Sheet processing apparatus, control method therefor and storage medium

A sheet processing apparatus includes an alignment unit configured to align sheets stacked on a stack tray. The sheet processing apparatus determines whether or not a part of sheets stacked on the stack tray has been removed from the stack tray. When it is determined that a part of sheets stacked on the stack tray has been removed from the stack tray, the sheet processing apparatus inhibits an alignment of the sheets using the alignment unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet processing apparatus that has a function of aligning sheets stacked on a stack tray, a control method for the sheet processing apparatus, and a storage medium.

2. Description of the Related Art

For sheet processing apparatuses that stack a large number of sheets, there has been demand for the ability to discharge and align the sheets with a high degree of accuracy. Japanese Patent Laid-Open No. 2006-206331 suggests a sheet alignment process in which alignment members are provided on a stack tray, and sheets are piled up in such a manner that the positions of edge surfaces of the sheets parallel to a sheet discharge direction are lined up by the alignment members coming into and out of contact with the edge surfaces of the sheets.

The aforementioned conventional technique has the following problem. For example, if a user removes a part of sheets stacked on the stack tray, there is a possibility that sheets stacked on the stack tray may be misaligned. If an alignment process is applied to the sheets on the stack tray in this state, the sheet quality could possibly be reduced due to bending of the sheets stacked in a misaligned manner, and due to sliding of the bottom surfaces of the alignment members against the sheets stacked in a misaligned manner.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem. The present invention provides a technique to apply an alignment process to sheets stacked on a stack tray in a sheet processing apparatus without reducing the sheet quality.

According to one aspect of the present invention, there is provided a sheet processing apparatus comprising: a stacking control unit configured to control to stack sheets on a stack tray; an alignment unit configured to align sheets stacked on the stack tray; a determination unit configured to determine whether or not a part of sheets stacked on the stack tray has been removed from the stack tray; and a control unit configured to inhibit alignment by the alignment unit in a case where the determination unit determines that a part of sheets stacked on the stack tray has been removed from the stack tray.

According to another aspect of the present invention, there is provided a sheet processing apparatus comprising: a stacking control unit configured to control to stack sheets on a stack tray; an alignment unit configured to align sheets stacked on the stack tray; and a control unit configured to inhibit a process for alignment by the alignment unit, wherein when all of sheets stacked on the stack tray have been removed from the stack tray, the control unit cancels inhibition of the alignment.

According to still another aspect of the present invention, there is provided a control method for a sheet processing apparatus that includes a stacking control unit configured to control to stack sheets on a stack tray and an alignment unit configured to align sheets stacked on the stack tray, the control method comprising steps of: determining whether or not a part of sheets stacked on the stack tray has been removed from the stack tray; and inhibiting alignment by the alignment unit in a case where it has been determined that a part of sheets stacked on the stack tray has been removed from the stack tray.

According to yet another aspect of the present invention, there is provided a computer-readable storage medium storing a program for causing a computer to execute steps of a control method for a sheet processing apparatus that includes a stacking control unit configured to control to stack sheets on a stack tray and an alignment unit configured to align sheets stacked on the stack tray, the control method comprising steps of: determining whether or not a part of sheets stacked on the stack tray has been removed from the stack tray; and inhibiting alignment by the alignment unit in a case where it has been determined that a part of sheets stacked on the stack tray has been removed from the stack tray.

According to the present invention, a technique can be provided that applies an alignment process to sheets stacked on a stack tray without reducing the sheet quality.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the following embodiments are not intended to limit the scope of the appended claims, and that not all the combinations of features described in the embodiments are necessarily essential to the solving means of the present invention.

FIG. 1is a configuration diagram showing a cross-sectional configuration of main parts of an image forming system according to embodiments of the present invention.

This image forming system includes an image forming apparatus10and a finisher500which serves as a sheet stacker. In the image forming system (sheet processing apparatus) described herein, the finisher500is connected to the image forming apparatus10. It should be noted, however, that the present invention is not limited in this way, and is applicable to any sheet processing apparatus with a mechanism to discharge and stack sheets. That is to say, the image forming system, the image forming apparatus and the sheet stacker can each serve as an example of the sheet processing apparatus. The image forming apparatus10includes an image reader200that reads an image from an original, and a printer350that forms (prints) the read image on a sheet.

A document feeder100feeds originals set on an original tray101one by one in order starting from the top original, conveys the originals along a curved path and past a predetermined pickup position on a glass platen102, then discharges the originals onto a discharge tray112. Note that the originals are set on the original tray101with their front sides up. At this time, a scanner unit104is fixed at a predetermined reading position. When an original passes the reading position, an image of the original is read by the scanner unit104. When the original passes the reading position, the original is irradiated with light from a lamp103in the scanner unit104, and reflected light from the original is directed to a lens108via mirrors105,106and107. Light that has passed through this lens108is focused on an imaging surface of an image sensor109, converted into image data, and output. The image data output from the image sensor109is input as a video signal to an exposure unit110in the printer350.

The exposure unit110in the printer350outputs laser light that has been modulated based on a video signal input from the image reader200. A photosensitive drum111is irradiated with and scanned by this laser light using a polygon mirror119. An electrostatic latent image corresponding to the laser light that has scanned the photosensitive drum111is formed on the photosensitive drum111. This electrostatic latent image on the photosensitive drum111turns into a visible image by being developed using the developer supplied from a developer113.

