Sheet processing device, image forming system, and method of additionally folding sheet bundle

The present invention is concerning a sheet processing device comprising: a pressing unit that includes a first pressing roller arranged on one side of a thickness direction of a folded sheet bundle, and a second pressing roller and a third pressing roller arranged on the other side across a fold line part of the folded sheet bundle, and a moving unit that moves the pressing unit in a state in which each of a first line and a second line is not parallel to the thickness direction of the folded sheet bundle, the first line connecting the rotational center of the first pressing roller and the rotational center of the second pressing roller, and the second line connecting the rotational center of the first pressing roller and the rotational center of the third pressing roller.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2013-167889 filed in Japan on Aug. 12, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet processing device, an image forming system, and a method of additionally folding a sheet bundle, and specifically relates to a sheet processing device having a function for folding a sheet recording medium such as paper, recording paper, and transfer paper (hereinafter, simply referred to as a “sheet” in this specification), an image forming system including the sheet processing device, and a method of additionally folding a sheet bundle performed by the sheet processing device.

2. Description of the Related Art

Conventionally, in some postprocessing devices used in combination with an image forming apparatus such as a copying machine, center parts of one or more sheets are stitched and the center part of the sheet bundle is folded with a pair of folding rollers arranged in parallel in a sheet folding direction to bind a saddle-stitched booklet. Already known is a technique for additional-folding with a roller moving along a spine of the booklet to reinforce a fold of the saddle-stitched booklet.

In such an additional-folding technique, a roller waiting outside the booklet (sheet bundle) is moved on the spine (fold line part) of the booklet to additionally fold the spine of the booklet with an additional-folding roller.

As such kind of additional-folding technique, known is the invention disclosed in Japanese Patent Application Laid-open No. 2009-126685 or Japanese Patent Application Laid-open No. 2006-321622, for example.

Japanese Patent Application Laid-open No. 2009-126685 discloses a sheet folding device including a folding unit that folds a carried sheet-like recording medium, and an additional-folding unit that moves and pressurizes on a fold line part of the sheet recording medium in a direction orthogonal to a sheet carrying direction to perform additional-folding after the folding processing by the folding unit. In the sheet folding device, the additional-folding unit is arranged to be inclined in a direction in which a force is generated in a moving direction when the fold line part is pressurized with respect to a normal on a medium surface of the sheet recording medium.

Japanese Patent Application Laid-open No. 2006-321622 discloses a sheet bundle spine processing device including a fold processing unit that moves while pinching front and rear surfaces of a spine fold line part of a folded sheet bundle to arrange the shape of the fold line part, a spine processing unit that moves while pressing a spine of the spine fold line part of the sheet bundle to flatten the spine, and a selection unit that selects and activates at least one of the fold processing unit and the spine processing unit.

In the technique disclosed in Japanese Patent Application Laid-open No. 2009-126685, although a direction of an energizing force is inclined from a moving direction of an additional-folding mechanism in order to reduce a load, the additional-folding mechanism is configured by a fixed receiving member opposed to a pressure roller, so that a pressing force to a sheet bundle is generated in the thickness direction of the sheet bundle. Due to this, rigidity is required for the device, the size of the device is increased, and the cost is increased accordingly.

In the technique disclosed in Japanese Patent Application Laid-open No. 2006-321622, a fold processing unit for reinforcing a fold line part includes three or more additional-folding rollers. The fold processing unit including a pair of two rollers for reinforcing the fold line part generates a pressurizing force in a direction orthogonal to a moving direction, and the third roller for flattening the spine of the fold line part generates the pressurizing force in a direction orthogonal to the pressurizing force generated by the pair of two rollers in a sheet carrying direction. Due to this, similarly to the technique disclosed in Japanese Patent Application Laid-open No. 2009-126685, rigidity is required for the device, the size of the device is increased, and the cost is increased accordingly.

In view of the conventional arts, there is a need to enable the additional-folding with a small pressurizing force, and reduce the size and cost of the device.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a sheet processing device comprising: a pressing unit that presses a fold line part of a folded sheet bundle; and a moving unit that moves a pressing position of the pressing unit in a fold direction of the folded sheet bundle, wherein the pressing unit includes a first pressing roller arranged on one side of a thickness direction of the folded sheet bundle, and a second pressing roller and a third pressing roller arranged on the other side across the fold line part of the folded sheet bundle, and the pressing unit is arranged in a state in which each of a first line and a second line is not parallel to the thickness direction of the folded sheet bundle, the first line connecting the rotational center of the first pressing roller and the rotational center of the second pressing roller, and the second line connecting the rotational center of the first pressing roller and the rotational center of the third pressing roller.

The present invention also provides an image forming system including a sheet processing device, wherein the sheet processing device comprises; a pressing unit that presses a fold line part of a folded sheet bundle, a moving unit that moves a pressing position of the pressing unit in a fold direction of the folded sheet bundle, and the pressing unit includes a first pressing roller arranged on one side of a thickness direction of the folded sheet bundle, and a second pressing roller and a third pressing roller arranged on the other side across the fold line part of the folded sheet bundle, and the pressing unit is arranged in a state in which each of a first line and a second line is not parallel to the thickness direction of the folded sheet bundle, the first line connecting the rotational center of the first pressing roller and the rotational center of the second pressing roller, and the second line connecting the rotational center of the first pressing roller and the center of the third pressing roller.

