BACKGROUND
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The present disclosure relates to a sheet folding apparatus and an image forming system.
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A known sheet folding apparatus is coupled to an image forming apparatus. The image forming apparatus prints an image on a sheet and feeds the printed sheet to the sheet folding apparatus. The sheet folding apparatus can perform a folding process to fold the printed sheet.
SUMMARY
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According to one aspect of the present disclosure, a sheet folding apparatus includes a main conveying passage, a first folding conveying passage, a pair of first switchback rollers, a folding portion, and a control portion. Along the main conveying passage, a sheet is conveyed. The first folding conveying passage branches off from the main conveying passage, and, in a folding process performed on the sheet, the sheet is drawn out of the main conveying passage into the first folding conveying passage. The pair of first switchback rollers forms a first switchback nip that nips the sheet at a position on the main conveying passage downstream, along the sheet conveying direction, of a first drawing position at which the first folding conveying passage branches off. The pair of first switchback rollers can rotate forward and reverse. The pair of first switchback rollers, by rotating forward, conveys the sheet downstream along the sheet conveying direction. The folding portion performs the folding process. The control portion controls the folding process. The folding portion includes a first roller, a second roller, and a third roller. The second roller is in pressed contact with the first roller at a position on the main conveying passage upstream of the first drawing position along the sheet conveying direction so as to be rotatable together with the first roller. The second roller forms a conveyance nip together with the first roller. The second roller, when the folding portion is driven, rotates in such a direction as to convey the sheet toward the first drawing position. The third roller is in pressed contact with the second roller at a position on the first folding conveying passage downstream of the first drawing position along the sheet drawing direction so as to be rotatable together with the second roller. The third roller forms a first folding nip together with the second roller. The third roller, when the folding portion is driven, rotates in such a direction as to draw the sheet out of the main conveying passage into the first folding conveying passage. When making the folding portion perform the folding process, the control portion drives the folding portion and rotates the pair of first switchback rollers forward and thereby conveys the sheet along the main conveying passage. After the leading edge of the sheet passes through the first switchback nip, the control portion stops driving the folding portion and stops rotating the pair of first switchback rollers forward and thereby stops conveying the sheet. After stopping conveying the sheet, the control portion starts rotating the pair of first switchback rollers reverse and restarts driving the folding portion and thereby draws a slack part of the sheet that develops at the first drawing position into the first folding nip to form a first folding line on the sheet. In the folding process, when the slack part of the sheet is drawn into the first folding nip, the control portion first starts rotating the pair of first switchback rollers reverse and then restarts driving the folding portion.
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According to another aspect of the present disclosure, an image forming system includes the sheet folding apparatus and an image forming apparatus. The image forming apparatus prints an image on the sheet and feeds the printed sheet to the sheet folding apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
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- Fig. 1 is an external appearance of an image forming system according to the embodiment.
- Fig. 2 is a schematic diagram showing the internal structure of a sheet postprocessing apparatus according to the embodiment.
- Fig. 3 is a schematic diagram of a sheet Z-folded in the sheet postprocessing apparatus according to the embodiment.
- Fig. 4 is a block diagram of a mechanism relating to a folding process performed in the sheet postprocessing apparatus according to the embodiment.
- Fig. 5 is a schematic diagram of a folding portion and its vicinity in the sheet postprocessing apparatus according to the embodiment.
- Fig. 6 is a schematic diagram for illustration of the folding process performed in the sheet postprocessing apparatus according to the embodiment.
- Fig. 7 is a schematic diagram for illustration of the folding process performed in the sheet postprocessing apparatus according to the embodiment.
- Fig. 8 is a schematic diagram for illustration of the folding process performed in the sheet postprocessing apparatus according to the embodiment.
- Fig. 9 is a graph for illustration of tests conducted to check the effects of the embodiment.
DETAILED DESCRIPTION
< Configuration of an Image Forming System >
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As shown in Fig. 1, an image forming system 100S according to an embodiment includes a sheet postprocessing apparatus 100 and an image forming apparatus 200. The sheet postprocessing apparatus 100 is coupled to the image forming apparatus 200. Coupled to the image forming apparatus 200, the sheet postprocessing apparatus 100 together with the image forming apparatus 200 constitutes the image forming system 100S.
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For example, the sheet postprocessing apparatus 100 is an optional apparatus and can be attached to and detached from the image forming apparatus 200. The sheet postprocessing apparatus 100 is disposed outside the image forming apparatus 200. This, however, is not meant as any limitation. The sheet postprocessing apparatus 100 can be incorporated in the image forming apparatus 200.
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The image forming apparatus 200 is a multifunction peripheral having copying and other functions. The image forming apparatus 200 can instead be a printer. The image forming apparatus 200 conveys a sheet S (not shown in Fig. 1) and prints an image on the sheet S being conveyed. The image forming apparatus 200 feeds the printed sheet S to the sheet postprocessing apparatus 100. The type of sheet S is not particularly limited.
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The image forming apparatus 200 includes a printing portion (not shown). The printing portion prints an image on a sheet S. The printing portion can perform printing by an inkjet method or by an electrophotographic method.
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In a case where the printing portion prints by an inkjet method, the printing portion at least includes an ink head. The printing portion prints an image on a sheet S with ink. That is, the printing portion ejects ink toward the sheet S and attaches the ink to the sheet S.
