Image forming system

Abstract

An image forming system includes an image forming apparatus that that forms an image on a paper sheet and a sheet finishing device that performs finishing on a paper sheet discharged from the image forming apparatus. The sheet finishing device is disposed beneath the image forming apparatus.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2009-202468 filed in Japan on Sep. 2, 2009 and Japanese Patent Application No. 2009-051877 filed in Japan on Mar. 5, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet finishing device that is disposed integrally or separately with respect to an image forming apparatus such as a copying machine, a printer, or a printing machine and that performs predetermined finishing processing on a paper sheet having an image formed thereon, and relates to an image forming system that includes the sheet finishing device and the image forming apparatus.

2. Description of the Related Art

Sheet finishing devices are known in art that are disposed integrally or separately with respect to an image forming apparatus such as a copying machine, a printer, or a printing machine. The sheet finishing device performs predetermined finishing processing such as stacking, aligning, stapling, saddle stitching, and folding with respect to a paper sheet (recording medium) having an image formed thereon in the image forming apparatus (see Japanese Patent No. 3940008, Japanese Patent Application Laid-open No. 2007-161468, and Japanese Patent No. 3973973).

An image forming system is built by assembling a sheet finishing device with an image forming apparatus (main body).

Typically, it is common practice to dispose a sheet finishing device laterally with respect to the main body of the image forming apparatus. Such a configuration leads to an increase in the total occupancy area of the image forming system. In particular, the occupancy area of the image forming system increases when a sheet finishing device having a saddle stitching mode and a variety of folding modes is installed.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve the problems in the conventional technology.

According to an aspect of the present invention there is provided an image forming system including an image forming apparatus that forms an image on a paper sheet; and a sheet finishing device that performs finishing of a paper sheet discharged from the image forming apparatus. The sheet finishing device includes an aligning unit that stacks and aligns a plurality of paper sheets on an alignment tray thereby forming a sheet stack, and a stapling processing unit that performs stapling with respect to the sheet stack. The sheet finishing device is disposed beneath the image forming apparatus.

The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram for explaining an overall configuration of an image forming system according to a first embodiment of the present invention;

FIG. 2 is an explanatory diagram for explaining an overall configuration of an image forming system according to a second embodiment of the present invention;

FIG. 3 is an explanatory diagram for explaining an overall configuration of an image forming system according to a third embodiment of the present invention; and

FIG. 4 is an explanatory diagram for explaining an overall configuration of an image forming system according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. The present invention is not limited to these exemplary embodiments.

FIG. 1 is a front longitudinal sectional view of an overall configuration of an image forming system including a sheet finishing device according to a first embodiment of the present invention.

The image forming system includes a sheet finishing device 1 and an image forming apparatus 100. The image forming apparatus 100 can be a copying machine, a printer, a printing machine etc.

In the image forming apparatus 100, tasks such as setting paper sheets inside the apparatus (setting paper sheets by pulling out a sheet feed tray) or replacing/refilling consumable components is performed by opening and closing a door 101 disposed on the front surface (right side in FIG. 1). The image forming apparatus 100 includes a sheet feed tray 105, an image forming unit 106, an optical writing unit 107, and a sheet discharging path 108.

The sheet finishing device 1 is disposed beneath the image forming apparatus 100 and includes a feed inlet 2 and an entry roller pair 3 though which enters a paper sheet P that is discharged from a discharging outlet 103 at the lower back portion of the image forming apparatus 100; an aligning unit 10 that is disposed on the downstream side of a feed path 4 and that sequentially discharges and stacks paper sheets as a sheet stack on an alignment tray 11; a stapling processing unit 20 that performs edge stapling or saddle stitching on the sheet stack and discharges the stapled sheet stack in the anterior direction of the apparatus (right direction in FIG. 1); a folding processing unit (center folding processing unit) 30 that performs center folding on the sheet stack that has been stapled (edge-stapled or saddle-stitched) by the stapling processing unit 20; and a control unit (not illustrated) that controls the abovementioned operations. Meanwhile, the center folding processing unit performs center folding at the central part of the sheet stack along the sheet conveying direction.

