Processing device and image forming device

Abstract

After post-processes have been performed on sheet bundles which have been stacked in a post-processing tray 16, the sheet bundles are alternately shifted in the paper conveyance lateral direction and each of these shifted sheet bundles are conveyed from the post-processing tray 16 to the discharge port by a sheet receiving member 18, and the sheet bundle is discharged in the shifted condition to a paper discharge tray 13 by a pair of discharge rollers 12 which are located at the discharge port. The pair of discharge rollers 12 have an upper discharge roller 22 and an opposing lower discharge roller 24 which open and close freely, and a solenoid for switching between a closed condition which grasps the sheet bundle and an opened condition which does not grasp the sheet bundle. The lower discharge roller 22 and the upper discharge roller 24 are closed by the solenoid 40 at predetermined timing based on the sheet size.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a post-processing device, and particularly a processing device which performs post-processing such as stapling of bundles of sheets onto which an image has been formed. The invention further relates to an image forming device such as a copier, printer, fax machine, or a multifunction machine thereof equipped with this post-processing device.

2. Background Information

Conventionally, post-processing devices are connected to or built into image forming devices such as multifunction machines or the like. These post-processing devices stack multiple sheets (copy paper, OHP film, or the like) which have completed printing on a post-processing tray, and then staple bundles of these sheets or perform sorting or the like in the post-processing tray.

With these post-processing devices, the sheet bundles must be smoothly discharged to a sheet discharge tray or the like external to the device in order to smoothly perform the alignment operation, which is a leading operation to the post-processes, and to prevent problems with bending, wrinkling, or tearing of the thick sheet bundles after the post-processing, and various technologies have been proposed for this purpose.

For instance, as shown in FIG. 7, the technology disclosed in Japanese Laid Open Patent Application No. 2002-167115 (Patent Reference 1) has a pair of discharge rollers 100 consisting of a bottom discharge roller 101 and a top discharge roller 102 which has a closed position where the rollers 101, 102 are in contact and form a nip, and an open position where both rollers 101, 102 are separated to allow passage of a sheet bundle. With these conventional post-processing devices 103, both rollers 101, 102 are mutually compressed by the forces of a spring 104 when the pair of discharge rollers 100 is in the closed position. Furthermore, the bottom discharge roller 101 and the top discharge roller 102 are separated against the force of the spring 104 when the pair of discharge rollers 100 is in the open position, and therefore bundles of large-size sheets (A3, B4, 11×17, 8.5×14 or the like) can easily pass through the pair of discharge rollers 100.

When the pair of discharge rollers 100 is in the open position, a lever 106 will rotate in the clockwise direction and the lead edge of the lever 106 will push down on the upstream side of an upper discharge guide 108, when a solenoid 105 is turned ON. Thereby the upper discharge guide 108 will rotate in the clockwise direction of the figure with a fixed shaft 107 as a fulcrum, and the upper discharge roller 102 will be moved above and away from the bottom discharge roller 101. Furthermore, when the upper discharge guide 108 rotates, the fulcrum shaft 109 will move downward and the bottom discharge guide 110 will rotate in the clockwise direction of the figure with a fulcrum shaft 111 as the fulcrum. Thereby the lower discharge guide 110 will move to the upper position until the top surface passes the outer circumference surface of the bottom discharge roller 101, and the sheet bundle is able to smoothly pass through without contacting the outer circumferential surface of the bottom discharge roller 101.

Furthermore, the technology disclosed in Japanese Laid Open Patent Application No. H11-92019 (Patent Reference 2) moves the pair of discharge rollers from the open state to the closed state (nip state) when the trailing end of the sheet bundle in the direction of conveyance reaches a position 80 mm before passing through the pair of discharge rollers, and closes the pair of discharge rollers after most of the sheet bundle has passed through the pair of discharge rollers (open state) in order to minimize vertical staggering of the sheet bundle.

However, with the conventional technology of Patent Reference 1, when a small size sheet bundle is discharged with the lower discharge roller 101 and the upper discharge roller 102 of the pair of discharge rollers 100 in the closed state (nip state), the sheet bundle will be vertically staggered, the staggering force will act on the stapling region, and stapled sheet bundle will easily become damaged. Furthermore, there is a possibility that unstapled sheet bundles will become staggered or alignment defects will occur (If the curl is severe or if there are many sheets, the sheets near the lower discharge roller 101 side will be conveyed first). Furthermore, even when a large sheet bundle is discharged, the staple bundle will have problems with bundle staggering and alignment defects.

Furthermore, when only a fixed location (80 mm) from the trailing end of the sheet bundle in the conveyance direction is nipped as with the conventional technology of Patent Reference 2, and the sheet bundle stapling is a single point binding in the corner, if multiple sheet bundles are discharge to the discharge tray, the multiple sheet bundles which have been discharged will form an incline and drop out. In this case, the multiple sheet bundles which have been stapled may be alternately shifted in a direction orthogonal to the paper conveyance direction, but when the sheet bundles are shifted in the direction orthogonal to the paper conveyance direction, the center of gravity in the direction orthogonal to the sheet bundle will protrude from a push up member which receives and conveys the trailing end of the sheet bundle, and conveyance problems will occur such as the sheet bundle will be conveyed at an incline when being conveyed. Therefore, if a location 80 mm from the trailing end of the sheet bundle in the conveyance direction is nipped and the pair of discharge rollers close after most of the sheet bundle has been pushed up, the sheet bundle will become inclined and drop out during conveyance prior to the sheet bundle being nipped by the pair of discharge rollers.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a post-processing device and an image forming device which can shift each sheet bundle in order to prevent conveyance problems with the sheet bundle after post-processing, and enable discharging to the discharge trade in a shifted state.