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In a case where the printing portion prints by an electrophotographic method, the printing portion includes a photosensitive drum, a charging device, a developing device, an exposure device, a transfer roller, etc. The printing portion prints an image on a sheet S with toner. That is, the printing portion forms an electrostatic latent image and transfers to the sheet S a toner image obtained by developing the electrostatic latent image.
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The sheet postprocessing apparatus 100 receives a sheet S from the image forming apparatus 200. The sheet postprocessing apparatus 100 conveys the sheet S and performs, as post processing, a punching process, a folding process, a stapling process, a booklet process, and the like on the sheet S. The processes specifically mentioned are merely examples and not all of them need to be available. Any other process can be available as postprocessing.
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The sheet postprocessing apparatus 100 can be configured to be usable alone. In that case, the sheet postprocessing apparatus 100 is provided with a set tray to set a sheet S on. The sheet S set on the set tray is carried into the sheet postprocessing apparatus 100, which then performs postprocessing on the sheet S.
< Configuration of a Sheet Postprocessing Apparatus >
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As shown in Fig. 2, the sheet postprocessing apparatus 100 is installed on a substantially flat floor surface FL. The direction perpendicular to the floor surface FL (i.e., vertical direction) is the top-bottom direction of the sheet postprocessing apparatus 100. Of directions parallel to the floor surface FL (i.e., horizontal directions), the direction perpendicular to the plane of Fig. 2 is the front-rear direction of the sheet postprocessing apparatus 100, and the left-right direction in Fig. 2 is the left-right direction of the sheet postprocessing apparatus 100.
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The sheet postprocessing apparatus 100 has a carry-in port 1000, a main discharge port 101, and a subsidiary discharge port 102. The sheet postprocessing apparatus 100 also has a main tray T1 and a subsidiary tray T2.
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The carry-in port 1000 is provided at the side of the sheet postprocessing apparatus 100 at which it is coupled to the image forming apparatus 200. Via the carry-in port 1000, a sheet S is fed from the image forming apparatus 200 to the sheet postprocessing apparatus 100. The main discharge port 101 and the subsidiary discharge port 102 are provided at the side of the sheet postprocessing apparatus 100 opposite from its side at which it is coupled to the image forming apparatus 200. Via either the main discharge port 101 or the subsidiary discharge port 102, the sheet S is discharged out of the sheet postprocessing apparatus 100.
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The main tray T1 and the subsidiary tray T2 are provided at the side of the sheet postprocessing apparatus 100 opposite from its side at which it is coupled to the image forming apparatus 200. Above the main tray T1, the subsidiary tray T2 is disposed. The sheet postprocessing apparatus 100 discharges the sheet S to the main tray T1 or the subsidiary tray T2 to stack it on the destination tray. On the main tray T1, the sheet S discharged through the main discharge port 101 is stacked; on the subsidiary tray T2, the sheet S discharged through the subsidiary discharge port 102 is stacked.
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The sheet postprocessing apparatus 100 has a main conveying passage P1 and a subsidiary conveying passage P2. The main conveying passage P1 and the subsidiary conveying passage P2 are conveying passages for the sheet S. The main conveying passage P1 extends substantially parallel from the carry-in port 1000 to reach the main discharge port 101. The subsidiary conveying passage P2 branches diagonally upward to the left from the main conveying passage P1 to reach the subsidiary discharge port 102.
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The sheet postprocessing apparatus 100 conveys the sheet S from the carry-in port 1000 toward the main tray T1 or the subsidiary tray T2. When the sheet S is stacked on the main tray T1, the sheet postprocessing apparatus 100 conveys the sheet S along the main conveying passage P1. When the sheet S is stacked on the subsidiary tray T2, the sheet postprocessing apparatus 100 directs the sheet S conveyed along the main conveying passage P1 to the subsidiary conveying passage P2 and then conveys the sheet S along the subsidiary conveying passage P2. In the following description, the conveying direction of the sheet S conveyed along the main conveying passage P1 (or subsidiary conveying passage P2) is referred to simply as the "sheet conveying direction."
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The sheet postprocessing apparatus 100 is provided with a punching unit PU, a stapling unit SU, and a booklet unit BU. The punching unit PU, the stapling unit SU, and the booklet unit BU each perform corresponding postprocessing on the sheet S.
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The punching unit PU is disposed at an upstream part of the main conveying passage P1 along the sheet conveying direction (in other words, near the carry-in port 1000). The punching unit PU performs as postprocessing a punching process to perforate the sheet S. Through the punching process, a punch hole is formed in the sheet S.
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The stapling unit SU performs as postprocessing a stapling process to bind a bundle of sheets S with a staple. In the stapling process, the sheet S in the main conveying passage P1 is directed to a processing tray PT. On the processing tray PT, a plurality of sheets S are stacked. The stapling unit SU performs the stapling process on the plurality of sheets S stacked on the processing tray PT.
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The booklet unit BU performs as postprocessing a booklet-forming process to middle-fold a middle-bound bundle of sheets S. The booklet unit BU includes a stapling portion for middle-binding and, operating this stapling portion, it middle-binds the bundle of sheets S with a staple.
