Patent ID: 12240725

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention are described below with reference to the accompanying drawings.

FIG.1is a schematic illustration of an image forming system1S according to the present embodiment, viewed from the front side. The image forming system1S includes an image forming apparatus1that forms an image on a sheet, a sheet processing apparatus4that processes a sheet having, thereon, an image formed by the image forming apparatus1, a relay unit14that conveys the sheet from the image forming apparatus1to the sheet processing apparatus4, and an image reading device2. A variety of sheets (print media) of different sizes and materials can be used. Examples of a sheet include paper, such as plain paper and thick paper, surface-treated sheet materials, such as a plastic film, fabric, and coated paper, and specially shaped sheet materials, such as envelopes and index paper. The operation performed by each of devices constituting the image forming system1S is briefly described and, subsequently, the operation performed by the sheet processing apparatus4is described in detail below.

The image forming apparatus1includes an electrophotographic image forming unit8for forming an image, and a feeding device6for feeding sheets to the image forming unit8one by one. The image forming unit8is a cartridge integrally incorporating a photosensitive drum9, which is an image bearing member (an electrophotographic photosensitive member), and a charging device and a developing device for performing an electrophotographic process by acting on the photosensitive drum9. A scanner unit15serving as an exposure device is disposed above the image forming unit8, and a transfer roller10serving as a transfer device is disposed at a position facing the photosensitive drum9. A fixing device11, discharge rollers12a, and reverse rollers12bare disposed above the transfer roller10. The fixing device11has a heat fixing configuration and includes, for example, a cylindrical film, a heater unit that includes a heater and that is disposed inside the film, and a pressure roller in pressure contact with the heater via the film.

A plurality of feeding devices6for feeding sheets are disposed below the image forming unit8. Each of the feeding devices6includes a cassette6aserving as a storage unit (a storage box) for storing a plurality of sheets and a feeding unit6bfor feeding sheets one by one from the cassette6a.

When the image forming apparatus1performs an image forming operation, the surface of the photosensitive drum9is uniformly charged by the charging device in the image forming unit8, and the scanner unit15emits a laser beam to the surface of the photosensitive drum9on the basis of image information and forms an electrostatic latent image. The electrostatic latent image is developed (visualized) with toner serving as a developer supplied from the developing device, and a toner image is formed on the surface of the photosensitive drum9.

In parallel with the operation performed by the image forming unit8, sheets are fed one by one from the cassette6aby the feeding unit6bin any of the feeding devices6and are conveyed toward registration rollers7. After correcting the skew of the sheet, the registration rollers7feed the sheet to a transfer portion between the photosensitive drum9and the transfer roller10in synchronization with the formation of the toner image by the image forming unit8. Then, the toner image is transferred from the photosensitive drum9to the sheet in the transfer portion.

The sheet that has passed through the transfer portion is delivered to the fixing device11. In the fixing device, when the sheet is nipped by the film and the pressure roller and passes through a fixing nip (a nip between the heater unit and the pressure roller), the toner on the sheet is heated and pressurized. Thus, a toner image is fixed onto the sheet.

In the case of single-sided printing, the sheet that has passed through the fixing device11is discharged from the image forming apparatus1by the discharge rollers12aand is received by the relay unit14. In the case of double-sided printing, the sheet having a toner image formed on the first side and having passed through the fixing device11is guided by the reverse rollers12b, is switched back by the reverse rollers12b, and is conveyed again to the registration rollers7via a re-conveying path13. Thereafter, an image is formed on a second side opposite to the first side by passing through the transfer portion and the fixing device11, and the sheet is delivered to the relay unit14by the discharge rollers12a.

The image reading device2is attached to the top of the image forming apparatus1. The image reading device2includes a reading sensor2sthat reads image information from an original and an original conveying unit that conveys the originals one by one to the reading sensor2s. The image forming apparatus1can perform both a copying operation of forming an image based on image information acquired by the image reading device2and a printing operation of forming an image based on image information received from the outside of the image forming apparatus1.

According to the present embodiment, the relay unit14is disposed in a space (also referred to as an internal discharge space) between the image forming apparatus1and the image reading device2in the vertical direction (the vertical direction when the image forming system1S is installed on a horizontal plane). The relay unit14conveys the sheet discharged from the image forming apparatus1in a substantially horizontal direction viewed from the front side, toward the sheet processing apparatus4that is installed alongside of the image forming apparatus1on a common installation surface with the image forming apparatus1. The relay unit14includes a sheet sensor52serving as a detection unit for detecting passage of a sheet. The sheet sensor52is, for example, a reflective photosensor that emits infrared light onto the conveying path and detects light reflected by a sheet passing through the conveying path to determine the presence of the sheet. While the image forming system15including the relay unit14is used as an example, a sheet may be delivered directly from the image forming apparatus1to the sheet processing apparatus4.

Furthermore, the image forming apparatus1includes a display unit5(an operation unit, an operation display unit) that serves as a user interface of the image forming system1S. The display unit5has a function of displaying the operation status of the system, such as paper jamming and malfunction and an instruction for the user to perform an operation, such as replacement of consumables in the apparatus and removal of a jammed sheet. The user can operate the touch panel function of a display of the display unit5, numeric keys, and the like to perform various settings and provide instructions to the image forming system1S.

Note that the configuration of the image forming apparatus is not limited to the direct transfer system illustrated inFIG.1. The configuration may be an intermediate transfer system in which a toner image formed in the image forming unit is transferred onto a sheet via an intermediate transfer member. The image forming apparatus may be a color image forming apparatus using a plurality of image forming units. In addition, the image forming mechanism is not limited to the electrophotographic method, and may employ, for example, an inkjet printing unit or an offset printing mechanism.

Sheet Processing Apparatus

The sheet processing apparatus4includes a sheet processing device71that processes a sheet. The sheet processing apparatus4has a function of discharging, as a processing result, sheets that are received from the image forming apparatus1and are processed by the sheet processing device71. Alternatively, the sheet processing apparatus4can discharge, as a processing result, sheets received from the image forming apparatus1without performing a binding process.

The sheet processing apparatus4includes a receiving path81, an internal discharge path82, a first discharge path83, and a second discharge path84as conveying paths for conveying sheets. Furthermore, the sheet processing apparatus4includes, as discharge destinations for discharging sheets, an upper discharge tray25and a lower discharge tray37each protruding outward from an apparatus main body4A (a housing in which the receiving path81, the internal discharge path82, the first discharge path83, and the second discharge path84are provided) to the outside of the apparatus main body4A. The receiving path81is a conveying path for receiving a sheet from the image forming apparatus1and conveying the sheet, and the internal discharge path82is a conveying path for conveying a sheet toward the sheet processing device71. The first discharge path83is a conveying path for discharging a sheet to the upper discharge tray25, and the second discharge path84is a conveying path for discharging a sheet to the lower discharge tray37. As described above, according to the present embodiment, the receiving path81and the first discharge path83form a first conveying path toward the upper discharge tray25serving as a first stacking member, and the internal discharge path82is provided as a second conveying path that branches from the first conveying path. In addition, the second discharge path84is provided as a third conveying path extending from the sheet processing device71toward the lower discharge tray37serving as a second stacking member.

