SHEET POST-PROCESSING APPARATUS

Abstract

A sheet post-processing apparatus includes a sheet conveyance passage along which a sheet is conveyed and a driving roller and a driven roller that are arranged opposite each other across a folding conveyance passage branching off the sheet conveyance passage and that are kept in pressed contact with each other. The sheet post-processing apparatus double-folds the sheet passing through a nip portion between the driving and driven rollers and conveys the double-folded sheet. The nip portion is formed with one of the driving and driven rollers pivoting about a pivoting shaft to be pressed against the other. To one of the rotation shaft of the driving roller and the pivoting shaft, the driving shaft of the driving motor is directly coupled. The other of the rotation shaft of the driving roller and the pivoting shaft is coupled to the driving shaft via a driving transmission gear.

Claims

1. A sheet post-processing apparatus, comprising: a sheet conveyance passage along which a sheet is conveyed; and a driving roller and a driven roller that are arranged opposite each other across a folding conveyance passage branching off the sheet conveyance passage, the driving roller and the driven roller being kept in pressed contact with each other, the sheet post-processing apparatus double-folding the sheet passing through a nip portion formed between the driving roller and the driven roller, the sheet post-processing apparatus then conveying the double-folded sheet, wherein the nip portion is formed as a result of one of the driving roller and the driven roller pivoting about a pivoting shaft so as to be pressed against the other, to one of a rotation shaft of the driving roller and the pivoting shaft, a driving shaft of a driving motor is directly coupled, and the other of the rotation shaft of the driving roller and the pivoting shaft is coupled to the driving shaft via a driving transmission gear.

2. The sheet post-processing apparatus according to claim 1, wherein the driving shaft of the driving motor is positioned with respect to the pivoting shaft.

3. The sheet post-processing apparatus according to claim 1, wherein a plurality of driven rollers are provided for one driving roller to form a plurality of nip portions, a plurality of driving motors are provided, the driven rollers pivot with respect to the driving roller, and to the pivoting shaft, driving shafts of the driving motors are directly coupled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic diagram showing a configuration of an image forming system comprising a sheet post-processing apparatus 1 according to one embodiment of the present disclosure and an image forming apparatus 200 to which the sheet post-processing apparatus 1 is coupled;

[0010] FIG. 2 is a side sectional view schematically showing a configuration of the sheet post-processing apparatus 1 according to one embodiment of the present disclosure;

[0011] FIG. 3 is a side view of a folded sheet S, specifically a side sectional view of a sheet S that is Z-folded;

[0012] FIG. 4 is a side view of the folded sheet S, specifically a side sectional view of a sheet S that is outward triple-folded;

[0013] FIG. 5 is a side view of the folded sheet S, specifically a side sectional view of a sheet S that is inward triple-folded;

[0014] FIG. 6 is a sectional part view around a sheet folding unit 100 in the sheet post-processing apparatus 1 according to one embodiment of the present disclosure;

[0015] FIG. 7 is a sectional view around the sheet folding unit 100 in the sheet post-processing apparatus 1 according to one embodiment of the present disclosure, showing a first stage in the progress of the inward triple-folding of the sheet S;

[0016] FIG. 8 is an enlarged view around a first folding nip NI in the sheet folding unit 100 in FIG. 7, showing a state in which the sheet S has been drawn completely at the first stage;

[0017] FIG. 9 is a diagram showing a state in which, from the state in FIG. 8, a pair of second assist rollers 3r2 have been rotated backward to let the sheet S sag;

[0018] FIG. 10 is a diagram showing a state in which, from the state in FIG. 9, the pair of second assist rollers 3r2 have been rotated further backward and a first folding guide 104 has been moved to a folding position to let the sheet S enter the first folding nip N1;

[0019] FIG. 11 is a sectional view around the sheet folding unit 100 in the sheet post-processing apparatus 1 according to one embodiment of the present disclosure, showing a second stage of the progress of the inward triple-folding of the sheet S;

[0020] FIG. 12 is a sectional view around the sheet folding unit 100 in the sheet post-processing apparatus 1 according to one embodiment of the present disclosure, showing a third stage of the progress of the inward triple-folding of the sheet S;

[0021] FIG. 13 is a sectional view around the sheet folding unit 100 in the sheet post-processing apparatus 1 according to one embodiment of the present disclosure, showing a fourth stage of the progress of the inward triple-folding of the sheet S; and

[0022] FIG. 14 is an enlarged sectional part view around a pair of first folding rollers 103 and a pair of second folding rollers 107 in the sheet post-processing apparatus 1 according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

[0023] An embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a configuration of an image forming system comprising a sheet post-processing apparatus 1, which includes a sheet folding unit 100 according to the embodiment of the present disclosure, and an image forming apparatus 200, to which the sheet post-processing apparatus 1 is coupled.

