Sheet stacking device and image forming system

Abstract

To provide a sheet stacking device and an image forming system that improve sheet alignment.SOLUTION: A sheet stacking device includes: a retractable belt 86 that has elasticity and moves the top sheet stacked on a stacking tray 76 in a sheet conveying direction DF toward an abutment surface 84b; a drive gear 87 that abuts against one side of the retractable belt 86 to rotate the retractable belt 86; and a driven roller 88 that forms a nip section N1 sandwiching the retractable belt 86 between itself and the drive gear 87 and follows by abutting on the other surface of the retractable belt 86 at the nip section N1. The drive gear 87 and the driven roller 88 are arranged such that, when viewed from the direction of the rotation axis of the drive gear 87, a nip line NL that is tangent to the retractable belt 86 at the nip section N1 and extends from the nip section N1 to the downstream side in the movement direction of the retractable belt 86 extends downstream of the nip section N1 in the sheet conveying direction DF and toward the stacking tray 76 from the nip section N1.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a sheet stacking device for stacking sheets and an image forming system using the same. [Background technology]

[0002] Image forming apparatuses use sheet stacking devices such as large-capacity stackers for stacking sheets on which images have been formed. Patent Document 1 describes a sheet stacking device in which a gripper supported by a timing belt grips and transports a sheet, and then a pull-in belt aligns the leading edge of the sheet in the transport direction by striking it against a stopper. In this sheet stacking device, a drive roller in contact with the inner circumferential surface and a driven roller in contact with the outer circumferential surface are disposed above the pull-in belt, forming a nip between them and sandwiching the pull-in belt. The pull-in belt is rotated by the rotation of the drive roller. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-203046 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the sheet stacking device described in Patent Document 1, the drive roller and driven roller are located at the top of the pull-in belt, and the force that the drive roller and driven roller apply to the pull-in belt at the nip is not directed toward the sheet (downward). This causes the pull-in belt to be pulled away from the top surface of the sheet, making it difficult to increase the pressure that the pull-in belt applies to the sheet. In particular, when attempting to align heavy sheets, the frictional force generated by the weight of the sheet and the friction between the stacked sheets exceeds the conveying force of the pull-in belt, potentially preventing the sheet from reaching the stopper and resulting in poor alignment.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sheet stacking device and an image forming system that can improve sheet alignment. [Means for solving the problem]

[0006] One aspect of the present invention is a sheet stacking device comprising: a loading section on which sheets are loaded; a transport section that transports the sheets toward the loading section; a stop section against which the leading edge of the sheet in the sheet transport direction abuts; a belt member that is elastic and moves the top sheet loaded on the loading section in the sheet transport direction toward the stop section; a driving rotor that abuts against one side of the belt member to rotate the belt member; and a driven rotor that forms a nip section between the driving rotor and the belt member and abuts against the other side of the belt member at the nip section to be driven; wherein the driving rotor and the driven rotor are arranged so that, when viewed from the direction of the rotational axis of the driving rotor, a line that tangent to the belt member at the nip section, extending from the nip section downstream in the movement direction of the belt member, extends downstream in the sheet transport direction of the nip section and toward the loading section of the sheet transport direction of the nip section.

[0007] Another aspect of the present invention is an image forming system comprising an image forming device having an image forming unit that forms an image on a sheet, and the above-mentioned sheet stacking device, wherein the sheet stacking device receives and stacks sheets on which an image has been formed by the image forming unit from the image forming device. [Effects of the Invention]

