Patent ID: 12252370

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the subject matter of the terms of the claims. Multiple features are described in the embodiments, but limitation is not made to require all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.

First Embodiment

Image Forming System

FIG.1illustrates an image forming system100including an image forming apparatus1, an image reading apparatus2, and a post-processing apparatus4. The image forming apparatus1forms an image on a sheet P. Although any method can be used for the image forming method of the image forming apparatus1, such as an electrophotographic method, an ink jet method, an offset printing method, or a thermal transfer method, the electrophotographic method will be used here as an example. The image reading apparatus2generates image data by reading an image of a document, and outputs the image data to the image forming apparatus1. The post-processing apparatus4executes post-processing (e.g., punching, stapling, binding) on the sheet P. Note that a relay conveyance apparatus that relays the sheet P from the image forming apparatus1to the post-processing apparatus4may be connected between the image forming apparatus1and the post-processing apparatus4.

The image forming apparatus1includes a plurality of paper feed devices6which hold a plurality of the sheets P. The paper feed device6feeds one sheet at a time at predetermined feed intervals. The sheet P fed from the paper feed device6is corrected for skew by registration rollers7, and is then conveyed to a conveyance nip part by the registration rollers7. The conveyance nip part is formed by a photosensitive drum9rotatably supported in an image forming unit8, and a transfer roller10to which a predetermined transfer voltage is applied. The surface of the photosensitive drum9undergoes exposure, charging, latent image formation, and developing in the image forming unit8, and a toner image is formed thereon as a result. Specifically, an electrostatic latent image is formed by a laser scanner unit15using a laser beam to expose the surface of the photosensitive drum9, which has been uniformly charged. The conveyance nip part transfers the toner image from the photosensitive drum9to the sheet P. The sheet P is conveyed to a fixer11, and the fixer11applies heat and pressure to the sheet P and the toner image to fix the toner image onto the sheet P. A horizontal conveyance section14conveys the sheet P which has passed through the fixer11, and discharges that sheet P to the post-processing apparatus4. When double-sided printing is executed, the sheet P is conveyed to reversing rollers12, and the reversing rollers12execute switch-back conveyance in which the leading end and the following end of the sheet P are reversed. The sheet P is sent to a re-feeding section13as a result. The re-feeding section13conveys the sheet P to the registration rollers7again. Then, an image is formed on the sheet P again.

The post-processing apparatus4includes a buffer section81and a post-processing section71. The buffer section81includes a bundle forming section60that forms a sheet bundle by stacking a plurality of the sheets P and then temporarily holds the sheet bundle. The buffer section81may temporarily hold only one sheet P. The buffer section81may discharge sheets P to an upper tray25without stopping the sheets P. The post-processing section71accumulates a predetermined number of sheets P and then performs alignment processing and binding processing. The alignment processing includes alignment processing in the longitudinal direction (the conveyance direction of the sheets P) and alignment processing in the lateral direction (the direction orthogonal to the conveyance direction). The post-processing apparatus4has conveyance paths R1, R2, R3, and R4. The conveyance path R1is a conveyance path from entrance rollers21to a branch point Rx. The conveyance path R2is a conveyance path connecting the branch point Rx with the post-processing section71. The conveyance path R3is a conveyance path from the branch point Rx to a conveyance roller pair24. The conveyance path R4is a conveyance path from the post-processing section71to a discharge roller pair36. In the following, the end part of the sheet P on the front side in the conveyance direction will be called a “leading end”, and the end part of the sheet P on the rear side in the conveyance direction will be called a “following end”. Additionally, of the two end parts of the sheet P, the end part that enters the post-processing apparatus4first will be called a “first end”, and the end part that enters the post-processing apparatus4after will be called a “second end”. Note that switch-back conveyance may result in the leading end changing from the first end to the second end and the following end changing from the second end to the first end.

The entrance rollers21are conveyance rollers that accept the sheet P conveyed from the horizontal conveyance section14into the post-processing apparatus4and convey that sheet P. The horizontal conveyance section14is provided with conveyance rollers16that convey the sheet P, and a sheet sensor17. The sheet sensor17detects the leading end and the following end of the sheet P and outputs detection signals. A conveyance distance from a detection position of the sheet sensor17to the detection position of a sheet sensor27is indicated by “L_buff1”.

When the sheet sensor17detects the leading end of the sheets P, the image forming apparatus1outputs a report signal S1notifying the post-processing apparatus4that a sheet P will be brought in. In the present embodiment, the image forming apparatus1outputs the report signal S1while the sheet P is passing the sheet sensor17. The post-processing apparatus4may start controlling the conveyance of the sheet P based on the timing at which the report signal S1is received. The report signal S1may be a signal which is at low level (or high level) while the sheet P is passing the sheet sensor17, and is at high level (or low level) while no sheet P is passing the sheet sensor17. In this case, the change in the level of the report signal S1indicates the passage timing of the leading end and the passage timing of the following end.

The post-processing apparatus4includes the upper tray25and a lower tray37. When the discharge destination of the sheet P is the upper tray25, the sheet P is passed from a conveyance roller pair22to the conveyance roller pair24, and is discharged to the upper tray25. The conveyance roller pair22is a conveyance roller pair provided downstream from the entrance rollers21in the conveyance direction of the sheets P. The conveyance roller pair24is a conveyance roller pair provided downstream from the conveyance roller pair22in the conveyance direction of the sheets P. The conveyance roller pair24can rotate both forward and in reverse, and may therefore also be called a “reversing roller pair”.

When the discharge destination of the sheet P is the lower tray37, the conveyance of the sheet P stops temporarily after the following end (the second end) of the sheet P passes a backflow prevention valve23. The conveyance roller pair24then switches the sheet P back, such that the second end of the sheet P changes from the following end to the leading end. The leading end (the second end) of the sheet P is guided to the conveyance path R2by the backflow prevention valve23, and is conveyed further downstream by a conveyance roller pair26. Once the leading end (the second end) of the sheet P reaches the conveyance roller pair26, the conveyance roller pair24changes from a pinching state (a contact state) to an open state (a separated state). In other words, the two rollers constituting the conveyance roller pair24separate. This enables the conveyance roller pair24to accept a subsequent sheet P. The conveyance roller pair26stops temporarily in a state where the conveyance roller pair26is pinching the sheet P. When the subsequent sheet P passes a predetermined position, the conveyance roller pair26starts rotating in reverse. This causes the sheet P to be conveyed toward the conveyance roller pair24. As a result, subsequent sheets P are stacked upon the preceding sheet P, and a sheet bundle is formed. Having the conveyance roller pair26repeatedly switch back the sheets P or an incomplete sheet bundle makes it possible to buffer a plurality of sheets P regardless of the lengths of the sheets P. This operation will be called a “buffer operation” or a “stacking operation”. The mechanisms involved in the buffer operation may be said to be the bundle forming section60and the buffer section81. The buffer operation can enable the image forming apparatus1to continue forming images onto sheets P while the post-processing section71is executing post-processing. In other words, the overall productivity of the image forming system100is maintained by having the subsequent sheet P stand by in the buffer section81until the post-processing on the preceding sheet P is complete.

The sheet P conveyed from the conveyance roller pair26is fed through a conveyance roller pair28to kick-out rollers29, and is then conveyed to the post-processing section71. The post-processing section71has an upper guide31and a lower guide32, and the sheet P is guided by the upper guide31and the lower guide32.

A sheet sensor38is disposed in a conveyance section connecting the conveyance roller pair28with the kick-out rollers29. Like the other sheet sensors, the sheet sensor38is a reflective photosensor that determines whether or not a sheet P is present. An alignment reference plate39is disposed at the part of the post-processing section71which is furthest downstream. When the leading end (the second end) of the sheet P butts against the alignment reference plate39, the sheet bundle is aligned in the longitudinal direction.

A flexible pressing guide56is fixed to the upper guide31. The pressing guide56makes contact with the sheet P within the post-processing section71at a predetermined pressure. A half-moon roller33is a paddle member for pushing the sheet P, which has passed the kick-out rollers29, into the alignment reference plate39. The half-moon roller33is rotatably supported by the upper guide31downstream from the pressing guide56. After the following end (the first end) of the sheet P passes the sheet sensor38, the half-moon roller33conveys the sheet P toward the alignment reference plate39. The half-moon roller33may be called a “longitudinal alignment roller”. The contact force of the half-moon roller33on the sheet P is adjusted to the extent that the half-moon roller33slips on the sheet P when the sheet P makes contact with the alignment reference plate39. Additionally, a bundle pressing flag30is rotatably supported downstream from the kick-out rollers29. The bundle pressing flag30keeps the following end of the sheet P from lifting such that the following end (the first end) of a sheet P loaded in the post-processing section71and the leading end (the second end) of the subsequent sheet P do not interfere with each other.

