SHEET DISCHARGING DEVICE AND SHEET POST-PROCESSING APPARATUS THEREWITH, AND IMAGE FORMING SYSTEM

Abstract

A protruding member is supported so as to be reciprocatable between a protrusion position and a retraction position. The protrusion position is where the protruding member protrudes from a discharge port to above a stacking tray and brings, into contact with its top surface, the leading edge of a sheet discharged by a pair of discharging rollers to guide it in the discharging direction. The retraction position is where the protruding member is retracted from above the stacking tray. A moving mechanism has a supporting holder movably holding the protruding member and makes the held protruding member move between the protrusion position and the retraction position. A sensing portion sensing whether the protruding member is in the retraction position is disposed in the supporting holder.

Claims

1. A sheet discharging device comprising: a pair of discharging rollers discharging a sheet through a discharge port; a stacking tray disposed downstream of the pair of discharging rollers with respect to a discharging direction of the sheet, the stacking tray having stacked thereon the sheet discharged by the pair of discharging rollers; a protruding member supported so as to be reciprocatable between a protrusion position where the protruding member protrudes from the discharge port to above the stacking tray and where the protruding member brings, into contact with a top surface thereof, a leading edge of the sheet discharged by the pair of discharging rollers to guide the sheet in the discharging direction, and a retraction position where the protruding member is retracted from above the stacking tray; and a moving mechanism having a supporting holder movably holding the protruding member, the moving mechanism making the protruding member move between the protrusion position and the retraction position, wherein the sheet discharging device further comprises a sensing portion sensing whether the protruding member is in the retraction position, and the sensing portion is disposed in the supporting holder.

2. The sheet discharging device according to claim 1, wherein the sensing portion is an optical sensor including a light emitting portion and a light receiving portion disposed opposite each other and senses, when the protruding member enters or retracts from an optical path of the optical sensor, whether the protruding member is in the retraction position.

3. The sheet discharging device according to claim 2, wherein the optical sensor is disposed at a downstream end part of the protruding member in a retraction direction thereof, and the sensing portion senses, when the protruding member enters the optical path of the optical sensor, presence of the protruding member in the retraction position.

4. A sheet post-processing apparatus comprising: the sheet discharging device according to claim 1; and a post-processing mechanism performing predetermined post-processing on the sheet and conveying the post-processed sheet to the sheet discharging device.

5. An image forming system comprising: the sheet post-processing apparatus according to claim 4; and an image forming apparatus forming an image on the sheet and conveying the sheet having the image formed thereon to the sheet post-processing apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic diagram of an image forming system S including an image forming apparatus 200 and a sheet post-processing apparatus 5 according to an embodiment of the present disclosure.

[0010] FIG. 2 is a side sectional view schematically showing the internal structure of a sheet discharging device 10 according to the embodiment of the present disclosure.

[0011] FIG. 3 is a perspective view of the structure around a protruding member 13 in the sheet discharging device 10 according to the embodiment of the present disclosure.

[0012] FIG. 4 is an enlarged perspective view of the structure around the protruding member 13 in the sheet discharging device 10 according to the embodiment of the present disclosure.

[0013] FIG. 5 is a side view of a supporting holder 20 in the sheet discharging device 10 according to the embodiment of the present disclosure as seen from an axial direction.

[0014] FIG. 6 is an enlarged perspective view of the structure around a tip part of the protruding member 13 in the sheet discharging device 10 according to the embodiment of the present disclosure.

[0015] FIG. 7 is a sectional view of the supporting holder 20, cut orthogonally to the top-bottom direction, in the sheet discharging device 10 according to the embodiment of the present disclosure.

DETAILED DESCRIPTION

[0016] Now, a description will be given of a sheet post-processing apparatus 5 and an image forming system S configured with the sheet post-processing apparatus 5 according to an embodiment of the present disclosure with reference to the accompanying drawings.

[0017] 1. Configuration of Image Forming System: FIG. 1 is a schematic diagram of an image forming system S including an image forming apparatus 200 and a sheet post-processing apparatus 5 according to an embodiment of the present disclosure. The image forming system S includes the image forming apparatus 200 and the sheet post-processing apparatus 5.