The present invention also provides a method of additionally folding a folded sheet bundle, comprising: arranging a first pressing roller on one side of a thickness direction of the folded sheet bundle, and arranging a second pressing roller and a third pressing roller on the other side of the thickness direction of the folded sheet bundle; holding a fold line part of the folded sheet bundle between the first pressing roller and the second and the third pressing rollers; and moving the first, the second, and the third pressing rollers in a fold direction of the folded sheet bundle to additionally fold the fold line part of the folded sheet bundle in a state in which each of a first line and a second line is not parallel to the thickness direction of the folded sheet bundle, the first line connecting the rotational center of the first pressing roller and the center of the second pressing roller, and the second line connecting the rotational center of the first pressing roller and the center of the third pressing roller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, in that an additional-folding roller moves in a sheet width direction of a saddle-stitched booklet to additionally fold a spine of the booklet, additional-folding processing is characteristically performed while holding a sheet with three additional-folding rollers and causing mountain-shaped deformation of the sheet.

The following describes an embodiment of the present invention with reference to the drawings.

FIG. 1is a diagram illustrating a system configuration of an image processing system including an image forming apparatus and a plurality of sheet processing devices according to the embodiment. In the embodiment, first and second sheet postprocessing devices 1 and 2 are coupled to a rear stage of an image forming apparatus PR in this order.

The first sheet postprocessing device 1 is a sheet postprocessing device having a function of preparing a sheet bundle for receiving sheets one by one from the image forming apparatus PR, overlapping and adjusting the sheets successively, and preparing the sheet bundle at a stack part. The first sheet postprocessing device 1 discharges the sheet bundle from a sheet bundle discharge roller10to the second sheet postprocessing device 2 at the rear stage. The second sheet postprocessing device 2 is a saddle-stitch bookbinding device that receives the carried sheet bundle and performs saddle-stitching and center-folding (herein, the second sheet postprocessing device is also referred to as a saddle-stitch bookbinding device).

The saddle-stitch bookbinding device 2 discharges the bound booklet (sheet bundle) as it is, or discharges it to a sheet processing device at the rear stage. The image forming apparatus PR forms a visible image on a sheet recording medium based on input image data or image data of a read image. Examples of the image forming apparatus PR include a copying machine, a printer, a facsimile, or a digital multifunction peripheral having at least two functions thereof. The image forming apparatus PR may employ a known method such as an electrophotographic method and a droplet injection method. Any image forming method may be employed.

As illustrated inFIG. 1, the saddle-stitch bookbinding device 2 includes an inlet carrying path241, a sheet-through carrying path242, and a center-folding carrying path243. An inlet roller201is arranged on the most upstream part in a sheet carrying direction of the inlet carrying path241, and the aligned sheet bundle is carried in the device from the sheet bundle discharge roller10of the first sheet postprocessing device 1. In the following description, an upstream side in the sheet carrying direction is simply referred to as an upstream side, and a downstream side in the sheet carrying direction is simply referred to as a downstream side.

A bifurcating claw202is arranged on the downstream side of the inlet roller201of the inlet carrying path241. The bifurcating claw202is arranged in the horizontal direction of the figure, and bifurcates the carrying direction of the sheet bundle into the sheet-through carrying path242or the center-folding carrying path243. The sheet-through carrying path242is a carrying path that horizontally extends from the inlet carrying path241and guides the sheet bundle to a processing device (not illustrated) on the rear stage or a paper discharge tray. The sheet bundle is discharged to the rear stage by an upper paper discharge roller203. The center-folding carrying path243is a carrying path that extends vertically downward from the bifurcating claw202and performs saddle-stitching and center-folding processing on the sheet bundle.

The center-folding carrying path243includes a bundle carrying upper guide plate207that guides the sheet bundle above a folding plate215for center-folding, and a bundle carrying lower guide plate208that guides the sheet bundle below the folding plate215. The bundle carrying upper guide plate207includes a bundle carrying upper roller205, a rear-end hitting claw221, and a bundle carrying lower roller206arranged thereon in order from the upper part. The rear-end hitting claw221is erected on a rear-end hitting claw driving belt222driven by a driving motor (not illustrated). The rear-end hitting claw221hits (presses) the rear end of the sheet bundle SB toward a movable fence described later due to a reciprocative rotation operation of a rear-end hitting claw driving belt222to perform an aligning operation of the sheet bundle SB. When the sheet bundle SB is carried in, and when the sheet bundle SB is moved up for center-folding, the rear-end hitting claw221is retracted from the center-folding carrying path243of the bundle carrying upper guide plate207(position represented by a dashed line inFIG. 1).

Reference numeral294denotes a rear-end hitting claw HP sensor for detecting a home position of the rear-end hitting claw221, which detects, as the home position, the position represented by the dashed line inFIG. 1(position represented by a solid line inFIG. 2) after that the rear-end hitting claw221retracted from the center-folding carrying path243. The rear-end hitting claw221is controlled based on the home position.

The bundle carrying lower guide plate208includes a saddle-stitching stapler S1, a saddle-stitching jogger fence225, and a movable fence210arranged thereon in order from the upper part. The bundle carrying lower guide plate208is a guide plate that receives the sheet bundle SB carried through the bundle carrying upper guide plate207. A pair of the saddle-stitching jogger fences225is arranged in the width direction, and in the lower part, the movable fence210on which a front end of the sheet bundle SB abuts (by which the front end of the sheet bundle SB is supported) is arranged in a vertically movable manner.

The saddle-stitching stapler S1is a stapler that stitches the center part of the sheet bundle SB. The movable fence210moves in the vertical direction while supporting the front end of the sheet bundle SB, and positions the center position of the sheet bundle SB at a position opposed to the saddle-stitching stapler S1. At this position, staple processing, that is, the saddle-stitching is performed. The movable fence210is supported by a movable fence driving mechanism210aand movable from a position of a movable fence HP sensor292illustrated in the upper part of the figure to the lowermost position. A movable range of the stroke of the movable fence210on which the front end of the sheet bundle abuts is secured so as to be able to process the maximum size and the minimum size that can be processed by the saddle-stitch bookbinding device 2. For example, a rack and pinion mechanism is used as the movable fence driving mechanism210a.