The aligning unit 10 aligns the paper sheets in the conveying direction and the width direction (perpendicular direction to the conveying direction). The stapling processing unit 20 includes an edge stapling unit (not illustrated) that staples an edge of the sheet stack and a saddle stitching unit (not illustrated) that staples the central part of the sheet stack. Moreover, at the topside of the stapling processing unit 20 is disposed a driver unit 21 that includes a stapler pin container (not illustrated) and a stapler pin pushing unit (not illustrated); while at the lower side of the stapling processing unit 20 is disposed a clincher unit 22 used in folding the ends of stapler pins.

An edge-stapled sheet stack that has been edge-stapled by the stapling processing unit 20 is placed on an edge-stapled-stack tray (first discharging tray) 25, while a center-folded sheet stack that is folded in center after being saddle-stitched by the stapling processing unit 20 is placed on a center-folded-stack tray (second discharging tray) 26. The trays 25 and 26 have independent configurations. More particularly, the edge-stapled-stack tray 25 is disposed on the downstream side (right side) of the stapling processing unit 20 and the center-folded-stack tray 26 is disposed on the upper side of the edge-stapled-stack tray 25.

The folding processing unit 30 is a center folding processing unit that is disposed on the upstream side of the stapling processing unit 20 and that performs center folding of a stapled sheet stack. When center folding is to be performed, a saddle-stitched sheet stack is reversely-conveyed from the stapling processing unit 20 to the center folding processing unit.

The sheet finishing device 1 is disposed beneath the image forming apparatus 100 and a recording medium (paper sheet) discharged from the lower back portion of the image forming apparatus 100 is guided into the sheet finishing device 1. The entry roller pair 3 then conveys the paper sheet on the alignment tray 11. The paper sheet gets aligned on the alignment tray 11 in the direction (width direction) perpendicular to the sheet conveying direction by a jogger fence 12 disposed on the near side as well as the rear side. The alignment in the sheet conveying direction is performed by a return roller 13 with reference to a rear end fence 14.

Once the sheet stack is aligned in the sheet conveying direction and the width direction on the alignment tray 11, a movable sheet-stack conveying roller 40 disposed on the upper side moves toward a fixed sheet-stack conveying roller 41 disposed on the lower side so that the sheet stack is nipped therebetween and conveyed to the stapling processing unit 20 disposed on the downstream side. The movable sheet-stack conveying roller 40 and the fixed sheet-stack conveying roller 41 are driving rollers that are driven by a driving force of a motor (not illustrated) and that enhance the conveyance quality (sheet feed precision/positional accuracy of sheet stack). The movable sheet-stack conveying roller 40 can move up and down with respect to the fixed sheet-stack conveying roller 41 and is configured to form a nip with the fixed sheet-stack conveying roller 41. Thus, when a paper sheet passes through the nip position between the rollers 40 and 41, a conveying force is exerted on the paper sheet.

In the case of edge stapling performed by the stapling processing unit 20, the sheet stack is conveyed to the downstream side after the stapling is performed at a predetermined position. Then, the sheet stack is conveyed and stacked on the edge-stapled-stack tray 25 by a pair of edge stapling discharging rollers 45.

In the case of saddle stitching performed by the stapling processing unit 20; after the sheet stack is aligned, the movable sheet-stack conveying roller 40 moves toward the fixed sheet-stack conveying roller 41 so that the sheet stack is nipped therebetween and conveyed to the stapling processing unit 20 on the downstream side. Then, the stapling processing unit 20 performs stapling at a saddle stitching position. Upon completion of saddle stitching, the sheet stack is reversely-conveyed by the sheet-stack conveying rollers 40 and 41 to a folding position on the upstream side. At the folding position in the folding processing unit 30, a folding plate 31 and a pair of folding rollers 32 perform center folding of the sheet stack. Then, a pair of center-folded-sheet discharging rollers 33 discharges and stacks the center-folded sheet stack on the center-folded-stack tray 26. More particularly, the folding plate 31 is configured to move up and down at the folding position and moves toward a space between the pair of folding rollers 32, which are juxtaposed over the top surface of the sheet stack, so that the intermediary position of the sheet stack gets folded.