[0018] The image forming apparatus 200 is what is called a multifunction peripheral capable of monochrome printing equipped with the functions of, for example, printing (copying), scanning (image reading), facsimile transmission, and the like. The image forming apparatus 200 includes a document conveying portion 203 and an image reading portion 204. The document conveying portion 203 is placed on the top face of a body portion 201. The image reading portion 204 is disposed below Z2 the document conveying portion 203, inside the body portion 201. The image of a document placed on the document conveying portion 203 or of a document placed on a contact glass, not shown, on the top face of the image reading portion 204 is read by the image reading portion 204.

[0019] The image forming apparatus 200 further includes a sheet feeding portion 205, a sheet conveying portion 206, an exposure portion 207, an image forming portion 208, a transferring portion 209, a fixing portion 210, a sheet discharging portion 211, a relay portion 212, and a body control portion 213.

[0020] The sheet feeding portion 205 stores a plurality of sheets P and feeds out, while separating, the sheets P one by one during printing. The sheet conveying portion 206 conveys a sheet P fed from the sheet feeding portion 205 to the transferring portion 209 and then the fixing portion 210, and also sorts the sheet P after fixing to the sheet discharging portion 211 or to the relay portion 212. The exposure portion 207 shines laser light controlled based on image data toward the image forming portion 208.

[0021] The image forming portion 208 includes a photosensitive drum 2081 as an image carrying member and a development device 2082. In the image forming portion 208, the laser light shone from the exposure portion 207 forms, on the surface of the photosensitive drum 2081, an electrostatic latent image based on a document image. The development device 2082 feeds toner to the electrostatic latent image to develop it into a toner image. The transferring portion 209 transfers, to the sheet P, the toner image that the image forming portion 208 has formed on the surface of the photosensitive drum 2081. The fixing portion 210 heats and presses the sheet P having the toner image transferred to it so as to fix the toner image to the sheet P.

[0022] The sheet P after fixing is conveyed to the sheet discharging portion 211 or to the relay portion 212. The sheet discharging portion 211 is disposed below Z2 the image reading portion 204. The sheet discharging portion 211 has an opening in its front face and permits the sheet after printing (printed matter) to be retrieved at the front. The relay portion 212 is disposed below the sheet discharging portion 211. The relay portion 212 has its downstream end in the sheet conveying direction coupled to the sheet post-processing apparatus 5. The sheet after printing (printed matter) conveyed to the relay portion 212 passes through the relay portion 212 to be conveyed to the sheet post-processing apparatus 5.

[0023] The body control portion 213 includes a CPU, an image processing portion, and a memory, none of which is shown, along with other electronic circuits and components, none of which is shown. The CPU controls the operation of different components provided in the image forming apparatus 200 based on programs and data for control stored in the memory to perform processes to carry out the functions of the image forming apparatus 200. The sheet feeding portion 205, the sheet conveying portion 206, the exposure portion 207, the image forming portion 208, the transferring portion 209, and the fixing portion 210 individually receive commands from the body control portion 213 and cooperate to perform printing on the sheet P. The memory is configured as a combination of a nonvolatile memory device such as a program ROM (read only memory) and a data ROM, and a volatile memory device such as a RAM (random access memory), none of which is shown.

[0024] The sheet post-processing apparatus 5 is removably coupled to the image forming apparatus 200 from a side face of it. The sheet post-processing apparatus 5 includes a post-processing housing 50, a sheet conveying passage 42 disposed in the post-processing housing 50, a processing tray 8, a punching portion 61, a stapling portion 62, a pair of conveying rollers 71, a pair of intermediate rollers 72, a first sheet sensing portion S1, a pair of discharging rollers 73, a second sheet sensing portion S2, a sheet discharging device 10, and a post-processing control portion 100.

[0025] In the embodiment, the punching portion 61 and the stapling portion 62 constitute a post-processing mechanism. In other words, the sheet post-processing apparatus 5 includes a post-processing mechanism and the post-processing mechanism performs predetermined post-processing on the sheet P and conveys the post-processed sheet P to the sheet discharging device 10.

[0026] The post-processing housing 50 has a sheet introduction port 41 provided in a side face of it opposite the image forming apparatus 200. The sheet P having passed through the relay portion 212 passes through the sheet introduction port 41 to be introduced into the sheet post-processing apparatus 5.