[0024] As shown in FIG. 1, the image forming apparatus 200 prints images on sheets (paper) on the basis of image data input from the outside via a network communication portion, which is not shown, or on the basis of image data read by an image reading portion 201 arranged in an upper part of the image forming apparatus 200.

[0025] The sheet post-processing apparatus 1 is removably coupled to a side face of the image forming apparatus 200. The sheet post-processing apparatus 1 performs post-processing such as a punching process, a binding process, and a folding process on the sheets that have been subjected to image formation (printed) by the image forming apparatus 200. Note that the sheet post-processing apparatus 1 need not be one that performs post-processing on sheets that are automatically conveyed from the image forming apparatus 200, and may be one that performs post-processing on sheets that are set on a tray, which is not shown, by the user and that the sheet post-processing apparatus 1 itself conveys to a position where it can perform the post-processing.

[0026] FIG. 2 is a side sectional view schematically showing a configuration of the sheet post-processing apparatus 1 including the sheet folding unit 100 according to this embodiment. As shown in FIG. 2, the sheet post-processing apparatus 1 includes a sheet loading port 2, a first sheet conveyance passage (sheet conveyance passage) 3, a first sheet discharge portion 4, a second sheet conveyance passage 5, a second sheet discharge portion 6, a third sheet conveyance passage 7, a third sheet discharge portion 8, a post-processing portion 9, and a post-processing control portion (control portion) 10.

[0027] The sheet loading port 2 is an opening that is provided in the side face of the sheet post-processing apparatus 1 facing the image forming apparatus 200. The sheets conveyed from the image forming apparatus 200 to the sheet post-processing apparatus I are conveyed into the sheet post-processing apparatus 1 through the sheet loading port 2.

[0028] The first sheet conveyance passage 3 extends from the sheet loading port 2 to the first sheet discharge portion 4 substantially horizontally in a direction (leftward in FIG. 2) away from the image forming apparatus 200. Note that, this direction from the sheet loading port 2 to the first sheet discharge portion 4 is referred to as the sheet conveyance direction in the first sheet conveyance passage 3. The sheet loading port 2 is located at the upstream end of the first sheet conveyance passage 3 in the sheet conveyance direction. The first sheet conveyance passage 3 has a plurality of pairs of conveyance rollers 3r, which convey the sheets conveyed in the sheet post-processing apparatus 1 through the sheet loading port 2 toward the first sheet discharge portion 4.

[0029] The first sheet discharge portion 4 is provided in the side face of the sheet post-processing apparatus 1 opposite from its side face facing the image forming apparatus 200. The first sheet discharge portion 4 is arranged at the downstream end of the first sheet conveyance passage 3 in the sheet conveyance direction. The first sheet discharge portion 4 has a first discharge port 41, a pair of first discharge rollers 42, and a first discharge tray 43.

[0030] The first discharge port 41 is located at the downstream end of the first sheet conveyance passage 3 in the sheet conveyance direction. The pair of first discharge rollers 42 are arranged at the first discharge port 41. The first discharge tray 43 is located downstream of the first discharge port 41 in the sheet conveyance direction. The sheets having been conveyed through the first sheet conveyance passage 3 and reached the first discharge port 41 are discharged by the pair of first discharge rollers 42 through the first discharge port 41 to the first discharge tray 43. The first discharge tray 43 is one of the final discharge destinations of the sheets that have been subjected to the post-processing by the sheet post-processing apparatus 1.

[0031] The second sheet conveyance passage 5 branches from a first branch portion (branch portion) 31 on the first sheet conveyance passage 3 and extends to the second sheet discharge portion 6 in the direction away from the image forming apparatus 200 (leftward in FIG. 2), laterally upward. The first branch portion 31 is arranged downstream of a perforating portion 91 with respect to the sheet conveyance direction in the first sheet conveyance passage 3. Note that this direction from the first branch portion 31 to the second sheet discharge portion 6 is referred to as the sheet conveyance direction in the second sheet conveyance passage 5. The first branch portion 31 is located at the upstream end of the second sheet conveyance passage 5 in the sheet conveyance direction. The second sheet conveyance passage 5 has a plurality of pairs of conveyance rollers 5r, and diverts the sheets conveyed through the first sheet conveyance passage 3 at the first branch portion 31 to convey them toward the second sheet discharge portion 6.

[0032] The first branch portion 31 has a first switching guide 311. The first switching guide 311 pivots between a first position (broken line PI in FIG. 7) at which it guides the sheets conveyed from the sheet loading port 2 through the first sheet conveyance passage 3 along the first sheet conveyance passage 3 to the first discharge port 41 and a second position (solid line P2 in FIG. 7) at which it guides the sheets diverted from the first sheet conveyance passage 3 to the second sheet conveyance passage 5. The first switching guide 311 pivots also to a third position (broken line P3 in FIG. 7) at which it guides the sheets having been subjected to the folding process and passed through a second folding conveyance passage 106, which will be described later, to the second sheet conveyance passage 5. The first switching guide 311 is connected to a drive mechanism (not shown) and its operation is controlled by the post-processing control portion 10.