Once the alignment of a predetermined number of the sheets P (a sheet bundle) in the post-processing section71is complete, a stapler50executes a binding operation. When the binding operation is complete, a guide driving unit35moves a discharge guide34from a standby position toward the discharge roller pair36. The discharge guide34pushes the sheet bundle toward the discharge roller pair36as a result. Note that the leading end and the following end of the sheet bundle are once again switched by the discharge guide34. Once the leading end (the first end) of the sheet bundle reaches the discharge roller pair36, the discharge guide34stops and then returns to the standby position again. The discharge roller pair36discharges the sheet bundle received from the discharge guide34to the lower tray37.

An operation unit5has a display device that displays operation statuses of the image forming system100, such as jams, malfunctions, and the like. The operation unit5instructs a user to replace consumable items, remove sheets P that have jammed, and the like.

Post-Processing Section

FIG.2Ais a perspective view of the post-processing section71.FIG.2Bis a perspective view of the post-processing section71in a state where the upper guide31is open. The post-processing section71includes the stapler50, the upper guide31, the lower guide32, the alignment reference plate39, the half-moon roller33, the discharge guide34, and the like. The post-processing section71causes the stapler50to perform binding processing on the sheet bundle discharged from the conveyance path R2, and forms a bound sheet bundle.

The upper guide31and the lower guide32form an intermediate loading part72where sheets P to be processed are loaded. The lower guide32serves as a loading unit for the sheets P discharged from the kick-out rollers29. The kick-out rollers29are conveyance rollers disposed furthest downstream in the conveyance path R2.

The bundle pressing flag30is provided downstream from the kick-out rollers29so as to be capable of pivoting. A lower face of the bundle pressing flag30is configured to press the following end part of a preceding sheet Pi discharged to the intermediate loading part72first (“i” is an index). As a result, the leading end of a subsequent sheet Pi+1 discharged by the kick-out rollers29after can pass above the following end of the preceding sheet Pi. In other words, the bundle pressing flag30prevents the sheets P from colliding with each other by moving the following end part of the sheet P discharged from the kick-out rollers29downward. According toFIG.2B, two bundle pressing flags30are provided. This is to press both end parts, in the width direction, of a variety of sizes of sheets P that can be processed by the post-processing section71.

The half-moon roller33is disposed above the lower guide32. The half-moon roller33is formed from an elastic material such as synthetic rubber, an elastomer resin, or the like. The half-moon roller33has a roller part33ahaving an outer circumferential surface adjusted to a predetermined coefficient of friction. The roller part33ais supported by a shaft33bwhich is rotatably supported by the upper guide31. The roller part33ais driven to rotate intermittently, one revolution at a time, by a drive transmission device including a gear unit33c. The roller part33ais noncircular when viewed from the axial direction of the shaft33b. The half-moon roller33is in a standby state before the sheet P is discharged to the intermediate loading part72. In the standby state, the half-moon roller33is held at a rotation angle at which the roller part33ais not exposed from the upper guide31. During a single revolution of the half-moon roller33, the roller part33ais temporarily exposed from an opening31aprovided in the upper guide31. As a result, the roller part33amakes contact with the top face of the sheet P loaded on the lower guide32and applies conveyance force to the sheet P. The contact pressure of the half-moon roller33against the sheet P is adjusted such that the half-moon roller33slips when the sheet P butts against the alignment reference plate39.

The pressing guide56, which is a flexible sheet member, is disposed in the intermediate loading part72. The pressing guide56is disposed so as to make contact with the lower guide32, and presses the top face of the sheet P loaded in the intermediate loading part72at a predetermined pressure.

The alignment reference plate39is provided downstream from the half-moon roller33in a discharge direction in which the sheet P is discharged by the kick-out rollers29. The alignment reference plate39has a reference wall39athat protrudes upward from the top face of the lower guide32, as a regulating part that makes contact with the end part of the sheet P. As illustrated inFIG.2A, two alignment reference plates39may be provided. The alignment reference plates39are provided one on each side in the direction orthogonal to the discharge direction of the sheets P (the width direction of the sheets P).

In the following, the direction in which the sheet P discharged by the kick-out rollers29moves toward the alignment reference plate39in the post-processing section71will be defined as a “longitudinal alignment direction X1”. The longitudinal alignment direction X1is a direction parallel to a forward feed direction of the sheets P in the conveyance path R2, and is a direction in which the half-moon roller33moves the sheets P toward the alignment reference plate39. The direction opposite to the longitudinal alignment direction X1, in which the sheet bundles are discharged from the post-processing section71, is defined as a “bundle discharge direction X2”.

When a plurality of sheets P are loaded in the intermediate loading part72, the sheets P are aligned in both the longitudinal alignment direction X1and the width direction. The alignment in the longitudinal alignment direction X1is achieved by the half-moon roller33and the alignment reference plate39. The alignment in the lateral direction is achieved by a lateral alignment jogger58causing the sheets P to butt against a lateral alignment reference plate52.

The stapler50performs binding processing at a predetermined position of the sheet bundle constituted by a plurality of sheets P. The stapler50is provided on the same side as the lateral alignment reference plate52in the width direction. The stapler50can furthermore move in the longitudinal alignment direction X1and the bundle discharge direction X2.

The lower guide32has a width sufficient to load legal-sized sheets P conveyed through long-side feeding. “Long-side feeding” refers to conveying the sheets P such that the direction of the long side of the sheets P is parallel to the longitudinal alignment direction X1.

The stapler50is capable of performing corner binding and long side binding. “Corner binding” refers to binding a corner part of the sheet bundle. “Long side binding” refers to the stapler50binding the sheet bundle at a plurality of positions along the long side thereof while moving relative to the sheet bundle.

Sheet Bundle Generation

A jam will occur if a subsequent sheet P is conveyed to the post-processing section71before a sheet bundle is discharged from the post-processing section71. It is therefore necessary for the post-processing apparatus4to cause the subsequent sheet P to stand by until the preceding sheet bundle is discharged from the post-processing section71. The post-processing apparatus4causes a subsequent plurality of sheets P to wait, in a stacked state, in the conveyance path R2and the conveyance path R3. When stacking a plurality of sheets P, the preceding sheet Pi and the subsequent sheet Pi+1 are stacked such that the sheet Pi+1 is shifted relative to the sheet Pi in the conveyance direction. This assists the alignment of the sheet Pi and the sheet Pi+1 in the longitudinal direction by the half-moon roller33.

FIGS.3A to3Dillustrate a method for generating a sheet bundle. As illustrated inFIG.3A, when a sheet P1undergoes switch-back conveyance by the conveyance roller pair24and reaches the conveyance roller pair26, the conveyance roller pair24and the conveyance roller pair26stop. At this time, the leading end of the sheet P1stops at a position downstream from the conveyance roller pair26by a predetermined distance. The post-processing apparatus4then causes the upper roller and the lower roller constituting the conveyance roller pair24to separate.

As illustrated inFIG.3B, after a predetermined length of time passes following the sheet sensor27detecting the following end of a sheet P2, the upper roller and the lower roller of the conveyance roller pair24make contact, the conveyance roller pair24and the conveyance roller pair26rotate, and the sheet P2is conveyed in the direction of the upper tray25. The predetermined length of time depends on the shift amount of the sheet P2relative to the sheet P1. Increasing the predetermined length of time increases the shift amount, whereas reducing the predetermined length of time reduces the shift amount.

As illustrated inFIG.3C, when the following end of the sheet P2reaches the branch point Rx, the rotation direction of the conveyance roller pair24and the conveyance roller pair26reverses, and the sheets P1and P2are conveyed in the direction of the post-processing section71. In other words, the sheets P1and P2are conveyed to the conveyance path R2.

As illustrated inFIG.3D, when the sheet P2reaches the conveyance roller pair26, the conveyance roller pair24and the conveyance roller pair26stop. The conveyance roller pair24moves from the contact state to the separated state.