Sheets used in the printing are picked up one by one from a sheet feeding tray114or115, which is provided in the printer350, by rotation of a pickup roller127or128. The sheets thus picked up are conveyed to the position of registration rollers126by rotation of sheet feeding rollers129or130. AlthoughFIG. 1shows only two sheet feeding trays for the sake of explanation, the printer350may include other sheet feeding trays that are not shown in the figures. Furthermore, additional sheet feeding trays may be provided by connecting an optional sheet feeding apparatus not shown in the figures to the printer350. When the leading edge of a sheet arrives at the position of the registration rollers126, the registration rollers126are driven and rotated at a predetermined timing so as to convey the sheet between the photosensitive drum111and a transfer unit116. Accordingly, a developer image formed on the photosensitive drum111is transferred to the fed sheet by the transfer unit116. The sheet to which the developer image has been thus transferred is conveyed to a fixing unit117. The fixing unit117fixes the image on the sheet by applying heat and pressure to the sheet. The sheet that has passed the fixing unit117is discharged to the outside of the printer350(to the finisher500) via a flapper121and discharge rollers118. In the case where images are formed on both sides of the sheet, the sheet is conveyed to a double-sided conveying path124via a reversing path122, then conveyed to the position of the registration rollers126again.

The following describes a configuration of a controller unit90that controls the entirety of the present image forming system with reference toFIG. 2.

As shown inFIG. 2, the controller unit90includes a CPU circuit unit900in which a CPU901, a ROM902and a memory unit903are built. The memory unit903is constituted by a RAM or an HDD. The CPU901performs basic control of the entirety of the present image forming system, and is connected to the ROM902in which control programs are written and to the memory unit903used for processing via an address bus and a data bus. The CPU901also performs overall control of controllers911,921,922,931,941and951based on the control programs stored in the ROM902. The memory unit903temporarily holds control data and is used as a working area for calculation processing associated with control.

An document feed controller911controls driving of the document feeder100based on instructions from the CPU circuit unit900. An image reader controller921controls driving of the above-described scanner unit104, image sensor109, and the like, and transfers an image signal output from the image sensor109to an image signal controller922. The image signal controller922converts an analog image signal from the image sensor109into a digital signal, applies various types of processing to the digital signal, converts the digital signal into a video signal, and outputs the video signal to a printer controller931. The image signal controller922also converts a digital image signal input from a computer905via an external I/F904into a video signal by applying various types of processing to the digital image signal, and outputs the video signal to the printer controller931. The operations of processing executed by this image signal controller922are controlled by the CPU circuit unit900.

The printer controller931controls the exposure unit110and the printer350based on an input video signal so as to form images and convey sheets. A finisher controller951is mounted on the finisher500, and controls driving of the entirety of the finisher500by exchanging information with the CPU circuit unit900. The details of this control will be described later. A console unit controller941exchanges information with an operation display unit400and the CPU circuit unit900. The operation display unit400includes, for example, a plurality of keys for setting various types of functions related to image formation, and a display unit for displaying information showing the states of settings. The console unit controller941outputs key signals corresponding to operations applied to the keys to the CPU circuit unit900, and displays corresponding information on the operation display unit400based on signals from the CPU circuit unit900.

FIG. 3is a diagram for describing the operation display unit400in the image forming apparatus10according to embodiments of the present invention.

For example, a start key402, a stop key403, numeric keys404to413, a clear key415, and a reset key416are arranged on the operation display unit400. The start key402is used to start the image forming operations. The stop key403is used to interrupt the image forming operations. The numeric keys404to413are used to, for example, enter numbers. A display unit420is also arranged on the operation display unit400. A touchscreen is formed on the upper part of the display unit420. Software keys can be generated on a screen of the display unit420.

This image forming apparatus10includes various process modes as post-process modes, including no sort, sort, shift-sort, staple-sort, and the like. The settings and the like for these process modes are input from the operation display unit400. For example, a post-process mode is set as follows. When a “Finish” software key417is selected on a default screen shown inFIG. 3, a menu selection screen is displayed on the display unit420. On this menu selection screen, a post-process mode is set.

The following describes a configuration of the finisher500with reference toFIGS. 4A and 4B.FIGS. 4A and 4Bare diagrams for describing a configuration of the finisher500according to embodiments of the present invention.FIG. 4Ashows the finisher500as viewed from the front, andFIG. 4Bshows stack trays700and701in the finisher500as viewed in a direction opposing a sheet discharge direction.

First, a process in which the finisher500receives sheets discharged from the image forming apparatus10and discharges them onto the stack tray700or701will be described with reference toFIG. 4A.

The finisher500receives sheets discharged from the image forming apparatus10in order, and executes post-processes such as a process for aligning the plurality of received sheets in a bundle, and a staple process for binding the trailing edges of the bundle of sheets using a stapler. The finisher500receives a sheet discharged from the image forming apparatus10along a conveyance path520using a pair of conveyance rollers511. The sheet that has been received using the pair of conveyance rollers511is conveyed via pairs of conveyance rollers512,513and514. Sheet sensors570,571,572and573are provided on the conveyance path520to detect passing of the sheet. The pair of conveyance rollers512is provided in a shift unit580together with the sheet sensor571.

The shift unit580can move the sheet in a sheet width direction orthogonal to a sheet conveyance direction using a later-described shift motor M5(FIG. 5). By driving the shift motor M5while the pair of conveyance rollers512is holding the sheet therebetween, the sheet can be offset in the width direction while being conveyed. In a shift-sort mode, the position of a bundle of sheets is moved in the width direction on a per-copy basis. For example, an offset amount of 15 mm toward the front (front shift), or an offset amount of 15 mm toward the back (back shift), is set with respect to the center position in the width direction. When no designation is made regarding the shift, sheets are discharged at the same position as in the front shift.

When the finisher500detects that a sheet has passed the shift unit580based on the input from the sheet sensor571, the finisher500drives the shift motor M5(FIG. 5) to place the shift unit580back to the center position. A switching flapper540, which directs a sheet conveyed in a reverse fashion by the pair of conveyance rollers514to a buffer path523, is arranged between the pair of conveyance rollers513and the pair of conveyance rollers514. The switching flapper540is driven by a later-described solenoid SL1(FIG. 5).