[0033] The second sheet discharge portion 6 is provided in the side face of the sheet post-processing apparatus 1 opposite from its side face facing the image forming apparatus 200, above the first sheet discharge portion 4. The second sheet discharge portion 6 is arranged at the downstream end of the second sheet conveyance passage 5 in the sheet conveyance direction. The second sheet discharge portion 6 has a second discharge port 61, a pair of second discharge rollers 62, and a second discharge tray 63.

[0034] The second discharge port 61 is located at the downstream end of the second sheet conveyance passage 5 in the sheet conveyance direction. The pair of second discharge rollers 62 are arranged at the second discharge port 61. The second discharge tray 63 is located downstream of the second discharge port 61 in the sheet conveyance direction. The sheets having been conveyed through the second sheet conveyance passage 5 and reached the second discharge port 61 are discharged by the pair of second discharge rollers 62 through the second discharge port 61 to the second discharge tray 63. The second discharge tray 63 is one of the final discharge destinations of the sheets that have been subjected to the post-processing by the sheet post-processing apparatus 1. In addition, sheets that are not subjected to post-processing, sheets of small sizes, and the like are also discharged to the second discharge tray 63.

[0035] The third sheet conveyance passage 7 branches from a second branch portion 32 on the first sheet conveyance passage 3 and extends downward to the third sheet discharge portion 8. Note that the direction from the second branch portion 32 to the third sheet discharge portion 8 is referred to as the sheet conveyance direction in the third sheet conveyance passage 7. The second branch portion 32 is located downstream of the first branch portion 31 with respect to the sheet conveyance direction in the first sheet conveyance passage 3, at the upstream end of the third sheet conveyance passage 7 in the sheet conveyance direction. The third sheet conveyance passage 7 has a plurality of pairs of conveyance rollers 7r, and diverts the sheets conveyed through the first sheet conveyance passage 3 at the second branch portion 32 to convey them toward the third sheet discharge portion 8.

[0036] The second branch portion 32 has a second switching guide 321. The second switching guide 321 pivots between a first position (see FIG. 5) at which it guides the sheets conveyed from the sheet loading port 2 through the first sheet conveyance passage 3 along the first sheet conveyance passage 3 to the first discharge port 41 and a second position (not shown) at which it guides the sheets conveyed from the sheet loading port 2 through the first sheet conveyance passage 3, then passed through the second branch portion 32, and then switched back to the third sheet conveyance passage 7. The second switching guide 321 is connected to a drive mechanism (not shown) and its operation is controlled by the post-processing control portion 10.

[0037] The third sheet discharge portion 8 is provided in the side face of the sheet post-processing apparatus 1 opposite from its side face facing the image forming apparatus 200, below the first sheet discharge portion 4 (near the lower end of the sheet post-processing apparatus 1). The third sheet discharge portion 8 has a third discharge port 81, a pair of third discharge rollers 82, and a third discharge tray 83.

[0038] The third discharge port 81 is located at the downstream end of the third sheet conveyance passage 7 in the sheet conveyance direction. The pair of third discharge rollers 82 are arranged at the third discharge port 81. The third discharge tray 83 is located downstream of the third discharge port 81 in the sheet conveyance direction. The sheets having been conveyed through the third sheet conveyance passage 7 and reached the third discharge port 81 are discharged by the pair of third discharge rollers 82 through the third discharge port 81 to the third discharge tray 83. The third discharge tray 83 is one of the final discharge destinations of the sheets that have been subjected to the post-processing by the sheet post-processing apparatus 1.

[0039] The post-processing portion 9 performs predetermined post-processing to the sheets on which images have been formed by the image forming apparatus 200 and which then have been conveyed into the sheet post-processing apparatus 1. The post-processing portion 9 includes a perforating portion 91, a stapling portion 92, a sheet folding unit 100, and a bookbinding portion 94.

[0040] The perforating portion 91 is arranged closely downstream of the sheet loading port 2 in the first sheet conveyance passage 3. The perforating portion 91 performs a perforating process on the sheets conveyed in the first sheet conveyance passage 3 to form punched holes in then.

[0041] The stapling portion 92 is arranged closely upstream of the first sheet discharge portion 4 with respect to the sheet conveyance direction in the first sheet conveyance passage 3. The stapling portion 92 performs a stapling process (binding process) on a bundle of sheets formed by stacking together a plurality of sheets to bind the bundle of sheets.