The folding plate215, a pair of folding rollers230, an additional-folding roller unit260, and a lower paper discharge roller231are arranged between the bundle carrying upper guide plate207and the bundle carrying lower guide plate208, that is, substantially at the center part of the center-folding carrying path243. The additional-folding roller unit260is configured such that the additional-folding rollers are arranged on upper and lower sides of a paper discharge carrying path between the pair of folding rollers230and the lower paper discharge roller231. The folding plate215can reciprocate in the horizontal direction of the figure. A nip of the pair of folding rollers230is positioned in an operating direction of folding-operation, and a paper discharge carrying path244is arranged on the extended line therefrom. The lower paper discharge roller231is arranged on the most downstream side of the paper discharge carrying path244, and discharges a folded sheet bundle to the rear stage.

A sheet bundle detecting sensor291is arranged on the lower end of the bundle carrying upper guide plate207, and detects the front end of the sheet bundle SB that is carried in the center-folding carrying path243and passes through the center-folding position. A fold line part passage sensor293is arranged on the paper discharge carrying path244, detects the front end of the center-folded sheet bundle SB, and recognizes passage of the center-folded sheet bundle SB.

Generally, as illustrated in the operation explanatory diagrams ofFIG. 2toFIG. 6, a saddle-stitching operation and a center-folding operation are performed in the saddle-stitch bookbinding device 2 that is configured as illustrated inFIG. 1. That is, when saddle-stitching and center-folding are selected in an operation panel (not illustrated) of the image forming apparatus PR, the sheet bundle for which saddle-stitching and center-folding are selected is guided toward the center-folding carrying path243due to counterclockwise deviation of the bifurcating claw202. The bifurcating claw202is driven by a solenoid. Alternatively, the bifurcating claw202may be driven by a motor instead of the solenoid.

A sheet bundle SB carried in the center-folding carrying path243is carried downward in the center-folding carrying path243by the inlet roller201and the bundle carrying upper roller205. After passage thereof is checked by the sheet bundle detecting sensor291, the bundle carrying lower roller206carries the sheet bundle SB to a position at which the front end of the sheet bundle SB abuts on the movable fence210as illustrated inFIG. 2. At this time, the movable fence210stands by at different stop positions corresponding to sheet size information from the image forming apparatus PR, that is, information about a size in the carrying direction of each sheet bundle SB herein. In this case, inFIG. 2, the bundle carrying lower roller206holds the sheet bundle SB with the nip, and the rear-end hitting claw221stands by at the home position.

In this state, as illustrated inFIG. 3, holding pressure of the bundle carrying lower roller206is released (in a direction of the arrow a), the front end of the sheet bundle abuts on the movable fence210, and the sheet bundle is stacked in a state in which the rear end thereof is free. Accordingly, the rear-end hitting claw221is driven. Due to this driving, the rear end of the sheet bundle SB is hit by the rear-end hitting claw221and final alignment is performed in the carrying direction (in a direction of the arrow c).

Subsequently, the saddle-stitching jogger fence225performs an aligning operation in the width direction (direction orthogonal to a sheet carrying direction), and the movable fence210and the rear-end hitting claw221perform an aligning operation in the carrying direction. Accordingly, an adjusting operation of the sheet bundle SB in the width direction and the carrying direction is completed. In this case, a pushing amount of each of the rear-end hitting claw221and the saddle-stitching jogger fence225is changed and adjusted to an optimal value corresponding to size information of the sheet, information about the number of sheets of the sheet bundle, and thickness information of the sheet bundle.

Space in the carrying path is reduced when the bundle is thick, so that the sheet bundle cannot be completely adjusted in single adjusting operation in many cases. In such a case, the number of aligning operations is increased. Due to this, a better adjusted state can be achieved. Time required for sequentially overlapping the sheets on the upstream side is increased as the number of sheets increases, so that time until the next sheet bundle SB is received is prolonged. As a result, there is no time loss as a system even when the number of adjusting operations is increased, so that a good adjusted state can be efficiently achieved. Accordingly, the number of adjusting operations can be controlled depending on processing time on the upstream side.

A standby position of the movable fence210is normally set so that a saddle stitching position of the sheet bundle SB is opposed to a stitching position of the saddle-stitching stapler S1. This is because, when the adjusting operation is performed at this position, stitching processing can be directly performed at a stacked position without moving the movable fence210to the saddle stitching position of the sheet bundle SB. At this standby position, a stitcher of the saddle-stitching stapler S1is driven in a direction of the arrow b at the center part of the sheet bundle SB, stitching processing is performed between the stitcher and a clincher, and the sheet bundle SB is saddle-stitched.

The movable fence210is positioned by pulse control from the movable fence HP sensor292, and the rear-end hitting claw221is positioned by pulse control from the rear-end hitting claw HP sensor294. Positioning control of the movable fence210and the rear-end hitting claw221is performed by a central processing unit (CPU) of a control circuit (not illustrated) of the saddle-stitch bookbinding device 2.

The sheet bundle SB saddle-stitched in the state ofFIG. 3is transferred, as illustrated inFIG. 4, to a position where the saddle stitching position (center position in the carrying direction of the sheet bundle SB) is opposed to the folding plate215corresponding to upward movement of the movable fence210in a state in which pressurization by the bundle carrying lower roller206is released. This position is also controlled based on a detection position of the movable fence HP sensor292.

When the sheet bundle SB reaches the position ofFIG. 4, as illustrated inFIG. 5, the folding plate215moves in a nip direction of the pair of folding rollers230, abuts on the sheet bundle SB in the vicinity of a stapled portion thereof from a substantially orthogonal direction, and pushes out the sheet bundle SB to the nip side. The sheet bundle SB is pushed by the folding plate215, guided to the nip of the pair of folding rollers230, and pushed in the nip of the pair of folding rollers230that has been rotated in advance. The pair of folding rollers230pressurizes and carries the sheet bundle SB pushed in the nip. With this pressurizing and carrying operation, the center of the sheet bundle SB is folded and a simply bound sheet bundle SB is formed.FIG. 5illustrates a state in which the front end of a fold line part SB1 of the center-folded sheet bundle SB is held and pressurized by the nip of the pair of folding rollers230.