[0027] The sheet conveying passage 42 extends from the sheet introduction port 41 to above Z1 the processing tray 8 in the direction away from the image forming apparatus 200 (leftward in FIG. 1). On the top face of the processing tray 8, the sheet P can be temporarily stacked. The sheet conveying passage 42 stacks the sheet P introduced through the sheet introduction port 41 on the top face of the processing tray 8.

[0028] The processing tray 8 is inclined so as to have a downward slope from its downstream end toward its upstream end in the sheet conveying direction (X1-X2 direction).

[0029] The punching portion 61 is disposed between the sheet introduction port 41 and the downstream end of the sheet conveying passage 42 with respect to the sheet conveying direction (X1-X2 direction). The punching portion 61 punches the sheet P conveyed through the sheet conveying passage 42. Punching is processing to form punched holes (binding holes). Here, punched holes are formed along one side edge of the sheet along its width direction (Y1-Y2 direction) orthogonal to the sheet conveying direction (X1-X2 direction).

[0030] The stapling portion 62 is disposed below Z2 the sheet conveying passage 42, upstream X2 of the processing tray 8 in the sheet conveying direction (X1-X2 direction). The stapling portion 62 staples (binds) a bundle of sheets P stacked on the processing tray 8. Stapling is processing to bind the bundle of sheets P with a staple. Here, what is called edge binding is carried out, in which a corner part or an edge part of the bundle of sheets is bound with a staple.

[0031] The post-processing mechanism includes the pair of conveying rollers 71, the pair of intermediate rollers 72, and the first sheet sensing portion S1 arrayed in this order from upstream X2 in the sheet conveying direction, and the pair of conveying rollers 71 and the pair of intermediate rollers 72 convey the post-processed sheet P to the sheet discharging device 10.

[0032] The pair of conveying rollers 71 is disposed downstream of the punching portion 61, adjacent to it, with respect to the sheet conveying direction (X1-X2 direction). The pair of conveying rollers 71 conveys the punched or unpunched sheet downstream X1 in the sheet conveying direction.

[0033] The pair of intermediate rollers 72 is disposed in a downstream end part of the sheet conveying passage 42 with respect to the sheet conveying direction (X1-X2 direction). The pair of intermediate rollers 72 is located above Z1 an upstream end part of the processing tray 8. The pair of intermediate rollers 72 discharges the sheet P conveyed through the sheet introduction port 41 into the sheet conveying passage 42 onto the processing tray 8.

[0034] The first sheet sensing portion S1 is disposed closely downstream of the pair of intermediate rollers 72 with respect to the sheet discharging direction (see FIG. 2). The first sheet sensing portion S1 is a sensor that optically senses the sheet P; it senses the entry of the leading edge of the sheet P conveyed by the pair of conveying rollers 71 into the pair of intermediate rollers 72. The first sheet sensing portion S1 also senses the passage of the sheet P conveyed by the pair of intermediate rollers 72 through the pair of intermediate rollers 72.

[0035] 2. Configuration of Sheet Discharging Device: FIG. 2 is a side sectional view schematically showing the internal structure of the sheet discharging device 10. The sheet discharging device 10 includes a pair of discharging rollers 73, a stacking tray 11, a sheet pressing member 14, a paddle member 15, and a post-processing control portion 100. The sheet discharging device 10 further includes, in addition to the components just mentioned, a protruding member 13, a moving mechanism 26, and a sensing portion 90, of which the configuration will be described in detail later.

[0036] The pair of discharging rollers 73 discharges the sheet through a discharge port 2. The pair of discharging rollers 73 is disposed downstream of the pair of intermediate rollers 72 with respect to the sheet discharging direction. The pair of discharging rollers 73 overlaps with a downstream end part of the processing tray 8 with respect to the sheet discharging direction.

[0037] The pair of discharging rollers 73 includes a driving roller 731 (discharging roller) and a driven roller 732 in pressed contact with the driving roller 731 under a predetermined nip pressure. The driving roller 731 and the driven roller 732 together form a nip portion 73N that nips and conveys the sheet P. The nip portion 73N is released by a nip release mechanism (not shown) when the stapling portion 62 carries out stapling. The sheet P is stacked on the processing tray 8 with the nip portion 73N released. The stapled bundle of sheets is discharged to the stacking tray 11 by the pair of discharging rollers 73 with the nip portion 73N restored.