[0042] The sheet folding unit 100 is arranged downstream of the perforating portion 91, upstream of the stapling portion 92, with respect to the sheet conveyance direction in the first sheet conveyance passage 3. In other words, the sheet folding unit 100 is located upstream of the first branch portion 31 with respect to the sheet conveyance direction in the first sheet conveyance passage 3. The sheet folding unit 100 performs the folding process on a single sheet to form a fold line in it.

[0043] The sheet folding unit 100 can perform, on a single sheets, folding processes such as double-folding, Z-folding, outward triple-folding, and inward triple-folding. The configuration of the sheet folding unit 100 will be described in detail later.

[0044] FIGS. 3 to 6 are side views of the sheet S that is Z-folded, outward triple-folded, and inward triple-folded, respectively.

[0045] Z-folding is, for example as shown in FIG. 3, a folding method that folds a downstream part of the sheet S with respect to the sheet conveyance direction in the first sheet conveyance passage 3 in a Z-shape as seen from the sheet width direction orthogonal to the sheet conveyance direction. Of a Z-folded sheet S, a downstream part Sd downstream of a first fold line Fl in the first sheet conveyance passage 3 and an upstream part Su upstream of a second fold line F2 face each other in the up-down direction across a middle part Sc between the two fold lines. In the sheet conveyance direction, the lengths of the downstream part Sd and the middle part Sc of the sheet S are substantially the same and are smaller than the length of the upstream part Su.

[0046] Outward triple-folding is, for example as shown in FIG. 4, a folding method that folds the entire sheet S in a Z-shape as seen from the sheet width direction. Of an outward triple-folded sheet S, a downstream part Sd downstream of a first fold line F1 in the first sheet conveyance passage 3 and an upstream part Su upstream of a second fold line F2 of the sheet S face each other in the up-down direction across a middle part Sc between the two fold lines. In the sheet conveyance direction, the lengths of the downstream part Sd, the middle part Sc, and the upstream part Su of the sheet S are substantially the same.

[0047] Of an inward triple-folded sheet S, for example as shown in FIG. 5, an upstream part Su upstream of a first fold line Fl and a downstream part Sd downstream of the second fold line F2 in the sheet conveyance direction in the first sheet conveyance passage 3 face each other and make surface contact with each other in the up-down direction at one side (top side in FIG. 5) of the plane of a middle part Sc between the two fold lines.

[0048] The bookbinding portion 94 is arranged closely upstream of the third sheet discharge portion 8 in the sheet conveyance direction in the third sheet conveyance passage 7. The bookbinding portion 94 has a middle folding portion 941 and a middle binding portion 942. The bookbinding portion 94 performs a middle folding process and a middle stapling process to bend and bind a substantially middle part in the sheet conveyance direction of a bundle of sheets formed by stacking together a plurality of sheets, thereby to form booklets.

[0049] The post-processing control portion 10 includes a CPU, a storage portion, and other electronic circuits and electronic components (none of which is shown). The post-processing control portion 10 is communicably connected to a main body control portion in the image forming apparatus 200 (see FIG. 1). In response to instructions from the main body control portion, the post-processing control portion 10, using the CPU, controls the operation of the components provided in the sheet post-processing apparatus 1 on the basis of control programs and data stored in the storage portion. In this way, the post-processing control portion 10 performs processes related to the functions of the sheet post-processing apparatus 1. The first sheet conveyance passage 3, the first sheet discharge portion 4, the second sheet conveyance passage 5, the second sheet discharge portion 6, the third sheet conveyance passage 7, the third sheet discharge portion 8, and the post-processing portion 9 individually receive instructions from the post-processing control portion 10 and perform post-processing in cooperation with each other. Note that the functions of the post-processing control portion (control portion) 10 may be carried out by the main body control portion of the image forming apparatus 200.

[0050] Next, a configuration of the sheet folding unit 100 will be described with reference to FIGS. 6 and 7. FIGS. 6 and 7 are sectional part views around the sheet folding unit 100 in the sheet post-processing apparatus 1. The sheet folding unit 100 includes a first folding portion 101, a first folding conveyance passage 102, a pair of first folding rollers 103, a first folding guide 104, a second folding portion 105, a second folding conveyance passage 106, a pair of second folding rollers 107, and a second folding guide 108.

[0051] Along the first sheet conveyance passage 3, at two places on the sheet folding unit 100, pairs of conveyance rollers 3r are arranged. Hereinafter, of the pairs of conveyance rollers 3r arranged at two places on the sheet folding unit 100, the upstream pair of conveyance rollers 3r comprising a second roller (driven roller) 112 and a conveyance roller 114 is referred to as a pair of first assist rollers 3r1 and the downstream pair of conveyance rollers 3r is referred to as a pair of second assist rollers 3r2.