The sheet bundle SB folded in two at the center part in the state ofFIG. 5is carried by the pair of folding rollers230as the center-folded sheet bundle SB as illustrated inFIG. 6, held by the lower paper discharge roller231, and discharged to the rear stage. In this case, when the rear end of the center-folded sheet bundle SB is detected by the fold line part passage sensor293, the folding plate215and the movable fence210are returned to the home position and the bundle carrying lower roller206is returned to the pressurizing state to prepare for the next sheet bundle SB to be carried in. When the size and the number of sheets of the next job are the same, the movable fence210may move to the position ofFIG. 2again to stand by. These control processes are also performed by the CPU of the control circuit.

FIG. 7is a front view of a principal part illustrating a basic configuration of the additional-folding roller unit and the pair of folding rollers, andFIG. 8is a side view of the principal part viewed from the left side ofFIG. 7. The additional-folding roller unit260is arranged in the paper discharge carrying path244between the pair of folding rollers230and the lower paper discharge roller231, and includes a unit moving mechanism263, a guide member264, and a pressing mechanism265. The unit moving mechanism263reciprocates the additional-folding roller unit260in the depth direction of the figure (direction orthogonal to the sheet carrying direction) along the guide member264with a driving source and a driving mechanism (not illustrated). The pressing mechanism265is a mechanism that applies a pressure in the vertical direction to press the sheet bundle SB, and includes an upper additional-folding roller unit261and a lower additional-folding roller unit262.

The upper additional-folding roller unit261is supported by the unit moving mechanism263with a support member265bto be movable in the vertical direction, and the lower additional-folding roller unit262is mounted to the lower end of the support member265bof the pressing mechanism265so as not to be movable. The upper additional-folding roller261aof the upper additional-folding roller unit261can be in press-contact with the first and the second lower additional-folding rollers262aand262b, and the center-folded sheet bundle SB is held and pressurized in the nip configured by the three rollers. The pressurizing force is given by a pressurizing spring (an energizing unit)265cthat pressurizes the upper additional-folding roller unit261with an elastic force. The upper additional-folding roller unit261moves in the width direction (direction of the arrow D1inFIG. 8) of the center-folded sheet bundle SB as described later in the pressurized state, and performs additional-folding on the fold line part SB1.

FIG. 9is a diagram illustrating details about the guide member264. The guide member264includes a guiding path270that guides the additional-folding roller unit260in the width direction of the center-folded sheet bundle SB. Six paths are set in the guiding path270as follows:

1) a first guiding path271that guides the pressing mechanism265in a press-releasing state in forward movement;

2) a second guiding path272that guides the pressing mechanism265in a pressing state in forward movement;

3) a third guiding path273that switches the pressing mechanism265from the press-releasing state to the pressing state in forward movement;

4) a fourth guiding path274that guides the pressing mechanism265in the press-releasing state in backward movement;

5) a fifth guiding path275that guides the pressing mechanism265in the pressing state in backward movement; and

6) a sixth guiding path276that switches the pressing mechanism265from the press-releasing state to the pressing state in backward movement.

FIG. 10andFIG. 11are enlarged views of the principal part ofFIG. 9. As illustrated inFIG. 10andFIG. 11, a first path switching claw277is arranged at an intersection point between the third guiding path273and the second guiding path272, and a second path switching claw278is arranged at an intersection point between the sixth guiding path276and the fifth guiding path275. As illustrated inFIG. 11, the first path switching claw277can switch the third guiding path273to the second guiding path272, and the second path switching claw278can switch the sixth guiding path276to the fifth guiding path275. However, in the former case, the second guiding path272cannot be switched to the third guiding path273. In the latter case, the fifth guiding path275cannot be switched to the sixth guiding path276. That is, switching cannot be performed in a reverse direction. An arrow inFIG. 11represents a movement track of a guide pin265a.

The pressing mechanism265moves along the guiding path270because the guide pin265aof the pressing mechanism265is movably engaged in the guiding path270in a loosely fitted state. That is, the guiding path270functions as a cam groove, and the guide pin265afunctions as a cam follower to be displaced while moving along the cam groove.

FIG. 12toFIG. 22are operation explanatory diagrams of the additional-folding operation by the additional-folding roller unit260according to the embodiment.

FIG. 12illustrates a state in which the sheet bundle SB center-folded folded by the pair of folding rollers230is carried and stopped at an additional-folding position set in advance, and the additional-folding roller unit260is at a standby position. This state is an initial position of the additional-folding operation.

The additional-folding roller unit260starts to move forward in the right direction of the figure (direction of the arrow D2) from the initial position (FIG. 12) (FIG. 13). In this case, the pressing mechanism265in the additional-folding roller unit260moves along the guiding path270of the guide member264due to action of the guide pin265a. The pressing mechanism265moves along the first guiding path271immediately after the operation start. At this time, the first and the second lower additional-folding rollers262aand262bare in the press-releasing state with respect to the upper additional-folding roller261a. The press-releasing state means a state in which the upper additional-folding roller261a, the first and the second lower additional-folding rollers262aand262b, and the center-folded sheet bundle SB are in contact with each other but little pressure is applied thereto, or a state in which the upper additional-folding roller261a, the first and the second lower additional-folding rollers262aand262b, and the center-folded sheet bundle SB are separated from each other.