A flapper541, which switches between an upper discharge path521and a lower discharge path522, is arranged between the pair of conveyance rollers514and the pair of conveyance rollers515. The flapper541is driven by the later-described solenoid SL1. When the flapper541switches to the upper discharge path521, a sheet is directed to the upper discharge path521by the pair of conveyance rollers514which is driven and rotated by a buffer motor M2(FIG. 5). Then, the sheet is discharged onto the stack tray (discharge tray)701by the pair of conveyance rollers515which is driven and rotated by a discharge motor M3(FIG. 5). A sheet sensor574is provided on the upper discharge path521to detect passing of the sheet. When the flapper541switches to the lower discharge path522, the sheet is directed to the lower discharge path522by the pair of conveyance rollers514which is driven and rotated by the buffer motor M2. This sheet is further directed to a process tray630by pairs of conveyance rollers516to518which are driven and rotated by the discharge motor M3. Sheet sensors575and576are provided on the lower discharge path522to detect passing of the sheet. The sheet that has been directed to the process tray630is discharged onto the process tray630or the stack tray700, in accordance with a post-process mode, by a pair of bundle discharge rollers680driven and rotated by a bundle discharge motor M4(FIG. 5).

Next, an alignment mechanism that aligns a plurality of sheets discharged on the stack tray700or701will be described with reference toFIGS. 4A and 4B. As shown inFIG. 4B, alignment plates711aand711bthat are alignment members for aligning sheets discharged onto the stack tray701in the sheet width direction by coming into contact with both side edges (side surfaces parallel to the sheet conveyance direction) of the sheets are arranged on the stack tray701. The alignment plate711ais an example of a first alignment member and the alignment plate711bis an example of a second alignment member. These alignment plates711aand711bare represented by a reference sign711inFIG. 4A. Similarly, alignment plates710aand710bare arranged on the stack tray700. The alignment plates710aand710bare used to align sheets discharged onto the stack tray700in the sheet width direction. The alignment plates710aand710b, which are represented by a reference sign710inFIG. 4A, can be moved in the sheet width direction respectively by later-described lower tray alignment motors M11and M12(FIG. 5). InFIG. 4A, the alignment plates710aand710bare arranged respectively in the front and the back. On the other hand, the alignment plates711aand711bare similarly driven respectively by later-described upper tray alignment motors M9and M10(FIG. 5). InFIG. 4A, the alignment plates711aand711bare arranged respectively in the front and the back. Furthermore, the alignment plates710and711are moved up and down respectively by an alignment plate elevator motor M13for an upper tray (FIG. 5) and an alignment plate elevator motor M14for a lower tray (FIG. 5), which will be described later. More specifically, the alignment plates710and711are moved up and down about an alignment plate axis713between aligning positions where they actually execute an alignment process (FIG. 6A) and waiting positions where they wait (FIG. 6B).

The stack trays700and701can be raised and lowered by later-described tray elevator motors M15and M16(FIG. 5). A tray or the topmost surface of sheets on the tray is detected by later-described sheet sensors720and721(FIG. 4A). The finisher500performs control so that the tray or the topmost surface of sheets on the tray is always located at a certain position by driving and rotating the tray elevator motors M15and M16in accordance with the input from the sheet sensors720and721, as described later. Furthermore, sheet sensors730and731(FIG. 4A) detect whether or not there is any sheet on the stack trays701and700.

A description is now given of a configuration of the finisher controller951that controls driving of the finisher500with reference toFIG. 5.FIG. 5is a block diagram showing a configuration of the finisher controller951according to embodiments of the present invention.

The finisher controller951includes a CPU952, a ROM953, a memory unit954, and the like. The memory unit954may be constituted by a RAM, but may include an HDD. The finisher controller951controls driving of the finisher500by communicating with the CPU circuit unit900so as to perform exchange of data such as transmission/reception of commands, exchange of job information, and notification of sheet transfer, and executing various types of programs stored in the ROM953.

In order to convey sheets, the finisher500includes an entrance motor M1that drives and rotates the pairs of conveyance rollers511to513, a buffer motor M2, a discharge motor M3, a shift motor M5, solenoids SL1and SL2, and sheet sensors570to576. The finisher500also includes, as means to drive various types of members in the process tray630(FIG. 4A), a bundle discharge motor M4that drives the pair of bundle discharge rollers680, and alignment motors M6and M7that drive alignment members641(FIG. 4A). The finisher500further includes a swing guide motor M8that drives a swing guide to be raised and lowered. The finisher500further includes tray elevator motors M15and M16for raising and lowering the stack trays700and701, sheet sensors720and721(FIG. 4A), and sheet sensors730and731. In relation to alignment operations for sheets on the stack trays, the finisher500further includes upper tray alignment motors M9and M10, lower tray alignment motors M11and M12, an alignment plate elevator motor M13for the upper tray, and an alignment plate elevator motor M14for the lower tray.

The following describes sheet detection performed in the image forming apparatus10according to embodiments of the present invention with reference toFIGS. 12,13A and13B. Sheet detection denotes detection of the presence and absence of sheets stacked on the stack trays700and701, and detection of removal of (a part of) sheets stacked on the stack trays700and701(that is to say, a decrease in stacked sheets).

First, a description is given of a mechanism for detecting the presence and absence of sheets discharged and stacked on the stack trays700and701using the sheet sensors730and731with reference toFIG. 12.FIG. 12is an enlarged view of the stack tray701. Although the sheet sensor731arranged on the stack tray701will be described in the following example, the same goes for the sheet sensor730arranged on the stack tray700.

A portion indicated by a chain line inFIG. 12corresponds to the sheet sensor731arranged on a central portion of the stack tray701. The sheet sensor731is composed of a detection sensor1201utilizing a photo interrupter, a light-blocking plate1202, and a rotation axis1203of the light-blocking plate1202. When sheets are discharged onto the stack tray701, these sheets apply a load to the light-blocking plate1202in a direction toward the inside of the stack tray701. Consequently, the light-blocking plate1202rotates toward the inside of the stack tray701about the rotation axis1203, which serves as a spindle, and moves to a position where it blocks light from a light emitting unit to a light receiving unit in the detection sensor1201.