The receiving path81has, disposed therein, inlet rollers21, pre-branch rollers22, and an inlet sensor27. The first discharge path83has, disposed therein, discharge and reverse rollers24as a reversal conveying unit. The internal discharge path82has, disposed therein, internal discharge rollers26, intermediate conveying rollers28, kickout rollers29, and a pre-intermediate stacking sensor38. The second discharge path84has bundle discharge rollers36disposed therein. The pre-branch rollers22serve as a first conveying device of the present embodiment, the discharge and reverse rollers24serve as a second conveying device of the present embodiment, and the internal discharge rollers26serve as a third conveying device of the present embodiment. Each of the inlet rollers21, the pre-branch rollers22, the discharge and reverse rollers24, the internal discharge rollers26, the intermediate conveying rollers28, the kickout rollers29, and the bundle discharge rollers36is a roller pair in which the rollers are in contact with each other at the circumferential surface to form a nip that nips and conveys a sheet. The discharge and reverse rollers24also serve as a discharge device for discharging a sheet.

Both the inlet sensor27and the pre-intermediate stacking sensor38are examples of a sheet detection unit for detecting the passage of a sheet at a predetermined detection position in the conveying path in the sheet processing device. As the inlet sensor27and the pre-intermediate stacking sensor38, a reflective photosensor, for example, is used that emits infrared light to the inside of the conveying path and detects the light reflected by the sheet passing through the conveying path to determine the presence of the sheet.

The sheet conveying path in the sheet processing apparatus4is described below. A sheet conveyed from the image forming apparatus1via the relay unit14is received by the inlet rollers21of the sheet processing apparatus4and is conveyed to the pre-branch rollers22through the receiving path81. The inlet sensor27detects the sheet at a detection position between the inlet rollers21and the pre-branch rollers22.

The pre-branch rollers22conveys the sheet received from the inlet rollers21toward the first discharge path83.

At a predetermined time point after the inlet sensor27detects the passage of the trailing edge of the sheet, the pre-branch rollers22accelerate the sheet conveying speed to a speed higher than that of the relay unit14. Alternatively, the sheet conveying speed of the inlet rollers21may be set higher than that of the relay unit14, and the sheet conveying speed may be accelerated by the inlet rollers21upstream of the pre-branch rollers22. In this case, it is desirable to install a one-way clutch between the conveying roller of the relay unit14and a motor that drives the conveying roller so that the conveying roller runs idle even if the sheet is pulled by the inlet rollers21.

When the sheet discharge destination is the upper discharge tray25, the discharge and reverse rollers24discharge the sheet received from the pre-branch rollers22to the upper discharge tray25. In this case, the discharge and reverse rollers24decelerate the discharge speed to a predetermined discharge speed at a predetermined time point after the trailing edge of the sheet moves past the pre-branch rollers22.

When the sheet discharge destination is the lower discharge tray37, the discharge and reverse rollers24performs switchback conveyance of the sheet received from the pre-branch rollers22to convey the sheet to the internal discharge path82.

That is, the discharge and reverse rollers24convey the sheet toward the outside of the sheet processing apparatus4in the discharge direction and reverse their rotation directions to convey the sheet in the opposite direction before the trailing edge of the sheet in the discharge direction moves past the discharging and reversing rollers24. A check valve23is provided at a branching portion (between the pre-branch rollers22and the discharge and reverse rollers24) where the internal discharge path82branches from both the receiving path81and the first discharge path83upstream of the discharge and reverse rollers24in the discharge direction. The check valve23functions as a guide (a restricting member) that restricts the backward movement of the sheet switched back by the discharge and reverse rollers24to the receiving path81. That is, the discharge and reverse rollers24reverse the conveying direction of the sheet after the trailing edge of the sheet in the discharge direction moves past the check valve23to perform switchback conveyance.

The internal discharge rollers26, the intermediate conveying rollers28, and the kickout rollers29disposed in the internal discharge path82sequentially pass the sheet received from the discharge and reverse rollers24to the next rollers to convey the sheet toward the sheet processing device71. The pre-intermediate stacking sensor38detects the sheet positioned between the intermediate conveying rollers28and the kickout rollers29. The pre-intermediate stacking sensor38is, for example, a reflective photosensor that emits infrared light to the inside of the conveying path and detects the light reflected by the sheet passing through the conveying path to determine the presence of the sheet.

The sheet processing apparatus4includes a superposition processing unit4B including the discharge and reverse rollers24and the internal discharge rollers26and can perform an operation to superpose a plurality of sheets conveyed from the image forming apparatus1one on top of another by using the superposition processing unit4B. According to the present embodiment, the superposition processing unit4B holds, in the internal discharge path82, a first sheet conveyed through the receiving path81by using the discharge and reverse rollers24and the internal discharge rollers26. Subsequently, the superposition processing unit4B superposes a second sheet conveyed through the receiving path81on the first sheet. The superposition processing unit4B also has a function of outputting the superposed sheets onto the upper discharge tray25(superposed discharge) and a function of conveying the superposed sheets to the sheet processing device71(a buffer function). The configuration and operation of the superposition processing unit4B are described in detail below.

After aligning the plurality of sheets received from the internal discharge path82, the sheet processing device71performs a binding process at a predetermined position of the sheet bundle. The sheet processing device71includes a stapler50as processing equipment and an upper intermediate stacking guide31and a lower intermediate stacking guide32that constitute an intermediate stacking member (a processing tray) on which sheets to be processed are stacked.

A vertical alignment reference plate39serving as a reference member is disposed at the downstream end of the sheet processing device71in the conveying direction of the kickout roller29. The position of the sheet bundle in the vertical direction (the conveying direction) is aligned by bringing the edges of the sheets in the conveying direction into contact with the vertical alignment reference plate39. A half-moon roller33rotatably supported by the upper intermediate stacking guide31is provided downstream of the pressing guide56.

The half-moon roller33is a moving member (a paddle member, a conveying member) for bringing the sheet that has passed through the kickout rollers29into contact with the vertical alignment reference plate39. After the trailing edge of the sheet moves past the pre-intermediate stacking sensor38, the half-moon roller33conveys the sheet toward the vertical alignment reference plate39at a predetermined time point. The contact pressure of the half-moon roller33against the sheet is adjusted to such an extent that the half-moon roller33slips on the sheet when the sheet is in contact with the vertical alignment reference plate39. A flexible pressing guide56is fixed to the upper intermediate stacking guide31and presses the sheet in the sheet processing device71downward with a predetermined pressure to prevent the sheet from lifting. Furthermore, a bundle pressing flag30is rotatably supported downstream of the kickout rollers29to prevent the trailing edge of the sheet from lifting so that the trailing edge of the sheet already stacked in the sheet processing device71does not interfere with the leading edge of the succeeding sheet discharged by the kickout rollers29.

