotated, the second inclined surface 54b comes into contact with the outer peripheral surface of the boss 61 and starts to slide. When the vertex of the second inclined surface 54b reaches the lower vertex of the outer peripheral surface of the boss 61, the rotation angle of the main body 52 becomes the largest, and the displacement amount of the torsion coil spring 48, that is, the restoring force is the highest. Become.

  Even after the apex of the second inclined surface 54b exceeds the lower apex of the outer peripheral surface of the boss 61, the second inclined surface 54b slides along the outer peripheral surface of the boss 61. It rotates in the clockwise direction of FIG. That is, the restoring force of the torsion coil spring 48 decreases. When the second inclined surface 54 b is detached from the outer peripheral surface of the boss 61, the engaging surface 55 is engaged with the outer peripheral surface of the boss 61 by the restoring force of the torsion coil spring 48.

  As described above, in the case of the hook portion 53 of the hook member 47 ′ of the comparative example, as shown by the chain line in the lower graph of FIG. The restoring force of the spring 48 has a peak at a predetermined position (a position where the vertex of the second inclined surface 54b reaches the lower vertex of the boss 61), and gradually decreases after the peak.

  On the other hand, in the hook member 47 of the present embodiment, as shown in FIG. 8B, when the transport unit 28 rotates in the transport path forming direction, the second inclined surface 54a of the hook portion 53 is moved to the second position. The inclined surface 54b abuts on the outer peripheral surface of the boss 61 and is pressed by the boss 61 while sliding on the outer peripheral surface, so that the main body portion 52 is centered on the shaft portion 51 against the urging force of the torsion coil spring 48. As shown in FIG. 8B, it starts to rotate counterclockwise. In the hook portion 53 of the present embodiment, when the corner between the second inclined surface 54b and the engaging surface 55 reaches the lower vertex of the outer peripheral surface of the boss 61, the rotation angle of the main body 52 is the largest. Thus, the displacement amount of the torsion coil spring 48, that is, the restoring force is increased.

  Thereafter, the corner portion slides over the lower apex of the outer peripheral surface of the boss 61, but during this time, the displacement amount of the torsion coil spring 48 hardly changes. That is, the restoring force of the torsion coil spring 48 is maintained. When the corner portion is detached from the outer peripheral surface of the boss 61, the engaging surface 55 is engaged with the outer peripheral surface of the boss 61 by the restoring force of the torsion coil spring 48.

  As described above, in the case of the hook portion 53 of the hook member 47 of the present embodiment, as shown by the solid line in the lower graph of FIG. The return force of the spring 48 has a peak at a predetermined position (a position where the corner between the second inclined surface 54b and the engagement surface 55 reaches the lower vertex of the outer peripheral surface of the boss 61), and a predetermined rotation range. Within, the peak value is maintained and then decreases rapidly.

  As shown in the upper and lower graphs of FIG. 7, the hook member 47 of the present embodiment has a torsion coil up to the peak position of the reaction force received by the transport unit 28 in the rotation trajectory of the transport unit 28 to the transport path formation position. The return force of the spring 48 is formed so as to maintain a value higher than a predetermined value.

  When the transport unit 28 having the hook member 47 having the above configuration is rotated from the transport path opening position to the transport path forming position, the secondary transfer roller 24 and the other registration roller 35 of the transport unit 28 are connected to each other. A reaction force as shown in the upper graph of FIG. 7 is applied from the intermediate transfer belt 20 of the main body 2 and one of the registration rollers 34, and the transport unit 28 moves along the transport path in the transport path formation direction. The reaction force reaches a peak on the front side of the formation position.

  On the other hand, in the hook member 47 of the transport unit 28, the restoring force of the torsion coil spring 48 is maintained at a substantially maximum value until the reaction force received by the transport unit 28 reaches a peak. Then, at the same time as the reaction force received by the transport unit 28 passes the peak, the hook 53 is engaged with the boss 61 by this restoring force. Further, this restoring force is higher than the restoring force of the hook member 47 'of the conventional example by the difference indicated by D in the lower graph of FIG. Therefore, the hook portion 53 and the boss 61 can be engaged with a higher restoring force than the conventional hook member 47 ′.