[0052] The first folding portion 101 is arranged on the first sheet conveyance passage 3. Specifically, the first folding portion 101 is located downstream of the perforating portion 91 (see FIG. 2), upstream of the first branch portion 31 in the sheet conveyance direction in the first sheet conveyance passage 3.

[0053] The first folding conveyance passage 102 extends downward off from the first folding portion 101 on the first sheet conveyance passage 3 and extends downward. In this embodiment, the first folding conveyance passage 102 extends substantially perpendicularly downward from the first folding portion 101. A lower end part of the first folding conveyance passage 102 is connected to the third sheet conveyance passage 7.

[0054] The pair of first folding rollers 103 is arranged on the first folding conveyance passage 102 in the first folding portion 101. The pair of first folding rollers 103 comprises a first roller 111 arranged at one side across the first folding conveyance passage 102 and a second roller 112 arranged at the other side. The pair of first folding rollers 103 form a first folding nip (nip portion) NI with one of the first and second rollers 111 and 112 urged toward, into contact with, the other. The sheet having entered the first folding conveyance passage 102 passes through the first folding nip N1 and is conveyed to below the pair of first folding rollers 103.

[0055] The second roller 112 together with the conveyance roller 114 constitutes the pair of first assist rollers 3r1.

[0056] The first folding guide 104 is arranged opposite the first folding nip N1 in the first folding portion 101. Specifically, the first folding guide 104 is arranged upstream (top side in FIG. 6) of the first folding nip NI in the sheet conveyance direction in the first folding conveyance passage 102. If no folding process is performed on the sheet, the first folding guide 104 retracts in the direction farther away from the first folding nip NI than the first sheet conveyance passage 3, that is, to above the first sheet conveyance passage 3 in FIG. 6. Thus the sheet passing through the first sheet conveyance passage 3 does not make contact with the first folding guide 104.

[0057] The first folding guide 104 is connected to a guide drive mechanism (not shown) and can reciprocate in the direction toward and away from the first folding nip N1. The first folding guide 104 guides the sheet conveyed along the first sheet conveyance passage 3 to the first folding nip N1.

[0058] The second folding portion 105 is arranged on the first folding conveyance passage 102. Specifically, the second folding portion 105 is located downstream of the pair of first folding rollers 103, below the first folding nip NI in the sheet conveyance direction of the first folding conveyance passage 102.

[0059] The second folding conveyance passage 106 extends off from the second folding portion 105 on the first folding conveyance passage 102. The second folding conveyance passage 106 extends from the second folding portion 105 toward the side face (left in FIG. 6) of the sheet post-processing apparatus 1 where the first sheet discharge portion 4 is provided. In other words. The second folding conveyance passage 106 extends substantially in the same direction as the extending direction of the first sheet conveyance passage 3.

[0060] The first sheet conveyance passage 3 includes a junction portion 33 located downstream of the first branch portion 31 in the sheet conveyance direction. The second folding conveyance passage 106 joins the first sheet conveyance passage 3 at the junction portion 33. In other words, the junction portion 33 is arranged downstream of the first branch portion 31 in the sheet conveyance direction in the first sheet conveyance passage 3 and is where the sheet having undergone a folding process in the sheet folding unit 100 joins.

[0061] Specifically, in this embodiment, the junction portion 33 is located near the first switching guide 311. The first switching guide 311, at the second position (position indicated by a solid line in FIG. 6) at which it guides the sheets conveyed from the sheet loading port 2 through the first sheet conveyance passage 3 to the second sheet conveyance passage 5, guides the sheet having joined the first sheet conveyance passage 3 at the junction portion 33 and having undergone the folding process to the downstream end in the sheet conveyance direction in the first sheet conveyance passage 3. The first switching guide 311, at the second position, closes the upstream part of the first sheet conveyance passage 3 in the sheet conveyance direction at the junction portion 33.

[0062] The pair of second folding rollers 107 are arranged on the second folding conveyance passage 106 in the second folding portion 105. The pair of second folding rollers 107 comprise the first roller 111 arranged at one side across the second folding conveyance passage 106 and a third roller (driven roller) 113 arranged at the other side. The pair of second folding rollers 107 form a second folding nip N2 with one of the first and third rollers 111 and 113 urged toward, into contact with, the other. The sheet having entered the second folding conveyance passage 106 passes through the second folding nip N2 and is conveyed toward the junction portion 33 (to the left of the pair of second folding rollers 107 in FIG. 6).

[0063] The second folding guide 108 is arranged opposite the second folding nip N2 in the second folding portion 105. Specifically, the second folding guide 108 is arranged upstream (right in FIG. 6) of the second folding nip N2 in the sheet conveyance direction in the second folding conveyance passage 106. If no folding process is performed on the sheet, the second folding guide 108 retracts in the direction farther away from the second folding nip N2 than the first folding conveyance passage 102, that is, to the right of the first folding conveyance passage 102 in FIG. 6. Thus the sheet passing through the first folding conveyance passage 102 does not make contact with the second folding guide 108.