[0008] According to the present invention, the alignment of the sheet can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an image forming system according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing a control system of the image forming system according to the embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing a stack unit of the sheet stacking device according to the embodiment. [Figure 4] 5A and 5B are cross-sectional views showing a lead-in belt of a sheet stacking device according to an embodiment, in which FIG. 5A shows a tangential force at a nip portion, and FIG. 5B shows a tangent at the nip portion. [Figure 5] 1A and 1B are diagrams showing a stacking section of a sheet stacking device according to a comparative example, in which FIG. 1A is a cross-sectional view and FIG. [Figure 6] 10A and 10B are cross-sectional views showing the retraction belt of a sheet stacking device according to comparative examples, where (a) shows the case in which the nip portion is located at the top position of the retraction belt in comparative example 1, and (b) shows the case in which the nip portion is located on the abutment surface side of the top position of the retraction belt in comparative example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present embodiment will be described below with reference to the drawings. First, the schematic configuration of an image forming system 1 according to the present embodiment will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing the schematic configuration of the image forming system 1 according to the present embodiment. The image forming system 1 has an image forming apparatus 2 and a stacker 3 which is an example of a sheet stacking device. The image forming apparatus 2 has an image forming section 10 which forms an image on a sheet S, and the stacker 3 receives the sheet S on which the image has been formed by the image forming section 10 from the image forming apparatus 2 and stacks it.

[0011] [Image forming equipment] In this embodiment, the image forming apparatus 2 is a tandem-intermediate transfer laser beam printer that uses an electrophotographic process. The image forming apparatus 2 can form and output a full-color or monochrome image corresponding to print image data output from a host device such as an external computer 21 (see FIG. 2) connected to the control unit 20 onto a sheet S that is a recording medium. Note that, although this embodiment describes a case in which the image forming apparatus 2 is a tandem-intermediate transfer laser beam printer that uses an electrophotographic process, the present invention is not limited to this and may be, for example, an inkjet printer.

[0012] Sheets S are stored in a stacked form in sheet cassettes 61, 62, and 63, and are fed by respective feeding sections 61a, 62a, and 63a in accordance with the image formation timing. The sheets S fed by feeding sections 61a, 62a, and 63a pass through a conveying path 65 and are conveyed to a pair of registration rollers 66, which is a pre-transfer conveying section. On the other hand, sheets S stacked on manual sheet tray 64 are fed by feeding section 64a in accordance with the image formation timing and are conveyed to the pair of registration rollers 66 via a conveying path 67.

[0013] The registration roller pair 66 has a function of correcting skew by making a loop by hitting the sheet S conveyed from the sheet cassettes 61, 62, 63 and the manual sheet tray 64 and following the leading edge of the sheet S in the conveying direction. The registration roller pair 66 also has a function of conveying the sheet S to the secondary transfer unit 36 ​​at a predetermined timing in accordance with the timing of image formation on the sheet S, that is, in accordance with the toner image carried on the intermediate transfer belt 31. Thus, the registration roller pair 66 corrects skew of the sheet S, and then sends the sheet S to the secondary transfer unit 36 ​​at the desired timing.

[0014] In contrast to the process of transporting the sheet S to the secondary transfer unit 36 ​​described above, the process of forming an image in the image forming unit 10, in which the image is sent to the secondary transfer unit 36 ​​at the same timing, will now be described. The image forming unit 10 has four process cartridges PY, PM, PC, and PK corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (Bk). The four process cartridges PY, PM, PC, and PK have the same configuration except for the toner colors, so the yellow process cartridge PY will be described here as a representative. The image forming unit 10 has a process cartridge PY, an exposure device 13, a primary transfer roller 35, etc. The process cartridge PY has a photosensitive drum 11, a charging device 12, a developing device 14, a cleaner 15, etc.

[0015] The surface of the rotating photosensitive drum 11 is uniformly charged in advance by a charging device 12, and an exposure device 13 is driven based on the image information signal sent to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 11 is developed with toner by a developing device 14, and becomes visible as a toner image on the photosensitive drum 11. A predetermined pressure and electrostatic load bias are applied by a primary transfer roller 35, and the toner image is transferred onto the intermediate transfer belt 31. Any small amount of residual toner remaining on the photosensitive drum 11 after transfer is collected by a cleaner 15, and is prepared for the next image formation.