In this way, according to the first embodiment, it is possible to arrange the sheet finishing device 1 beneath the image forming apparatus 100 thereby reducing the installation area. As a result, the image forming system can be installed in a smaller place.

Moreover, since the edge-stapled-stack tray 25 and the center-folded-stack tray 26 have independent configurations and since the center-folded-stack tray 26 is disposed above the edge-stapled-stack tray 25, sheet stacks having different stapled conditions or folded conditions can be prevented from getting mixed and the occupancy area of the apparatus can be prevented from increasing.

Furthermore, since the folding processing unit 30 (folding plate 31, pair of folding rollers 32, etc.) is disposed on the upstream side of the stapling processing unit 20, the folding processing is performed rearward than the intermediary position in the longitudinal direction of the sheet finishing device 1. For that reason, it becomes possible to increase the space anterior to the folding processing unit 30 and use that space to dispose the trays 25 and 26, on which the sheet stacks are placed after being subjected to saddle stitching and center folding, respectively.

Moreover, the stapler pin container of the stapling processing unit 20 is disposed below the center-folded-stack tray 26 and the center-folded-stack tray 26 is configured to be at least partially openable and closable as illustrated by a dashed line in FIG. 1. Thus, the stapler pin container becomes replaceable from the front surface of the sheet finishing device 1. Herein, although the center-folded-stack tray 26 is configured to be partially openable and closable, it is also possible to configure the center-folded-stack tray 26 to be entirely openable and closable.

Meanwhile, if a stapling position in the stapling processing unit 20 is spaced-apart from a door 6 disposed at the front surface of the sheet finishing device 1 by a distance L1 that is almost half of the maximum sheet length that can be subjected to finishing processing, then the door 6 at the front surface need not be opened even in the case of performing saddle stitching of the maximum sheet size that can be subjected to finishing processing.

Similarly, if a nip position of the center-folded-sheet discharging rollers 33 is spaced-apart from the door 6 of the sheet finishing device 1 by a distance L2 that is equal to or more than half of the maximum sheet length, then a saddle-stitched sheet stack or a folded sheet stack can be stacked on the center-folded-stack tray 26 while keeping the door 6 closed.

Moreover, it is possible to perform center folding if the rear end fence 14 in the aligning unit 10 is spaced-apart from the folding position by a distance L3 that is at least half of the maximum sheet length. Besides, by keeping the distance L3, the size (longitudinal dimensions) of the sheet finishing device 1 can also be reduced.

FIG. 2 is an explanatory diagram for explaining an overall configuration of an image forming system according to a second embodiment of the present invention. In the image forming system shown in FIG. 2, a folding unit is disposed inside the sheet finishing device 1.

In the sheet finishing device 1 illustrated in FIG. 2, a folding unit 50 is disposed on the upstream side of the aligning unit 10 (in mid-course of the feed path 4). If a paper sheet discharged from the image forming apparatus 100 is not to be folded, then that paper sheet is conveyed to the aligning unit 10; and if a paper sheet discharged from the image forming apparatus 100 is to be folded, then that paper sheet is guided into the folding unit 50.

In the case when the folding unit 50 performs Z-folding, it conveys the Z-folded paper sheet to the aligning unit 10 that then aligns the paper sheet. Subsequently, the stapling processing unit 20 performs edge stapling and discharges the paper sheet to the edge-stapled-stack tray 25.

In the case when the folding unit 50 performs folding other than Z-folding, it conveys the folded paper sheet to the aligning unit 10 that then aligns the paper sheet. Subsequently, the stapling processing unit 20 performs stapling and discharges the paper sheet to the center-folded-stack tray 26.

In this particular configuration, the paper sheet P of a large size (e.g., A3-size) discharged from the lower back portion of the image forming apparatus 100 to the sheet finishing device 1 is guided by the entry roller pair 3 into the folding unit 50. However, if folding is not required, then the paper sheet P is conveyed as it is downward to the aligning unit 10.