[0064] The second folding guide 108 is connected to a drive mechanism (not shown) and can reciprocate in the direction toward to and away from the second folding nip N2. The second folding guide 108 guides the sheet conveyed along the first folding conveyance passage 102 to the second folding nip N2.

[0065] Next, the operation of the sheet folding unit 100 will be described with reference to FIGS. 8 to 13. As one example of the operation of the sheet folding unit 100, an inward triple-folding process by which the sheet is triple-folded inward as shown in FIG. 5 will be described. FIGS. 7, 11, 12, and 13 are sectional views around the sheet folding unit 100 in FIG. 6, showing a first, a second, a third, and a fourth stage, respectively, in the progress of the inward triple-folding of the sheet S. FIGS. 8 to 11 are diagrams showing the first stage of the inward triple-folding of the sheet S in more detail.

[0066] As shown in FIG. 7, the sheet S conveyed through the sheet loading port 2 (see FIG. 2) into the first sheet conveyance passage 3 has a downstream part of it in the sheet conveyance direction guided from the first branch portion 31 into the second sheet conveyance passage 5. The first switching guide 311 in the first branch portion 31 is located at the second position at which it guides the sheet S conveyed from the sheet loading port 2 through the first sheet conveyance passage 3 to the second sheet conveyance passage 5.

[0067] In the first folding portion 101, the first folding guide 104 is arranged in the direction farther away from the first folding nip NI than the first sheet conveyance passage 3, that is, at a position (retracted position) retracted above the first sheet conveyance passage 3 in FIG. 7.

[0068] FIG. 8 is an enlarged view around the first folding nip NI in the sheet folding unit 100 in FIG. 7, showing a state in which the sheet S has been drawn completely at the first stage. As shown in FIG. 8, when a part of the sheet S corresponding to the first fold line F1 reaches the first folding portion 101, the pairs of first and second assist rollers 3r1 and 3r2 and the pairs of conveyance rollers 5r (see FIG. 6) in the second sheet conveyance passage 5 stop being rotated and the sheet S stops being conveyed.

[0069] FIG. 9 is a diagram showing a state in which, from the state in FIG. 8, the pair of second assist rollers 3r2 have been rotated backward to let the sheet S sag. As shown in FIG. 9, with the pair of first assist rollers 3r1 at rest, rotating backward the pair of second assist rollers 3r2 and the pairs of conveyance rollers 5r in the second sheet conveyance passage 5 causes a part of the sheet S downstream of the pair of first assist rollers 3r1 to move upstream (rightward in FIG. 9) and the sheet S sags in the first folding portion 101. After that, the first folding guide 104 starts to move from the retracted position shown in FIG. 8 in the direction toward the first folding nip N1.

[0070] FIG. 10 is a diagram showing a state in which, from the state in FIG. 9, the pair of second assist rollers 3r2 have been rotated further backward and the first folding guide 104 have been moved to a folding position to let the sheet S enter the first folding nip N1. As shown in FIG. 10, the pair of second assist rollers 3r2 are rotated further backward, and the first folding guide 104 is moved to a position (folding position) where it makes contact with the first folding nip NI via the sheet S. As the first folding guide 104 moves from the retraction position to the folding position, the sagging part (folded part) of the sheet S is guided to the first folding nip N1. In this way, first letting the sheet S sag and then moving the first folding guide 104 to the folding position prevents an excessive load from the first folding guide 104 from acting on the sheet S and this helps prevent wrinkling and breakage of the sheet S.

[0071] FIG. 11 is a sectional view around the sheet folding unit 100, showing the second stage of the progress of the inward triple-folding of the sheet S. As shown in FIG. 11, on the sheet S having passed through the first folding nip N1, the first fold line F1 is formed.

[0072] The timing of forming the first fold line F1 in the sheet S is determined on the basis of the timing with which a sheet detection sensor (not shown) detects the downstream end of the sheet S in the sheet conveyance direction in the first sheet conveyance passage 3, the length of the sheet S in the sheet conveyance direction, and the conveyance speed of the sheet S. A similar description applies to the timing of forming the second fold line F2, which will be described later.

[0073] In the second folding portion 105, the second folding guide 108 is retracted in the direction farther away from the second folding nip N2 than the first folding conveyance passage 102, that is, to the right of the first folding conveyance passage 102 in FIG. 9.

[0074] The sheet S having passed through the first folding nip NI is conveyed, with a part of it corresponding to the first fold line FI as the leading end and with two areas extending along the sheet conveyance direction overlapping with each other, along the first folding conveyance passage 102 in the direction (downward) away from the pair of first folding rollers 103. An upstream part, in the sheet conveyance direction, of the sheet S having passed through the first folding conveyance passage 102 temporarily enters the third sheet conveyance passage 7.