[0016] The intermediate transfer belt 31 is stretched by rollers such as a drive roller 33, a tension roller 34, and an inner secondary transfer roller 32, and is driven to be transported in the direction D1. The image formation processes for each color, which are processed in parallel by the process cartridges PY, PM, PC, and PK, are performed at timings such that the image is superimposed on the toner image of the upstream color that has been primarily transferred onto the intermediate transfer belt 31. As a result, a full-color toner image is finally formed on the intermediate transfer belt 31 and transported to a secondary transfer unit 36. The secondary transfer unit 36 ​​is a toner image transfer nip portion for the sheet S, which is formed by the opposing inner secondary transfer roller 32 and outer secondary transfer roller 41, and transfers the toner image onto the sheet S by applying a predetermined pressure force and an electrostatic load bias.

[0017] Through the above-described sheet S transport process and image formation process, a full-color toner image is secondarily transferred onto the sheet S in the secondary transfer unit 36. The sheet S onto which the toner image has been secondarily transferred is transported to the fixing device 43 by the suction transport unit 42. The suction transport unit 42 transports the sheet S by air suction using a belt, a fan, or the like. The fixing device 43 holds the sheet S between opposing rollers or belts, and generally applies heat from a heat source such as a heater and a predetermined pressure to melt and fix the toner image on the sheet S. The sheet S with the fixed image thus obtained is transported to the discharge rollers 44.

[0018] Here, the conveyance path of the sheet S is selected from either the discharge conveyance path 45, which conveys the sheet directly to the stacker 3, or the reversal path 46, which conveys the sheet when double-sided image formation is required. When double-sided image formation is required, a switching member 47, which swings due to the action of a solenoid, is switched to its upper position, and the sheet S is pulled from the reversal path 46 to a switchback path 48. The rotation direction of the reversal roller 49 is reversed (switchback operation) to switch the leading and trailing ends of the sheet S, and the sheet S is conveyed to a double-sided conveyance path 50. Thereafter, the sheet S rejoins in time with the sheet S of the subsequent job conveyed from each sheet cassette 61, 62, 63, etc., and is sent to the secondary transfer unit 36 ​​via a pair of registration rollers 66. The image formation process for the back side (second side) is the same as that for the front side (first side) described above, so a description thereof will be omitted.

[0019] [Control Unit] FIG. 2 is a block diagram showing the configuration of the control unit 20. As shown in FIG. 2, the control unit 20 has a CPU circuit unit 22, an image signal control unit 23, a printer control unit 24, and an external interface 25. The CPU circuit unit 22 incorporates a CPU 22a, a ROM 22b, and a RAM 22c. The CPU 22a comprehensively controls the operation unit 26, the image signal control unit 23, the printer control unit 24, and the stacker control unit 27 using a control program stored in the ROM 22b. The external interface 25 is an interface (I / F) that connects the image forming apparatus 2 and the external computer 21, and converts print data from the external computer 21 into a bitmap image and transmits it to the image signal control unit 23 as image data. The RAM 22c temporarily stores control data and is used as a work area for arithmetic processing associated with control.

[0020] The image signal control unit 23 performs various processes on the digital image signal input from the external computer 21 via the external interface 25, converts the digital image signal into a video signal, and outputs it to the printer control unit 24. The processing operations by this image signal control unit 23 are controlled by the CPU circuit unit 22. The printer control unit 24 drives the exposure device 13 via an exposure control unit (not shown) based on the input video signal. The operation unit 26 has a plurality of keys for setting various functions related to image formation, a display unit for displaying information indicating the setting status, and the like, and allows the user to set the basis weight, size, type, etc. of the sheet S. The operation unit 26 outputs key signals corresponding to the operation of each key to the CPU circuit unit 22, and displays corresponding information on the display unit based on signals from the CPU circuit unit 22.

[0021] The stacker control unit 27 is mounted on the stacker 3, and controls the overall operation of the stacker, such as driving a belt drive motor 90 and a belt lift motor 91, which will be described later, by exchanging information with the CPU circuit unit 22. The details of this control will be described later. Note that, in this embodiment, the stacker control unit 27 is mounted on the stacker 3, but this is not limiting. For example, the stacker control unit 27 may be incorporated into the control unit 20 of the image forming apparatus 2, and the control unit 20 of the image forming apparatus 2 may control the stacker 3.