Although a sheet bundle constituted by two sheets P has been described here, this is merely an example. A sheet bundle constituted by three or more sheets P is generated by repeating the stacking operations (bundle generation operations). Note that the present embodiment assumes that a sheet bundle having a maximum of four sheets can be generated. As such, in a job in which 20 sheets P are conveyed consecutively to the post-processing section71, the generation of a sheet bundle constituted by four sheets P is repeated five times.

In the present embodiment, the shift amount, in the conveyance direction, between the adjacent sheet Pi and the sheet Pi+1 constituting a sheet bundle, is determined according to a delay time (delay distance) of the subsequent sheet P or a delay time (delay distance) of the preceding sheet bundle. This ensures a sufficient conveyance interval between the preceding sheet P (or sheet bundle) and the subsequent sheet P (or sheet bundle), and makes it easier to convey the sheets P normally. Note that the term “delay amount” will be introduced as a concept that can include both the delay time and the delay distance.

Conveyance Delay Determination

The post-processing apparatus4obtains a delay amount of the sheet P, caused by roller slippage or the like, for the conveyance of sheets from the image forming apparatus1to the buffer section81. For example, the post-processing apparatus4uses a timer or a counter to measure the length of time from when the report signal S1is received to when the leading end of the sheet P is detected by the sheet sensor27. A conveyance speed V of the sheet P is assumed to be known here. Accordingly, the post-processing apparatus4obtains a delay amount T_delay by obtaining an ideal conveyance time from the conveyance speed V and the distance L_buff1, and then subtracting the ideal conveyance time from the measured conveyance time.
T_delay=T_measure−T_ideal  EQ1

Here, T_ideal represents the ideal conveyance time. T_Measure represents the measured conveyance time.

The unit of the delay amount T_delay need not be time. For example, the delay amount T_delay may be obtained based on a count value of drive pulses from a motor that drives the entrance rollers21. Although the delay amount for the leading end of the sheet P is obtained here, a delay amount for the following end of the sheet P can also be obtained using the same method.

Longitudinal Alignment of Sheet Bundle

FIGS.4A to4Dillustrate a sheet bundle W constituted by three sheets P1, P2, and P3undergoing longitudinal alignment. The sheet P1is located at the bottom. The sheet P2is located in the middle. The sheet P3is located at the top.

When the sheet bundle W is fed into the post-processing section71, the half-moon roller33rotates, and the longitudinal alignment begins. As illustrated inFIGS.4A and4B, when the longitudinal alignment begins, the half-moon roller33makes contact with the sheet P1, and causes the sheet P1to butt against the alignment reference plate39. Because there is the shift amount between the sheet P1and the sheet P2, the half-moon roller33can make contact only with the sheet P1.

As illustrated inFIG.4C, the half-moon roller33makes contact with the sheet P2, and the sheet P2butts against the alignment reference plate39. As illustrated inFIG.4D, the half-moon roller33makes contact with the sheet P3, and the sheet P3butts against the alignment reference plate39. This completes the longitudinal alignment of the sheet bundle W.

The plurality of sheets P1to P3constituting the sheet bundle W are shifted from each other in the conveyance direction. The leading end of the sheet P1is the furthest forward, and the leading end of the sheet P3is the furthest to the rear. As such, the half-moon roller33can make contact with the sheets P1to P3in that order as time passes, and each of the sheets P1to P3can butt against the alignment reference plate39. The sheet bundle W can therefore be aligned longitudinally at a high level of precision.

The shift amount between two adjacent sheets may be determined by adding a predetermined margin to a distance L between the position where the half-moon roller33makes contact with the sheet P and the position of the alignment reference plate39. The margin may include a distance necessary for the longitudinal alignment. The margin may further include a distance determined taking into account friction between the sheets and the like. The distance L is 20 mm, for example.

Here, a larger amount of friction acts on the plurality of sheets P as the surface area of the sheets P increases. A large amount of friction acts on the plurality of sheets P when the sheets P have a surface finish (e.g., glossy paper or embossed paper). In this case, it is necessary for the post-processing section71to have advanced alignment capabilities. In other words, the shift amount is set to be sufficiently long relative to the distance L. If the alignment capabilities required for the post-processing section71are low, the shift amount can be set to be relatively short.

In the present embodiment, the shift amount is determined according to the alignment capabilities. The shift amount may furthermore be determined according to both the alignment capabilities and the delay amount T_delay. For example, in the case of a type of sheet P which requires low alignment capabilities, the shift amount may be determined based on the delay amount T_delay. On the other hand, in the case of a type of sheet P which requires high alignment capabilities, the shift amount may be set to a fixed value independent of the delay amount T_delay.

FIG.5Ais a table for determining the shift amount based on the required alignment capabilities and the delay amount. Note that the delay amount is converted to a distance. In this example, when the required alignment capabilities are relatively low and the delay amount T_delay is at least 5 mm, the shift amount is set to 25 mm. When the required alignment capabilities are relatively low and the delay amount T_delay is less than 5 mm, the shift amount is set to 30 mm. When the required alignment capabilities are relatively high, the shift amount is set to 30 mm independent of the delay amount. Although the shift amount is divided into two stages based on a single threshold (5 mm) inFIG.5A, this is merely an example. Providing n thresholds makes it possible to select n+1 shift amounts.

The required alignment capabilities are determined according to the type of the sheet P (e.g., the surface area, the basis weight, and surface finishing). These are merely examples, however. The post-processing apparatus4may determine the required alignment capabilities based on conditions of the environment in which the post-processing apparatus4is installed (e.g., temperature or humidity).

InFIG.5A, the shift amount is set to 30 mm uniformly when the required alignment capabilities are high, but this is merely an example. When the required alignment capabilities are high, the shift amount (e.g., 30 mm or 28 mm) may be set according to the delay amount. Note that 30 mm or 28 mm are shift amounts making it possible to ensure the minimum conveyance interval required for longitudinal alignment.

Control System (Controller)

FIG.6illustrates the control system of the image forming system100. A printer controller600is provided in the image forming apparatus1. A post-processing controller650is provided in the post-processing apparatus4. The printer controller600and the post-processing controller650are connected to each other by a communication interface, and cooperatively control the image forming system100.

The printer controller600includes a CPU601and a memory602. “CPU” is an acronym for “central processing unit”. The CPU601comprehensively controls the image forming apparatus1by executing programs stored in the memory602. For example, the CPU601causes the image forming unit8to form images, and causes the image reading apparatus2to read images. The memory602includes a non-volatile storage medium such as read-only memory (ROM) and a volatile storage medium such as random access memory (RAM). The memory602serves as a storage location for programs and data, as well as a work space for the CPU601to execute programs. The memory602is an example of a non-transitory storage medium in which is stored a program for controlling the image forming apparatus1.

The printer controller600is connected to an external device3(e.g., a personal computer, a smartphone, or a tablet computer) by an external I/F104. Note that “I/F” is an abbreviation for “interface”. The printer controller600accepts commands to execute image formation jobs and the like from the external device3. The printer controller600is connected to the operation unit5, which is a user interface of the image forming system100. The operation unit5includes a liquid crystal display device that presents information to the user, and input devices including physical buttons, a touch sensor, and the like that accept input operations made by the user. By communicating with the operation unit5, the printer controller600controls content displayed by the display device and receives information input through the input devices. The CPU601generates the report signal S1based on the result of the detection by the sheet sensor17, and transmits the report signal S1to the post-processing controller650. The report signal S1may be called a “notification signal” or a “detection signal”.

The post-processing controller650includes a CPU651, a memory652, and an I/O port653. The CPU651comprehensively controls the post-processing apparatus4by reading out and executing programs stored in the memory652. The memory652includes a non-volatile storage medium such as read-only memory (ROM) and a volatile storage medium such as random access memory (RAM). The memory652serves as a storage location for programs and data, as well as a work space for the CPU651to execute programs. The memory652is an example of a non-transitory storage medium in which is stored a program for controlling the post-processing apparatus4. The CPU651and the memory652communicate over a bus654. The CPU651is furthermore connected to the I/O port653by the bus654. The I/O port653receives the report signal S1, receives detection signals from the sheet sensors27and38, outputs control signals to motors M1to M14, and the like. The motors M1to M14are illustrated as including one or more drive circuits that drive motors based on control signals. The CPU651may obtain time information from an RTC655. “RTC” is an acronym for “real-time clock”.