When the alignment of a predetermined number of sheets on the intermediate stacking member is finished, the stapler50performs a binding operation. Then, the bundle discharge guide34serving as an extrusion member driven by a guide drive unit35moves in a direction from the standby position illustrated inFIG.1toward the bundle discharge rollers36(a bundle discharge direction). Thus, the sheet bundle is pushed out of the intermediate stacking member. When the leading edge of the sheet bundle in the bundle discharge direction reaches the bundle discharge rollers36, the bundle discharge guide34stops and returns to the standby position again. The bundle discharge rollers36serving as a discharge device (a fourth conveying device) discharges the sheet bundle received from the bundle discharge guide34to the lower discharge tray37.

Both the upper discharge tray25and the lower discharge tray37are movable vertically relative to the housing of the sheet processing apparatus4. Sheet presence sensors51and53for detecting the presence/absence of a sheet on a tray are disposed on the upper discharge tray25and the lower discharge tray37, respectively. The sheet presence sensors51and53are, for example, reflective photosensors that determine the presence/absence of a sheet by emitting infrared light upward from the tray stacking surface and detecting reflected light from the sheets. The sheet processing apparatus4further includes a sheet surface detection sensor that detects the upper surface position of the sheets (the sheet stack height) on each of the upper discharge tray25and the lower discharge tray37.

When the sheet surface detection sensor detects a sheet, the corresponding one of the upper discharge tray25and the lower discharge tray37tray is lowered in an A2 or B2 direction. When the sheet presence sensor51or53detects that the sheet has been removed from the upper discharge tray25or the lower discharge tray37, the tray is raised in the A1 or B1 direction. The upper discharge tray25and the lower discharge tray37are controlled to move up and down according to the number of stacked sheets so that the upper surfaces of the stacked sheets are positioned below the discharge and reverse rollers24and the bundle discharge rollers36in the vertical direction, respectively. According to the present embodiment, the upper discharge tray25serving as the first stacking member and the lower discharge tray37serving as the second stacking member are controlled to be raised and lowered by motor drive. However, the upper discharge tray25and the lower discharge tray37may be configured so as to be raised and lowered by an urging unit, such as a spring.

The stapler50is an example of the processing equipment. For example, a sorting mechanism for sorting sheets and a center-folding processing unit for center folding a plurality of sheets and perform saddle stitch book binding may be provided.

Superposition Processing Unit

FIG.2is an enlarged view of the superposition processing unit4B. The sheet conveying path between the inlet rollers21and the pre-branch rollers22(the receiving path81) consists of an upper inlet guide40and a lower inlet guide41. The sheet conveying path between the internal discharge rollers26and the intermediate conveying rollers28(the internal discharge path82) consists of an upper internal discharge guide46and a lower internal discharge guide47. A conveying guide that guides a sheet from the same side as the upper inlet guide40between the pre-branch rollers22and the discharge and reverse rollers24is referred to as an upper reverse guide42. A conveying guide that guides a sheet from the same side as the lower internal discharge guide47between the discharge and reverse rollers24and the internal discharge rollers26is referred to as a lower reverse guide43. The first discharge path83consists of the upper reverse guide42and the lower reverse guide43.

The sheet conveyed by the inlet rollers21is guided to the pre-branch rollers22by the upper inlet guide40and the lower inlet guide41. The inlet sensor27is disposed on the upper inlet guide40. As the inlet sensor27, a reflective photosensor can be used that determines the presence of a sheet at the detection position by emitting infrared light to the receiving path81and detecting reflected light from the sheet. In this case, a hole having a diameter greater than the diameter of the spotlight of the inlet sensor27is formed in a portion of the lower inlet guide41facing the inlet sensor27so that the infrared light is not reflected when a sheet does not pass through the receiving path81.

The check valve23is disposed downstream of the pre-branch rollers22and at a portion where the receiving path81and the internal discharge path82branch from the first discharge path83. The check valve23is rotatably supported by the upper internal discharge guide46via a rotating shaft23a. In addition, the check valve23is always urged by a spring (not illustrated) in a C2 direction (the clockwise direction inFIG.2) toward a position (refer toFIG.2) where the top end of the check valve23overlaps the upper reverse guide42as viewed from the axial direction of the rotating shaft23a(the width direction of a sheet). The spring constant of the spring is set to such a value that when a sheet delivered from the pre-branch rollers22is brought into contact with the check valve23, the check valve23rotates in the C1 direction (the counterclockwise direction inFIG.2) against the biasing force of the spring. Thus, the check valve23enables the sheet conveyed from the pre-branch rollers22toward the discharge and reverse rollers24to pass therethrough. In addition, when the trailing edge of the sheet in the receiving path81passes through the check valve23, the check valve23rotates in the C2 direction and restricts the sheet from returning from the discharge and reverse rollers24to the pre-branch rollers22.

The discharge and reverse rollers24consist of an upper roller24aand a lower roller24b. According to the present embodiment, driving force is input to both the upper roller24aand the lower roller24b, and the rotations of the upper roller24aand the lower roller24bare always synchronized.

The discharge and reverse rollers24are configured to contact each other (a close operation) and separate from each other (an open operation) by a plunger solenoid45. More specifically, one end of a separation lever44is connected to the roller shaft of the upper roller24a, and the separation lever44is supported by a lever fulcrum shaft44ain a rotatable manner with respect to the upper reverse guide42. A solenoid connection shaft44bprovided at the other end of the separation lever44is connected to a plunger of the plunger solenoid45.

When the plunger solenoid45is powered on, the plunger is attracted in a D1 direction by a magnetic force. Thus, the separation lever44rotates in an E1 direction, and the discharge and reverse rollers24are separated from each other (the nip of the roller pair is released). When the plunger solenoid45is powered off, the upper roller24ais brought into contact with the lower roller24bby the biasing force of a pressure spring48connected to the roller shaft of the upper roller24a, and the discharge and reverse rollers24are in contact with each other (the nip is closed). At this time, the separation lever44rotates in the E2 direction as the upper roller24amoves, and the plunger of the plunger solenoid45moves in the D2 direction.

The internal discharge rollers26form a roller pair adjacent to the discharge and reverse rollers24in the sheet conveying direction in the internal discharge path82. The roller pair is capable of forward rotation and reverse rotation. That is, the internal discharge rollers26can convey a sheet in both the direction from the discharge and reverse rollers24to the sheet processing device71(hereinafter referred to as a G1 direction) and the direction from the sheet processing device71to the discharge and reverse rollers24(hereinafter referred to as a G2 direction).