When coming to the third guiding path273near the center of the center-folded sheet bundle SB (FIG. 14), the pressing mechanism265starts to descend along the third guiding path273, pushes aside the first path switching claw277, and enters the second guiding path272(FIG. 15). At this time, the pressing mechanism265is in a state of pressing the upper additional-folding roller unit261, and the upper additional-folding roller unit261abuts on the center-folded sheet bundle SB to be in a pressing state.

The additional-folding roller unit260further moves in the direction of the arrow D2while keeping the pressing state (FIG. 16). Because the second path switching claw278cannot move in the reverse direction, the additional-folding roller unit260moves along the second guiding path272without being guided to the sixth guiding path276, passes through the center-folded sheet bundle SB, and reaches the final position of the forward movement (FIG. 17). After moving to this position, the guide pin265aof the pressing mechanism265is moved from the second guiding path272to the upper fourth guiding path274. As a result, position regulation of the guide pin265aby an upper surface of the second guiding path272is released, so that the upper additional-folding roller261amoves away from the first and the second lower additional-folding rollers262aand262bto be in the press-releasing state.

Subsequently, the additional-folding roller unit260starts to move backward with the unit moving mechanism263(FIG. 18). In the backward movement, the pressing mechanism265moves along the fourth guiding path274in the left direction of the figure (direction of the arrow D3). When the pressing mechanism265reaches the sixth guiding path276due to this movement (FIG. 19), the guide pin265ais pushed downward along the shape of the sixth guiding path276, and the pressing mechanism265is shifted from the press-releasing state to the pressing state (FIG. 20).

When entering the fifth guiding path275, the pressing mechanism265is in a completely pressing state, and moves through the fifth guiding path275as it is in the direction of the arrow D3(FIG. 21) to pass through the center-folded sheet bundle SB (FIG. 22).

The additional-folding roller unit260is reciprocated as described above to additionally fold the fold line part SB1 of the center-folded sheet bundle SB. In this case, the additional-folding roller unit260starts additional-folding from the center part of the center-folded sheet bundle SB to one side, and passes through one end SB2b of the center-folded sheet bundle SB. After that, additional-folding is performed such that the additional-folding roller unit260passes over the additionally folded part of the center-folded sheet bundle SB, starts additional-folding from the center part of the center-folded sheet bundle SB to the other side, and passes through the other end SB2a.

With such an operation, the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262bdo not come into contact with or pressurize each of the ends SB2a and SB2b of the center-folded sheet bundle SB from the outside of the center-folded sheet bundle SB when the additional-folding is started or when the additional-folding roller unit260passes through one end SB2b and returns to the other end SB2a. That is, when passing through the ends SB2a, SB2b of the center-folded sheet bundle SB from the outside of the end, the additional-folding roller unit260is in the press-releasing state. Due to this, no damage is caused to the ends SB2a and SB2b of the center-folded sheet bundle SB. Because the additional-folding is performed from near the center part of the center-folded sheet bundle SB toward the end SB2a or SB2b, a distance of traveling on the center-folded sheet bundle SB in a contact manner becomes short in additional-folding, so that twists that cause wrinkles and the like are hardly accumulated. Accordingly, no damage is caused to the ends SB2a and SB2b of the center-folded sheet bundle SB when the fold line part (spine) SB1 of the center-folded sheet bundle SB is additionally folded, so that it is possible to prevent curling up or wrinkles from being caused at the fold line part SB1 and the vicinity thereof due to accumulation of twists.

To prevent the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262bfrom running onto the end SB2a or SB2b from the outside of the end SB2a or SB2b of the center-folded sheet bundle SB, the operation is performed as shown byFIG. 12toFIG. 22. That is, as shown inFIG. 12, when La represents a distance by which the additional-folding roller unit260moves over the center-folded sheet bundle in the press-releasing state in forward movement, and Lb represents a distance by which the additional-folding roller unit260moves over the center-folded sheet bundle SB in the press-releasing state in backward movement, a relation between the length L in the width direction of the center-folded sheet bundle and the distances La and Lb needs to satisfy L>La+Lb (FIG. 12toFIG. 14, andFIG. 17toFIG. 19).

It is preferable that the distances La and Lb are set to be substantially the same, and pressing is started near the center part in the width direction of the center-folded sheet bundle SB (FIG. 16andFIG. 20).

In the additional-folding roller unit260according to the embodiment, the upper additional-folding roller unit261is configured to be movable in the vertical direction and the lower additional-folding roller unit262is configured not to be movable in the vertical direction. Alternatively, the lower additional-folding roller unit262can also be configured to be movable in the vertical direction. With such a configuration, the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262bsymmetrically perform a contacting/separating operation with respect to the additional-folding position. Accordingly, the additional-folding position is constant regardless of the thickness of the center-folded sheet bundle SB, so that the damage such as a scratch can be further prevented.

FIG. 23is a perspective view illustrating a detailed configuration of the additional-folding roller unit260, andFIG. 24is a diagram illustrating the additional-folding roller unit260ofFIG. 23viewed from a direction of the arrow D4.

The upper additional-folding roller261ais rotatably supported by an upper roller holder261bon the upper additional-folding roller unit261side, and the first and the second lower additional-folding rollers262aand262bare rotatably supported by a lower roller holder262con the lower additional-folding roller unit262side. The unit moving mechanism263includes a slider member263a, and the slider member263ais engaged with a timing belt (not illustrated) at a timing belt engaging part263b. Accordingly, when the timing belt is driven by a motor (not illustrated), the unit moving mechanism263moves in the width direction of the center-folded sheet bundle SB in synchronization with movement of the timing belt.

As described above, the upper additional-folding roller unit261is supported to be movable in the vertical direction (sheet thickness direction t: refer toFIG. 26) by the unit moving mechanism263with the support member265b, and the lower additional-folding roller unit262is mounted to the lower end of the support member265bof the pressing mechanism265so as not to be movable. That is, the first and the second lower additional-folding rollers262aand262bare mounted to the lower roller holder262cso as not to be movable in the sheet thickness direction t, and the upper additional-folding roller261ais mounted to the upper roller holder261bso as to be movable in the sheet thickness direction t.