[0022] [Stacker] 1, the image forming system 1 has a stacker 3 that stacks image-formed sheets S that are discharged from the image forming apparatus 2 after image formation. In this embodiment, the stacker 3 has a stack section 70 that stacks a large number of sheets S therein, a discharge tray 79 provided on the top surface of the main body, and a transport path 73 that transports the sheets S to a sheet processing apparatus (not shown) that is connected downstream of the stacker 3.

[0023] The sheet stacking operation of the stacker 3 will be described below with reference to Fig. 1. When a sheet S is discharged from the image forming apparatus 2, the sheet S is handed over to the entrance roller pair 71, and the conveying path is switched by the first switching member 72 in accordance with an instruction from the operation unit 26 or the like, and the sheet S is conveyed. When the user operates the operation unit 26 to specify the sheet stacking position as the discharge tray 79, the first switching member 72 is switched downward and the second switching member 92 is switched downward, and the sheet S is conveyed to the discharge tray 79 and discharged. When the user operates the operation unit 26 to specify conveyance to a sheet processing apparatus, the first switching member 72 is switched downward and the second switching member 92 is switched upward, and the sheet S passes through the conveying path 73 and is conveyed to the sheet processing apparatus from the exit roller pair 74. When the user operates the operation unit 26 to specify the sheet stacking position as the stacking tray 76 of the stack unit 70, that is, when stacking processing is selected, the sheet S is guided from the discharge roller pair 75 to the stack unit 70 by switching the first switching member 72 upward. That is, the discharge roller pair 75 is an example of a conveying unit, and conveys the sheet S toward the stacking tray 76.

[0024] [Stack section] The stack unit 70 includes a gripper belt 78, a gripper 77, a stopper 84, a retraction belt 86, and a stacking tray 76. The gripper belt 78 is an example of a second belt member, is suspended between a drive pulley 81 and a driven pulley 82, and is disposed above the stacking tray 76. The gripper belt 78 is rotated in the direction D2 by a belt motor (not shown). The gripper 77 is attached to the gripper belt 78 and moves in the direction D2 together with the gripper belt 78 to grip (sandwich) a sheet discharged from the pair of discharge rollers 75. After being discharged from the pair of discharge rollers 75, the sheet S is gripped by the gripper 77 and is transported above the stacking tray 76 in the sheet transport direction DF while being gripped by the gripper 77 and the pair of discharge rollers 75. That is, the gripper 77 moves in the sheet transport direction DF while gripping the leading edge of the sheet S transported in the sheet transport direction DF by the pair of discharge rollers 75.

[0025] In this embodiment, the gripper 77 includes two grippers: a first gripper 77a and a second gripper 77b. The first gripper 77a and the second gripper 77b are attached to the gripper belt 78 at different positions, but have the same configuration, so the following description will focus on one gripper 77. However, the number of grippers 77 is not limited to two, and may be one, or three or more.

[0026] The stopper 84 has a contact inclined surface 84a and abutting surface 84b. The contact inclined surface 84a is a surface provided at an angle with respect to the sheet conveyance direction DF, and the abutting surface 84b is a surface provided approximately perpendicular to the sheet conveyance direction DF. The sheet S, gripped and conveyed by the gripper 77 and the pair of discharge rollers 75, comes into contact with the contact inclined surface 84a of the stopper 84 and is released from the gripper 77. The sheet S released from the gripper 77 is guided to the abutting surface 84b by the retraction belt 86, whereby the position of the leading edge of the sheet S in the conveyance direction is aligned, and the trailing edge thereof is released from the pair of discharge rollers 75, and the sheet S is stacked on the stacking tray 76 with the leading edge position regulated. That is, the abutting surface 84b is an example of an abutting portion against which the leading edge of the sheet S in the sheet conveyance direction DF abuts.