Hardware Configuration

The hardware configuration of the image forming system1S according to the present embodiment is described below with reference toFIG.3.FIG.3mainly illustrates, of the hardware configuration of the image forming system1S, a portion related to the configuration of the sheet processing apparatus4. A video controller601performs overall control of the image forming system1S including the image forming apparatus1and the sheet processing apparatus4. An engine control unit602controls the image forming apparatus1.

A main control unit603controls the sheet processing apparatus4. A signal line604is a signal line for serial command transmission to transmit a command from the video controller601to the engine control unit602by serial communication, and a signal line605is similarly used to transmit a command from the video controller601to the main control unit603. A signal line606is a signal line for serial status transmission to transmit status data from the engine control unit602to the video controller601by serial communication in response to a command, and a signal line607is similarly used to transmit status data from the main control unit603to the video controller601. To perform an image forming operation, the video controller601transmits serial commands to the engine control unit602and the main control unit603and receives status data from the engine control unit602and the main control unit603. Thus, the video controller601performs control. In this way, when a plurality of apparatuses are connected and the image forming system1S operates, the video controller601manages the control and status of each of the apparatuses and ensures the consistency of the operations performed by the apparatuses.

The main control unit603includes a central processing unit (CPU)608that controls various operations performed by the sheet processing apparatus4and a random access memory (RAM)609that temporarily stores control data necessary for the operations performed by the sheet processing apparatus4.

The main control unit603further includes a nonvolatile read only memory (ROM)610that stores programs and control tables necessary for the operation performed by the sheet processing apparatus4. The main control unit603further includes a communication unit611for communicating with the video controller601, a system timer612that generates timings necessary for various controls, and an input and output (I/O) port613that inputs and outputs control signals from and to various units of the sheet processing apparatus4. The main control unit603is a control integrated circuit (IC) to which the above-described elements are connected via a bus614.

Input signals from the inlet sensor27and the sheet presence sensors51and53of the upper discharge tray25and the lower discharge tray37are transmitted to the main control unit603via input circuits615,626, and628, respectively. The control signals from the main control unit603are transmitted to an inlet motor641, a pre-branch motor642, a discharge and reverse motor643, an internal discharge motor644, and the plunger solenoid45via drive circuits618,619,620,621, and623, respectively. Thus, the driving of actuators is controlled.

Functional Block

The functional blocks of the present embodiment are described below with reference toFIG.4. The main control unit603illustrated inFIG.4has a function of performing a sheet conveying operation by using the sheet processing apparatus4. The main control unit603has at least the functions of the communication unit611, a system timer612, a sheet conveying controller701, a sensor controller720, a motor controller721, and a solenoid controller722.

The sensor controller720is a unit for inputting signals from the inlet sensor27and the sheet presence sensor51of the upper discharge tray25to the sheet conveying controller701. The sheet conveying controller701includes a superposed conveying controller711and a sheet count controller712. The sheet conveying controller701controls the motor controller721and the solenoid controller722on the basis of the input from the sensor controller720to achieve the operations performed by the superposition processing unit4B, the upper discharge tray25, and the lower discharge tray37. The superposed conveying controller711controls conveyance of a sheet to the superposition processing unit4B and the upper discharge tray25while managing the position of the sheet on the basis of mainly the input from the sensor controller720. The sheet count controller712determines the timing of discharging the superposed sheets to the upper discharge tray25on the basis of the maximum number of sheets that can be superposed by the superposition processing unit4B (the number of superposable sheets) and the current number of superposed sheets.

The inlet motor641drives the inlet rollers21, the pre-branch motor642drives the pre-branch rollers22, and the discharge and reverse motor643drives the discharge and reverse rollers24. The internal discharge motor644drives the internal discharge rollers26, and the plunger solenoid45drives the separation lever44. The operations performed by these elements to be driven are described in detail below.

Superposed Discharge Operation

An overview of a bundle discharge operation (a superposed discharge operation) in which the superposed conveying controller711superposes and discharges a plurality of sheets by the superposition processing unit4B is described with reference toFIGS.5A to5G. Hereinafter, among the sheets to be subjected to the superposed discharge operation, a sheet conveyed from the image forming apparatus1to the sheet processing apparatus4first (a first sheet) is referred to as a “sheet S1”, and a sheet conveyed from the image forming apparatus1to the sheet processing apparatus4second (a second sheet) is referred to as a “sheet S2”. In addition, the conveying speed of the pre-branch rollers22, the discharge and reverse rollers24, and the internal discharge rollers26before acceleration (the conveying speed in the relay unit14) is defined as V1, and the conveying speed after acceleration is defined as V2. The conveying speed when a sheet is discharged by the discharge and reverse rollers24is defined as V3. According to the present embodiment, the conveying speed V3can be changed according to the number of sheets in the bundle.

Referring toFIG.5A, at the time the trailing edge of the preceding sheet S1passes the inlet sensor27, the pre-branch rollers22and the discharge and reverse rollers24are accelerated from the speed V1to the speed V2. By accelerating the conveying speed of the sheet S1, even in the case where the image forming apparatus1is a high-performance machine with high throughput, the sheet interval required for switchback can be ensured between the sheet S1and the succeeding sheet S2. However, if the sheets S1and S2do not collide with each other, a configuration in which the conveying speed at the inlet sensor27is not accelerated may be employed. In this case, the conveying speed in the superposition processing unit4B may be set to V1at all times. At the time inFIG.5A, the discharge and reverse rollers24are conveying the sheet S1in an F2 direction.

Referring toFIG.5B, at the time the trailing edge of the sheet S1passes the inlet sensor27, moves a predetermined distance, and passes through the check valve23, the sheet S1is temporarily stopped. The “predetermined distance” is the distance at which the trailing edge of the sheet S1in the F2 direction has passed through the check valve23and does not reach the nip of the discharge and reverse rollers24.

Referring toFIG.5C, the discharge and reverse rollers24change their rotation directions and convey the sheet S1in an F1 direction at the speed V2. The driving of the internal discharge rollers26is started before the leading edge of the sheet S1in the F1 direction reaches the internal discharge rollers26, and the internal discharge rollers26further convey the sheet S1in the G1 direction.

Referring toFIG.5D, the sheet S1is nipped by the internal discharge rollers26. When the leading edge of the sheet S1in the G1 direction (the F1 direction) moves past the internal discharge rollers26and, thereafter, the sheet S1is conveyed by a predetermined distance, the conveyance of the sheet S1is stopped. The “predetermined distance” is less than the distance at which the leading edge of the sheet S1reaches the intermediate conveying rollers28. When the sheet S1is nipped by the internal discharge rollers26, the upper roller24aof the discharge and reverse rollers24is moved in the E1 direction by the separation lever44so as to be separated from the lower roller24b. Note that the discharge and reverse rollers24are driven so as to separate from each other before the leading edge of the succeeding sheet S2reaches the discharge and reverse rollers24.