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The sheet postprocessing apparatus 100 has a booklet conveying passage P3 that branches off the main conveying passage P1 to extend downward. The booklet conveying passage P3 leads to the booklet unit BU. When the booklet-forming process is performed, the sheet S is conveyed via the booklet conveying passage P3 to the booklet unit BU.
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The sheet postprocessing apparatus 100 further has a booklet tray T3. The booklet tray T3 is provided at the side of the sheet postprocessing apparatus 100 opposite from its side at which it is coupled to the image forming apparatus 200. The booklet tray T3 is disposed below the main tray T1. To the booklet tray T3, the booklet produced through the booklet-forming process is discharged.
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Here, the sheet postprocessing apparatus 100 is provided with a folding portion 1. That is, the sheet postprocessing apparatus 100 corresponds to a "sheet folding apparatus." The folding portion 1 performs, as postprocessing, a folding process to fold a sheet S. The folding portion 1 conveys a sheet S folded through a folding process toward the main discharge port 101. This will be described in detail later.
< Configuration of a Pair of Conveying Rollers >
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As shown in Fig. 2, the sheet postprocessing apparatus 100 includes a plurality of pairs of conveying rollers. The plurality of pairs of conveying rollers each include a pair of rollers that are kept in pressed contact with each other. The plurality of pairs of conveying rollers each convey the sheet S by rotating with the sheet S nipped between the pair of rollers.
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The sheet postprocessing apparatus 100 includes, as one pair of conveying rollers, a pair of discharge rollers 2. The pair of discharge rollers 2 is disposed in the main conveying passage P1. The pair of discharge rollers 2 forms a discharge nip in the main discharge port 101. That is, the pair of discharge rollers 2 is disposed in the main discharge port 101. The pair of discharge rollers 2 nips the sheet S (which can be a bundle of sheets S on the processing tray PT) in the main discharge port 101 and conveys the sheet S to discharge it through the main discharge port 101. The sheet S discharged through the main discharge port 101 is stacked on the main tray T1.
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The pair of discharge rollers 2 includes an upper roller 21 and a lower roller 22. The upper roller 21 is disposed above the main conveying passage P1 and the lower roller 22 is disposed below the main conveying passage P1. The upper and lower rollers 21 and 22 face each other across the main conveying passage P1 and are kept in pressed contact with each other. For example, the lower roller 22 has a discharge motor (not shown) coupled to it; as the discharge motor operates, the lower roller 22 rotates and, following it, the upper roller 21 rotates. The pair of discharge rollers 2 nips the sheet S between the upper and lower rollers 21 and 22. As the pair of discharge rollers 2 rotates in this state, the sheet S is discharged through the main discharge port 101.
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The upper roller 21 is rotatably supported on one end part of a roller arm (not shown). The roller arm is pivotable such that one end part of it swings up and down about a rotation shaft provided in another end part of it. Thus, the upper roller 21 can be separated from the lower roller 22, and the upper roller 21 can be brought into pressed contact with the lower roller 22. When the sheet S is discharged to the main tray T1, the upper and lower rollers 21 and 22 are in pressed contact with each other with the sheet S held in between.
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The sheet postprocessing apparatus 100 includes, as one pair of conveying rollers, a pair of intermediate rollers 20. The pair of intermediate rollers 20 is disposed at a part of the main conveying passage P1 upstream of the pair of discharge rollers 2 along the sheet conveying direction, downstream of the punching unit PU along the sheet conveying direction. The pair of intermediate rollers 20 forms a nip in the main conveying passage P1. The pair of intermediate rollers 20 rotates while nipping the sheet S to convey the sheet S toward the main discharge port 101.
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The pair of intermediate rollers 20 is disposed downstream of the folding portion 1 along the sheet conveying direction. Specifically, the pair of intermediate rollers 20 is disposed at a part of the main conveying passage P1 downstream of a junction position P30 (described later) along the sheet conveying direction. Here, the sheet S having undergone the folding process is returned from the junction position P30 to the main conveying passage P1. Thus, when the folding process is performed on the sheet S, the sheet S is conveyed by the pair of intermediate rollers 20 toward the main discharge port 101.
< Configuration of and Around the Folding Portion >
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As shown in Fig. 2, the folding portion 1 is disposed downstream of the punching unit PU along the sheet conveying direction. The folding portion 1 performs the folding process on the sheet S conveyed to it from the punching unit PU. The folding process can be performed on a sheet S having a punch hole formed in it or on a sheet S having no punch hole formed in it.
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One folding process that the folding portion 1 can perform is a process of Z-folding the sheet S. Performing this process as the folding process yields a sheet S as shown in Fig. 3. In the following description, a Z-folded sheet S is identified by the symbol Sz and such a sheet S is referred to as a Z-folded sheet Sz.
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The Z-folded sheet Sz has, at its front edge (i.e., downstream along the sheet conveying direction), a part folded in a Z-shape. Specifically, the Z-folded sheet Sz has a first folding line F1 and a second folding line F2. The Z-folded sheet Sz has a first part S1 and a second part S2 as Z-folded parts. The part from the front edge of the Z-folded sheet Sz to the first folding line F1 is the first part S1, and the part from the first folding line F1 to the second folding line F2 is the second part S2. The first and second parts S1 and S2 face each other.