  As described above, according to the color printer 1 of the present invention, when the transport unit 28 is rotated to the transport path forming position, the hook member 47 is automatically moved to the boss 61 only by the restoring force of the torsion coil spring 48. Can be engaged. Therefore, there is no need to forcibly push the conveyance unit 28 into rotation. Furthermore, since a member necessary for pressing from the outside becomes unnecessary, the number of parts can be reduced and the cost can be reduced.

  Further, since the hook portion 53 is engaged with the boss 61 after the torsion coil spring 48 is displaced so that the restoring force becomes the highest, the hook portion 53 and the boss 61 are reliably engaged. Therefore, the transport unit 28 can be reliably locked at the transport path forming position, and the transport path can be always formed correctly.

  Furthermore, since the above description of the embodiment of the present invention describes a preferred embodiment of the paper feeding device and the image forming apparatus according to the present invention, various technically preferable limitations are attached. However, the technical scope of the present invention is not limited to these embodiments unless specifically described to limit the present invention. That is, the above-described components in the embodiment of the present invention can be appropriately replaced with existing components and the like, and various variations including combinations with other existing components are possible. The description of the embodiment of the present invention described above does not limit the contents of the invention described in the claims.

1 Color printer (image forming device)
2 Device body 20 Intermediate transfer belt (image carrier)
24 Secondary transfer roller (transfer member)
28 Transport unit 31 Transport path 46 Engagement section 47 Hook member 48 Torsion coil spring (biasing member)
54 Guided surface 55 Engagement surface 61 Boss (engagement part)

Claims (2)

A transport unit that is rotatably provided in the apparatus body and forms or opens a sheet transport path with the apparatus body;
The apparatus main body and the transport unit each include an image carrier and a transfer member that are pressed against each other when the transport unit is rotated to a transport path forming position that forms the transport path. In the rotation trajectory in the path forming direction, the peak position of the reaction force received by the transfer member from the image carrier is provided so as to be closer to the front side than the transport path forming position,
The apparatus main body and the transport unit each have an engaging portion that engages with each other in a state where the transport path is formed,
One of the engaging portions is a boss,
The other engaging portion is a hook member that is rotatably provided and engages the boss, and an urging member that urges the hook member in a direction to engage the boss,
The hook member abuts against the boss during the rotation of the transport unit in the transport path forming direction and rotates in a direction against the biasing force of the biasing member, and then the return force of the biasing member Provided to rotate and engage with the boss,
The hook member is
When the transport unit rotates in the transport path forming direction, the first inclined surface is sequentially brought into contact with the boss and guided while sliding with the boss, and is inclined at an obtuse angle with respect to the first inclined surface. A guided surface having a second inclined surface;
An engagement surface that is provided closer to the pivot fulcrum of the hook member than the guided surface and engages the boss at the transport path forming position;
The engagement surface is formed along a circumferential direction of a circle centered on the rotation fulcrum,
The guided surface is formed such that the second inclined surface intersects the engagement surface at an acute angle,
Before the transport unit rotates to the peak position of the reaction force, the boss comes into contact with the first inclined surface of the guided surface of the hook member, and the hook member biases the biasing member. The return force of the urging member is increased by rotating in a direction against the movement of the urging member, and the boss is in contact with the second inclined surface of the guided surface of the hook member. The image forming apparatus according to claim 1, wherein a return force of the biasing member is maintained until the force is rotated to a peak position.   The apparatus main body includes a guide portion that guides the transfer member toward the image carrier,
  The guide portion is
  An inlet formed along the moving direction of the transfer member when the transport unit is rotated to the transport path forming position;
  A concave portion that is continuously formed at the entrance portion and that is recessed in a direction toward the axis of the image carrier when the transport unit is rotated to the transport path forming position;
  When rotating the transport unit to the transport path forming position, first, when the transfer member is guided along the inlet portion, the reaction force gradually increases, and the transfer member is moved to the inlet portion. The reaction force reaches a peak, and the reaction force decreases after the transfer member passes through the inlet portion, so that the peak position of the reaction force is the conveyance path formation position. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided in front of the image forming apparatus.

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