In the embodiment, as illustrated inFIG. 25, the axial cores (rotation axes) of the first and the second lower additional-folding rollers262aand262bare shifted in the sheet width direction of the center-folded sheet bundle SB with respect to the upper additional-folding roller261aas compared with the basic configuration of the additional-folding roller unit260illustrated inFIG. 7. The shift in the sheet width direction is a shift of a perpendicular (line t1in the sheet thickness direction) taken down from a rotation center of the upper additional-folding roller261ato a line connecting rotation centers of the first and the second lower additional-folding rollers262aand262bin a direction h orthogonal to the sheet thickness direction t (direction parallel to the moving direction of the additional-folding roller unit260). This shift amount is represented as δ inFIG. 27.

The shift δ is a shift between the rotation axes of the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262bin the moving direction of the additional-folding roller unit260.

FIG. 26is a schematic diagram illustrating a pressing state in which the fold line part SB1 of the center-folded sheet bundle SB is pressed with the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262b. In the embodiment, a direction of a tangent G to a nip N between the upper additional-folding roller261aand the first lower additional-folding roller262ais not parallel to a direction orthogonal to the thickness direction t of the center-folded sheet bundle SB. More specifically, when an angle with respect to the thickness direction t of the center-folded sheet bundle SB is assumed to be θ, 0°<θ<90° is satisfied.

Preferably, the angle θ is as follows: 60°<θ<90°.

A pressing force F generated between the upper additional-folding roller261aand the first lower additional-folding roller262ais in a direction orthogonal to the direction of the tangent G described above, so that the direction of the pressing force F is inclined with respect to the thickness direction t of the center-folded sheet bundle SB. Accordingly, as illustrated in the enlarged view of the pressed portion inFIG. 27, a force is generated for displacing the spine (fold line part SB1) of the center-folded sheet bundle SB in the thickness direction t of the center-folded sheet bundle SB. Due to this, as compared to a case in which a pressing force is generated in the thickness direction of the center-folded sheet bundle SB (θ=90 deg), a folding height (additional-folding effect) corresponding to a certain pressing force can be reduced. This force similarly acts on between the upper additional-folding roller261aand the second lower additional-folding roller262b. The direction of the force is, as illustrated inFIG. 27, symmetrical to the line t1taken down from a rotation center261a1of the upper additional-folding roller261ain the thickness direction t of the center-folded sheet bundle SB. This is because the first and the second lower additional-folding rollers262aand262bare arranged symmetrically with respect to the line t1.

That is, in the embodiment, the pressing force F1acts along a first line L1connecting the center261a1of the upper additional-folding roller261aand the center262a1of the first lower additional-folding roller262a, and the pressing force F2acts along a second line L2connecting the center261a1of the upper additional-folding roller261aand the center262b1of the second lower additional-folding roller262b. In this case, the direction of the pressing forces F1, F2are shifted from the thickness direction t of the center-folded sheet bundle SB, so that forces for bending the fold line part SB1, in other words, forces in a bending direction are applied to the fold line part SB1 in addition to the pressing forces F1, F2. Fibers of the sheet are stretched or cut due to the force in the bending direction and the sheet bundle is pressed in this state. Accordingly, the thickness of the fold line part SB1 can be reduced as compared to a case in which the sheet bundle SB is pressed only in the thickness direction t (θ=90 deg). A line h connecting the centers262a1and262b1of the first and the second lower additional-folding rollers262aand262bis orthogonal to the line t1in the thickness direction of the center-folded sheet bundle SB and parallel to the sheet width direction.

The angle θ is changed depending on the thickness of the center-folded sheet bundle SB. That is, the shift amount δ in the sheet width direction is constant, the distances between the center261a1and the centers262a1and262b1are reduced when the thickness of the sheet bundle SB is small, and the distances are increased when the thickness is large, so that the angle θ is reduced in the former case. This changes pressing forces F1and F2generated in nips N1and N2between the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262b, respectively.

In other words, regarding the angle θ set as described above, the direction of the tangent G at the nip N position is shifted with respect to the carrying direction (direction of the arrow D5) of the additional-folding roller unit260. “Shifted” means that the direction is inclined or not parallel to the carrying direction (direction of the arrow D5) of the additional-folding roller unit260.

As described above, when the directions of the pressing forces F1and F2are shifted from the thickness direction t of the center-folded sheet bundle SB, the force for bending the fold line part SB1, in other words, the forces in the bending direction are applied to the fold line part SB1 in addition to the pressing forces F1and F2. Due to this, the thickness of the fold line part SB1 can be reduced as compared to the case in which the center-folded sheet bundle SB is pressed only in the thickness direction t (θ=90 deg). This effect can be exhibited by inclining a line L connecting axes of two additional-folding rollers against (the line t1drawn in) the thickness direction t of the center-folded sheet bundle SB as illustrated inFIG. 30, for example. However, as illustrated inFIG. 27, the number of positions for bending the sheet bundle SB can be doubled if the configuration includes three rollers, that is, the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262bopposed thereto. As a result, a thickness reducing effect is obviously further improved.

The sheet bundle SB can be bent by the axis shift amount uniformly on the right and left in the moving direction (width direction of the sheet bundle: direction of the arrow D1) of the additional-folding roller unit260. In the embodiment, one side is additionally folded in the forward movement and the other side is additionally folded in the backward movement. By uniformly bending on the right and left, outputs from the driving source for the forward movement and the backward movement can be made the same, so that a control configuration is simplified.