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The folding process by the folding portion 1 is controlled by a control portion 3 (see Fig. 4). That is, the sheet postprocessing apparatus 100 includes a control portion 3. The control portion 3 controls the postprocessing performed on the sheet postprocessing apparatus 100.
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The control portion 3 includes processing circuits such as a CPU and an ASIC. The control portion 3 also includes a storage device such as a ROM and a RAM. The control portion 3 communicates with the main control portion (not shown) in the image forming apparatus 200. From the main control portion, the control portion 3 receives job information. The job information includes information on the postprocessing to be performed on the sheet postprocessing apparatus 100 and information on the number of copies and sheets to be printed. Based on these kinds of information, the control portion 3 controls the sheet postprocessing apparatus 100. For example, the control portion 3 controls driving sources such as motors and solenoids provided in the sheet postprocessing apparatus 100.
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Fig. 4 shows one example of the driving sources controlled by the control portion 3. As such driving sources, the sheet postprocessing apparatus 100 at least includes a first switchback motor M1, a second switchback motor M2, and a folding motor Mf. The first and second switchback motors M1 and M2 can each rotate forward and reverse.
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As shown in Fig. 5, the sheet postprocessing apparatus 100 has a first folding conveying passage FP1 and a second folding conveying passage FP2. When the folding portion 1 performs the folding process, the sheet S is drawn out of the main conveying passage P1 into the first folding conveying passage FP1. After that, the sheet S is drawn out of the first folding conveying passage FP1 into the second folding conveying passage FP2. In other words, when the folding portion 1 performs the folding process, the sheet S is drawn into the folding portion 1.
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The first folding conveying passage FP1 is part of the booklet conveying passage P3. The first folding conveying passage FP1 branches off the main conveying passage P1 to extend downward. The first folding conveying passage FP1 branches off the main conveying passage P1 at a position P10 on the main conveying passage P1. The position P10 corresponds to a "first drawing position." In the following description the position P10 is referred to as the first drawing position P10.
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The folding portion 1 has a first folding nip FN1 in the first folding conveying passage FP1. In the folding process by the folding portion 1, a part of the sheet S where the first folding line F1 is to be formed is, at the first drawing position P10, drawn into the first folding nip FN1. This forms the first folding line F1 in the sheet S. In the following description, the traveling direction of the sheet S being drawn out of the main conveying passage P1 into the first folding conveying passage FP1 is referred to as the sheet drawing direction. The direction leading from the first drawing position P10 via the first folding nip FN1 to a second switchback nip SN2 (described later) is the sheet drawing direction.
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The second folding conveying passage FP2 branches off the first folding conveying passage FP1 at a position P20 on the first folding conveying passage FP1 downstream of the first folding nip FN1 along the sheet drawing direction. The position P20 corresponds to a "second drawing position." In the following description, the position P20 is referred to as the second drawing position P20.
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The folding portion 1 has a second folding nip FN2 in the second folding conveying passage FP2. In the folding process by the folding portion 1, a part of the sheet S where the second folding line F2 is to be formed is drawn, at the second drawing position P20, into the second folding nip FN2. This forms the second folding line F2 in the sheet S. In this way, the Z-folded sheet Sz with the first and second folding lines F1 and F2 is obtained.
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The second folding conveying passage FP2 joins the main conveying passage P1 at the position P30 on the main conveying passage P1. The position P30 corresponds to a "junction position." In the following description, the position P30 is referred to as the junction position P30. The junction position P30 is a position on the main conveying passage P1 downstream of the first drawing position P10 along the sheet conveying direction (specifically a position downstream of a first switchback nip SN1 (described later) along the sheet conveying direction), upstream of the nip position in the pair of intermediate rollers 20 along the sheet conveying direction. The second folding nip FN2 is located between the second drawing position P20 and the junction position P30 on the second folding conveying passage FP2.
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Once drawn, at the second drawing position P20, into the second folding nip FN2, the sheet S is conveyed along the second folding conveying passage FP2. Then the sheet S (i.e., the Z-folded sheet Sz) being conveyed along the second folding conveying passage FP2 returns at the junction position P30 to the main conveying passage P1. In the following description, the conveying direction of the sheet S in the second folding conveying passage FP2 is referred to as the joining direction. The direction from the second drawing position P20 via the second folding nip FN2 toward the junction position P30 is the joining direction, and the sheet S is conveyed along the joining direction.
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The folding portion 1 includes a folding roller train 10 including a plurality of rollers. The folding roller train 10 includes a first roller R1, a second roller R2, a third roller R3, and a fourth roller R4. For example, in the folding roller train 10, the second or third roller R2 or R3 is coupled to the folding motor Mf (see Fig. 4). That is, in the folding roller train 10, the second or third roller R2 or R3 is a driving roller; and the other rollers are driven rollers that follow the driving roller to rotate. Note that the folding motor Mf can be coupled to the first or fourth roller R1 or R4.
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The first and second rollers R1 and R2 are disposed opposite each other across the main conveying passage P1. The second and third rollers R2 and R3 are disposed opposite each other across the first folding conveying passage FP1. The third and fourth rollers R3 and R4 are disposed opposite each other across the second folding conveying passage FP2.
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The second roller R2 is in pressed contact with the first roller R1 at a position on the main conveying passage P1 upstream of the first drawing position P10 along the sheet conveying direction and forms together with the first roller R1 a conveyance nip N0 in the main conveying passage P1. Note that the first roller R1 is disposed above the main conveying passage P1 and the second roller R2 is disposed below the main conveying passage P1. The second roller R2 makes pressed contact with the first roller R1 from below.