[0027] The distance between the retraction belt 86 and the pair of discharge rollers 75 is set to be shorter than the overall length of the sheet S to be discharged. Furthermore, the stacking tray 76, which is an example of a stacking section on which the sheets S are stacked, is configured to be movable up and down by a lifting mechanism inside the stacker 3. The stacking tray 76 is controlled to be lifted and lowered in accordance with the amount of sheets stacked on it, for example, based on the detection result of a sheet upper surface sensor that detects the sheets S at a predetermined height above the stacking tray 76, so that the upper surfaces of the sheets S stacked on the stacking tray 76 are maintained at a substantially constant height. That is, the retraction belt 86 moves the uppermost sheet S stacked on the stacking tray 76 in the sheet conveying direction DF toward the abutment surface 84b.

[0028] The next sheet S discharged from the discharge roller pair 75 is conveyed above the stacking tray 76 in the sheet conveying direction DF while its leading edge in the conveying direction is gripped by the next gripper 77, and is then stacked on the stacking tray 76. When the sheet S stacked on the stacking tray 76 is to be removed after the image forming job is completed or during the execution of the image forming job, the sheet S is first removed after the stacking tray 76 is lowered to a position below where the sheet can be removed.

[0029] In this embodiment, the stacking tray 76 is provided with a side regulating member (not shown) to maintain the alignment of the sheets S stacked on the stacking tray 76 in the sheet width direction. The side regulating member is movable in the sheet width direction, and, for example, every time a sheet S is discharged onto the stacking tray 76, it is moved from a sheet receiving position to a sheet side edge regulating position, thereby maintaining the alignment of the sheet S in the sheet width direction. Note that, although the present embodiment has been described with reference to a case in which the gripper 77 is provided, this is not limiting. For example, the gripper 77 may be omitted, and the sheet S may be transported directly from the discharge roller pair 75 to the stacking tray 76 using the discharge roller pair 75 as a transport means.

[0030] 3 is a cross-sectional view showing the configuration of the stacking unit 70. As shown in FIG. 3, the abutment surface 84b of the stopper 84 is provided so as to be located at the most downstream portion of the stacking tray 76 in the sheet conveying direction DF. The sheets S are guided to the abutment surface 84b by the retraction belt 86, and the leading edges of the sheets S in the sheet conveying direction DF abut against the abutment surface 84b, thereby aligning the leading edges of the sheets S. As a result, the sheets S are stacked on the stacking tray 76 in an aligned state.

[0031] In this embodiment, the retraction belt 86 is an example of a belt member and a first belt member, and is an endless belt made of an elastic and flexible material such as rubber, and having fine irregularities on its surface to provide high friction. The retraction belt 86 is supported by being sandwiched at a nip portion N1 between a drive gear 87 and a driven roller 88.

[0032] The drive gear 87 is an example of a driving rotor, and is disposed on the inner periphery of the pull-in belt 86 so as to abut against the inner periphery, which is one side of the pull-in belt 86, to rotate the pull-in belt 86. The drive gear 87 is connected to a belt drive motor 90 via a drive roller 85. Therefore, the rotational drive force of the belt drive motor 90 is transmitted to the drive gear 87 via the drive roller 85 to rotate the drive gear 87, which in turn rotates the pull-in belt 86. The driven roller 88 is an example of a driven rotor, and forms a nip N1 between the drive gear 87 and the pull-in belt 86. The driven roller 88 is disposed on the outer periphery of the pull-in belt 86 so as to abut against the outer periphery, which is the other side of the pull-in belt 86, at the nip N1, and is driven by the pull-in belt 86.