[0038] The driving roller 731 is supported on a driving roller shaft 731a so as to rotate together with the driving roller shaft 731a. To the driving roller shaft 731a, a drive source such as a motor is connected (not shown) and its rotation is controlled by the post-processing control portion 100. As the driving roller shaft 731a rotates, the two driving rollers 731 rotate concurrently together with the driving roller shaft 731a.

[0039] The second sheet sensing portion S2 is disposed closely downstream of the pair of discharging rollers 73. The second sheet sensing portion S2 includes an actuator and a photosensor (neither is shown) and can sense whether the sheet P is being discharged and whether the trailing end of the sheet P has passed through the pair of discharging rollers 73.

[0040] The stacking tray 11 is disposed downstream of the pair of discharging rollers 73 with respect to the discharging direction of the sheet P and has stacked on it the sheet P discharged by the pair of discharging rollers 73. The stacking tray 11 is supported such that it can ascend and descend. The stacking tray 11 has a sheet stacking face 11a formed on its top face. A sheet propping wall 11b constitutes the side face of the post-processing housing 50 opposite from the image formation apparatus 200. The sheet stacking face 11a is inclined upward Z1 as it extends away from the sheet propping wall 11b. An upstream end part of the sheet stacking face 11a with respect to the sheet discharging direction is located below Z2 the pair of discharging rollers 73.

[0041] The stacking tray 11 is a final discharge location for the sheet in the sheet post-processing apparatus 5. The bundle of sheets stapled on the processing tray 8 is discharged toward the stacking tray 11 by the pair of discharging rollers 73 and is stacked on the sheet stacking face 11a. If no stapling is carried out by the stapling portion 62, the sheet P is conveyed to the stacking tray 11 without being stacked on the processing tray 8.

[0042] The post-processing control portion 100 includes a CPU, which is not shown, and other electronic circuits and components, none of which is shown. The post-processing control portion 100 is connected to the body control portion 213 such that it can communicate with each other. The post-processing control portion 100 receives commands from the body control portion 213 and controls, with the CPU and based on programs and data for control stored in the memory, the operation of different components (the punching portion 61, the stapling portion 62, the pair of conveying rollers 71, the pair of intermediate rollers 72, the pair of discharging rollers 73, the processing tray 8, the sheet discharging device 10, the moving mechanism 26, and the like) in the sheet post-processing apparatus 5 to perform processes to carry out the functions of the sheet post-processing apparatus 5.

[0043] The sheet pressing member 14 is disposed upstream of the stacking tray 11 in the sheet discharging direction. The sheet pressing member 14 is disposed below Z2 the driving roller shaft 731a. Two sheet pressing members 14 are disposed along the sheet width direction (Y1-Y2 direction) of the stacking tray 11 at a predetermined interval in the sheet width direction (Y1-Y2 direction).

[0044] The sheet pressing member 14 is supported in a lower end part of it so as to be swingable about, as a fulcrum, a swing shaft 14a extending along the sheet width direction (Y1-Y2 direction). The sheet pressing member 14 swings, with one end part of it at its top as a free end, about the swing shaft 14a in the sheet discharging direction. The sheet pressing member 14 swings between a position where it presses, from above Z1, an upstream part of the sheet stacked on the stacking tray 11 in the discharging direction and a position where it releases the pressing of the sheets. The swinging of the sheet pressing member 14 is controlled by the post-processing control portion 100.

[0045] The sheet pressing member 14 presses the trailing end of the sheet P stacked on the sheet stacking face 11a from above Z1. Thus, even if the sheet to be discharged is curled, it is possible to straighten the sheet by pressing its trailing end.

[0046] A plurality of (here, four) paddle members 15 are provided coaxially with the driving roller shaft 731a. The paddle members 15 rotate independently of the driving roller shaft 731a. The four paddle members 15 are connected to a drive source such as a motor (not shown) and their rotation is controlled by the post-processing control portion 100.

[0047] Before the start of the discharge of the sheet P, the sheet pressing members 14 stay still in a position where they do not protrude toward the stacking tray 11 so as not to hinder the discharge of the sheet P. In addition, before the start of the discharge of the sheet P, the paddle members 15 stand by in a position where they do not protrude toward either the processing tray 8 or the stacking tray 11 so as not to hinder the discharge of the sheet P.