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In pressed contact with the first roller R1, the second roller R2 can rotate together with it. Driving the folding portion 1 (specifically, the folding motor Mf) makes the second roller R2 rotate together with the first roller R1 in the direction along which the sheet S at the conveyance nip N0 is conveyed toward the first drawing position P10.
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The third roller R3 is disposed downstream of the second roller R2 along the sheet conveying direction, below the main conveying passage P1. The third roller R3 does not convey the sheet S in the main conveying passage P1. The third roller R3 is in pressed contact with the second roller R2 at a position on the first folding conveying passage FP1 downstream of the first drawing position P10 along the sheet drawing direction and forms together with the second roller R2 a first folding nip FN1 in the first folding conveying passage FP1.
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In pressed contact with the second roller R2, the third roller R3 can rotate together with it. Driving the folding portion 1 (specifically, the folding motor Mf) makes the third roller R3 rotate together with the second roller R2 in the direction along which the sheet S in the main conveying passage P1 is drawn at the first drawing position P10 into the first folding conveying passage FP1 (i.e., the first folding nip FN1). In other words, driving the folding portion 1 (specifically, the folding motor Mf) makes the third roller R3 rotate together with the second roller R2 in the direction along which the sheet S at the first folding nip FN1 is conveyed toward the second drawing position P20.
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The fourth roller R4 is disposed below the second folding conveying passage FP2. The third roller R3 is disposed above the second folding conveying passage FP2. That is, the fourth roller R4 is disposed below the third roller R3. The fourth roller R4 is in pressed contact with the third roller R3 from below at a position on the second folding conveying passage FP2 downstream of the second drawing position P20 along the joining direction (but upstream of the junction position P30 along the joining direction) and forms together with the third roller R3 the second folding nip FN2 in the second folding conveying passage FP2.
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In pressed contact with the third roller R3, the fourth roller R4 can rotate together with it. Driving the folding portion 1 (specifically, the folding motor Mf) makes the fourth roller R4 rotate together with the third roller R3 in the direction along which the sheet S in the first folding conveying passage FP1 is drawn at the second drawing position P20 into the second folding conveying passage FP2 (i.e., the second folding nip FN2). In other words, driving the folding portion 1 (specifically, the folding motor Mf) makes the fourth roller R4 rotate together with the third roller R3 in the direction along which the sheet S at the second folding nip FN2 is conveyed toward the junction position P30.
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Driving the folding portion 1 (specifically, the folding motor Mf) makes the first to fourth rollers R1 to R4 all rotate. In Fig. 5, the first roller R1 rotates clockwise; the second roller R2, counterclockwise; the third roller R3, clockwise; and the fourth roller R4, counterclockwise.
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The sheet postprocessing apparatus 100 includes a pair of first switchback rollers 11. The pair of first switchback rollers 11 includes a pair of rollers disposed opposite each other across the main conveying passage P1. In pressed contact with each other, the pair of rollers in the pair of first switchback rollers 11 forms the first switchback nip SN1 in the main conveying passage P1.
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The first switchback nip SN1 is located at a part of the main conveying passage P1 downstream of the first drawing position P10 along the sheet conveying direction, upstream of the junction position P30 along the sheet conveying direction. That is, the pair of first switchback rollers 11 nips the sheet S at a position on the main conveying passage P1 downstream of the first drawing position P10 along the sheet conveying direction (but at a position upstream of the junction position P30 along the sheet conveying direction).
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The pair of first switchback rollers 11 is coupled to the first switchback motor M1 (see Fig. 4) and rotates with motive power transmitted from it. That is, the pair of first switchback rollers 11 can rotate forward and reverse. One roller of the pair of first switchback rollers 11 is a driving roller coupled to the first switchback motor M1 and the other roller is a driven roller that follows the one roller to rotate.
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Rotating the pair of first switchback rollers 11 forward causes the sheet S at the first switchback nip SN1 to be conveyed from upstream to downstream along the sheet conveying direction. On the other hand, rotating the pair of first switchback rollers 11 reverse causes the sheet S at the first switchback nip SN1 to be conveyed in the direction opposite to the sheet conveying direction. In other words, rotating the pair of first switchback rollers 11 reverse causes the sheet S at the first switchback nip SN1 to be switched back.
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The sheet postprocessing apparatus 100 includes a pair of second switchback rollers 12. The pair of second switchback rollers 12 includes a pair of rollers disposed opposite each other across the first folding conveying passage FP1. In pressed contact with each other, the pair of rollers of the pair of second switchback rollers 12 forms a second switchback nip SN2 in the first folding conveying passage FP1.
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The second switchback nip SN2 is located at a part of the first folding conveying passage FP1 downstream of the second drawing position P20 along the sheet drawing direction. That is, the pair of second switchback rollers 12 nips the sheet S at a position on the first folding conveying passage FP1 downstream of the second drawing position P20 along the sheet drawing direction.
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The pair of second switchback rollers 12 is coupled to the second switchback motor M2 (see Fig. 4) and rotates with motive power transmitted from it. That is, the pair of second switchback rollers 12 can rotate forward and reverse. One roller of the pair of the second switchback rollers 12 is a driving roller coupled to the second switchback motor M2, and the other roller is a driven roller that follows the one roller to rotate.