When the light from the light emitting unit to the light receiving unit in the detection sensor1201is blocked by the light-blocking plate1202(a blocked state), the detection sensor1201notifies the CPU952in the finisher controller951of information indicating the presence of sheets on the stack tray701. On the other hand, when the light from the light emitting unit to the light receiving unit in the detection sensor1201is not blocked (a transmissive state), the detection sensor1201notifies the CPU952of information indicating the absence of sheets on the stack tray701. Based on the information notified by the detection sensor1201, the CPU952notifies the CPU circuit unit900of the presence or absence of sheets on the stack tray701.

With reference toFIGS. 13A and 13B, the following describes a mechanism for detecting the removal of a part of sheets stacked on the stack trays700and701using the sheet sensors720and721. Although the stack tray701, the sheet sensor721and the tray elevator motor M16will be described in the following example, the same goes for the stack tray700, the sheet sensor720and the tray elevator motor M15.

The CPU952in the finisher controller951performs control such that, while sheets are being stacked on the stack tray701, the stack tray701is located at a position (height) where the sheet sensor721can detect the topmost sheet out of the stacked sheets. Alternatively, the CPU952may perform control such that, while sheets are being stacked on the stack tray701, the stack tray701is located at a position (height) where the sheet sensor721can detect at least an upper part of the stacked sheets adjacent to the topmost sheet. The CPU952raises and lowers the stack tray701as follows in accordance with a signal output from the sheet sensor721by controlling the tray elevator motor M16.

The sheet sensor721, which utilizes a photo interrupter, detects sheets based on the transmissive/blocked state between a light emitting unit and a light receiving unit in the photo interrupter, and outputs a signal indicating the transmissive/blocked state to the CPU952. When the sheet sensor721is placed in the blocked state, the CPU952lowers the stack tray701to a position where the sheet sensor721is placed in the transmissive state (FIG. 13A). Thereafter, the CPU952raises the stack tray701, and then stops the raising of the stack tray701when the sheet sensor721is placed in the blocked state (FIG. 13B). In this way, on the stack tray701, the topmost sheet out of the stacked sheets (or an upper part of the stacked sheets) is detected by the sheet sensor721. Note that the state where the topmost sheet is detected by the sheet sensor721, as shown inFIG. 13B, is hereinafter referred to as a “sheet surface detection state”.

While sheets are being stacked on the stack tray701, the CPU952controls the tray elevator motor M16(raises and lowers the stack tray701) so as to maintain the aforementioned sheet surface detection state. Consequently, the topmost sheet out of the stacked sheets remains at a certain position (height). Note that the CPU952maintains the sheet surface detection state (FIG. 13B) by, for example, lowering the stack tray701each time a certain number sheets have been printed (that is to say, in accordance with the thickness of the stacked sheets) during printing.

In the sheet surface detection state, if at least the topmost sheet out of the stacked sheets (or an upper part of the stacked sheets) is removed, the sheet sensor721switches from the blocked state to the transmissive state. In this case, the sheet sensor721accordingly outputs a signal indicating the transmissive state to the CPU952. That is to say, if the sheet sensor721detects the disappearance of the topmost sheet (or the upper part of the stacked sheets) that has been detected, it outputs, to the CPU952, a signal indicating the removal of a part of the sheets stacked on the stack tray701. When the CPU952receives the signal indicating that the sheet sensor721has been placed in the transmissive state during the sheet surface detection state, it determines that (a part of) the sheets have been removed from the stack tray701, and notifies the CPU circuit unit900of the removal. Thereafter, in order to restore the sheet surface detection state, the CPU952raises the stack tray701until the sheet sensor721is placed in the blocked state by controlling the tray elevator motor M16.

As described above, according to embodiments of the present invention, the sheet sensors720and721are examples of a first sensor that detects the removal of a part of sheets stacked on the stack trays700and701. Also, the sheet sensors730and731are examples of a second sensor that detects the presence and absence of sheets stacked on the stack trays700and701. Furthermore, the amount of sheets stacked on the stack trays700and701can be detected using the sheet sensors720and721. For example, the CPU952can obtain the amount of stacked sheets based on a difference between: the position (height) of the stack tray700or701during the sheet surface detection state, which corresponds to the position of the topmost sheet; and the position (height) where the sheet sensor720or721is situated.

The following describes a flow of sheets during a sort mode with reference toFIGS. 3,7,8A to8D,10A to10C, and11. When the user presses a “Select Sheet” key418on the default screen shown inFIG. 3on the operation display unit400of the image forming apparatus10, a sheet feeding tray selection screen as shown inFIG. 11is displayed on the display unit420. On this sheet feeding tray selection screen, the user selects sheets to be used for a job. It is assumed here that the user selects the size “A4” corresponding to a sheet feeding tray1.FIG. 11shows one example of the sheet feeding tray selection screen on which the size “A4” is selected.

When the user selects the “Finish” software key417on the default screen shown inFIG. 3on the operation display unit400of the image forming apparatus10, a finish menu selection screen shown inFIG. 10Ais displayed on the display unit420. When the user presses an OK button while a “Sort” key is selected on the finish menu selection screen shown inFIG. 10A, the sort mode is set.

In order to offset a bundle of sheets on a per-copy basis, the user presses the OK button while a “Shift” key is selected on the finish menu selection screen shown inFIG. 10A; as a result, a shift mode is set.

Once the user has designated the sort mode and entered a job, the CPU901in the CPU circuit unit900notifies the CPU952in the finisher controller951of information related to that job, such as the sheet size and the selection of the sort mode. Note that after sheets have been discharged in one print job, shift operations are applied to sheets printed in the next print job so that the sheets printed in the next print job are discharged at a different position from the sheets discharged in the previous job. Such shift operations applied for each print job are referred to as an inter-job shift.