In the embodiment, the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262bare rotatably configured to roll over and pressurize both faces of the sheet bundle SB to be additionally folded. Alternatively, the sheet bundle SB can be pressurized with a fixed member instead of the roller. However, in this case, an outer shape of the fixed member should be curved surface as illustrated inFIG. 27to generate the pressing force F in a direction inclined with respect to the thickness direction of a booklet. When the pressing force F is generated with the fixed member in the direction inclined with respect to the thickness direction of the booklet, a load for moving the fixed member in the sheet width direction is increased. To reduce the load, it is preferable to use a rolling member such as the roller as in the embodiment.

Regarding the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262b, as shown inFIG. 28(a), diameters d2and d3of the first and the second lower additional-folding rollers262aand262bare preferably made smaller than a diameter d1of the upper additional-folding roller261a. By making the diameters d2and d3smaller than the diameter D1, the additional-folding roller unit260can be downsized. In the embodiment, the relation among the diameters d1, d2, and d3is made as described above because the rollers are used. When the fixed member having the curved surface is used, a dimensional relation in the width direction of the center-folded sheet bundle SB may be made the same as a dimensional relation of the diameters.

The embodiment may also be configured so as to be able to change the shift amount δ of the first and the second lower additional-folding rollers262aand262bfrom the upper additional-folding roller261a. If the shift amount δ can be changed as described above, folding strength can be controlled by deformation of the sheet bundle SB due to the shift amount δ and the pressurizing force. For example, the folding strength can be increased when the number of sheets is large, and the folding strength can be reduced when the number of sheets is small. The folding strength can be reduced at a portion of a staple needle to prevent deformation of the staple needle or prevent damage to a folding roller.FIG. 28(a) illustrates the positions of the first and the second lower additional-folding rollers262aand262bwhen the center-folded sheet bundle SB is strongly bent.FIG. 28(b) illustrates the positions of the first and the second lower additional-folding rollers262aand262bwhen the center-folded sheet bundle SB is weakly bent. When the shift amount δ can be changed as described above, the pressurizing force to the center-folded sheet bundle SB, that is, bending of the sheets can be controlled with a simple configuration while keeping the same energizing unit265c.

In the embodiment described above, the upper additional-folding roller261ais arranged above the center-folded sheet bundle SB, and the first and the second lower additional-folding rollers262aand262bare arranged below the center-folded sheet bundle SB. Alternatively, as shown inFIG. 29, two rollers261uaand261ubmay be arranged above the center-folded sheet bundle and one roller262umay be arranged below the center-folded sheet bundle to obtain the same effect. The additional-folding roller unit260illustrated inFIG. 29is configured such that the additional-folding roller unit260illustrated inFIG. 25is turned upside down, and a unit moving mechanism263u, a pressing mechanism265u, a pressurizing spring265uc, and the like are reversely arranged. However, these mechanisms are not necessarily reversed. The example ofFIG. 29is exemplary only.

The following configuration can be made as a development of the embodiment described above. The above embodiment is configured so as to be able to change the shift amount δ of the first and the second lower additional-folding rollers262aand262bfrom the upper additional-folding roller261a. Accordingly, as illustrated inFIG. 31, deformation of the fold line part can be prevented when the shift amount δ between the second lower additional-folding roller262band the upper additional-folding roller261asatisfies δ=0. The folding strength can be reduced in a case in which the number of sheets is small, or in a case of preventing damage to the folding roller or deformation of the staple needle at the portion of the staple needle.

Selection mode of additional-folding strength can be increased to improve convenience of a user. That is, the same effect as in the case of including two rollers inFIG. 30can be obtained with three rollers. Specifically, any of the first and the second lower additional-folding rollers262aand262bis configured to be released in the sheet thickness direction t. Alternatively, the upper additional-folding roller261ais configured to be arranged externally with respect to any of the first and the second lower additional-folding rollers262aand262b(FIG. 32). Accordingly, similarly to the case inFIG. 30, the sheet bundle SB is pressurized and additionally folded by inclining, with respect to the thickness direction t of the sheet bundle, the direction of the tangent to the nip between two rollers, that is, the upper additional-folding roller261aand the second lower additional-folding roller262binFIG. 32.

In this way, it is possible to control the pressurizing force to the center-folded sheet bundle, that is, the bending of the sheets with a simple configuration.

As described above, the following effects are exhibited according to the embodiment.

(1) The sheet processing device includes pressing means for holding and pressing the fold line part SB1 of the center-folded sheet bundle SB and the additional-folding roller unit260(moving means) for moving the pressing position of the pressing means in a fold direction (direction of the arrow D1) of the sheet bundle SB. The pressing means includes the upper additional-folding roller261a(first pressing roller) arranged on one side of the thickness direction of the sheet bundle SB and the first and the second lower additional-folding rollers262aand262b(second and third pressing roller) arranged on the other side across the fold line part SB1 of the center-folded sheet bundle SB. The first line L1connects the center261a1of the upper additional-folding roller261a(first pressing roller) and the center262a1of the first lower additional-folding roller262a(second pressing roller), and the second line L2connects the center262a1of the upper additional-folding roller261a(first pressing roller) and the center262b1of the second lower additional-folding roller262b(third pressing roller). The additional-folding roller unit260(moving means) causes a state in which each of the first line L1and the second line L2is not parallel to the thickness direction t of the center-folded sheet bundle SB, and moves the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262b(the first, the second, and the third pressing roller) in the width direction (direction of the arrow D1) of the sheet bundle SB. Accordingly, additional-folding can be performed with a small pressurizing force and the size and the cost of the device can be reduced.