[0033] The stack unit 70 has a lifting unit that raises and lowers the drive gear 87 and the driven roller 88 to raise and lower the pull-in belt 86. In this embodiment, the lifting unit has a belt lifting motor 91 (see FIG. 2) and a lifting mechanism (not shown) that raises and lowers the drive roller 85 and the driven roller 88 by the driving force of the belt lifting. The lifting and lowering of the drive roller 85 and the driven roller 88 changes the amount of penetration of the pull-in belt 86 into the sheets S stacked on the stacking tray 76. Here, the penetration amount of the pull-in belt 86 is the difference in the vertical distance from the nip portion N1 to the lower end of the pull-in belt 86 when the pull-in belt 86 is not in contact with the sheet and when it is in contact with the sheet. In other words, the penetration amount of the pull-in belt 86 is the amount of elastic deformation caused by the pull-in belt 86 coming into contact with the sheet S. In this way, by making it possible for the control unit 20 to adjust the penetration amount of the retraction belt 86, it is possible to adjust the amount of lift of the drive roller 85 and the driven roller 88 based on sheet information such as the basis weight / size / type of the sheet S. As a result, by appropriately controlling the penetration amount of the retraction belt 86, it is possible to apply a conveying force appropriate for the sheet S to be stacked from the retraction belt 86 to the sheet S.

[0034] [Comparative Example] 5(a) to 6(b), the positions of the drive roller 516a and the driven roller 516b in the stocker unit 570 of the stacker 503 according to the comparative example will be described. In this comparative example, as shown in FIGS. 5(a) and 5(b), the alignment of the leading edge of the sheet in the sheet conveying direction DF is performed by a gripper 515, a pull-in belt 516, and a regulating plate 514. After the sheet S is conveyed by the gripper 515, the pull-in belt 516 is rotated in the direction indicated by the arrow, so that the sheet S discharged onto the stacking tray 576 abuts against the regulating plate 514, thereby aligning the sheet S in the sheet conveying direction DF. The pull-in belt 516 rotates while being sandwiched between a drive roller 516a disposed inside the belt and a driven roller 516b that faces the drive roller 516a and nips the pull-in belt 516. Rotating the drive roller 516a rotates the pull-in belt 516, and in the rotated state, the pull-in belt 516 presses the sheet S using its elastic force, thereby applying an appropriate conveying force and achieving alignment.

[0035] Meanwhile, in recent years, image forming apparatuses have been required to handle a wider variety of sheets S than before. For example, they need to handle sheets S with large basis weights / sizes, such as packages. Such sheets S are heavy, so the retraction belt 516 needs a larger conveying force to ensure that the sheets hit the regulating plate 514. However, the stacker 503 configured in the comparative example may not be able to meet this requirement, as will be explained below.

[0036] 6(a) and 6(b) show the positions of the drive roller 516a and the driven roller 516b in Comparative Examples 1 and 2, respectively. In Comparative Example 1 shown in Fig. 6(a), the drive roller 516a and the driven roller 516b are arranged at the uppermost position of the retractable belt 516. In Comparative Example 2 shown in Fig. 6(b), the drive roller 516a and the driven roller 516b are arranged between the uppermost position of the retractable belt 516 and the downstream end position of the retractable belt 516 in the sheet conveying direction DF.

[0037] In a configuration in which the retractable belt 516 is rotated by being nipped between the drive roller 516a and the driven roller 516b, the retractable belt 516 receives a tangential force in the rotational direction of the drive roller 516a at the nip position between the drive roller 516a and the driven roller 516b. In the arrangement positions of the drive roller 516a and the driven roller 516b in Comparative Examples 1 and 2, the direction of the tangential force FT that the retractable belt 516 receives from the drive roller 516a is different from the direction of the elastic force F of the retractable belt 516. As a result, the retractable belt 516 is pulled in a direction away from the upper surface of the sheet, and the pressure force of the retractable belt 516 decreases.

[0038] As a result, the frictional force between the retraction belt 516 and the upper surface of the sheet decreases, thereby reducing the conveying force, and when attempting to align a heavy sheet S, the frictional force generated by the weight of the sheet S and the friction between the stacked sheets S exceeds the conveying force of the retraction belt 516. As a result, there is a risk that the regulating plate 514 will not be able to convey the sheet S, resulting in poor alignment.