FIG. 7is a diagram for describing the conveyance of sheets in the finisher according to embodiments of the present invention, and inFIG. 7, the parts that are shown in the above-describedFIG. 4Aare given the same reference signs as inFIG. 4A.

When the image forming apparatus10discharges a sheet P to the finisher500, the CPU901in the CPU circuit unit900notifies the CPU952in the finisher controller951of the start of sheet transfer. The CPU901also notifies the CPU952in the finisher controller951of sheet information, such as shift information and sheet width information of the sheet P. Upon receiving the notification of the start of sheet transfer, the CPU952drives and rotates the entrance motor M1, the buffer motor M2and the discharge motor M3. As a result, the pairs of conveyance rollers511,512,513,514and515shown inFIG. 7are driven and rotated, thus making the finisher500receive and transfer the sheet P discharged from the image forming apparatus10. The sheet sensor571detects the sheet P when the pair of conveyance rollers512holds the sheet P therebetween. Accordingly, the CPU952offsets the sheet P in the width direction by moving the shift unit580through driving of the shift motor M5. When the shift information included in the sheet information notified from the CPU901shows “no shift designation”, sheets are equally offset by 15 mm toward the front.

When the flapper541is driven and rotated by the solenoid SL1to be situated in the position shown inFIG. 7, the sheet P is directed to the upper discharge path521. Then, when the sheet sensor574detects passing of the trailing edge of the sheet P, the CPU952discharges the sheet P onto the stack tray701by driving and rotating the discharge motor M3so that the sheet P is conveyed by the pair of conveyance rollers515at a speed suited for stacking.

Next, a description is given of the alignment operations during a sort mode, using an example of the front shift operations, with reference toFIGS. 8A to 8D.FIGS. 8A to 8Dare diagrams for describing the positions of the alignment plates711aand711bon the stack tray701as viewed in a direction opposing the sheet discharge direction.

As shown inFIG. 8A, before a job is started, the pair of alignment plates711aand711bwaits at default positions. As shown inFIG. 8B, when the job is started, the front alignment plate711amoves to an alignment waiting position that is distant from a front sheet edge position X1by a predetermined retracted amount M. Note, the front sheet edge position X1is distant from the center position of the stack tray701by a distance obtained by adding a shift amount Z to W/2 which is half of the sheet width. The alignment plate711awaits at this alignment waiting position until a sheet is discharged. On the other hand, the back alignment plate711bwaits at an alignment waiting position that is distant from a back sheet edge position X2by the predetermined retracted amount M. Note, the back sheet edge position X2is distant from the center position of the stack tray701by a distance obtained by subtracting the shift amount Z from W/2 which is half of the sheet width. When a predetermined time period has elapsed since the sheet P was discharged onto the stack tray701, the front alignment plate711amoves toward the center of the stack tray701by a predetermined push amount 2M so as to press the sheet P against the stopped back alignment plate711bas shown inFIG. 8C. As a result, the sheet P is moved toward the alignment plate711bby the retracted amount M. When a predetermined period has elapsed since the sheet P was pressed against the alignment plate711bin the above manner, the alignment plate711ais retracted to the alignment waiting position as shown inFIG. 8D. More specifically, the alignment plate711ais retracted away from the sheet P in the sheet width direction by 2M which is twice the retracted amount M, then waits until the next sheet is discharged onto the stack tray701. Provided that the offset amount Z is 15 mm and the retracted amount M is 5 mm, the front alignment plate711apushes the sheet P by 5 mm during the alignment operations, and therefore the offset amount of the sheet P after the alignment operations is 10 mm. By repeating the above operations, a sheet P is aligned each time it is discharged onto the stack tray701.

The following describes a flow of sheets during a shift-sort mode with reference toFIGS. 3,7,9A to9G, and10A to10C. The shift-sort mode is set when the OK key is pressed while the “Sort” and “Shift” keys are selected on the finish menu selection screen shown inFIG. 10B.

Once the user has designated the shift-sort mode and entered a job, the CPU901in the CPU circuit unit900notifies the CPU952in the finisher controller951of the selection of the shift-sort mode, similarly to the case of a no sort mode. The following describes the operations for a shift-sort mode in the case where one “copy” is composed of three sheets.

When the image forming apparatus10discharges a sheet P to the finisher500, the CPU901in the CPU circuit unit900notifies the CPU952in the finisher controller951of the start of sheet transfer. Upon receiving the notification of the start of sheet transfer, the CPU952drives the entrance motor M1, the buffer motor M2and the discharge motor M3. As a result, the pairs of conveyance rollers511,512,513,514and515shown inFIG. 7are driven and rotated, thus making the finisher500receive and transfer the sheet P discharged from the image forming apparatus10. When the sheet sensor571detects that the sheet P is held between the pair of conveyance rollers512, the CPU952offsets the sheet P by moving the shift unit580through driving of the shift motor M5. The sheet P is offset by 15 mm toward the front when the shift information of the sheet P notified from the CPU901shows “front”, and by 15 mm toward the back when the shift information of the sheet P notified from the CPU901shows “back”.

The flapper541is driven and rotated by the solenoid SL1to be situated in the position shown in the figures, and the sheet P is directed to the upper discharge path521. When the sheet sensor574detects passing of the trailing edge of the sheet P, the CPU952discharges the sheet P onto the stack tray701by driving the discharge motor M3so that the pair of conveyance rollers515is rotated at a speed suited for stacking.