The plurality of functions of the printer controller600and the post-processing controller650are implemented by the CPUs601and651, respectively. However, some or all of the plurality of functions may be implemented in one or more independent hardware circuits such as ASICs or the like, or implemented as program modules.

The motor M1rotationally drives the entrance rollers21. The motor M2rotationally drives the conveyance roller pair22. The motor M3rotationally drives the conveyance roller pair24. The motor M4shifts the conveyance roller pair24to the contact state by rotating in the CW direction, and shifts the conveyance roller pair24to the separated state by rotating in the CCW direction. “CW” stands for “clockwise”. “CCW” stands for “counterclockwise”. These rotation directions are merely examples. The motor M5moves the conveyance roller pair24in a first direction orthogonal to the conveyance direction by rotating in the CW direction, and moves the conveyance roller pair24in a second direction orthogonal to the conveyance direction by rotating in the CCW direction. The motor M6rotationally drives the conveyance roller pair26. The motor M7rotationally drives the kick-out rollers29. The motor M8drives the half-moon roller33intermittently, one revolution at a time. The motor M9moves the lateral alignment jogger58in the width direction. The motor M10moves the stapler50in the longitudinal alignment direction X1and the bundle discharge direction X2. The motor M11causes the stapler50to bind the sheet bundle W. The motor M12drives the guide driving unit35to slide the discharge guide34. When the motor M12rotates in the CW direction, the discharge guide34moves in the longitudinal alignment direction X1. When the motor M12rotates in the CCW direction, the discharge guide34moves in the bundle discharge direction X2. The motor M13rotationally drives the discharge roller pair36. The motor M14shifts the discharge roller pair36to the contact state by rotating in the CW direction, and shifts the discharge roller pair36to the separated state by rotating in the CCW direction.

CPU Functions

FIG.7illustrates functions which are realized by the CPU651executing a control program and are involved in the generation of a sheet bundle W. The post-processing controller650has a conveyance control unit710, a bundle control unit711, a delay determination unit712, a shift amount determination unit714, and the like.

The conveyance control unit710controls the conveyance of sheets P by driving the motors M1to M14based on detection signals from the sheet sensors27and38and the report signal S1from the image forming apparatus1. The conveyance control unit710controls the post-processing section71based on post-processing instructions transmitted from the printer controller600. The post-processing instructions may include sheet number information indicating the total number of sheets P constituting the sheet bundle W, discharge destination information indicating the discharge destination (conveyance destination) of the sheets P, and the like.

The delay determination unit712determines the delay amount for the sheet P conveyed from the image forming apparatus1to the post-processing apparatus4based on the report signal S1and the detection signal from the sheet sensor27. Additionally, based on the detection signal from the sheet sensor27, the delay determination unit712determines the delay amount for the sheet bundle W conveyed from the buffer section81to the post-processing section71. The shift amount determination unit714determines the shift amounts among the plurality of sheets constituting the sheet bundle W based on the delay amounts output from the delay determination unit712, and sets the shift amount in the bundle control unit711.

Note that a capability determination unit713is optional, and may determine the alignment capabilities required to successfully generate the sheet bundle W based on environmental conditions (e.g., temperature, humidity) obtained by an environmental sensor721. The capability determination unit713may determine the alignment capabilities required to successfully generate a sheet bundle based on type information (e.g., the basis weight, size, and surface finish of the sheet) input from the operation unit5or the external device3. The shift amount determination unit714may determine the shift amount corresponding to the combination of alignment capabilities and the delay amount by referring to a table stored in the memory652based on the alignment capabilities and the delay amount.

The bundle control unit711controls the generation of the sheet bundle W by driving the motor M3, the motor M4, the motor M6, and the like based on the detection signal from the sheet sensor27and the shift amount determined by the shift amount determination unit714. When the sheet sensor27detects the following end of the sheet P, the bundle control unit711drives the motor M4and brings the conveyance roller pair24into contact after a predetermined length of time corresponding to the shift amount has passed. Furthermore, the motor M3is rotated in reverse, and the motor M6is rotated in reverse as well. As a result, the shift amount between a preceding sheet bundle Wi and a subsequent sheet bundle Wi+1 becomes the shift amount determined by the shift amount determination unit714.

A discharge destination selection unit715is optional. If reducing the shift amount alone is not enough to ensure a sufficient interval between the sheets P, the discharge destination selection unit715changes the discharge destination of the sheets P. As a result, the sheet P is discharged to a different discharge destination than the discharge destination specified by the image forming apparatus1. This prevents jams from occurring.

Flowcharts

FIGS.8to11illustrate a bundle generation method executed by the CPU651according to a program. When the printer controller600supplies a sheet P from the paper feed device6and starts printing according to a print job, the CPU651executes the following processing for each sheet P.

In step S801, the CPU651(the delay determination unit712) determines whether the leading end of the sheet P has been detected by the sheet sensor17. For example, the CPU651may determine whether the leading end of the sheet P is detected based on the report signal S1. The report signal S1may change from low level to high level when the leading end of the sheet P is detected, for example. When the leading end of the sheet P is detected by the sheet sensor17, the CPU651moves the sequence to step S802.

In step S802, the CPU651(the delay determination unit712) obtains, from the RTC655, a time T1at which the leading end of the sheet P is detected by the sheet sensor27, and stores the time T1in the memory652.

In step S803, the CPU651(the delay determination unit712) determines whether the leading end of the sheet P has been detected by the sheet sensor27. When the leading end of the sheet P is detected by the sheet sensor27, the CPU651moves the sequence to step S804.

In step S804, the CPU651(the delay determination unit712) obtains, from the RTC655, a time T2at which the leading end of the sheet P is detected by the sheet sensor27, and stores the time T2in the memory652.

In step S805, the CPU651(the bundle control unit711) starts sheet number determination. The sheet number determination will be described in detail later with reference toFIG.9.

In step S806, the CPU651(the delay determination unit712) obtains a conveyance time T_measure based on times T1and T2.
T_measure=T2−T1  EQ2

In step S807, the CPU651(the delay determination unit712) calculates the delay amount T_delay based on the conveyance time T_measure. Equation EQ1 may be used here.

FIG.9illustrates the details of the sheet number determination of step S805. In step S901, the CPU651(the bundle control unit711) determines whether the following end of the sheet P has been detected by the sheet sensor27. When the following end of the sheet P is detected by the sheet sensor27, the CPU651moves the sequence to step S902.

In step S902, the CPU651(the bundle control unit711) determines whether the sheet P for which the following end has been detected by the sheet sensor27is the first sheet among a predetermined number of sheets P constituting the sheet bundle W. The CPU651is notified by the printer controller600of the total number of sheets that constitute the sheet bundle W (the predetermined number of sheets). The CPU651manages the sheets P by assigning a number to the sheet P each time the sheet sensor27detects the leading end of the sheet P. Therefore, a remainder obtained by dividing the number of the sheet P by the predetermined number of sheets indicates the order of those sheets in the sheet bundle W. If the detected sheet P is the first sheet, the CPU651moves the sequence to step S903. In step S903, the CPU651(the bundle control unit711) starts processing the first sheet. The processing of the first sheet will be described in detail later with reference toFIG.10. On the other hand, if the detected sheet P is the second or a subsequent sheet, the CPU651moves the sequence to step S904. In step S904, the CPU651(the bundle control unit711) starts processing the second and subsequent sheets. The processing of the second and subsequent sheets will be described in detail later with reference toFIG.11.

FIG.10illustrates the processing of the first sheet in the sheet bundle W. In step S1001, the CPU651(the bundle control unit711) determines whether the following end of the sheet P has reached the branch point Rx. For example, the CPU651determines whether a predetermined length of time Tm has elapsed from the timing at which the following end of the sheet P was detected by the sheet sensor27. The predetermined length of time Tm is obtained by dividing the conveyance distance from the sheet sensor27to the branch point Rx by the conveyance speed V. When the following end of the sheet P reaches the branch point Rx, the conveyance direction of the sheet P can be reversed and the sheet P can be fed to the conveyance path P2. The CPU651therefore moves the sequence to step S1002.

In step S1002, the CPU651(the bundle control unit711) switches the rotation direction of the conveyance roller pair24. As a result, the sheet P drawn into the conveyance path R3of the buffer section81is fed to the conveyance path R2.