Referring toFIG.5E, after the trailing edge of the succeeding sheet S2passes the inlet sensor27, the pre-branch rollers22and the discharge and reverse rollers24are accelerated to the speed V2in the same manner as the preceding sheet S1. When the trailing edge of the sheet S2passes the inlet sensor27and, thereafter, a predetermined time T_wait elapses, the internal discharge rollers26start rotating again toward the discharge and reverse rollers24, and the sheet S1is conveyed in the G2 direction. The predetermined time T_wait is described in more detail below. When the relative speeds of the sheets S1and S2become equal, the upper roller24aof the discharge and reverse rollers24is driven in the E2 direction and comes into contact with the lower roller24b, and the discharge and reverse rollers24nip the sheets S1and S2at the same time. At this time, the leading edge of the sheet S1and the leading edge of the sheet S2in the F2 direction are aligned. In addition, before the discharging and reversing rollers24nip the sheets S1and S2, the rotation speed of the discharge and reverse rollers24is adjusted so as to be equal to the speed V2, which is the conveying speed of the sheets S1and S2.

Referring toFIG.5F, when the trailing edge of the sheet S2passes through the check valve23, the sheets S1and S2form a sheet bundle S′ in which both the leading edges and trailing edges of the sheets S1and S2in the F2 direction are aligned.

Referring toFIG.5G, the speed of the sheet bundle S′ is changed to the speed V3before a distance L from the discharge and reverse rollers24, and the sheet bundle S′ is discharged to the upper discharge tray25by the discharge and reverse rollers24.

Thus, the operation of superposing and discharging the two sheets S1and S2while aligning the two sheets S1and S2in the superposition processing unit4B (the superposed discharge operation) is completed. When the image forming operation is continuously performed on a large number of sheets, two-sheet bundles are stacked on the upper discharge tray25by repeating the above-described superposed discharge operation.

Advantages of the present embodiment are described below, compared with the case where the sheets S1and S2are discharged one by one without being subjected to the superposed discharge operation. When the sheets S1and S2are discharged one by one, the positions and postures of the sheets S1and S2that have passed through the discharge and reverse rollers24may be lost before the sheets S1and S2land on the upper surface of the upper discharge tray25or the upper surface of the sheets on the upper discharge tray25. This is because while falling down, each of the sheets S1and S2receives air resistance and, thus, moves in all directions as viewed from above.

In contrast, according to the present embodiment, the positions of the sheets S1and S2are aligned in the sheet conveyance direction and the sheets S1and S2are superposed in advance and are discharged, so that the positions and postures of the sheets S1and S2are less likely to be lost.

When the sheet bundle discharged through the superposed discharge operation is compared with the sheets discharged one by one, the projected areas of the sheet (bundle) and the single sheet as viewed from above are the same, but the weight of the sheet bundle is two times the weight of the single sheet. For this reason, the sheet bundle is less susceptible to air resistance. As a result, even when the sheet discharge speed of the discharge and reverse rollers24is increased to improve the productivity of the image forming system1S and the productivity of the sheet processing apparatus4, a degradation of the sheet stackability can be avoided.
Three or More Sheet Superposed Discharge Operation

While the above description has been made with reference to the conveyance of two sheets, the sheet processing apparatus4of the present embodiment can perform a superposed discharge operation to align the positions of three or more sheets, superpose the sheets on top of another in the superposition processing unit4B, and discharge the sheets to the upper discharge tray25.

When the superposed discharge operation is performed for three sheets, two sheets S1and S2are first superposed in the same procedure as described above with reference toFIGS.5A to5F. Thereafter, the discharge and reverse rollers24illustrated inFIG.5Fare reversed again so that the sheet bundle S′ is conveyed in the G1 direction. Subsequently, a third sheet S3is subjected to operations the same as those performed on the sheet S2inFIGS.5C to5Fwhile the sheet bundle S′ is being subjected to operations the same as those performed on the sheet S1inFIGS.5C to5F.

As a result, after the sheet bundle S′ is temporarily stopped while being held by the internal discharge rollers26in the internal discharge path82, when the predetermined time T_wait elapses since the inlet sensor27detected the trailing edge of the third sheet S3, the internal discharge rollers26convey the sheet bundle S′ in the G2 direction. Thereafter, the discharge and reverse rollers24that have been open is closed, so that the three sheets S1, S2, and S3are nipped by the discharge and reverse rollers24at the same time. When the trailing edge of the sheet S3passes through the check valve23, a sheet bundle is formed in which both the leading edges and the trailing edges of the three sheets S1, S2, and S3are aligned.

When the number of sheets in the superposed discharge operation is three, the sheet bundle is directly discharged in the G2 direction by the discharge and reverse rollers24and is stacked on the upper discharge tray25. When the number of sheets in the superposed discharge operation is four or more, the discharge and reverse rollers24convey the sheet bundle again in the G1 direction and repeats the same operations as inFIGS.5C to5F. In this manner, the number of sheets to be superposed can be increased.

The sheet count controller712manages the number of sheets to be superposed in the superposition processing unit4B on the basis of the number of sheets superposable by the superposition processing unit4B and information regarding the sheet to be conveyed. That is, the sheet count controller712determines whether the sheet conveyed to the superposition processing unit4B is immediately discharged to the upper discharge tray25or is superposed on top of another.

As an example of the determination technique, let N denote the number of superposable sheets by the superposition processing unit4B. Then, the sheet count controller712generates a sheet bundle of N−1 sheets and discharges the sheet bundle to the upper discharge tray25. Only when the sheet count controller712determines that the Nth sheet is the last sheet, the number of sheets to be superposed is set to N. In this way, the sheet count controller712prevents discharge of the Nth sheet to the upper discharge tray25as one sheet.

As a specific example, the number of superposable sheets by the superposition processing unit4B is five in the configuration example according to the present embodiment. In this case, the sheet count controller712repeatedly performs the superposed discharge operation for four sheets and stacks a sheet bundle of the four sheets on the upper discharge tray25. At this time, if the sheet count controller712determines that the fifth sheet is the last sheet and the last sheet is discharged as one sheet if the superposed discharge operation for four sheets is repeated to the end, a superposed discharge operation for five sheets including the last sheet is performed, and the sheets are discharged to the upper discharge tray25. If the last sheet is superposed on another sheet even after the superposed discharge operation for four sheets is performed to the end, the sheet bundle is discharged to the upper discharge tray25when the sheet bundle including the last sheet is formed.