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Rotating the pair of second switchback rollers 12 forward causes the sheet S at the second switchback nip SN2 to be conveyed from upstream to downstream along the sheet drawing direction. On the other hand, rotating the pair of second switchback rollers 12 reverse causes the sheet S at the second switchback nip SN2 to be conveyed in the direction opposite to the sheet drawing direction. In other words, rotating the pair of second switchback rollers 12 reverse causes the sheet S at the second switchback nip SN2 to be switched back.
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The folding portion 1 includes a first guide G1 and a second guide G2. The first guide G1 is disposed at the first drawing position P10. The second guide G2 is disposed at the second drawing position P20.
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The first guide G1 is coupled to a first guide drive mechanism (not shown). The first guide drive mechanism includes a drive source to drive the first guide G1. The type of drive source is not particularly limited, and thus a motor, a solenoid, or the like can be used. With motive power transmitted from the first guide drive mechanism, the first guide G1 can move between a first separate position and a first close position. The control portion 3 controls the first guide drive mechanism to move the first guide G1 appropriately.
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The position of the first guide G1 in Fig. 5 is the first separate position. That is, the first separate position is a position where the first guide G1 is away from the first folding nip FN1. On the other hand, the first close position is a position where the first guide G1 is closer to the first folding nip FN1 than (when it is) at the first separate position (the position of the first guide G1 in Fig. 6). While details will be given later, when a slack part of the sheet S that develops at the first drawing position P10 is drawn into the first folding nip FN1, the first guide G1 moves from the first separate position to the first close position to lead the slack part of the sheet S to the first folding nip FN1.
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The second guide G2 is coupled to a second guide drive mechanism (not shown). The second guide drive mechanism includes a drive source to drive the second guide G2. The type of drive source is not particularly limited, and thus a motor, a solenoid, or the like can be used. With motive power transmitted from the second guide drive mechanism, the second guide G2 can move between a second separate position and a second close position. The control portion 3 controls the second guide drive mechanism to move the second guide G2 appropriately.
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The position of the second guide G2 in Fig. 5 is the second separate position. That is, the second separate position is a position where the second guide G2 is away from the second folding nip FN2. On the other hand, the second close position is a position where the second guide G2 is closer to the second folding nip FN2 than (when it is) in the second separate position (the position of the second guide G2 in Fig. 7). While details will be given later, when a slack part of the sheet S that develops at the second drawing position P20 is drawn into the second folding nip FN2, the second guide G2 moves from the second separate position to the second close position to lead the slack part of the sheet S to the second folding nip FN2.
< Z-Folding of Sheet >
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Now, with reference to Figs. 5 to 7, the folding process by the folding portion 1 will be described. The folding process described below is a process to Z-fold the sheet S. Note that, in Figs. 6 and 7, to be referred to in conjunction with Fig. 5, the reference signs for the first and second drawing positions P10 and P20 are omitted.
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When no folding process is performed on the sheet S, the first guide G1 is held in the first separate position (see Fig. 5). With the first guide G1 held in the first separate position, by the first guide G1, the sheet S being conveyed along the main conveying passage P1 is guided toward the first switchback nip SN1. That is, the sheet S is not drawn into the first folding nip FN1. Thus, with no folding process performed on it, the sheet S is stacked on the processing tray PT. Or, without being stacked on the processing tray PT, the sheet S is discharged to and stacked on the main tray T1 or the subsidiary tray T2.
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On the other hand, when making the folding portion 1 perform the folding process, the control portion 3 holds the first guide G1 in the first separate position and the second guide G2 in the second separate position (see Fig. 5). In this state, the control portion 3 drives the folding portion 1. The control portion 3 also rotates the pairs of first and second switchback rollers 11 and 12 each forward. That is, the control portion 3 conveys the sheet S along the main conveying passage P1.
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Then, after the leading edge of the sheet S being conveyed along the main conveying passage P1 passes through the first switchback nip SN1, the control portion 3 stops driving the folding portion 1 and stops rotating the pair of first switchback rollers 11 forward. That is, the control portion 3 stops the conveyance of the sheet S.
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The time to stop the conveyance of the sheet S is set based on the length from the leading edge of the sheet S to the first folding line F1 on it (i.e., the length of the first part S1 in Fig. 3). Specifically, when, after the leading edge of the sheet S passes through the first switchback nip SN1, a part of the sheet S being conveyed along the main conveying passage P1 corresponding to the first folding line F1 reaches the first drawing position P10, the control portion 3 stops the conveyance of the sheet S. That is, the shorter the first part S1 of the sheet S, the earlier the time to stop the conveyance of the sheet S comes; the longer the first part S1 of the sheet S, the later the time to stop the conveyance of the sheet S comes.
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After stopping the conveyance of the sheet S, the control portion 3 starts rotating the pair of first switchback rollers 11 reverse. The control portion 3 restarts driving the folding portion 1; then it moves the first guide G1 from the first separate position to the first close position. In this way, the control portion 3 forms the first folding line F1 on the sheet S. Note that the time to start moving the first guide G1 from the first separate position to the first close position is the same as the time to start rotating the pair of first switchback rollers 11 reverse.