[0039] [Drive gear and driven roller arrangement in this embodiment] Next, the direction of the force acting on the pull-in belt 86 depending on the position of the nip portion N1 between the drive gear 87 and driven roller 88 of the pull-in belt 86 in this embodiment will be described with reference to FIGS. 4(a) and 4(b). FIGS. 4(a) and 4(b) show the arrangement of the drive gear 87 and driven roller 88 that nip with the pull-in belt 86 in this embodiment. The pressure of the pull-in belt 86 against the upper surface of the sheet is applied by the elastic force of the pull-in belt 86. The pull-in belt 86 is positioned so that it penetrates the sheet S, and the pull-in belt 86 is deflected to generate the elastic force of the pull-in belt 86. Therefore, the elastic force of the pull-in belt 86 is directed toward the stacking tray 76, and the reaction force of the elastic force against the upper surface of the sheet acts as a friction force between the upper surface of the sheet and the pull-in belt 86. Therefore, to increase the conveying force, it is necessary to increase the force acting on the pull-in belt 86 in the direction of the elastic force.

[0040] Furthermore, in order for the retraction belt 86 to generate a force sufficient to move the sheet S against the increased conveying force resulting from the increase in the pressure of the retraction belt 86, it is necessary to increase the force acting on the retraction belt 86 in the direction of the abutment surface 84b. Therefore, in order to apply a greater conveying force to the sheet S and cause the sheet S to abut against the abutment surface 84b, it is desirable to apply a force to the retraction belt 86 in the direction of the stacking tray 76, which is the direction of the elastic force of the retraction belt 86, and in the direction of the abutment surface 84b, which is the direction in which the sheet S is conveyed.

[0041] As shown in Figure 4(a), the tangential force FT that the pull-in belt 86 receives from the drive gear 87 at the nip portion N1 between the drive gear 87 and the driven roller 88 is divided into a component in a direction horizontal to the upper surface of the stacking tray 76 and a component in a direction parallel to the abutment surface 84b. In Figure 4(a), the components of the tangential force FT in each direction are such that the direction of the tangential force that the pull-in belt 86 receives from the drive gear 87 increases the force toward the stacking tray 76 and the force toward the abutment surface 84b. Therefore, in order to apply a larger conveying force to the sheet S and cause the sheet S to abut against the abutment surface 84b, the arrangement shown in Figure 4(a) is desirable.

[0042] Next, we will explain the range of the position of the nip portion N1 between the drive gear 87 and the driven roller 88. Fig. 4(b) shows the cross-sectional arrangement of the pull-in belt 86, drive gear 87, and driven roller 88. As shown in Fig. 4(b), when the smaller angle formed by the nip line NL between the drive gear 87 and the driven roller 88 and the upper surface of the stacking tray 76 is set to θ, the range of θ for the arrangement of the nip portion N1 between the drive gear 87 and the driven roller 88 of the pull-in belt 86 is 0°<θ<90°.

[0043] Here, the nip line NL is also a line that extends from the nip portion N1 downstream in the movement direction of the pull-in belt 86, among the tangents to the pull-in belt 86 at the nip portion N1, when viewed from the rotational axis direction of the drive gear 87. In this case, the drive gear 87 and the driven roller 88 are disposed so that the nip line NL extends downstream of the nip portion N1 in the sheet conveying direction DF and toward the stacking tray 76 side (the stacking portion side) from the nip portion N1, when viewed from the rotational axis direction of the drive gear 87. Also, as shown in FIG. 4(b), centers 87c and 88c of the drive gear 87 and the driven roller 88 are defined, respectively, when viewed from the rotational axis direction of the drive gear 87. In this case, the centers 87c and 88c are disposed so that they are upstream of the center of the movable range of the pull-in belt 86 when it is rotationally driven in the sheet conveying direction DF and toward the stacking tray 76 side, when viewed from the rotational axis direction of the drive gear 87. The movable range in which the retraction belt 86 is positioned when it is rotationally driven here means, for example, the maximum movable range, since the retraction belt 86 elastically deforms when it rotates.

[0044] As described above, in the stacker 3 of this embodiment, the drive gear 87 and the driven roller 88 are arranged so that the nip line NL extends downstream of the nip portion N1 in the sheet conveying direction DF and toward the stacking tray 76 from the nip portion N1. Therefore, even when attempting to align a heavy sheet S, the conveying force of the pull-in belt can be increased, so that the sheet S can be conveyed to the abutment surface 84b, improving alignment.