That is, when executing a job of discharging a predetermined number of sheets to the upper discharge tray25, the sheet count controller712changes the number of sheets in a bundle formed through the superposed discharge operation in accordance with a predetermined number of sheets so that each of the predetermined number of sheets is always included in a sheet bundle of two or more sheets formed through the superposed discharge operation and is discharged to the upper discharge tray25. As a result, it is possible to prevent a single sheet from being discharged to the upper discharge tray25and, thus, prevent a degradation of the sheet stackability. Note that the technique for controlling the number of sheets in the superposed discharge operation is not limited thereto. Any technique that avoids discharge of a single sheet can be employed. For example, in the above-described example, the number of sheets in the successive superposed discharge operations may be four, . . . , four, three, and two.

Way to Find T_wait

The timing management (a method for obtaining T_wait described above) is described that is performed by the superposed conveyance controller711to align the leading edges of the sheets S1and S2in the superposition processing unit4B.

FIG.7Aillustrates the positional relationship between the sheets S1and S2at the moment the inlet sensor27detects the trailing edge of the sheet S2. A distance L1is the distance from the detection position of the inlet sensor27to the nip position of the discharge and reverse rollers24(the length measured along the receiving path81and the first discharge path83). A distance L2is the distance from the position where after passing the internal discharge rollers26, the leading edge of the reversed sheet S2moves a predetermined distance d1and stops to the nip of the discharge and reverse rollers24(the length measured along the first discharge path83and the internal discharge path82).

FIG.7Billustrates the positional relationship between the sheets S1and S2when conveyance of the sheet S1inFIG.7Ais started in the F2 direction (the G2 direction) and the conveying speed of the sheet S1becomes equal to the conveying speed of the sheet S2. At this time, it is assumed that the trailing edges of the sheets S1and S2in the F2 direction are shifted from each other by a protrusion amount Kt.

FIG.7Cillustrates a change in the speed of each of the sheets S1and S2during the operations illustrated inFIGS.7A and7B. InFIG.7C, “A” represents the moment when the inlet sensor27detects the trailing edge of the sheet S2as illustrated inFIG.7Aand, thus, the pre-branch rollers22start accelerating from the speed V1to the speed V2with a constant acceleration. InFIG.7C, “B” represents the time the sheet S2has completed accelerating to the speed V2.

InFIG.7C, “C” represents the time a predetermined time T_wait has elapsed since the inlet sensor27detected the trailing edge of the sheet S2, that is, the time the internal discharge rollers26start conveying the sheet S1in the G2 direction. InFIG.7C, “D” represents the time the relative speed between the sheets S1and S2becomes zero as illustrated inFIG.7B.

Let T_merge denote the elapsed time from A to D. Let T1denote the time required for the pre-branch rollers22to accelerate from the speed V1to the speed V2(the elapsed time from A to B). Let T2denote the time from acceleration of the pre-branch rollers22to the speed V2until start of the rotation of the internal discharge rollers26(the elapsed time from B to C). As can be seen from the definitions of T1, T2and T_wait, T_wait=T1+T2. Let T3denote the time required for the stopped sheet S1to accelerate to the speed V2with a constant acceleration (the elapsed time from C to D).

Let X2denote the distance that the sheet S1moves from the position inFIG.7Ato the position inFIG.7B. Then, as can be seen from the above description, X2is the distance that the sheet S1moves from C to D inFIG.7Cand can be given by the following equation:
X2=(V2×T3)/2  (1).

In addition, let X1denote the distance that the sheet S2moves from the position inFIG.7Ato the position inFIG.7B. Then, X1is the distance that the sheet S2moves from A to D inFIG.7Cand can be given by the following equation:
X1=(V1+V2)×T1/2+V2×(T2+T3)  (2).

From the positional relationship between the sheets S1and S2at the time inFIG.7B, the following relationship holds:
L1−X1=L2−X2−Kt(3).

Substituting equations (1) and (2) into equation (3) and expanding and rearranging the equation yields the following equation:
L1−L2+Kt=(T1/2)×V1+(T1/2+T2+T3/2)×V2  (4).

Substituting T_wait=T1+T2into the above equation (4) and rearranging the equation, the waiting time T_wait from when the trailing edge of the sheet S2passes the inlet sensor27to when the internal discharge rollers26start conveying the sheet S1is given for the protrusion amount Kt by the following equation:
T_wait=(L1−L2+Kt)/V2−(T1/2)×V1/V2+(T1−T3)/2  (5).

To align the leading and trailing edges of the sheets S1and S2and superpose the sheets S1and S2, the waiting time T_wait can be calculated by setting Kt=0 in the above equation (5). By starting the conveyance of the sheet S1by the internal discharge rollers26on the basis of the calculated T_wait, the sheet bundle S′ in which the leading and trailing edges of the sheets S1and S2are aligned can be formed. In addition, by using the same value of T_wait when three or more sheets are superposed, a sheet bundle in which the leading and trailing edges of the sheets are aligned can be formed.

Control Example

An example of a method for controlling the sheet processing apparatus4that achieves the superposed discharge operation described with reference toFIGS.5A to5Gis described below with reference to the flowchart illustrated inFIGS.6A and6B. This flow is executed each time the main control unit603of the sheet processing apparatus4receives a notification from the video controller601that one sheet is discharged from the image forming apparatus1. The steps of the flowchart are executed by the superposed conveying controller711illustrated inFIG.4unless otherwise specified.

In the following description, the term “first sheet” refers to a sheet conveyed first to the sheet processing apparatus4among the sheets to be superposed in the superposition processing unit4B to form a sheet bundle. For example, when four sheets are superposed and discharged to the upper discharge tray25, the sheet conveyed to the sheet processing apparatus4after the last sheet of the preceding sheet bundle (that is, the (4n+1)th sheet) is the first sheet. The term “last sheet” refers to a sheet that is conveyed to the sheet processing apparatus4last among the sheets to be superposed in the superposition processing unit4B to form a sheet bundle (that is, the 4nth sheet in the above example).

In step S101, rotation of the inlet rollers21and the pre-branch rollers22is started at the speed V1. Thereafter, the processing proceeds to step S102. If the inlet rollers21and the pre-branch rollers22are already rotating at the speed V1, the rotation of the rollers is continued.

In step S102, it is determined whether the current sheet is a first sheet. If Yes, then the processing proceeds to step S103, and if No, the processing proceeds to step S106.

In step S103, the discharge and reverse rollers24are brought into contact with each other, and the rotation of the discharging and reversing rollers24is started in a direction in which the first sheet is conveyed toward the upper discharge tray25(the G2 direction) at the speed V1(refer to the sheet S1inFIG.5A). The processing proceeds to step S104.

In step S104, it is determined whether the trailing edge of the first sheet has passed the inlet sensor27. If Yes, the processing proceeds to step S105, and if No, the processing proceeds to step S104.

In step S105, the pre-branch rollers22and the discharge and reverse rollers24are accelerated to the speed V2(refer to the sheet S1inFIG.5A). The processing proceeds to step S111.

In step S106, it is determined whether the trailing edge of the current sheet (one of the second and succeeding sheets) has passed the inlet sensor27. If Yes, the processing proceeds to step S107, and if No, the processing proceeds to step S106.