To perform edge stapling of A3-size paper sheets after aligning them in A4-size, the A3-size paper sheets need to be Z-folded into A4 size. For that, the A3-size paper sheets entering via the entry roller pair 3 are conveyed toward the folding unit 50 by a switching operation of a switching claw 51. The switching claw 51 is held by a spring (not illustrated) in an orientation that guides a paper sheet toward the aligning unit 10. When a solenoid (not illustrated) is switched ON, the switching claw 51 rotates and switches to an orientation that guides a paper sheet in the direction toward the folding unit 50. When the solenoid is kept OFF, the switching claw 51 guides paper sheets in the downward direction without change.

The folding unit 50 includes a first conveying unit 52, a second conveying unit 53, a third conveying unit 54, a fourth conveying unit 55, an upper end stopper 53a disposed in the second conveying unit 53, a rear end stopper 54a disposed in the third conveying unit 54, a first folding roller 56, a second folding roller 57, a third folding roller 58, a pressure roller 59, and a branching claw 60.

First, depending on the fold size and the fold type, the upper end stopper 53a and the rear end stopper 54a are moved by a stepping motor (not illustrated) to predetermined positions inside the second conveying unit 53 and the third conveying unit 54, respectively. The pressure roller 59 and the first folding roller 56 convey a paper sheet into the second conveying unit 53 including the upper end stopper 53a. By continuing the conveyance even after an end of the paper sheet abuts against the upper end stopper 53a, a slack is formed in the paper sheet. The slack eventually gets nipped between the first folding roller 56 and the second folding roller 57 so that the paper sheet gets folded for the first time. The folded part is then conveyed toward the third conveying unit 54 including the rear end stopper 54a. By continuing the conveyance even after the folded part abuts against the rear end stopper 54a, a slack that is identical to the previous slack is formed in the rear portion of the paper sheet. The slack eventually gets nipped between the second folding roller 57 and the third folding roller 58 so that the paper sheet gets folded for the second time. Subsequently, the paper sheet subjected to Z-folding in the abovementioned manner is guided by the branching claw 60 to the fourth conveying unit 55 and then to the aligning unit 10. Upon being subjected to alignment and edge stapling, the paper sheet gets discharged to the edge-stapled-stack tray 25.

In the case of performing outer-three-folding, inner-three-folding, double folding, or quarto folding in the folding unit 50; a paper sheet conveyed from the entry roller pair to the folding unit is then conveyed to a folding section by a switching claw. Then, depending on the sheet size and the fold type, the upper end stopper 53a and the rear end stopper 54a are moved to the respective predetermined positions and the folding processing is performed in an identical manner to that of Z-folding. The folded paper sheet is then conveyed by the branching claw toward the center-folded-stack tray 26. The center-folded-sheet discharging rollers 33 then discharge the folded paper sheet on the center-folded-stack tray 26.

In this way, the folding unit 50 is disposed in the upper part of the space inside the sheet finishing device 1, the stapling processing unit 20 is disposed in the lower part of the space inside the sheet finishing device 1, and the folding processing unit 30 performs center folding with upward folding direction. Because of such a configuration, the center-folded-stack tray 26, on which center-folded sheet stacks are placed, can also be used as the stack tray for stacking paper sheets that are folded singularly (outer-three-folding, inner-three-folding, double folding, quarto folding, etc.). That enables achieving reduction in the size of the sheet finishing device 1.

FIG. 3 is an explanatory diagram for explaining an overall configuration of an image forming system according to a third embodiment of the present invention. The description with reference to FIG. 3 is given to indicate that it is possible to alternately manufacture the configuration illustrated in FIG. 2 (including the folding processing unit 30 and the stapling processing unit 20 that is capable of edge stapling and saddle stitching) and the configuration illustrated in FIG. 3 (exclusively used as an edge stapling unit).

More particularly, in the configuration illustrated in FIG. 2, the folding processing unit 30 and the stapling processing unit 20, which is capable of edge stapling and saddle stitching, are disposed at the bottom surface of the device along the longitudinal direction. However, from the perspective of a user needing to perform only edge stapling, the edge-stapled-stack tray 25 is disposed in a narrow space. Alternatively, the folding processing unit 30 and the stapling processing unit 20 are replaced with the large-capacity edge-stapled-stack tray 25 and an edge stapling unit 23 is detachably attached to the rear end fence 14 of the aligning unit 10, while keeping the housing and the other constituent elements of the sheet finishing device 1 intact. Thus, the configurations illustrated in FIGS. 2 and 3 become mutually replaceable so that sheet finishing devices performing only edge stapling and sheet finishing devices performing edge stapling as well as saddle stitching can be manufactured without difficulty. That makes it possible to meet the user demands in a speedy manner and at a low cost. Meanwhile, if the folding unit 50 is disposed in the configuration illustrated in FIG. 3, then it also becomes possible to perform center folding.