[0048] The post-processing control portion 100 starts to rotate the paddle members 15 after the trailing end of the sheet P (an upstream end part of it in the sheet discharging direction) has passed through the nip portion 73N, before the sheet P is stacked on the sheet stacking face 11a. Then, the paddle members 15 make contact with the trailing end of the sheet P discharged from the pair of discharging rollers 73 and pushes down from above Z1, as if tapping, a part of the sheet P near its trailing end toward the sheet stacking face 11a.

[0049] From this state, as the paddle members 15 further rotate, the paddle members 15, while pulling the sheet P upstream in the discharging direction of the sheet P along the stacking tray 11, press a part of the sheet P near its trailing end against the sheet propping wall 11b of the stacking tray 11.

[0050] After the paddle members 15 start to rotate, before they pass across the upstream end of the stacking tray 11 in the sheet discharging direction, the sheet pressing members 14 start to be swung. Then, the sheet pressing member 14 moves to a pressing position at which it presses, from above Z1, an upstream part of the sheet stacked on the stacking tray 11 in the discharging direction.

[0051] When the sheet post-processing apparatus 5 ends the stacking of the sheet, the upstream end of the sheet P in the discharging direction makes contact with the sheet propping wall 11b provided upstream of the stacking tray 11 in the sheet discharging direction. Thus, the sheet P is aligned at a predetermined position on the stacking tray 11.

[0052] 3. Configuration of Protruding Member and Moving Mechanism: FIG. 3 is a perspective view of the structure around the protruding member 13 in the sheet discharging device 10. FIG. 4 is an enlarged perspective view of the structure around the protruding member 13. FIG. 5 is a side view of a supporting holder 20 as seen from an axial direction. Note that, in FIG. 5, the sensing portion 90 is hatched for clarity. FIG. 6 is an enlarged perspective view of the structure around a tip part of the protruding member 13.

[0053] The protruding member 13 is a member in the shape of a rod extending along the sheet discharging direction in the form of an arc. The protruding member 13 is disposed below Z2 the sheet discharge port 2 (see FIG. 2). Specifically, the protruding member 13 is disposed below Z2 the discharging passage of the sheet discharged from the pair of discharging rollers 73 along the processing tray 8. A plurality of (in the embodiment, two) protruding members 13 are provided at a predetermined interval across a middle part of the stacking tray 11 with respect to the sheet width direction (Y1-Y2 direction). The protruding member 13 and the paddle member 15 are disposed side by side with respect to the sheet width direction (Y1-Y2 direction).

[0054] The supporting holder 20 is fixed to the post-processing housing 50 and is included in the moving mechanism 26, which will be described later. The supporting holder 20 is provided one at each of positions overlapping with the protruding members 13 with respect to the sheet width direction (Y1-Y2 direction) (see FIG. 3).

[0055] The supporting holder 20 has side walls 21a and 21b, a guide rail 22, a cover rib 23, and a positioning protrusion 24 (see FIGS. 3 and 5).

[0056] The side walls 21a and 21b are plate-form parts formed at opposite ends of the supporting holder 20 with respect to the axial direction (Y1-Y2 direction). The side walls 21a and 21b face each other along the axial direction (Y1-Y2 direction). The side walls 21a and 21b have a collar supporting hole 25 penetrating them along the axial direction (Y1-Y2 direction). The protruding member 13 is disposed between the side walls 21a and 21b with respect to the axial direction (Y1-Y2 direction).

[0057] The guide rail 22 has the shape of a rib protruding from the side walls 21a and 21b inward of the supporting holder 20 with respect to the axial direction (Y1-Y2 direction). The guide rail 22 extends along the arc shape of the protruding member 13, parallel to the movement direction of the protruding member 13. The cover rib 23 is provided opposite the guide rail 22 with respect to the direction orthogonal to both the axial direction (Y1-Y2 direction) and the sheet discharging direction. A gap is formed between the cover rib 23 and the guide rail 22.

[0058] The protruding member 13 is disposed between the guide rail 22 and the cover rib 23. The protruding member 13 is supported so as to be reciprocatable along the guide rail 22 between a protrusion position P1 and a retraction position P2. The supporting holder 20 movably holds the protruding member. In the following description, the direction along which the protruding member 13 moves is referred to simply as movement direction.