In step S1003, the CPU651(the bundle control unit711) determines whether the sheet P has reached the conveyance roller pair26. As described above, the CPU651knows the current conveyance position of the sheet P based on an elapsed time from the timing at which the sheet sensor27detected the following end. When the elapsed time reaches the predetermined length of time Tm, the CPU651determines that the sheet P has reached the conveyance roller pair26and moves the sequence to step S1004.

In step S1004, the CPU651(the bundle control unit711) drives the motor M4to separate the conveyance roller pair24. In step S1005, the CPU651(the bundle control unit711) conveys the sheet P about 10 mm from the conveyance roller pair26. In step S1006, the CPU651(the bundle control unit711) stops the conveyance roller pairs24and26. As a result, the first sheet P1in the sheet bundle W stops at a position about 10 mm past the conveyance roller pair26. In other words, the leading end of the first sheet P1is at a position about 10 mm past the conveyance roller pair26.

In steps S1001, S1003, and S1005, the position of the sheet P is determined based on the elapsed time from the timing at which the sheet sensor27detected the sheet P, but this is merely an example. The CPU651may count the drive pulses of the motors M2, M3, and M6and determine the conveyance position of the sheet P based on the sum of the count values. Alternatively, a sheet sensor (not shown) may be disposed in a position about 10 mm past the conveyance roller pair26. Based on a detection result from this sheet sensor (not shown), the CPU651may detect that the leading end of the first sheet P1is located about 10 mm past the conveyance roller pair26. Similarly, a sheet sensor may be disposed at the branch point Rx. This sheet sensor may detect that the following end of the sheet P has reached the branch point Rx. Similarly, a sheet sensor for detecting that the sheet P has reached the conveyance roller pair26may be disposed upstream from the conveyance roller pair26.

FIG.11illustrates the processing of the second and subsequent sheets in the sheet bundle W (processing corresponding to step S904). Step S1100is processing for determining the shift amount. As an example, it is assumed here that the shift amount is determined based on the alignment capabilities and the delay amount.

In step S1101, the CPU651(the capability determination unit713) determines whether the alignment capabilities required for the sheet P are low. The alignment capabilities are determined based on the type information of the sheet P (e.g., the surface area, surface finish, and basis weight) or the surrounding environmental conditions, as described above. The CPU651may calculate the alignment capabilities based on the type information of the sheet P and the environmental conditions, and determine whether the alignment capabilities are lower than a threshold. The calculation equations, calculation tables, or calculation modules for the alignment capabilities are assumed to be stored in the ROM of the memory652in advance. If the alignment capabilities are high, the CPU651moves the sequence to step S1120. In step S1120, the CPU651(the shift amount determination unit714) sets the shift amount to a first predetermined value (e.g., 30 mm), and then moves the sequence to step S1104. On the other hand, if the alignment capabilities are low, the CPU651moves the sequence to step S1102.

In step S1102, the CPU651(the delay determination unit712) determines whether the delay amount T_delay of the sheet P is at least a threshold (e.g., 5 mm). If the delay amount T_delay is at least 5 mm, the CPU651moves the sequence to step S1103. On the other hand, if the delay amount T_delay is less than 5 mm, the CPU651moves the sequence to step S1120.

In step S1103, the CPU651(the shift amount determination unit714) sets the shift amount to a second predetermined value (e.g., 25 mm), which is lower than the first predetermined value (e.g., 30 mm), and then moves the sequence to step S1104.

In step S1104, the CPU651(the bundle control unit711) obtains the time from the RTC655and determines whether that time is a drive timing of the preceding sheet Pi. The “drive timing of the preceding sheet Pi” refers to the timing for pulling the preceding sheet Pi, which is standing by across the conveyance path R2and the conveyance path R3, back to the buffer section81. This timing is determined according to the shift amount. In other words, this timing is the timing at which a predetermined length of time has elapsed after the following end of the subsequent sheet Pi+1 was detected by the sheet sensor27. The predetermined length of time is a length of time corresponding to the shift amount. When the drive timing for the preceding sheet Pi arrives, the CPU651moves the sequence to step S1105.

In step S1105, the CPU651(the bundle control unit711) drives the conveyance roller pairs24and26. The conveyance roller pair24rotates in the direction that pulls the preceding sheet Pi and the subsequent sheet Pi+1 into the buffer section81. The conveyance roller pair26rotates in the direction that feeds the preceding sheet Pi into the buffer section81.

In step S1106, the CPU651(the bundle control unit711) brings the conveyance roller pair24into contact. In step S1107, the CPU651(the bundle control unit711) determines whether the following end of the subsequent sheet Pi+1 has reached the branch point Rx. When the following end of the subsequent sheet Pi+1 reaches the branch point Rx, the CPU651moves the sequence to step S1108.

In step S1108, the CPU651(the bundle control unit711) switches the rotation direction of the conveyance roller pair24. As a result, a sheet bundle W constituted by the preceding sheet Pi and the subsequent sheet Pi+1 is fed into the conveyance path R2. Note that the sheet bundle W may be constituted by preceding sheets Pi−1 and Pi, and the subsequent sheet Pi+1. Furthermore, the sheet bundle W may be constituted by preceding sheets Pi−2, Pi−1, and Pi, and the subsequent sheet Pi+1.

In step S1109, the CPU651(the bundle control unit711) determines whether the sheet bundle W is complete. The CPU651manages the total number of sheets P constituting the sheet bundle W (the predetermined number of sheets), and the number of each sheet P. When the remainder obtained by dividing the number of the sheet P by the predetermined number of sheets is zero, the CPU651determines that the sheet bundle W is complete, and the present processing ends. If the remainder obtained by dividing the number of the sheet P by the predetermined number of sheets is not zero, the CPU651determines that the sheet bundle W is incomplete, and moves the sequence to step S1110. The sheet bundle W being incomplete means that a subsequent sheet Pi+2, which is to be added to the sheet bundle W, is present in the buffer section81.

In step S1110, the CPU651(the bundle control unit711) determines whether the sheet bundle W has reached the conveyance roller pair26. The determination method used here is the same as that in step S1003. When the sheet bundle W reaches the conveyance roller pair26, the CPU651moves the sequence to step S1111.

In step S1111, the CPU651(the bundle control unit711) drives the motor M4to separate the conveyance roller pair24. In step S1112, the CPU651drives the motors M3and M6to convey the sheet bundle W about 10 mm from the conveyance roller pair26.

In step S1113, the CPU651(the bundle control unit711) stops the conveyance roller pair24and the conveyance roller pair26by stopping the motor M3and the motor M6. The flowchart illustrated inFIG.11is then executed again for the subsequent sheet Pi+2.

In steps S1104, S1107, S1110, and S1112, the position of the sheet P or the sheet bundle W may be managed based on either the elapsed time or drive pulse count values, as described above. Additional sheet sensors may also be employed as described above.

According to the first embodiment, the shift amount is determined based on the delay amount of the sheet P. Additionally, according to the first embodiment, the shift amount is determined based on the alignment capabilities for the sheet P. Furthermore, according to the first embodiment, the shift amount is determined based on the delay amount of the sheet P and the alignment capabilities for the sheet P. For example, if the required alignment capabilities are low, the shift amount is reduced, which shortens the overall length of the sheet bundle W including the sheet P for which the conveyance was delayed. As a result, the time required for alignment is shortened. The time required to feed the sheet bundle W to the post-processing section71is shortened as well. In addition, the interval between the subsequent sheet P or the subsequent sheet bundle W and the preceding sheet bundle W is lengthened. As such, the subsequent sheet P or the subsequent sheet bundle W and the preceding sheet bundle W are less likely to make contact with each other. On the other hand, if the alignment capabilities are high, or if the sheet conveyance is not delayed, the shift amount of the sheet P is set to a sufficiently long value.

It is therefore possible to reduce the effect of delays in the conveyance of the sheets P while maintaining the alignment capabilities in the post-processing section71. In other words, the conveyance and the post-processing of the sheets P can be continued.

As described above, according to the present embodiment, the shift amount between sheets in a sheet bundle W is determined based on the delay amount of the sheet P. This improves the productivity of the post-processing apparatus4while maintaining the shift amount required for longitudinal alignment.

Second Embodiment

In the first embodiment, the shift amount was determined according to the delay amount of the sheet P that occurs upstream from the buffer section81. In a second embodiment, the shift amount for a subsequent sheet bundle W is determined based on the delay amount of a sheet bundle W that occurs downstream from the buffer section81. In the second embodiment, the descriptions in the first embodiment will be used for matters that are the same as, or similar to, those in the first embodiment.