In the sheet finishing device 1 illustrated in FIG. 2 that is capable of performing edge stapling as well as saddle stitching, the stapling position is spaced-apart from the door 6 disposed at the front surface of the sheet finishing device 1 by a distance smaller than the maximum sheet size. Thus, to enable stacking of an edge-stapled sheet stack on the edge-stapled-stack tray 25, the door 6 at the front surface needs to be kept open. Instead, a hole can be formed so that an edge-stapled sheet stack does not make contact with the door 6 or, as illustrated in FIG. 4, a small door 6a can be disposed that opens when pushed by an edge-stapled sheet stack. Such a configuration enables stacking of sheet stacks while keeping the door 6 at the front surface closed.

In this way, in the present embodiment, since a sheet finishing device capable of performing center folding is disposed within the installation area of an image forming apparatus, it is possible to provide the sheet finishing device and an image forming system that do not take any extra occupancy area.

Moreover, in the sheet finishing device disposed beneath the image forming apparatus, a folding processing unit is disposed on the upstream side and a stapling processing unit is disposed on the downstream side so that a space can be secured for housing a stack tray for saddle-stitched sheet stacks.

Furthermore, by disposing a driver unit that includes a stapler pin container and a stapler pin pushing unit below a center-folded-stack tray, the stapler pin container can be replaced by opening the center-folded-stack tray from the front surface of the sheet finishing device.

Moreover, since a stapling position in a stapling unit is spaced-apart from a door at the front surface of the sheet finishing device by a distance that is almost half of the maximum sheet length, it becomes possible to perform saddle stitching without having to open the door disposed at the front surface of the sheet finishing device.

Furthermore, since the nip position of a discharging roller pair used in discharging a saddle-stitched sheet stack is spaced apart from the door of the sheet finishing device by a distance equal to or more than half of the maximum sheet length, it becomes possible to perform saddle stitching without having to open the door disposed at the front surface of the sheet finishing device.

Moreover, by discharging folded sheet stacks and saddle-stitched sheet stacks to a common tray, stacking of paper sheets can be performed while reducing the size of the sheet finishing device.

Furthermore, by replacing the stapling processing unit capable of performing edge stapling as well as saddle stitching and the folding processing unit with a large-capacity edge-stapled-stack tray and by detachably attaching an edge stapling unit to an aligning unit, the two different configurations become mutually replaceable so that sheet finishing devices performing only edge stapling and sheet finishing devices performing edge stapling as well as saddle stitching can be manufactured without difficulty. That makes it possible to meet the user demands in a speedy manner and at a low cost.

Moreover, if a folding unit and the stapling processing unit are integrated into a detachable configuration and if a stapling processing unit is made detachably attachable at an end of the aligning unit; then, in the case of a dedicated edge stapling device, the folding unit and the stapling processing unit is removed and a stapler for edge stapling is newly disposed so that the cost can be reduced and a sheet stack of the maximum size can be stacked inside the device at the time of stapling.

Furthermore, the conveying rollers that convey a sheet stack to the stapling position are disposed across the conveying path and operate in pair. Thus, by driving both the conveying rollers, the horizontal conveyance of the sheet stack can be performed with less misalignment in the paper sheets.

Moreover, since the folding processing unit disposed on the upstream side of the stapling processing unit folds a sheet stack in the substantially central part, it is possible to configure a sheet finishing device that performs center folding in the center of saddle stitching.

Furthermore, since the rear end fence in the aligning unit is spaced-apart from the folding position by a distance that is half of the maximum sheet length, it becomes possible to minimize the depth of the sheet finishing device.