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As the pair of first switchback rollers 11 starts being rotated reverse, a part of the sheet S at the first switchback nip SN1 advances in the direction opposite to the sheet conveying direction. Meanwhile, as the folding portion 1 restarts being driven, a part of the sheet S at the conveyance nip N0 advances in the sheet conveying direction. Thus, part of the sheet S becomes slack at the first drawing position P10. At this time, as shown in Fig. 6, the first guide G1 moves from the first separate position to the first close position, so that the slack part of the sheet S that has developed at the first drawing position P10 is drawn into the first folding nip FN1, and the drawn part passes through the first folding nip FN1 in the sheet drawing direction. This forms the first folding line F1 on the sheet S.
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Subsequently, after the part of the sheet S at which the first folding line F1 is formed passes through the second switchback nip SN2, the control portion 3 stops driving the folding portion 1 and stops rotating the pair of second switchback rollers 12 forward. That is, the control portion 3 stops the conveyance of the sheet S drawn into the first folding nip FN1.
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The time to stop the conveyance of the sheet S drawn into the first folding nip FN1 is set based on the length from the first folding line F1 to the second folding line F2 on the sheet S (i.e., the length of the second part S2 in Fig. 3). Specifically, when, after the first folding line F1 on the sheet S passes through the second switchback nip SN2, a part of the sheet S drawn into the first folding nip FN1 corresponding to the second folding line F2 reaches the second drawing position P20, the control portion 3 stops the conveyance of the sheet S drawn into the first folding nip FN1. That is, the shorter the second part S2 of the sheet S drawn into the first folding nip FN1, the earlier the time to stop the conveyance of the sheet S comes; the longer the second part S2 of the sheet S drawn into the first folding nip FN1, the later the time to stop the conveyance of the sheet S comes.
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After stopping the conveyance of the sheet S drawn into the first folding nip FN1, the control portion 3 starts rotating the pair of second switchback rollers 12 reverse. The control portion 3 restarts driving the folding portion 1; then it moves the second guide G2 from the second separate position to the second close position. In this way, the control portion 3 forms the second folding line F2 on the sheet S. Note that the time to start moving the second guide G2 from the second separate position to the second close position is the same as the time to start rotating the pair of second switchback rollers 12 reverse.
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As the pair of second switchback rollers 12 starts being rotated reverse, a part of the sheet S at the second switchback nip SN2 advances in the direction opposite to the sheet drawing direction. Meanwhile, as the folding portion 1 restarts being driven, a part of the sheet S at the first folding nip FN1 advances in the sheet drawing direction. Thus, part of the sheet S becomes slack at the second drawing position P20. At this time, as shown in Fig. 7, the second guide G2 moves from the second separate position to the second close position, so that the slack part of the sheet S that has developed at the second drawing position P20 is drawn into the second folding nip FN2, and the drawn part passes through the second folding nip FN2 in the joining direction. This forms the second folding line F2 on the sheet S. In this way, the Z-folded sheet Sz is obtained.
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Subsequently, the Z-folded sheet Sz in the second folding conveying passage FP2 returns at the junction position P30 to the main conveying passage P1. When postprocessing is performed on the processing tray PT, the Z-folded sheet Sz is stacked on the processing tray PT, and, after the postprocessing on the processing tray PT, it is discharged through the main discharge port 101 to be stacked on the main tray T1. On the other hand, when no postprocessing is performed on the processing tray PT, the Z-folded sheet Sz is not stacked on the processing tray PT and is discharged from the main discharge port 101 to be stacked on the main tray T1.
< Time to Start Driving Rollers when Drawing Sheet into Folding Nip >
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In the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the first folding nip FN1, the control portion 3 starts rotating the pair of first switchback rollers 11 reverse and then restarts driving the folding portion 1. In other words, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the first folding nip FN1, the control portion 3 shifts the time to start rotating the pair of first switchback rollers 11 reverse from the time to restart driving the folding portion 1 (i.e., it starts rotating the pair of first switchback rollers 11 reverse earlier). In still other words, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the first folding nip FN1, the control portion 3 starts rotating the pair of first switchback rollers 11 reverse and, after a first predetermined period after that, restarts driving the folding portion 1. The first predetermined period is a period longer than 0 and is determined in advance by a manufacturer.
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In this way, in the embodiment, it is possible to prevent the displacement of the first folding line F1 formed on the sheet S from the target position. That is, it is possible to reduce variations among a plurality of sheets S in the position of the first folding line F1. For example, even if the driving mechanisms for the folding portion 1 and the pair of first switchback rollers 11 have variations in their components or deterioration over time, it is possible to prevent the displacement of the first folding line F1 formed on the sheet S from the target position. In addition, regardless of the types of sheet S subjected to the folding process, it is possible to prevent the displacement of the first folding line F1 formed on the sheet S from the target position.
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Specifically, in the embodiment, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the first folding nip FN1, a state occurs in which, with the folding portion 1 suspended from being driven, the pair of first switchback rollers 11 is rotated reverse. In this state, of the sheet S, a part at the conveyance nip N0 does not advance in the sheet conveying direction, and a part at the first switchback nip SN1 advances in the direction opposite to the sheet conveying direction.