This is because the upper additional-folding roller261athat presses the upper surface of the center-folded sheet bundle SB and the first and the second lower additional-folding rollers262aand262bthat press the lower surface of the center-folded sheet bundle SB are arranged so that each of the first and the second lines L1and L2connecting the respective centers of the upper and lower rollers is not in parallel to the thickness direction t of the center-folded sheet bundle SB, in other words, the centers262a1and262b1of the first and the second lower additional-folding rollers262aand262bare shifted from the center261a1of the upper additional-folding roller261ain the sheet width direction. With such an arrangement, when the sheet bundle SB is held among the three additional-folding rollers261a,262a, and262b, the fold line part SB1 of the center-folded sheet bundle SB can be additionally folded while causing mountain-shaped deformation with the three additional-folding rollers261a,262a, and262b. As a result, the additional-folding effect can be obtained with a smaller force than that in the case of simply compressing the sheet bundle SB.

(2) The upper additional-folding roller261a(first pressing roller) is positioned between the first and the second lower additional-folding rollers262aand262b(second and third pressing rollers) in the width direction (direction of the arrow D1) of the sheet bundle SB (refer toFIG. 27andFIGS. 28(a),28(b)), so that the center-folded sheet bundle SB can be deformed in a mountain-shape (V-shape) and a force in the bending direction can also be applied to the fold line part SB1 of the center-folded sheet bundle SB. Due to the force in the bending direction, the thickness of the fold line part SB1 can be reduced as compared to the case of pressing the center-folded sheet bundle SB only in the thickness direction t.

(3) The shift amount δ of the center262a1position of the first lower additional-folding roller262a(second pressing roller) from the line t1drawn from the center261a1of the upper additional-folding roller261a(first pressing roller) in the thickness direction t of the sheet bundle SB is the same as the shift amount δ of the center262b1position of the second lower additional-folding roller262b(third pressing roller) from the line t1(FIG. 27), so that additional-folding can be performed while uniformly bending on the right and left when one side is additionally folded in the forward movement and the other side is additionally folded in the backward movement. Accordingly, outputs from the driving source for the forward movement and the backward movement can be made the same, so that the control configuration is simplified.

(4) Each of the diameters d2and d3(dimension in the sheet width direction) of the first and the second lower additional-folding rollers262aand262b(the second pressing roller and the third pressing roller) is smaller than the diameter d1(dimension in the sheet width direction) of the upper additional-folding roller261a(first pressing roller), so that the additional-folding roller unit260can be downsized.

(5) The first lower additional-folding roller262aor the second lower additional-folding roller262b(the second pressing roller or the third pressing roller) is movable in the sheet width direction (direction of the arrow D1) with respect to the upper additional-folding roller261a(first pressing roller), so that it is possible to change the shift amount δ of the first and the second lower additional-folding rollers262aand262hfrom the upper additional-folding roller261a. Accordingly, the folding strength can be controlled by deformation of the center-folded sheet bundle SB due to the shift amount δ and the pressurizing force.

(6) The first lower additional-folding roller262aor the second lower additional-folding roller262b(the second pressing roller or the third pressing roller) is movable to the same position in the sheet width direction (position over the line t1drawn from the center261a1of the upper additional-folding roller261ain the thickness direction t of the center-folded sheet bundle SB) with respect to the upper additional-folding roller261a(first pressing roller), so that pressing can be performed with a shift amount 0 even though the pressing has been conventionally performed with a predetermined shift amount δ other than 0 (refer toFIG. 31). Accordingly, additional-folding can be performed in a mode in which the folding strength is weak, and options for the folding strength can be increased.

(7) The upper additional-folding roller261a(the first pressing roller) is arranged externally with respect to the first lower additional-folding roller262aor the second lower additional-folding roller262b(the second pressing roller or the third pressing roller) in the sheet width direction (refer toFIG. 32), so that additional-folding can be performed with two rollers, that is, two upper and lower additional-folding rollers261aand262b(or262a). Accordingly, options for the folding strength can be increased.

(8) The guiding path270that includes the first to sixth guiding paths271to276for causing the upper additional-folding roller261a(first pressing roller) and the first and the second lower additional-folding rollers262aand262b(second and third pressing rollers) to be in the pressing state and the press-releasing state is provided, so that deformation of the rollers can be prevented by causing the press-releasing state when the additional-folding operation is not performed.

(9) An image forming system that includes the image forming apparatus PR and the sheet postprocessing devices (sheet processing devices 1 and 2) described in the above (1) to (8) is provided, so that the image forming system can exhibit the effects of the above (1) to (8).

(10) The upper additional-folding roller261a(first pressing roller) is arranged on one side of the thickness direction t of the center-folded sheet bundle SB, and the first and the second lower additional-folding rollers262aand262b(second and third pressing rollers) are arranged on the other side of the thickness direction t of the center-folded sheet bundle SB. The fold line part SB1 of the center-folded sheet bundle SB is held between the upper additional-folding roller261a(first pressing roller) and the first and the second lower additional-folding rollers262aand262b(second and third pressing rollers). The first line L1connects the center261a1of the upper additional-folding roller261a(first pressing roller) and the center262a1of the first lower additional-folding roller262a(second pressing roller), and the second line L2connects the center262a1of the upper additional-folding roller261a(first pressing roller) and the center262b1of the second lower additional-folding roller262b(third pressing roller). The additional-folding roller unit260(moving means) causes a state in which each of the first line L1and the second line L2is not parallel to the thickness direction t of the center-folded sheet bundle SB, and moves the upper additional-folding roller261aand the first and the second lower additional-folding rollers262aand262b(the first, the second, and the third pressing rollers) in the width direction of the center-folded sheet bundle to additionally fold the fold line part SB1 of the center-folded sheet bundle SB. Accordingly, additional-folding can be performed with a small pressurizing force and the size and the cost of the device can be reduced.

In the description of the effects of the embodiment, each component to be described in the scope of claims corresponding to each unit in the embodiment is put in brackets, or denoted by a reference numeral, to clarify the correspondence relation therebetween. According to the present invention, additional-folding can be performed with a small pressurizing force and the size and the cost of the device can be reduced.