[0059] The protrusion position P1 is a position where the protruding member 13 protrudes from the supporting holder 20 with respect to the movement direction (the position indicated by two-dot chain lines in FIGS. 2 and 3). Specifically, the protrusion position P1 is where the protruding member 13 protrudes from the discharge port 2 to above Z1 the stacking tray 11 and where the protruding member 13 brings, into contact with its top surface, the leading edge of the sheet P discharged by the pair of discharging rollers 73 to guide it in the discharging direction. The retraction position P2 is where the protruding member 13 is retracted inside the supporting holder 20 with respect to the movement direction (the position indicated by solid lines in FIG. 2 and by broken and solid lines in FIG. 5). Specifically, the retraction position P2 is where the protruding member 13 is retracted from above Z1 the stacking tray 11.

[0060] Note that, of opposite directions along the movement direction, the direction in which the protruding member 13 moves toward the protrusion position P1 is referred to as protrusion direction, and the direction in which the protruding member 13 moves toward the retraction position P2 is referred to as retraction direction.

[0061] The positioning protrusion 24 is continuous with a lower end part of the guide rail 22 (a downstream end part in the retraction direction). The positioning protrusion 24 protrudes from the guide rail 22 so as to be orthogonal to the guide rail 22. The positioning protrusion 24 faces the protruding member 13 along the movement direction (see FIG. 5).

[0062] When the protruding member 13 moves in the retraction direction and reaches the retraction position P2, the protruding member 13 makes contact with the positioning protrusion 24. In this state, the protruding member 13 is restrained from moving in the retraction direction by the positioning protrusion 24 to be positioned, within the retraction position P2, at a reference position P2 farthest from the protrusion position P1. When the protruding member 13 is at the reference position P2, the tip of the protruding member 13 (a downstream end part in the protrusion direction) is located inward (upstream in the protrusion direction) of the tip of the supporting holder 20.

[0063] The moving mechanism 26 makes the protruding member 13 move between the protrusion position P1 and the retraction position P2. The moving mechanism 26 is configured with the supporting holder 20 described above, a rotary shaft 32, a pinion gear 27, a rack gear 31, and a driving device 131. That is, the moving mechanism 26 includes the supporting holder 20.

[0064] The rotary shaft 32 extends parallel to the driving roller shaft 731a. The rotary shaft 32 is inserted in the collar supporting holes 25 in the supporting holders 20. The rotary shaft 32 faces the protruding member 13 along a radial direction. Around the rotary shaft 32, the pinion gear 27 is fitted (see FIG. 4).

[0065] The pinion gear 27 is a spur gear with a plurality of gear teeth on its outer circumferential surface. The pinion gear 27 is at its center along the radial direction penetrated by the rotary shaft 32. The pinion gear 27 is disposed one at each of positions overlapping with the protruding members 13 along the longitudinal direction of the rotary shaft 32. The pinion gear 27 is located between a pair of side walls 21a and 21b of the supporting holder 20 with respect to the axial direction (Y1-Y2 direction). The pinion gear 27 faces the protruding member 13 along the radial direction.

[0066] The rack gear 31 has a plurality of gear teeth in a row along the movement direction of the protruding member 13. The rack gear 31 is formed on a facing face 37, opposite the pinion gear 27, of the protruding member 13 (see FIG. 6).

[0067] The rack gear 31 and the pinion gear 27 can be meshed with each other. With the pinion gear 27 and the rack gear 31 meshed with each other, they constitute a rack-and-pinion mechanism with the pinion gear 27 as a pinion gear. Thus, with the pinion gear 27 and the rack gear 31 meshed with each other, as the pinion gear 27 rotates, the rack gear 31 moves along the rotation direction of the pinion gear 27. This moves the protruding member 13.

[0068] The driving device 131 is configured with a drive motor 807, a drive transmission pulley 806, and a drive transmission belt 805 (see FIG. 3). The drive motor 807 includes a body portion 808, a motor shaft 809 protruding from the body portion 808, and a motor gear 810 fixed to an end part of the motor shaft 809. The drive motor 807 outputs a rotary driving force via the motor shaft 809 and the motor gear 810. The rotation (e.g., rotation angle or turns of rotation) of the drive motor 807 is controlled by the post-processing control portion 100.