The following describes the operations of the alignment plates at the time of the shifting, using the exemplary case where the shift direction is changed from the front to the back, with reference toFIGS. 9A to 9G.FIGS. 9A to 9Gshow the stack tray701as viewed in a direction opposing the sheet discharge direction. When a retracting operation of the front alignment plate711ais finished as shown inFIG. 9A, the alignment plates711aand711bare raised off the stack tray701by a predetermined amount as shown inFIG. 9B. Next, the alignment plates711aand711bmove in the sheet width direction to their respective alignment waiting positions for the next sheet. As shown inFIG. 9C, the front alignment plate711amoves to an alignment waiting position that is distant from the front sheet edge position X1by the predetermined retracted amount M. Note, the front sheet edge position X1is distant from the center position of the stack tray701by a distance obtained by subtracting the shift amount Z from W/2 which is half of the sheet width. The back alignment plate711bmoves to an alignment waiting position that is distant from the back sheet edge position X2by the predetermined retracted amount M. Note, the back sheet edge position X2is distant from the center position of the stack tray701by a distance obtained by adding the shift amount Z to W/2 which is half of the sheet width. Once the alignment plates711aand711bhave moved to their respective alignment waiting positions, the alignment plates711aand711bmove toward the stack tray701by a predetermined amount and wait until the next sheet is discharged onto the stack tray701as shown inFIG. 9D. At this time, the alignment plate711ais in contact with the top surface of the already-stacked sheets.

When a predetermined time period has elapsed since a sheet P was discharged onto the stack tray701as shown inFIG. 9E, the alignment plate711bmoves toward the center of the stack tray701by the predetermined push amount 2M so as to press the sheet P against the alignment plate711aas shown inFIG. 9F. When a predetermined time period has elapsed in the state ofFIG. 9F, the alignment plate711bis retracted away from the center of the stack tray701by the predetermined push amount 2M and waits until the next sheet is discharged onto the stack tray701as shown inFIG. 9G.

As described above, when the shift direction is changed, alignment plates are first raised off a stack tray in the upward direction, then lowered after changing the aligning positions; in this way, a sheet is aligned each time it is discharged onto the stack tray.

When a “Select Discharge Destination” key is selected on the finish menu selection screen shown inFIG. 10A, a discharge destination selection screen shown inFIG. 10Cis displayed on the display unit420. When the user selects a discharge destination and presses the OK key, the discharge destination is selected, and the finishing menu selection screen shown inFIG. 10Ais displayed on the display unit420.

First Embodiment

Problem in Alignment Process

As described above with reference toFIGS. 4A and 4B, the finisher500includes alignment plates710a,710b,711aand711bas alignment mechanism for aligning a plurality of sheets discharged onto the stack trays700and701. For example, the finisher500uses the pair of alignment plates711aand711bwhen executing an alignment process for aligning a plurality of sheets P stacked on the stack tray710in the width direction.FIG. 14Ashows the case where the alignment process is applied to the plurality of sheets P discharged onto the stack tray701using the alignment plates711aand711b. The plurality of sheets P are aligned in the width direction, which is indicated by arrows1400, by the alignment plates711aand711bmoving in the width direction and coming into contact with the side edges of the plurality of sheets P at the positions shown inFIG. 14A.

However, if the user removes a part of the plurality of sheets P discharged onto the stack tray701, the sheets P stacked on the stack tray701may be misaligned as shown inFIG. 14B. Should the alignment process be applied to the sheets P in this state, there is a possibility that the sheets may be damaged by the alignment plates711aand711bmoving in the directions indicated by the arrows1400and coming into contact with the sheets P. For example, there is a possibility that the sheets may be bent by the alignment plates711aand711bwhen the alignment plates711aand711bcome into contact with the misaligned sheets (in particular, the portion indicated by the reference sign1410). Furthermore, there is a possibility that toner on the sheets may be removed by the bottom surfaces of the alignment plates711aand711bsliding against the surfaces of misaligned sheets. Moreover, if the toner that has attached to the bottom surfaces of the alignment plates711aand711battaches to other parts of the same sheet or to other sheets, there is a possibility that the quality of sheets (and of images printed on the sheets) may be reduced.

The present embodiment addresses the above problem as follows: if a part of sheets stacked on the stack trays700and701is removed from these stack trays, an alignment process for the sheets is inhibited. In other words, after a part of the sheets has been removed, an alignment process is not applied to sheets remaining on the stack trays700and701. In this way, bending of sheets and removal of toner are prevented, and the quality of sheets discharged onto the stack trays700and701is not reduced by an alignment process.

The following is a more specific description of alignment operations for sheets according to a first embodiment with reference toFIG. 15.FIG. 15is a state transition diagram related to alignment operations for sheets according to the first embodiment. In the present embodiment, the CPU952in the finisher controller951switches the state of alignment operations for sheets that have been discharged and stacked on the stack trays700and701based on information from the sheet sensors720and721and from the sheet sensors730and731. Note that the CPU952controls alignment operations for sheets for each of the stack trays700and701independently. Since the control for the alignment operations is the same for both of the stack trays700and701, the stack tray701will be discussed below.

When the sheet sensor731detects no sheet on the stack tray701, the CPU952controls the lower tray alignment motors M11and M12and the alignment plate elevator motor M14for the lower tray such that alignment operations are applied to sheets that are to be discharged onto the stack tray701thereafter. That is to say, the CPU952places the alignment operations for sheets on the stack tray701in a permitted state (state1501). Then, if sheets start to be discharged and stacked on the stack tray701, the CPU952places the stack tray701in the sheet surface detection state based on a signal output from the sheet sensor721.

Subsequently, if a part of the sheets stacked on the stack tray701is removed, the sheet sensor721switches from the blocked state to the transmissive state, and a signal indicating the transmissive state is output to the CPU952. In response, the CPU952determines that a part of the sheets stacked on the stack tray701has been removed, that is to say, the amount of sheets stacked on the stack tray701has decreased, and places the alignment operations (alignment process) for the sheets on the stack tray701in an inhibited state (state1502). Consequently, even if sheets are discharged and stacked on the stack tray701thereafter, the alignment operations for sheets using the alignment plates711aand712bare not executed, thereby making it possible to prevent the occurrence of the above-mentioned problem caused by the execution of the alignment operations.