[0075] When a part of the sheet S corresponding to the second fold line F2 (see FIG. 4) reaches the second folding portion 105, the pairs of second and first assist rollers 3r2 and 3r1, the pairs of conveyance rollers 5r in the second sheet conveyance passage 5, the pair of first folding rollers 103, and the pairs of conveyance rollers 7r in the third sheet conveyance passage 7 stop being rotated and the sheet S stops being conveyed.

[0076] FIG. 12 is a sectional view around the sheet folding unit 100, showing the third stage of the progress of the inward triple-folding of the sheet S. First the sheet S stops being conveyed and then the pairs of conveyance rollers 7r in the third sheet conveyance passage 7 are rotated backward so that, as shown in FIG. 12, a part of the sheet S downstream of the second folding portion 105 in the sheet conveyance direction (i.e., a part below the second folding portion 105 in FIG. 12) moves upstream (upward in FIG. 12) and the sheet S sags at the second folding portion 105.

[0077] Next, the second folding guide 108 moves in the direction toward the second folding nip N2 to make contact with the sheet S. The contact with the second folding guide 108 results in, as shown in FIG. 12, a sagging part (folded part) of the sheet S being guided to the second folding nip N2 in the pair of second folding rollers 107. In the sheet S having passed through the second folding nip N2, the second fold line F2 is formed (see FIG. 13).

[0078] FIG. 13 is a sectional view around the sheet folding unit 100, showing the fourth stage of the progress of the inward triple-folding of the sheet S. As shown in FIG. 13, the sheet S having passed through the second folding nip N2 is conveyed, with a part of it corresponding to the second fold line F2 as the leading end and with three areas extending along the sheet conveyance direction overlapping with one another, along the second folding conveyance passage 106 in the direction away from the pair of second folding rollers 107. An upstream part, in the sheet conveyance direction, of the sheet S having passed through the second folding conveyance passage 106 enters the junction portion 33. At this time, in the junction portion 33, by the first switching guide 311 arranged in the first position, the sheet S is guided to the first sheet conveyance passage 3 and is discharged through the first discharge port 41 to the first sheet discharge portion 4 (see FIG. 2).

[0079] When the folding process is performed on the sheet S in the sheet folding unit 100, the post-processing control portion 10 first guides a downstream part, in the sheet conveyance direction, of the sheet S conveyed through the sheet loading port 2 into the first sheet conveyance passage 3 from the first branch portion 31 into the second sheet conveyance passage 5 and then, with the conveyance direction of the sheet S reversed, guides the sheet S to the sheet folding unit 100 to perform the folding process on the sheet S. Then the post-processing control portion 10 lets the sheet S having undergone the folding process join the first sheet conveyance passage 3 at the junction portion 33.

[0080] While the above description deals with the inward triple-folding of the sheet S, the Z-folding of the sheet S shown in FIG. 3 and the outward triple-folding of the sheet S shown in FIG. 4 can be performed in similar manners by the procedure shown in FIGS. 7 to 13 with the timing of forming the first and second fold lines F1 and F2 in the sheet S changed appropriately.

[0081] When the sheet S is double-folded, in a state where the first folding guide 104 is arranged at the folding position as shown in FIGS. 8 and 9, the sheet S is conveyed into the sheet folding unit 100. Thus the leading end of the sheet S is guided along the first folding guide 104 and the second roller 112 to the first folding nip N1 (see FIG. 14). Next, the sheet S is stopped at a position where it at its middle faces the second folding nip N2 in the pair of second folding rollers 107. In this state, the second folding guide 108 is moved in the direction toward the second folding nip N2 to make contact with the sheet S so that the middle of the sheet S is guided to the second folding nip N2 in the pair of second folding rollers 107. In this way, a folding line is formed in the sheet S having passed through the second folding nip N2, that is, double-folding is performed.

[0082] FIG. 14 is an enlarged sectional part view around the pair of first folding rollers 103 and the pair of second folding rollers 107. In this embodiment, the first roller (driving roller) 111 is supported so as to be rotatable about a rotation shaft 111a. The second roller (driven roller) 112 is supported so as to be rotatable about a rotation shaft 112a. The opposite ends of the rotation shaft 112a in the axial direction are rotatably supported at one end of a supporting portion 112c. The other end of the supporting portion 112c is pivotably supported on a pivoting shaft 112b. Thus the second roller 112 is supported so as to be pivotable about the pivoting shaft 112b.

[0083] The first folding nip NI is formed as a result of the second roller (driven roller) 112 pivoting about the pivoting shaft 112b to be pressed against the first roller (driving roller) 111.