[0045] That is, when the drive configuration of the retraction belt 86 according to this embodiment is applied, a larger conveying force can be applied to the sheet S by increasing the pressure of the retraction belt 86, so that the conveying force exceeds the frictional resistance force generated by the weight of the sheet S and the friction between the sheets S. This makes it possible for even a heavy sheet S with a higher basis weight to abut against the abutment surface 84b, improving the consistency of the sheet S in the conveying direction.

[0046] Furthermore, according to the image forming apparatus 2 of this embodiment, the drive gear 87 is disposed on the inner circumferential side of the pull-in belt 86, so that the contact area with the pull-in belt 86 can be made larger than when the drive gear 87 is disposed on the outer circumferential side. This reduces slippage between the drive gear 87 and the pull-in belt 86, enabling the drive force to be transmitted efficiently.

[0047] In the above embodiment, the retractable belt 86 is supported only by the drive gear 87 and the driven roller 88, but the present invention is not limited to this. For example, one or more guide rollers that are in contact with the inner peripheral surface of the retractable belt 86 and driven by the retractable belt 86 may be provided. In this case, for example, two guide rollers may be provided: a first guide roller that guides the upstream end of the retractable belt 86 in the sheet conveying direction DF, and a second guide roller that guides the downstream end. [Explanation of symbols]

[0048] 1...image forming system, 2...image forming apparatus, 3...stacker (sheet stacking device), 10...image forming section, 75...discharge roller pair (conveying section), 76...loading tray (loading section), 77...gripper, 78...gripper belt (second belt member), 84b...second contact surface (abutment section), 86...pull-in belt (belt member, first belt member), 87...drive gear (drive rotating body), 88...driven roller (driven rotating body), 91...belt lifting motor (lifting section), N1...nip section, S...sheet

Claims

1. a loading section on which sheets are loaded; a conveying section that conveys the sheet toward the stacking section; an abutting portion against which the leading edge of the sheet in the sheet conveying direction abuts; a belt member having elasticity and configured to move the topmost sheet stacked on the stacking section in the sheet conveying direction toward the abutment section; a driving rotor that contacts one surface of the belt member and drives the belt member to rotate; a driven rotor that forms a nip portion between the driving rotor and the belt member and that contacts the other surface of the belt member at the nip portion and is driven by the belt member, The driving rotor and the driven rotor are arranged such that, when viewed from the rotational axis direction of the driving rotor, a line extending from the nip portion to the downstream side in the moving direction of the belt member among tangents to the belt member at the nip portion extends downstream of the nip portion in the sheet conveying direction and toward the stacking portion side of the nip portion. A sheet stacking device characterized by:

2. one surface of the belt member is an inner circumferential surface of the belt member, the other surface of the belt member is an outer circumferential surface of the belt member, the driving rotor is disposed on the inner circumferential side of the belt member, The driven rotor is disposed on the outer circumferential side of the belt member.

2. The sheet stacking device according to claim 1, wherein:

3. The centers of the driving rotor and the driven rotor are disposed, as viewed from the rotation axis direction of the driving rotor, on the upstream side in the sheet conveying direction and on the stacking unit side of the center of a movable range in which the belt member is rotated.

2. The sheet stacking device according to claim 1, wherein:

4. the belt member is a first belt member, a second belt member disposed above the loading section; a gripper attached to the second belt member, the gripper moving in the sheet conveying direction while gripping the leading edge of the sheet conveyed in the sheet conveying direction by the conveying unit, 2. The sheet stacking device according to claim 1, wherein:

5. a lifting unit that lifts and lowers the driving rotor and the driven rotor to lift and lower the belt member; 2. The sheet stacking device according to claim 1, wherein:

6. an image forming apparatus having an image forming unit that forms an image on a sheet; The sheet stacking device according to any one of claims 1 to 5, the sheet stacking device receives from the image forming device and stacks the sheets on which the images have been formed by the image forming unit. An image forming system comprising:

Images