Delay Determination for Sheet Bundle

The post-processing apparatus4generates a sheet bundle W in the buffer section81and conveys the sheet bundle W to the post-processing section71. When conveying a sheet bundle W from the buffer section81to the post-processing section71, the conveyance of the sheet bundle W may be delayed due to roller slippage and the like. In addition, the plurality of sheets P constituting a sheet bundle W may shift during conveyance, increasing the overall length of the sheet bundle W. As a result, the timing at which the following end of the sheet bundle W enters the post-processing section71may be delayed. In the second embodiment, the delay determination unit712measures the conveyance time from the timing at which the conveyance of the sheet bundle W is started from the position indicated inFIG.3Dto when the sheet sensor38detects the leading end of the sheet bundle W. The delay determination unit712obtains the delay amount of the sheet bundle W from the ideal conveyance time, corresponding to a conveyance distance L_buff2 during the time described above, and the measured conveyance time. The delay determination unit712may also measure a transit time from when the leading end of the sheet bundle W is detected by the sheet sensor38to when the following end of the sheet bundle W is detected. The delay determination unit712obtains the delay amount of the following end of the sheet bundle W based on an ideal transit time and a measured transit time for the sheet bundle W.

For example, a delay amount T_bndl_delay1 of the leading end of the sheet bundle W can be calculated from the following equation.
T_bndl_delay1=T_bndl_measure1−T_bndl_ideal1  EQ3

Here, T_bndl_measure1 represents the measured conveyance time. T_bndl_ideal1 represents the ideal conveyance time.

For example, a delay amount T_bndl_delay2 of the following end of the sheet bundle W can be calculated from the following equation.
T_bndl_delay2=T_bndl_measure2−T_bndl_ideal2  EQ4

“T_bndl_measure2” indicates the measured transit time. “T_bndl_ideal2” indicates the ideal transit time. The ideal transit time T_bndl_ideal2 can be calculated from the following equation.
T_bndl_ideal2=(L1+L_shift×(n−1))/V_bndl  EQ5

Here, n represents the total number of sheets P constituting the sheet bundle W. L1 represents the length of the sheet P in the conveyance direction. L_shift represents the shift amount of the sheet P. V_bndl represents the conveyance speed of the sheet bundle W. In this manner, the delay amounts T_bndl_delay1 and T_bndl_delay2 are calculated using time as a unit. However, these items may be calculated using the count value of motor drive pulses as a unit.

Delay Amount of Preceding Sheet Bundle and Shift Amount Applied to Subsequent Sheet Bundle

In the second embodiment too, the shift amount may be determined based on the alignment capabilities and the delay amount. For example, the shift amount may be reduced according to the delay amount.

For example, if the required alignment capabilities are low, the shift amount is determined according to the delay amounts T_bndl_delay1 and T_bndl_delay2. On the other hand, if the required alignment capabilities are high, the shift amount is determined to be a fixed value, independent of the delay amounts T_bndl_delay1 and T_bndl_delay2. The delay amounts T_bndl_delay1 and T_bndl_delay2 are the delay amounts of the preceding sheet bundle with respect to the sheet bundle to which the shift amount is applied.

FIG.5Billustrates a table holding shift amounts according to combinations of required alignment capabilities and delay amounts. This table may be stored in the ROM of the memory652. If the required alignment capabilities are low, and the delay amount T_bndl_delay1 is less than 15 mm and at least 5 mm, the shift amount is determined to be 25 mm. Alternatively, if the required alignment capabilities are low, and the delay amount T_bndl_delay2 is less than 15 mm and at least 5 mm, the shift amount is determined to be 25 mm. If the required alignment capabilities are low, and both the delay amounts T_bndl_delay1 and T_bndl_delay2 are less than 5 mm, the shift amount is determined to be 30 mm. If the required alignment capabilities are high, the shift amount is set to 30 mm independent of the delay amount.

In a third embodiment too, it is assumed that the post-processing apparatus4can generate a sheet bundle W constituted by a maximum of four sheets P. When the shift amount is set to 25 mm, the overall length of the sheet bundle W is about 15 mm shorter than when the shift amount is a normal shift amount of 30 mm. In other words, the delay amount arising for the preceding sheet bundle Wi−1 is absorbed or canceled out by shortening the overall length of the subsequent sheet bundle Wi.

If the delay amount for the preceding sheet bundle Wi−1 is at least 15 mm, the delay amount cannot be fully absorbed by the subsequent sheet bundle Wi alone. In this case, the shift amount of the sheet bundle Wi and the shift amount of the subsequent sheet bundle Wi+1 are reduced. This case will be described in detail in the third embodiment. Although two levels are set for the shift amount according to the delay amount in the second embodiment, three or more levels may be set.

Flowchart

The flowchart of the first embodiment is also used in the second embodiment, but some of the steps are changed. The parts which are changed will therefore be described in detail. A case where the delay amount is at least 15 mm will not be described here.

FIG.12illustrates step S1100of the second embodiment. As illustrated inFIG.12, step S1102described above has been replaced with step S1200. In step S1200, the CPU651(the delay determination unit712) determines whether the delay amount T_bndl_delay1 or T_bndl_delay2 of the preceding sheet bundle Wi−1 is at least 5 mm. If both of the two delay amounts are less than 5 mm, the CPU651moves the sequence to step S1120. In step S1120, the CPU651sets the shift amount applied to the subsequent sheet bundle Wi to, for example, 30 mm. If at least one of the two delay amounts is at least 5 mm, the CPU651moves the sequence to step S1103. In step S1103, the CPU651sets the shift amount applied to the subsequent sheet bundle Wi to, for example, 25 mm.

FIG.13is a flowchart illustrating processing for obtaining the delay amount of the sheet bundle W. The CPU651executes the following processing according to a control program stored in the ROM of the memory652. Note that the leading end of the sheet bundle W stops about 10 mm downstream from the conveyance roller pair26.

In step S1301, the CPU651(the conveyance control unit710) starts driving the motors M3, M6, M7, and the like to start conveying the sheet bundle W. In step S1302, the CPU651obtains a time T3from the RTC655and stores the time T3in the RAM of the memory652.

In step S1303, the CPU651(the delay determination unit712) determines whether the leading end of the sheet bundle W has been detected by the sheet sensor38. When the sheet sensor38detects the leading end of the sheet bundle W, the CPU651moves the sequence to step S1304.

In step S1304, the CPU651(the delay determination unit712) obtains a time T4from the RTC655and stores the time T4in the RAM of the memory652. In step S1305, the CPU651obtains the conveyance time T_bndl_measure1 of the leading end of the sheet bundle W based on the times T3and T4.
T_bndl_measure1=T4−T3  EQ6

In step S1306, the CPU651(the delay determination unit712) obtains the delay amount T_bndl_delay1 of the leading end of the sheet bundle W based on the conveyance time T_bndl_measure1. Note that Equation EQ3 may be used at this time.

In step S1307, the CPU651(the delay determination unit712) determines whether the following end of the sheet bundle W has been detected by the sheet sensor38. When the sheet sensor38detects the following end of the sheet bundle W, the CPU651moves the sequence to step S1308.

In step S1308, the CPU651(the delay determination unit712) obtains a time T5from the RTC655and stores the time T5in the RAM of the memory652. In step S1309, the CPU651(the delay determination unit712) obtains the time required for the entire sheet bundle W to pass the sheet sensor38(the transit time T_bndl_measure2) based on the times T4and T5.
T_bndl_measure2=T5−T4  EQ7

In step S1310, the CPU651(the delay determination unit712) obtains the delay amount T_bndl_delay2 of the following end of the sheet bundle W based on the transit time T_bndl_measure2. Equation EQ4 may be used for this.

In this manner, according to the second embodiment, the shift amount applied to the subsequent sheet bundle Wi is set according to the delay amount of the preceding sheet bundle Wi−1 and the required alignment capabilities. This reduces the effect of delay in the sheet bundle W occurring downstream from the buffer section81. For example, if the required alignment capabilities for a subsequent sheet bundle Wi are low, reducing the shift amount will reduce the overall length of the subsequent sheet bundle Wi. As a result, the time required for longitudinal alignment is shortened. Furthermore, the time required to feed the sheet bundle Wi to the post-processing section71is also shortened. In other words, a sufficient interval is maintained between the subsequent sheet bundle Wi and a further subsequent sheet bundle Wi+1, which makes jams less likely to occur. On the other hand, if the required alignment capabilities are high, or if the conveyance of the sheet bundle Wi−1 is not delayed, the shift amount of the sheet bundle Wi is set to a sufficiently long value.