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In this case, as shown in Fig. 8, the slack part of the sheet S that develops at the first drawing position P10 approaches the second roller R2. The slack part of the sheet S that has developed at the first drawing position P10 then aligns with the outer circumferential surface of the second roller R2. In other words, the slack part of the sheet S that develops at the first drawing position P10 makes contact with the outer circumferential surface of the second roller R2. Meanwhile, the folding portion 1 (i.e., the second roller R2) stays suspended from being driven. This positions the sheet S and stabilizes the position of the first folding line F1 formed on the sheet S.
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Suppose that the time to start rotating the pair of first switchback rollers 11 reverse is the same as the time to restart driving the folding portion 1. Then, without the sheet S being positioned, the slack part of the sheet S is drawn into the first folding nip FN1. Thus, for example, if either of the driving mechanisms for the folding portion 1 and the pair of first switchback rollers 11 has a variation in a component or deterioration over time, the position of the first folding line F1 to be formed tends to vary among the plurality of sheets S.
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Now, a description will be given of the results of tests conducted to check the effects of the embodiment. In the test, with each of different time lags from when the pair of first switchback rollers 11 started being rotated reverse to when the folding portion 1 restarted to be driven, the first folding line F1 was formed on a plurality of sheets S. For each sheet S, the length of the first part S1 was measured.
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Fig. 9 shows the results of the test. The vertical axis of the graph in the diagram represents the length (mm) of the first part S1 of the sheet S. Here, the time lag from when the pair of first switchback rollers 11 starts being rotated reverse to when the folding portion 1 restarts to be driven corresponds to the degree of slackness of the sheet S at the first drawing position P10. Thus, the horizontal axis in the graph shown in Fig. 9 represents the degree (mm) of slackness of the sheet S at the first drawing position P10. The smaller the degree of slackness of the sheet S at the first drawing position P10, the smaller the time lag from when the pair of first switchback rollers 11 starts being rotated reverse to when the folding portion 1 restarts to be driven.
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In the test, the smaller the time lag from when the pair of first switchback rollers 11 started being rotated reverse to when the folding portion 1 restarted to be driven (i.e., the smaller the degree of slackness of the sheet S at the first drawing position P10), the larger the variations in the length of the first part S1 observed among the plurality of sheets S. Specifically, when the time lag was zero from when the pair of first switchback rollers 11 started being rotated reverse to when the folding portion 1 restarted to be driven (in Fig. 9, at zero mm on the horizontal axis), the lengths of the first part S1 varied greatly with a maximum value of about 87 mm and a minimum value of about 84 mm.
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By contrast, with a certain time lag provided from when the pair of first switchback rollers 11 started being rotated reverse to when the folding portion 1 restarted to be driven, the lengths of the first part S1 varied little among the plurality of sheets S. Specifically, when, after the pair of first switchback rollers 11 started to be rotated reverse such that the sheet S had a slack part as large as about 8 mm, after a certain time lag, the folding portion 1 restarted to be driven (in Fig. 9, at eight mm on the horizontal axis), the lengths of the first part S1 varied little with a maximum value of about 82 mm and a minimum value of about 81 mm.
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The above observations reveal the following. In the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the first folding nip FN1, it is possible to reduce variations in the position of the first folding line F1 among the plurality of sheets S by first starting to rotate the pair of first switchback rollers 11 reverse and then restarting the folding portion 1.
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Note that, in the embodiment, control proceeds similarly when forming the second folding line F2 on the sheet S as when forming the first folding line F1 on the sheet S. That is, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the second folding nip FN2, the control portion 3 first starts rotating the pair of second switchback rollers 12 reverse and then restarts driving the folding portion 1. In other words, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the second folding nip FN2, the control portion 3 shifts the time to start rotating the pair of second switchback rollers 12 reverse from the time to restart driving the folding portion 1 (i.e., it starts rotating the pair of second switchback rollers 12 reverse earlier). In still other words, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the second folding nip FN2, the control portion 3 first starts rotating the pair of second switchback rollers 12 reverse and, after a second predetermined period after that, restarts driving the folding portion 1. The second predetermined period is a period longer than zero and is determined in advance by a manufacturer.
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In this way, in the embodiment, it is possible to prevent the displacement of the second folding line F2 formed on the sheet S from the target position. That is, it is possible to reduce variations among a plurality of sheets S in the position of the second folding line F2.
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In the embodiment, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the first folding nip FN1, the control portion 3 first starts rotating the pair of first switchback rollers 11 reverse and then, before the first guide G1 reaches the first close position from the first separate position, the control portion 3 restarts driving the folding portion 1. At that time, if the time to restart driving the folding portion 1 is too late, the slack part of the sheet S having developed at the first drawing position P10 is damaged. Thus, it is preferable to restart driving the folding portion 1 before the first guide G1 reaches the first close position from the first separate position.
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In the embodiment, in the folding process performed by the folding portion 1, when the slack part of the sheet S is drawn into the second folding nip FN2, the control portion 3 first starts rotating the pair of second switchback rollers 12 reverse and then, before the second guide G2 reaches the second close position from the second separate position, the control portion 3 restarts driving the folding portion 1. If the time to restart driving the folding portion 1 is too late, the slack part of the sheet S having developed at the second drawing position P20 is damaged. Thus, it is preferable to restart driving the folding portion 1 before the second guide G2 reaches the second close position from the second separate position.