In the present embodiment, the inhibition of the alignment operations for sheets may further be cancelled in accordance with a change in the stacked state of sheets on the stack tray701. More specifically, if all of sheets stacked on the stack tray701are removed from the stack tray701, the inhibition of the alignment operations (alignment process) may be cancelled. This is because, if all of discharged sheets are removed from the stack tray701, the above-mentioned misalignment in the stacked sheets is resolved, and therefore the alignment operations for sheets that are to be discharged thereafter do not cause the occurrence of the above-mentioned problem.

If all of sheets stacked on the stack tray701are removed while the alignment operations are in the inhibited state (1502), the sheet sensor731detects no sheet on the stack tray701, and a signal indicating the detection of no sheet is output to the CPU952. In response, the CPU952determines that all of sheets stacked on the stack tray701have been removed, that is to say, the amount of sheets stacked on the stack tray701has reached 0 (zero), and places the alignment operations (alignment process) for sheets on the stack tray701in the permitted state (state1501). In the above manner, if the alignment operations for sheets have been interrupted, it is possible to automatically resume the alignment operations for sheets and provide the user with sheets to which the alignment process has been applied in accordance with a change in the stacked state of sheets on the stack tray700.

<Procedure of Processing for Execution of Print Job>

With reference toFIG. 16, the following describes a procedure of sheet processing for the execution of a print job according to the present embodiment. Note that the processes of steps in this flowchart are realized in the finisher500by the CPU952in the finisher controller951reading a program stored in the ROM953to the memory unit954and executing the read program. Also, the execution of a print job is realized by the CPU901in the image forming apparatus10reading a program stored in the ROM902to the memory unit903and executing the read program.

First, in step S1601, the CPU901starts the execution of the print job. It will be assumed that, in the print job, the execution of an alignment process in the finisher500is designated, and the stack tray701is designated as a discharge destination for sheets to which the image forming apparatus10has applied a print process. It should be noted, however, that the CPU952can control each of the stack trays700and701independently. In accordance with an instruction from the CPU901, the CPU952controls the finisher500to discharge conveyed sheets onto the stack tray701and apply an alignment process to the discharged sheets using the alignment plates711aand711b. While the sheets are being stacked on the stack tray701, the CPU952performs control to place the stack tray701in the sheet surface detection state as described earlier.

During the execution of the print process and the alignment process based on the print job, the CPU952determines in step S1602whether or not a part of sheets stacked on the stack tray701has been removed (that is to say, the amount of stacked sheets has decreased) based on a signal output from the sheet sensor721. If the CPU952determines that the amount of stacked sheets has decreased, it proceeds to the process of step S1603and determines whether or not all of the stacked sheets have been removed (that is to say, the amount of stacked sheets has reached 0) based on a signal output from the sheet sensor731. If the CPU952determines that the amount of stacked sheets has not reached 0, it proceeds to the process of step S1604and controls the finisher500to interrupt the alignment process. Thereafter, the processing moves to step S1606.

On the other hand, if the CPU952determines in step S1602that the amount of stacked sheets has not decreased, it proceeds to the process of step S1605and determines whether or not the execution of the print job has finished. Unless the execution of the print job has finished, the CPU952returns to the process of step S1602and controls the finisher500to continue the alignment process for the sheets stacked on the stack tray701. This is because, if a part of the sheets has not been removed from the stack tray701, there will be no occurrence of a reduction in the sheet quality caused by the alignment process for sheets stacked in a misaligned manner.

If the CPU952determines in step S1603that the amount of stacked sheets has reached 0, it proceeds to the process of step S1605without interrupting the alignment process, and determines whether or not the execution of the print job has finished. Unless the execution of the print job has finished, the CPU952returns to the process of step S1602and controls the finisher500to continue the alignment process for the sheets stacked on the stack tray701. This is because, if all of the sheets have been removed from the stack tray701, there will be no occurrence of the state where sheets are stacked in a misaligned manner, and there will be no occurrence of a reduction in the sheet quality caused by the alignment process.

While the alignment process is being interrupted, the CPU952determines in step S1606whether or not all of the stacked sheets have been removed (that is to say, the amount of stacked sheets has reached 0) based on a signal output from the sheet sensor731. If the CPU952determines that the amount of stacked sheets has reached 0, it proceeds to the process of step S1607, controls the finisher500to resume the alignment process that has been interrupted, and returns to the process of step S1602. On the other hand, if the CPU952determines that the amount of stacked sheets has not reached 0, it proceeds to the process of step S1608and determines whether or not the execution of the print job has finished. Unless the execution of the print job has finished, the CPU952returns to the process of step S1606and repeats the determination process of step S1606.

In the case where the CPU952determines that the execution of the print job has finished in step S1605or step S1606, if the alignment process be in execution, it waits until all sheets are discharged and then completes the alignment process. Thereafter, the sequence of processes is ended.

As described above, even when the removal of a part of sheets stacked on the stack trays700and701has led to misalignment of the stacked sheets, it is possible to prevent a reduction in the sheet quality caused by the alignment process for sheets. Furthermore, if all of the sheets stacked on the stack trays700and701are removed during the inhibition of the alignment process, the inhibition of the alignment operations for sheets is cancelled; as a result, the alignment process can be resumed at an appropriate timing, and the user can be provided with sheets to which the alignment process has been applied.

Second Embodiment

In the first embodiment, after an alignment process for sheets is interrupted, the alignment process for sheets is not resumed unless all of sheets stacked on the stack trays700and701are removed. For this reason, in the case where, for example, the image forming apparatus10is shared among a plurality of users, the alignment process cannot be applied to sheets corresponding to a print job for which the execution is instructed by a certain user unless all of the stacked sheets are removed by any of the users while the alignment process is being interrupted. In view of this, it would be desirable to provide a mechanism for automatically resuming the alignment process even if all of the stacked sheets are not removed.