In step S107, the pre-branch rollers22and the discharge and reverse rollers24are accelerated to the speed V2. As a result, the conveying speed of the current sheet is accelerated from the speed V1to the speed V2(refer to the sheet S2inFIG.5D). The processing proceeds to step S108.

In step S108, it is determined whether a predetermined time T_wait has elapsed since the time the trailing edge of the current sheet passed the inlet sensor27. If Yes, the processing proceeds to step S109, and if No, the processing proceeds to step S108.

In step S109, rotation of the internal discharge rollers26is started again in the direction in which the sheet is conveyed toward the discharge and reverse rollers24(the F2 direction) at a speed V2(refer to the sheet S1inFIG.5D). The processing proceeds to step S110.

In step S110, at the time the conveying speed of the sheets (a bundle) conveyed by the internal discharge rollers26and the conveying speed of the current sheet become equal, the upper roller24aof the discharge and reverse rollers24is moved in the E2 direction so as to come into contact with the lower roller24b(refer toFIG.5E). As a result, the sheets (the bundle) conveyed by the internal discharge rollers26and the current sheet are nipped by the discharge and reverse rollers24at the same time (refer toFIG.5E). The processing proceeds to step S111.

In step S111, it is determined whether the current sheet is the last sheet. If Yes, the processing proceeds to step S112, and if No, the processing proceeds to step S116.

In step S112, the sheet bundle including the last sheet is discharged to the upper discharge tray25(refer toFIG.5F). That is, the sheet conveyance started in step S107or S109by using the discharge and reverse rollers24and the internal discharge rollers26is continued.

In step S113, when the trailing edge of the sheet bundle reaches the distance L from the discharge and reverse rollers24, the conveying speed of the discharge and reverse rollers is changed to the speed V3, and the sheet bundle is discharged to the upper discharge tray25. According to the present embodiment, the discharge speed V3is set according to the number of sheets in a sheet bundle to be discharged.

In step S114, it is determined whether the trailing edge of the sheet bundle has passed through the discharge and reverse rollers24. If Yes, the processing proceeds to step S115, and if No, the processing proceeds to step S114.

In step S115, the pre-branch rollers22is decelerated to the speed V1, and the discharge and reverse rollers24and the internal discharge rollers26are stopped. Thus, the flow ends. If the current sheet is the last sheet in the job (if no more sheets are conveyed from the image forming apparatus1), the inlet rollers21and pre-branch rollers22are also stopped in step S115.

In step S116, it is determined whether the trailing edge of the current sheet (a sheet other than the last sheet) has passed through the check valve23. If Yes, the processing proceeds to step S117, and if No, the processing proceeds to step S116.

In step S117, the discharge and reverse rollers24and the internal discharge rollers26are temporarily stopped (refer to the sheet S1inFIG.5B). The processing proceeds to step S118.

In step S118, rotation of the discharge and reverse rollers24and rotation of the internal discharge rollers26are started in a rotation direction for conveying the sheets (the bundle) in the direction after reversal (the F1 direction, G1 direction) at the speed V2(refer to the sheet S1inFIG.5C). The processing proceeds to step S119.

In step S119, it is determined whether the leading edge of the sheets (the bundle) has passed through the internal discharge rollers26. If Yes, the processing proceeds to step S120, and if No, the processing proceeds to step S119.

In step S120, the upper roller24ais separated from the lower roller24bof the discharge and reverse rollers24. The processing proceeds to step S121.

In step S121, at the position where the leading edge of the sheets (the bundle) has passed through the internal discharge rollers26and has been conveyed by a predetermined distance, the pre-branch rollers22is decelerated to the speed V1, and the discharge and reverse rollers24and the internal discharge rollers26are stopped. Thus, the flow ends. As a result, the sheets (the bundle), which are the target of the superposed discharge operation and are still superposed on other sheets, are held while being nipped by the internal discharge rollers26(refer to the sheet S1inFIG.5D).

As described in step S113, according to the present embodiment, the discharge speed V3is set according to the sheet bundle to be discharged. The reason for this setting is described below with reference toFIG.8. The flight distance of the sheet bundle discharged by the discharge and reverse rollers24varies according to the number of sheets in a bundle. If an air resistance R is not taken into account, the flight trajectory of the sheet bundle is determined by the initial speed V3and a discharge angle θ at the time of discharge of a sheet material. Therefore, the flight distance is constant regardless of the number of sheets in a bundle. In reality, the air resistance R acts on the sheet material, and the discharge trajectory of the sheet bundle is changed for each number of sheets in the bundle.

For this reason, if the discharge speed V3is constant regardless of the number of sheets in a bundle, variations occur in the flight distance of the sheet bundle from the discharge and reverse rollers24, as illustrated inFIG.8, leading to a degradation of stackability or a discharge failure. If the flight distance of the discharged sheet bundle is too large, the sheet bundle may jump out the sheets already stacked on the upper discharge tray25. If the flight distance of the sheet bundle is insufficient, the trailing edge of the sheet bundle is caught by the discharge and reverse rollers24, which causes a discharge failure.

Therefore, according to the present embodiment, the discharge speed V3is set according to the number of sheets in a bundle to be discharged to avoid the above-described issues.FIG.9Aillustrates the flight trajectories when the discharge speed is set to a constant value regardless of the number of sheets in a bundle, andFIG.9Billustrates the flight trajectories when the discharge speed is changed according to the number of sheets in a bundle.

As illustrated inFIG.9A, when the discharge speed is set to a constant value (a discharge speed V31) regardless of the number of sheets in a bundle, the flight distance of the bundle from the discharge and reverse rollers24varies. Accordingly, as illustrated inFIG.9B, different discharge speeds are set. That is, the discharge speed for the 2 sheet bundle is set to V32, the discharge speed for the 3 sheet bundle is set to V33, and the discharge speed for the 4 sheet bundle is set to V34. As a result, as illustrated inFIG.9B, the flight distance of the sheet bundle from the discharge and reverse rollers24can be made constant. As the number of sheets in a bundle increases, the mass of the bundle increases. Thus, the bundle of sheets is less likely to be influenced by the air resistance, so the flight distance of the bundle of sheets increases. Therefore, the discharge speed V3is set such that the discharge speed V3decreases with increasing number of sheets in the bundle.

That is, when the number of sheets in the sheet bundle is a first number of sheets (for example, 2 sheets), the discharge speed V3is set to a first discharge speed (for example, a discharge speed V32). When the number of sheets in the sheet bundle is a second number of sheets that is greater than the first number of sheets (for example, 3 sheets), the discharge speed V3is set to a second discharge speed that is lower than the first discharge speed (for example, a discharge speed V33).