According to the second embodiment, it is possible to reduce the effect of delay in the conveyance of sheet bundles W while maintaining the alignment capabilities. As such, even if a delay occurs for the preceding sheet bundle Wi−1, the conveyance and post-processing of the subsequent sheet bundles Wi and Wi+1 can continue.

According to the second embodiment, the shift amount of the subsequent sheet bundle Wi is determined according to the delay amount of the preceding sheet bundle Wi−1. This maintains the shift amount required for longitudinal alignment and improves the productivity of the post-processing apparatus4.

Third Embodiment

A third embodiment describes measures for a case where there is a large delay amount for a sheet P or a sheet bundle W, mentioned in the second embodiment. In other words, if the delay amount is too large, reducing the shift amount for a single sheet P or a single sheet bundle W does not sufficiently reduce the effect of the delay. Furthermore, the delay will continue to affect the subsequent sheet bundles W.

Accordingly, in the third embodiment, when the delay amount is large, buildup of delay is suppressed by reducing each shift amount for a plurality of sheet bundles W. In addition, the delay amount may be large and the alignment capabilities required may be high. In such cases, other measures may be necessary. Such measures will be described hereinafter. In the third embodiment, the descriptions in the first or second embodiment will be used for matters that are the same as, or similar to, those in the first or second embodiment.

Delay Amount and Shift Amount

In the third embodiment, the first embodiment is applied when the alignment capabilities required for the post-processing section71to align sheet bundles are low. On the other hand, if the delay amount T_delay is greater than a threshold, a reduction in the shift amount is applied not only to the sheet bundle Wi, but also to the further subsequent sheet bundle Wi+1.

On the other hand, as mentioned in the first embodiment, it is difficult to reduce the shift amount when the required alignment capabilities are very high. Furthermore, as mentioned in the second embodiment, when the delay amount is too large, it becomes difficult to ensure a sufficient interval between the sheets even when reducing the shift amount, which makes it difficult to convey the sheets P and the sheet bundles W normally. Accordingly, in the third embodiment, the discharge destination of the sheet P is switched to a discharge bin located closest to the buffer section81(e.g., the upper tray25), without generating a sheet bundle W, in order to reduce the occurrence of jams.

FIG.5Cis a table illustrating shift amounts, adjustment targets, and discharge destinations corresponding to combinations of alignment capabilities and delay amounts. This table, too, may be stored in the ROM of the memory652. If the required alignment capabilities are low and the delay amount is at least a threshold Th2(e.g., 15 mm), the shift amount is determined to be 25 mm. The reduction in the shift amount is applied to two consecutive sheet bundles. If the required alignment capabilities are low and the delay amount is less than the threshold Th2and at least a threshold Th1(e.g., 5 mm), the shift amount is determined to be 25 mm. The reduction in the shift amount is applied to a single sheet bundle W. If the delay amount is sufficiently small (e.g., if the delay amount is less than the threshold Th1), the shift amount is kept at a default value. In other words, a relatively large shift amount is selected. On the other hand, if the required alignment capabilities are high, the discharge destination of the sheet P is switched from the post-processing section71to the upper tray25.

Flowcharts

FIG.14is a flowchart illustrating processing for the second and subsequent sheets P in the third embodiment. The ways in which the third embodiment differs from the first and second embodiments will mainly be described here as well. In particular, steps S1101to S1103inFIG.11have been changed to steps S1401to S1415.

In step S1401, the CPU651(the delay determination unit712) determines whether the delay amount T_delay is at least the threshold Th1(e.g., 5 mm). If the delay amount T_delay is at least the threshold Th1, the CPU651moves the sequence to step S1402.

In step S1402, the CPU651(the capability determination unit713) determines whether the required alignment capabilities are low. If the required alignment capabilities are low, the CPU651moves the sequence to step S1403.

In step S1403, the CPU651(the shift amount determination unit714) sets the shift amount to 25 mm. In step S1404, the CPU651(the shift amount determination unit714) determines whether the delay amount T_delay is at least the threshold Th2(e.g., 15 mm). If the delay amount T_delay is at least the threshold Th2, the CPU651moves the sequence to step S1405. In step S1405, the CPU651(the shift amount determination unit714) sets a number of bundles M, which is the total number of sheet bundles W for which the shift amount is adjusted, to 2. On the other hand, if the delay amount T_delay is determined to be less than the threshold Th2in step S1404, the CPU651moves the sequence to step S1406. In step S1406, the CPU651(the shift amount determination unit714) sets the number of bundles M to 1. The CPU651then executes steps S1104to S1113.

The number of bundles M is a counter that counts the number of sheet bundles W for which the shift amount is to be reduced when the delay amount T_delay is large. If the number of bundles M is 2, the reduction in the shift amount is applied to both the sheet bundle Wi held in the bundle forming section60and the subsequent sheet bundle Wi+1.

If it is determined in step S1401that the delay amount T_delay is less than Th1, the CPU651moves the sequence to step S1407. In step S1407, the CPU651(the shift amount determination unit714) decrements the number of bundles M by 1. In other words, 1 is subtracted from the number of bundles M.

In step S1408, the CPU651(the shift amount determination unit714) determines whether the number of bundles M is already 0. If the number of bundles M is 0, the CPU651moves the sequence to step S1409. In step S1409, the CPU651(the shift amount determination unit714) sets the shift amount to 30 mm, rather than reducing the shift amount. The CPU651then executes steps S1104to S1113.

If the number of bundles M is not 0 in step S1408, the CPU651moves the sequence to step S1410. In step S1410, the CPU651(the shift amount determination unit714) sets the shift amount to 25 mm to reduce the shift amount. The CPU651then executes steps S1104to S1113.

If the alignment capabilities are determined to be high in step S1402, the CPU651moves the sequence to step S1411. This is because a small value cannot be set for the shift amount when the alignment capabilities required for the post-processing section71are high.

In step S1411, the CPU651(the discharge destination selection unit715) changes the discharge destination of the preceding sheet P and the subsequent sheet P present in the bundle forming section60from the lower tray37to the upper tray25. In step S1412, the CPU651brings the conveyance roller pair24into contact. In step S1413, the CPU651determines whether a sheet P has been discharged to the upper tray. For example, it is determined whether the following end of the sheet P has exited the conveyance roller pair24. This may be determined, for example, based on the time that has elapsed after the following end of the sheet P passed the sheet sensor27. By bringing the conveyance roller pair24into contact, the preceding sheet P present in the bundle forming section60is also discharged to the upper tray25. All sheets P that will constitute the same sheet bundle are discharged to the upper tray25. When the sheet P is discharged, the CPU651moves the sequence to step S1414. In step S1414, the CPU651stops the conveyance roller pair24by stopping the motor M3. In step S1415, the CPU651(the discharge destination selection unit715) returns the discharge destination to the lower tray37.

Incidentally, there may be another sheet P that follows the sheet bundle discharged to the upper tray25. If no delay has occurred for this other sheet P, the post-processing job may be resumed.

On the other hand, subsequent sheets P belonging to the same post-processing job as the post-processing job to which the sheet P discharged to the upper tray25belongs may also be discharged to the upper tray25. In this case, the CPU651(the discharge destination selection unit715) may change the discharge destination information of all subsequent sheets P belonging to the same post-processing job to the upper tray25in step S1415.

All of the specific values described in the first to third embodiments are merely examples. For example, in the third embodiment, the number of bundles M is set to a maximum of 2, but this number may instead be set to 3 or higher. Through this, the reduction in the shift amount may be applied to three or more sheet bundles W.

In the third embodiment, there are three combinations of the shift amount and the number of bundles M according to the delay amount of the sheet P, but four or more combinations may be provided. For example, there may be three or more options for the shift amount, and there may be three or more options for the number of bundles M.

According to the third embodiment, the shift amount of a subsequent plurality of sheet bundles W is determined based on the delay amount of the sheet P or the sheet bundle W. This improves the productivity of the post-processing apparatus4while maintaining the shift amount required for longitudinal alignment.