In a second embodiment, the alignment process is resumed in accordance with the positions of the stack trays700and701in the vertical direction (or the amount of stacked sheets), not only if all of sheets stacked on these stack trays are removed, but also if a part of the sheets stacked on these stack trays is removed. In this way, the alignment process can be resumed automatically without the occurrence of a reduction in the sheet quality caused by the alignment process for sheets stacked in a misaligned manner.

<Procedure of Processing for Execution of Print Job>

With reference toFIG. 17, the following describes a procedure of sheet processing for the execution of a print job according to the present embodiment. Similarly to the first embodiment (FIG. 16), the processes of steps in this flowchart are realized in the finisher500by the CPU952in the finisher controller951reading a program stored in the ROM953to the memory unit954and executing the read program. Also, the execution of a print job is realized by the CPU901in the image forming apparatus10reading a program stored in the ROM902to the memory unit903and executing the read program. The following description is simplified by focusing on the portions that are different from the first embodiment.

In step S1701, the CPU901starts the execution of the print job. Then, in accordance with an instruction from the CPU901, the CPU952controls the finisher500to discharge conveyed sheets onto the stack tray701and apply an alignment process to the discharged sheets using the alignment plates711aand711b. Note that step S1701to step S1705are similar to step S1601to step S1605according to the first embodiment. In step S1704, the CPU952controls the finisher500to interrupt the alignment process and proceeds to the process of step S1706.

In step S1706, the CPU952performs control to place the stack tray701, on which the amount of stacked sheets has decreased as a result of removing a part of the sheets, in the sheet surface detection state again. The CPU952adjusts the position (height) of the stack tray701by controlling the tray elevator motor M16to place the stack tray701in the sheet surface detection state. Furthermore, in step S1707, the CPU952identifies the position of the stack tray701based on the state of the tray elevator motor M16. It should be noted here that, while in the sheet surface detection state, the position of the stack tray701changes in accordance with the amount of stacked sheets. Therefore, the CPU952stores, in the memory unit954, information indicating the position of the stack tray701as the amount of stacked sheets upon interrupting the alignment process.

Next, in step S1708, the CPU952determines whether or not the amount of sheets stacked on the stack tray701has reached 0, similarly to step S1606. If the CPU952determines that the amount of stacked sheets has reached 0, it controls the finisher500to resume the alignment process in step S1709, similarly to step S1607. On the other hand, if the CPU952determines that the amount of stacked sheets has not reached 0, it proceeds to the process of step S1710.

In step S1710, the CPU952determines whether or not the amount of sheets stacked on the stack tray701has increased by a predetermined amount from the amount of stacked sheets upon interrupting the alignment process for sheets (that is to say, upon removal of a part of the stacked sheets). Note that the predetermined amount denotes an amount of stacked sheets equivalent to the size of the alignment members711aand711bin the vertical direction.

If the alignment members711aand711bare operated after removing a part of the stacked sheets, there is a possibility that the alignment members711aand711bmay come into contact with sheets remaining on the stack tray701. On the other hand, if the stack tray701is in the sheet surface detection state, there is a possibility that the alignment process can be resumed after a predetermined amount of sheets are newly stacked on the sheets remaining on the stack tray701through the execution of the print job. More specifically, the stack tray701in the sheet surface detection state is lowered by the tray elevator motor M16in accordance with stacking of sheets. In this way, when the stack tray701is lowered to a position where the alignment members711aand711bdo not come into contact with the sheets that have remained on the stack tray701after removing a part of the sheets, the above-mentioned reduction in the sheet quality does not occur even if the alignment process is resumed.

Therefore, when the stack tray701is lowered from a position where a part of the sheets remaining on the stack tray701was removed by a distance corresponding to the size of the alignment members711aand711bin the vertical direction, the alignment process can be resumed without reducing the sheet quality. In the present embodiment, if the CPU952determines in step S1710that the amount of stacked sheets has increased by the predetermined amount, it controls the finisher500to resume the alignment process that has been interrupted, and returns to the process of step S1702. On the other hand, if the CPU952determines in step S1710that the amount of stacked sheets has not increased by the predetermined amount, it proceeds to the process of step S1711and determines whether or not the execution of the print job has finished. Unless the execution of the print job has finished, the CPU952returns to the process of step S1708and repeats the determination processes of step S1708and step S1710.

As described above, according to the present embodiment, even when the removal of a part of sheets stacked on the stack trays700and701has led to misalignment of the stacked sheets, it is possible to prevent a reduction in the sheet quality caused by the alignment process for sheets. Furthermore, even if all of the stacked sheets are not removed during the inhibition of the alignment process, it is possible to automatically cancel the inhibition of the alignment process and resume the alignment process, without reducing the sheet quality due to the alignment process.

Other Embodiments

The above embodiments have described the example in which the sheet sensor721detects the removal of sheets from a stack tray. The present invention, however, is not limited in this way; alternatively, the removal of sheets on a stack tray may be detected by providing the stack tray with a sensor that measures the weight of sheets stacked on the stack tray. For example, the CPU952may determine that a part of sheets on the stack tray has been removed if the weight of the sheets on the stack tray has decreased from 20 g to 10 g. On the other hand, the CPU952may determine that all of the sheets on the stack tray have been removed if the weight of the sheets on the stack tray has decreased from 20 g to 0 g.

The control performed by the CPU901and the CPU952in the above-described embodiments may instead be performed by a single CPU. In this case, that CPU may be included either in the image forming apparatus10or in the finisher500.

This application claims the benefit of Japanese Patent Application No. 2012-264736, filed Dec. 3, 2012, which is hereby incorporated by reference herein in its entirety.