As a result, regardless of the number of sheets in the bundle, the sheet bundle can be discharged to the target position, improving the stackability. Note that the discharge speed V3can be changed by the time the trailing edge of the sheet bundle passes through the discharge and reverse rollers24at the latest.

Instead of changing the discharge speed V3according to the number of sheets in the bundle, a threshold may be set for the number of sheets in a bundle. For example, when the number of sheets in the bundle is 2 or 3, the discharge speed V3may be set to the first discharge speed. When the number of sheets in the bundle is 4 (which is greater than or equal to the threshold), the discharge speed V3may be set to the second discharge speed (in this case, the threshold is 4 sheets). The discharge speed V3can be appropriately set according to the discharge angle of the discharge and reverse rollers24, the positional relationship between the upper discharge tray25and the discharge and reverse rollers24, and the like.

In some cases, the flight distance changes according to the basis weight of the sheet, giving an impact on the stackability. For example,FIG.10Aillustrates the discharge trajectory of a sheet bundle S′w1with a basis weight of W1. The discharge speed V3is set to one of V32to V34according to the number of sheets in the bundle. In this setting, when a sheet bundle S′w2with a basis weight of W2is discharged, the flight distance differs from that of the sheet bundle S′w1with a basis weight of W1(FIG.10B). More specifically, the influence of air resistance increases with decreasing basis weight of the sheets and, thus, the flight distance of the bundle of the sheets decreases.

Accordingly, when a bundle (a first sheet bundle) consisting of a plurality of sheets of a first basis weight is formed, the discharge speed V3is set to a third discharge speed. When a bundle (a second sheet bundle) consisting of a plurality of sheets with a second basis weight (the sheets with a basis weight that is less than the first basis weight) is formed, the discharge speed V3is set to a fourth discharge speed. The fourth discharge speed is set so as to be greater than the third discharge speed.

In addition, in some cases, the flight distance varies according to the size of the sheet, giving an impact on the stackability. In this case, the setting of the discharge speed V3may be changed according to the sheet size and the number of sheets in the same manner as described above. Furthermore, in some cases, the curl direction of the sheets varies according to the print mode (for example, double-sided printing or single-sided printing) or the medium type (FIGS.11A and11B). The effect of the air resistance R on a sheet bundle may vary according to the curl direction, resulting in a difference in flight distance. As a result, variations in the flight distance of the discharged sheet bundle may occur, and the stackability may deteriorate. In this case, the setting of the discharge speed V3may be changed according to the print mode or the medium type and the number of sheets in the bundle in the same manner as described above.

As described above, according to the present embodiment, when a plurality of sheets that are continuously conveyed are discharged onto the first stacking member, the superposition processing unit4B can superpose the plurality of sheets while aligning the edges of the sheets and, thereafter, discharge the sheets. As a result, the stackability of the sheets on the first stacking member can be improved while maintaining the productivity. In addition, when the superposition processing unit4B superposes a plurality of sheets while aligning the edges of the sheets and, thereafter, discharge the sheets, the discharge speed can be changed according to the number of sheets that form the bundle. As a result, the flight distance of the sheet bundle discharged onto the first stacking member from the discharge and reverse rollers24can be made constant and, thus, the sheet stackability can be improved.

While the configuration example of the present embodiment has been described with reference to the maximum number of sheets that can be superposed by the superposition processing unit4B (the number of superposable sheets) being five, the number of superposable sheets can be appropriately changed according to the particular configuration of the superposition processing unit4B and the performance required for the superposition processing unit4B.

Buffer Operation Performed by Sheet Processing Device

The superposition processing unit4B of the present embodiment can also operate as a buffer unit that superposes and holds sheets received from the image forming apparatus1while the sheet processing device71is processing sheets. By performing the buffer operation, collision of sheets in the sheet processing device71is avoided without decreasing the productivity of the image forming apparatus1. As a result, the productivity of the image forming system1S is improved.

When the buffer operation is performed, the operation performed by the superposition processing unit4B is basically common to the superposed discharge operation, except that the bundle of superposed sheets is conveyed to the sheet processing device71via the internal discharge path82. That is, in the operations illustrated inFIGS.5A to5G, the bundle of superposed sheets illustrated inFIG.5Fis not discharged to the upper discharge tray25but is conveyed to the sheet processing device71via, for example, the internal discharge rollers26. In addition, after the sheet bundle is conveyed to the sheet processing device71, the succeeding sheets for which buffering is not needed are switched back one by one by the discharge and reverse rollers24, and the sheets are conveyed to the sheet processing device71.

In the buffer operation, a protrusion amount Kt (FIG.7B) may be set so that the leading edges of the superposed sheets are shifted from each other by a predetermined distance. In this case, it is desirable to set the protrusion amount Kt so that the lower sheet (the sheet S1inFIG.7B) in the sheet processing device71protrudes further downstream in the sheet conveying direction toward the sheet processing device71. In this way, the half-moon roller33can be brought into contact with each of the sheets in the bundle superposed through the buffer operation, and an aligning operation can be effectively performed.

As described above, the superposition processing unit4B of the present embodiment has the function of performing a superposed discharge operation when discharging sheets to the outside of the sheet processing apparatus4without the processing performed by the sheet processing device71and also has the function of buffering sheets to be processed by the sheet processing device71. As a result, the size and cost of the apparatus can be reduced as compared with the configuration including two mechanisms for superposing sheets in order to achieve the above-described two functions.

Modification

According to the present embodiment, the internal discharge path82serving as the second conveying path communicates with the sheet processing device71. However, a configuration in which the second conveying path communicates with a discharge destination other than the sheet processing device71may be employed. For example, the sheet processing device71may be removed, and a sheet conveyed via the internal discharge path82may be discharged to the lower discharge tray37without being processed. Alternatively, an configuration may be employed in which the second conveying path has a dead end and does not communicate with the outside of the sheet processing apparatus4.

In addition, while the present embodiment has been described with reference to the sheet discharge apparatus of the sheet processing apparatus4provided separately from the image forming apparatus1, the present technology is applicable to a sheet discharge apparatus that discharges a sheet from the image forming apparatus1or other apparatuses that handle sheets.

In addition, according to the present embodiment, the bundle discharge rollers36for discharging the sheets processed by the sheet processing device71to the lower discharge tray37can be applied as the discharge device. When the bundle discharge rollers36discharge a sheet bundle, the discharge speed may be appropriately set according to the number of sheets that form the sheet bundle.

OTHER EMBODIMENTS

The present invention can be also implemented by performing the following processing. That is, a program that provides at least one of the functions of the above-described embodiment is supplied to a system or apparatus via a network or a storage medium, and at least one processor of the computer of the system or apparatus reads and executes the program. Alternatively, the present invention is implemented by using a circuit (for example, an application specific integrated circuit (ASIC)) that provides the at least one function.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2021-189216 filed Nov. 22, 2021, which is hereby incorporated by reference herein in its entirety.