Technical Spirit Derived from Embodiments

Aspect 1

The image forming apparatus1is an example of a conveyance apparatus in a preceding stage. The “conveyance apparatus in a stage preceding the post-processing apparatus” is a conveyance apparatus present upstream from the post-processing apparatus in the conveyance direction of the sheets. The conveyance apparatus in the stage may be connected to the post-processing apparatus directly, or may be connected to the post-processing apparatus indirectly. In other words, another conveyance apparatus may be interposed between the conveyance apparatus in the stage and the post-processing apparatus. The conveyance path R1is an example of a first conveyance path. The buffer section81and the bundle forming section60function as a buffer unit (buffer mechanism). The conveyance path R2is an example of a second conveyance path. The post-processing section71is an example of a post-processing unit (a post-processing machine). The CPU651is an example of a control unit (a processor).

According to the first and third embodiments, the CPU651obtains a delay amount of a sheet conveyed from the conveyance apparatus in the stage and, based on the delay amount, sets a shift amount between a plurality of the sheets constituting the sheet bundle in the buffer unit. According to the second embodiment, the CPU651obtains a delay amount of a preceding other sheet bundle conveyed from the buffer unit to the post-processing unit and, based on the delay amount, sets a shift amount between a plurality of the sheets constituting the sheet bundle in the buffer unit. This makes it easier to achieve normal conveyance of sheets or sheet bundles in the post-processing apparatus4.

Aspect 2

The half-moon roller33and the alignment reference plate39are an example of an alignment unit.

Taking the alignment capabilities required for aligning the sheet bundle into account in this manner makes the alignment of the sheet bundle less likely to fail. In addition, the shift amount can be reduced while maintaining the alignment accuracy of the sheet bundle.

Aspects 3 and 4

The environmental sensor721is an example of a detection unit that detects an environmental condition of a surrounding environment in which the post-processing apparatus is installed.

For example, a high-temperature and high-humidity environment increases the friction between sheets, and thus higher alignment capabilities are required. Accordingly, by taking environmental conditions into account, the shift amount can be reduced while maintaining the alignment accuracy of the sheet bundle.

Aspect 5

The operation unit5and the CPU651are an example of an obtainment unit.

Friction acting between sheets varies depending on the type of the sheets. Accordingly, by taking the type of the sheets into account, the shift amount can be reduced while maintaining the alignment accuracy of the sheet bundle. Note that one or both of the environmental conditions and the type information may be taken into account as parameters affecting the alignment capabilities.

Aspect 6

The surface area, size, basis weight, and surface finish processing of the sheets all affect the friction acting between the sheets. Accordingly, by taking the type of the sheets into account, the shift amount can be reduced while maintaining the alignment accuracy of the sheet bundle.

Aspect 7

A large shift amount is set when the delay amount is small, and a small shift amount is set when the delay amount is large. In other words, an appropriate shift amount is set according to the delay amount.

Aspect 8

If the delay amount is very large, maintaining normal conveyance may not be possible simply by adjusting the shift amount alone. Similarly, if the required alignment capabilities are very large, maintaining normal conveyance may not be possible simply by adjusting the shift amount alone. In such cases, the CPU651may discharge the sheets to the upper tray25without going through the post-processing section71. This makes it possible to suppress the occurrence of jams inside the post-processing apparatus4.

Aspect 9

If the required alignment capabilities are very large, maintaining normal conveyance may not be possible simply by adjusting the shift amount alone. In such cases, the CPU651may discharge the sheets to the upper tray25without going through the post-processing section71. This makes it possible to suppress the occurrence of jams inside the post-processing apparatus4.

Aspect 10

When a sheet bundle for which normal conveyance cannot be ensured even after adjusting the shift amount is produced, a subsequent sheet bundle is also discharged to outside the post-processing apparatus4without conveying the sheet bundle to the post-processing section71.

Aspect 11

The conveyance destination of the sheet (e.g., the upper tray25, the lower tray37, or the post-processing section71) may be selected according to the delay amount. For example, a sheet bundle can be discharged to outside the post-processing apparatus4without being conveyed to the post-processing section71.

Aspect 12

If the delay amount is too large, it may be difficult to achieve normal conveyance simply by reducing the shift amount for a single sheet or a single sheet bundle. Accordingly, normal conveyance may be achieved by reducing the shift amount for at least two sheets or at least two sheet bundles.

Aspect 13

The delay amount may be obtained based on a conveyance time from a timing at which the sheet passes a first conveyance position (e.g., the sheet sensor17) to a timing at which the sheet passes a second conveyance position (e.g., the sheet sensor27).

This makes it possible to accurately detect a delay amount occurring upstream from the post-processing apparatus4. An appropriate shift amount can be determined as a result.

Aspect 14

The timing at which the sheet passes a predetermined position may be recognized based on a signal such as the report signal S1in this manner.

Aspect 15

A detection unit (e.g., the sheet sensor38) that detects, at a predetermined position, the preceding other sheet bundle conveyed from the second conveyance path to the post-processing unit may further be provided.

The delay amount of the preceding other sheet bundle may be obtained based on the timing at which the sheet sensor38detects the preceding other sheet bundle.

This ensures that the delay amount occurring downstream from the buffer section81is detected accurately. An appropriate shift amount can be determined as a result.

Aspect 16

The shift amount may be determined by taking into account both the delay amount occurring upstream from the bundle forming section60and the delay amount occurring downstream.

Aspect 17

In this manner, the shift amount is reduced when at least one of the two delay amounts suggests the possibility of a jam occurring in the future. Normal conveyance is maintained as a result.

Aspect 18

The memory652is an example of a storage unit that stores a usage history of the post-processing apparatus. For example, the CPU651may set the shift amount based on (i) the delay amount and (ii) the usage history, which is a parameter that affects the alignment capabilities.

The more the post-processing apparatus4is used, the more the conveyance capabilities of the conveyance roller pairs21,22,24,26, and28can decrease. Similarly, the alignment capabilities of the half-moon roller33can decrease. This means that the usage history is correlated with the alignment capabilities. It is therefore possible to set a more appropriate shift amount by setting the shift amount while taking the usage history into account.

Aspect 19

The number of sheets and operating time are correlated with a drop in the alignment capabilities of the half-moon roller33. Accordingly, a more appropriate shift amount can be set by taking these factors into account.

Aspect 20

The CPU651receives post-processing instructions from the printer controller600and executes post-processing according to the post-processing instructions. The post-processing apparatus4executes post-processing on the sheet P, outputs the sheet P to the upper tray25or the lower tray37without performing post-processing on the sheet P, or the like. Accordingly, a drop in the alignment capabilities of the half-moon roller33depends on the post-processing instructions. If the CPU651stores the post-processing instructions in the memory652as a usage history, the alignment capabilities of the half-moon roller33can be estimated more accurately.

Aspect 21

The conveyance roller pair22is an example of a first conveyance roller pair. The conveyance roller pair24is an example of a second conveyance roller pair. The conveyance roller pair26is an example of a third conveyance roller pair.

According to Aspect 21, a method of generating a sheet bundle using switch-back conveyance is realized. Switch-back conveyance has advantages such as reducing the length of the conveyance path needed to stack sheets. On the other hand, when a sheet delay occurs, the interval between a preceding sheet and a subsequent sheet decreases, making interference with the normal conveyance of sheets likely to occur. A method that adjusts the shift amount according to the delay amount is therefore advantageous.

Aspect 22

In this manner, the shift amount may be adjusted by adjusting the drive timing of the conveyance roller pairs.

Aspect 23

The motor M4is an example of a switching unit that switches the second conveyance roller pair between a contact state and a separated state.

In this manner, bringing the two rollers constituting the conveyance roller pair into contact or separating the rollers from each other makes it possible to generate sheet bundles smoothly.

Aspect 24

The backflow prevention valve23is an example of a guiding member that guides sheets or sheet bundles from the buffer unit to the second conveyance path.

This makes it possible to generate sheet bundles smoothly using switch-back conveyance.

Aspect 25

A post-processing apparatus included in an image forming system may be the post-processing apparatus according to any one of Aspects 2 to 24.

The present disclosure is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present disclosure. Therefore, to apprise the public of the scope of the present disclosure, the following claims are made.

OTHER EMBODIMENTS

Embodiment(s) of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure 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. 2022-068471, filed Apr. 18, 2022 which is hereby incorporated by reference herein in its entirety.