[0084] Likewise, the third roller (driven roller) 113 is supported so as to be rotatable about a rotation shaft 113a. The opposite ends of the rotation shaft 112a in the axial direction are rotatably supported at one end of a supporting portion (not shown). The other end of the supporting portion is pivotably supported on a pivoting shaft (not shown). In this way, the third roller 113 is supported so as to be pivotable about the pivoting shaft (not shown). The second folding nip N2 is formed as a result of the third roller (driven roller) 113 pivoting about the pivoting shaft (not shown) to be pressed against the first roller (driving roller) 111.

[0085] In this embodiment, to the pivoting shaft 112b of the second roller (driven roller) 112, a driving shaft of a driving motor (not shown) is directly coupled. To the pivoting shaft 112b, a driving output gear 132 is coaxially coupled and, to the rotation shaft 111a of the first roller (driving roller) 111, a driving input gear 136 is coaxially coupled. The driving output and input gears 132 and 136 are coupled together via driving transmission gears 133, 134, and 135. That is, the rotation shaft 111a of the first roller (driving roller) 111 is coupled to a driving shaft of a driving motor (not shown) via the driving transmission gears 133, 134, and 135.

[0086] In this embodiment, the driving transmission gears 133, 134, and 135 constitute a gear train that couples together the driving output gear 132 and the driving input gear 136, but the gear train can have any number of driving transmission gears other than three.

[0087] The driving output gear 132 meshes with the driving transmission gear 133 and the driving transmission gear 133 meshes with the driving transmission gear 134. The driving transmission gear 134 meshes with the driving transmission gear 135. The driving transmission gears 133, 134, and 135 are idle gears. The driving transmission gear 135 meshes with the driving input gear 136 and the driving transmission gear 133 meshes with the driving output gear 132.

[0088] A rotative driving force fed from the driving motor (not shown) is transmitted from the driving output gear 132 via the driving transmission gears 133, 134, and 135 to the driving input gear 136. Specifically, the driving motor (not shown) is rotated (rotated forward) so that the driving output gear 132 rotates forward (clockwise in FIG. 14), so the driving input gear 136 rotates forward (clockwise in FIG. 14) via the driving transmission gears 133, 134, and 135 and the first roller (driving roller) 111 rotates forward (clockwise in FIG. 14). The second roller (driven roller) 112 is pressed against the first roller (driving roller) 111. In this way, when the double-folded sheet passes through the first folding nip (nip portion) N1, the second roller (driven roller) 112 is prevented from moving away from the first roller (driving roller) 111. It is thus possible to reduce variation of the gear pitch and enhance the speed and quietness of the folding process for the sheet. By using a single power source to rotate the first roller (driving roller) 111 and the second roller (driven roller) 112, it is possible to make the apparatus compact and reduce the number of components of the apparatus.

[0089] The embodiment of the present disclosure described above is not meant to limit the scope of the disclosure, which can thus be implemented with various modifications made without departing from the spirit of the present disclosure. For example, in the embodiment described above, to the pivoting shaft 112b of the second roller (driven roller) 112, the driving shaft of the driving motor (not shown) is directly coupled; instead, to the rotation shaft 111a of the first roller (driving roller) 111, the driving shaft of the driving motor (not shown) may be directly coupled.

[0090] That is, to one of the rotation shaft 111a of the first roller (driving roller) 111 and the pivoting shaft 112b of the second roller (driven roller) 112, the driving shaft of the driving motor may be directly coupled and the other of the rotation shaft 111a of the first roller (driving roller) 111 and the pivoting shaft 112b of the second roller (driven roller) 112 may be coupled to the driving shaft via the driving transmission gears 133, 134, and 135.

[0091] While this embodiment deals with the formation of the first folding nip N1, the second folding nip N2 can be formed in a similar manner. That is, to one of the rotation shaft 111a of the first roller (driving roller) 111 and the pivoting shaft (not shown) of the third roller (driven roller) 113, the driving shaft of the driving motor may be directly coupled and the other of the rotation shaft 111a of the first roller (driving roller) 111 and the pivoting shaft (not shown) of the second roller (driven roller) 112 may be coupled to the driving shaft via driving transmission gears (not shown). In that case, if a plurality of driving motors are provided, to the pivoting shafts, the rotation shafts of the driving motors are directly coupled, respectively.

[0092] While the above description deals with an example where the sheet folding unit 100 includes the pair of first folding rollers 103 and the pair of second folding rollers 107 comprising three rollers, namely the first to third rollers 111 to 113, this is not meant to limit the present disclosure; a configuration is also possible where the sheet folding unit 100 includes only the pair of first folding roller 103 comprising the first and second rollers 111 and 112.

[0093] The present disclosure is applicable to sheet post-processing apparatuses that perform a folding process to form a folding line in a sheet.