[0069] The drive transmission pulley 806 is a toothed pulley fixed to the rotary shaft 32 and rotates together with the rotary shaft 32. The drive transmission belt 805 is an endless toothed belt wound around the motor gear 810 and the drive transmission pulley 806.

[0070] When the drive motor 807 outputs a rotary driving force, the motor gear 810 rotates and the rotary driving force is transmitted via the drive transmission belt 805 and the drive transmission pulley 806 to the rotary shaft 32, so that the rotary shaft 32 rotates. As the rotary shaft 32 rotates, as described above, the moving mechanism 26 moves the two protruding members 13 concurrently between the protrusion position P1 and the retraction position P2.

[0071] 4. Configuration of Sensing Portion: FIG. 7 is a sectional view of the supporting holder 20 cut orthogonally to the top-bottom direction (Z1-Z2 direction). In FIG. 7, the protruding member 13 is indicated by broken lines. The sensing portion 90 is disposed in the supporting holder 20 and senses whether the protruding member 13 is in the retraction position P2. Specifically, the sensing portion 90 is disposed at a lower end part (downstream end part in the retraction direction) of the guide rail 22 (see FIG. 5). The sensing portion 90 is disposed upstream of the positioning protrusion 24 in the retraction direction. This allows the sensing portion 90 to sense, before the protruding member 13 reaches the positioning protrusion 24, the presence of the protruding member 13 in the retraction position P2.

[0072] Specifically, the sensing portion 90 is an optical sensor 91 including a light emitting portion 91a and a light receiving portion 91b disposed opposite each other. In the embodiment, the light emitting portion 91a and the light receiving portion 91b are disposed on the side wall portion 21a and the side wall portion 21b, respectively. The light emitting portion 91a and the light receiving portion 91b face each other in the width direction (Y1-Y2 direction) of the sheet P. Note that the light emitting portion 91a can be disposed on the side wall portion 21b with the light receiving portion 91b disposed on the side wall portion 21a.

[0073] Conventionally, the sensing portion 90 is disposed on the protruding member 13 and then the sensing portion 90 inevitably moves together with the protruding member 13. This entails a risk of the sensing portion 90 breaking by touching a component around it. In addition, there is also a risk of a lead wire connected to the sensing portion 90 breaking by touching a component around it. By contrast, in the embodiment, the sensing portion 90 is disposed in the supporting holder 20. This prevents the sensing portion 90 or the lead wire connected to the sensing portion 90 from touching a component around them when the protruding member 13 moves. Thus, it is possible to provide a sheet discharging device 10 less prone to breakage.

[0074] The sensing portion 90 senses, when the protruding member 13 enters the optical path of the optical sensor 91, the presence of the protruding member 13 in the retraction position P2. On the other hand, the sensing portion 90 senses, when the protruding member 13 is retracted from the optical path of the optical sensor 91, the absence of the protruding member 13 in the retraction position P2. This allows the sensing portion 90 to more reliably sense the entry and retraction of the protruding member 13.

[0075] The post-processing control portion 100 stops driving the moving mechanism 26 on sensing the presence of the protruding member 13 in the retraction position P2. This prevents the moving mechanism 26 from keeping driving despite the presence of the protruding member 13 in the retraction position P2 and thus ending in breaking the protruding member 13 and the supporting holder 20.

[0076] The above embodiment is not meant as any limitation on the present disclosure and thus various modifications can be made without departing from the spirit of the present disclosure. For example, while, in the embodiment, the image forming apparatus 200 in the image forming system S is a multifunction peripheral capable of monochrome printing, this is not meant as any limitation. Examples of the image forming apparatuses 200 include monochrome copiers and monochrome printers as well as image forming apparatuses capable of color printing such as color copiers and color printers.

[0077] For example, the sensing portion 90 can be provided one on each of the supporting holders 20 of which there are two to correspond to the two protruding members 13, or it can be provided on only one of them.

[0078] While, in the embodiment, the optical sensor 91 is used as the sensing portion 90, this is not meant as any limitation on the present disclosure. As the sensing portion 90, instead of the optical sensor 91, a contact sensor can be used.

[0079] The present disclosure finds application in sheet post-processing apparatuses that are disposed downstream of an image forming apparatus to perform predetermined post-processing on a sheet discharged from the image forming apparatus.