Moreover, at a saddle-stitched-sheet discharging location on the door at the front surface of the sheet finishing device, a hole can be formed to avoid hindrance in sheet stack conveyance or a small door can be disposed that opens when pushed by the sheet stack from inside. Because of that, even if edge stapling of a sheet stack of the maximum length is performed, the sheet stack can be discharged without having to open the door at the front surface.

Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.

Claims

1. An image forming system comprising:

an image forming apparatus that forms an image on a paper sheet; and

a sheet finishing device that performs finishing of a paper sheet discharged from the image forming apparatus, wherein

the sheet finishing device includes an aligning unit that stacks and aligns a plurality of paper sheets on an alignment tray thereby forming a sheet stack, and a stapling processing unit that performs stapling with respect to the sheet stack, and

the sheet finishing device is disposed beneath the image forming apparatus.

2. The image forming system according to claim 1, wherein

the stapling processing unit includes an edge stapling unit that subjects the sheet stack to edge stapling by stapling an edge of the sheet stack, and a saddle stitching unit that subjects the sheet stack to saddle stitching by stapling a central part of the sheet stack, and

the sheet finishing device includes a center folding processing unit that subjects the sheet stack to center folding by folding, in center along a sheet conveying direction, the sheet stack subjected to the saddle stitching at the saddle stitching unit, a first discharging tray that houses the sheet stack subjected to the edge stapling at the edge stapling unit, and a second discharging tray that houses the sheet stack subjected to the center folding at the center folding processing unit.

3. The image forming system according to claim 2, wherein

the center folding processing unit includes a configuration to fold a central part of a sheet stack held horizontally in upward direction,

the stapling processing unit includes a driver unit including a detachable stapler pin container containing a stapler pin and a stapler pin pushing unit, and a clincher unit that folds a tip of the stapler pin, and

the driver unit is disposed beneath the second discharging tray and is configured in such a way that, by opening and closing the second discharging tray entirely or partially, the staple pin container is replaceable.

4. The image forming system according to claim 1, wherein a stapling position in the stapling processing unit is spaced-apart from a door disposed at a front surface of the sheet finishing device by a distance that is about half of a maximum sheet length.

5. The image forming system according to claim 2, wherein a nip portion of a pair of center-folded-sheet discharging rollers that guide the sheet stack subjected to saddle stitching to the second discharging tray is spaced-apart from a door disposed at a front surface of the sheet finishing device by a distance substantially equal to or more than half of a maximum sheet length.

6. The image forming system according to claim 2, wherein

a folding unit is disposed on an upstream side of the aligning unit in such a way that, when a paper sheet discharged from the image forming apparatus is not to be folded, the paper sheet is conveyed to the aligning unit and, when the paper sheet is to be folded, the paper sheet is guided into the folding unit,

when the folding unit performs Z-folding, a paper sheet subjected to Z-folding is conveyed to the aligning unit that aligns the paper sheet after which the stapling processing unit performs edge stapling and discharges the paper sheet to the first discharging tray, and

when the folding unit performs folding other than Z-folding, a paper sheet subjected to folding is conveyed to the aligning unit that aligns the paper sheet after which the stapling processing unit performs stapling and discharges the paper sheet to the second discharging tray.

7. The image forming system according to claim 2, wherein

the center folding processing unit and the stapling processing unit are replaceable with a large-capacity edge-stapled-stack tray, and

an edge stapling unit is detachably attached to the aligning unit.

8. The image forming system according to claim 1, further comprising a pair of conveying rollers that are disposed across a conveying path for conveying the sheet stack aligned by the aligning unit to the stapling processing unit, wherein

each of the pair of conveying rollers is a driving roller.

9. The image forming system according to claim 2, wherein

the aligning unit includes a sheet rear end fence that determines a position of a rear end of a paper sheet, and

the sheet rear end fence is spaced-apart from a folding position in the center folding processing unit by a distance that is about half of a maximum sheet length.

10. The image forming system according to claim 1, further comprising an edge-stapled-sheet discharging unit including either one of a hole that ensures that conveyance of a sheet stack is not hindered by a door disposed at a front surface of the sheet finishing device and a door that is openable when pushed by a sheet stack from inside.