A first aspect of the present invention is a post-processing device which stacks multiple sheets on a post-processing tray after performing post-processing on the multiple sheet bundles, alternately shifts each sheet bundle in a direction that is orthogonal to the paper conveyance direction, conveys each of the shifted sheet bundles from the post-processing tray to a discharge port using sheet conveying means, and discharges the sheet bundles in a shifted state on to a sheet discharging tray using a pair of discharge rollers positioned at the discharge port, wherein:

the pair of discharge rollers has an upper discharge roller and an opposing lower discharge roller which freely open and close;

and further comprising driving means for switching the upper discharge roller and the lower discharge roller between a closed state which allows the sheet bundle to be grasped and discharged, and an opened state where the sheet bundle is not grasped; and

wherein the lower discharge roller and the upper discharge roller are closed by a controlling means at predetermined timing based on the sheet size or the number of sheets.

A second aspect of the present invention is the post-processing device according to the first aspect, wherein the predetermined timing is for a fixed period of time after the lead edge of the sheet bundle in the conveyance direction reaches the pair of discharge rollers.

A third aspect of the present invention is the post-processing device according to the first aspect, wherein the predetermined timing is for a fixed period of time from the moment conveyance of the sheet bundle by the sheet conveying means begins.

A fourth aspect of the present invention is the post-processing device according to any one of the first to third aspects, wherein the trailing end side of the sheet bundle in the conveyance direction is nipped based on the sheet size of the sheet bundle.

A fifth aspect of the present invention is the post-processing device according to any one of the first to fourth aspects, wherein the trailing end side of the sheet bundle in the conveyance direction is nipped as the number of sheets in the sheet bundle increases.

According to a sixth aspect of the present invention, an image forming device comprises an image forming unit which forms an image on a sheet, and the post-processing device according to any one of the first to fifth aspects for performing post-processing of sheets on to which an image has been formed.

With the present invention, a lower discharge roller and an upper discharge roller positioned at a discharge port are closed at predetermined timing based on the sheet size or the number of sheets, so the post-processed sheet bundles can be bound in a shifted state so that conveyance problems will not occur, and the post-processed sheet bundles can be discharged on to the paper discharge tray without the sheet bundles becoming staggered. Furthermore, even when performing post-processing of small size sheet bundles, damage to the sheet bundle can be prevented by nipping by the pair of discharge rollers.

These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of this original disclosure:

FIG. 1 is a schematic block diagram of the post-processing device and image forming device of the present invention;

FIG. 2 is a front view diagram of the lower unit of the post-processing device;

FIG. 3 is a cross-sectional side view of the same;

FIG. 4 is a diagram showing the construction of the pair of discharge rollers of the post-processing device;

FIG. 5 is a perspective view of the discharge port side of the pair of discharge rollers (closed state) of the post-processing device;

FIG. 6 is a perspective view of the discharge port side of the pair of discharge rollers (opened state) of the post-processing device; and

FIG. 7 is a diagram showing the construction of a pair of discharge rollers for a conventional post-processing device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment for carrying out the present invention will be described in detail based on the drawings.

Simplified Structure of a Post-Processing Device and Image Forming Device Equipped Therewith

FIG. 1 shows the simplified structure of the post-processing device 1 of an embodiment of the present invention and an image forming device 2 equipped therewith.

As shown in FIG. 1, a sheet (copy paper, OHP film or the like) 4 fed from a paper feed tray 3 is printed with an image by an image forming unit 5, and then conveyed along the sheet conveyance path 8 of the post-processing device 1 by a pair of discharge rollers 7 on the side of the image forming device body 6. Incidentally, the operation for punching holes in the sheet 4 is performed by a punch unit 5 established on the sheet conveyance path 8, so hereinafter, in order to simplify the description, post-processing refers to those processes other than the hole punching operation, such as stapling or the like. If post-processing will not be performed, the sheet 4 which has been conveyed along the sheet conveyance path 8 of the post-processing device 1 is guided through the discharge path 11 by branched tabs 10 to a pair of discharge rollers 12 and is then conveyed onto a sheet discharging tray 13 by the pair of discharge rollers 12. Furthermore, when post-processing will be performed, the sheet 4 which has been conveyed along the sheet conveyance path 8 of the post-processing device 1 is conveyed through the post-conveyance path 14 by the branched tabs 10 to the post-processing unit 15. The post-processing unit 15 comprises an upper unit 28 and a lower unit 29, a post-processing tray 16, and a bending unit 19 or the like for bending stapled sheet bundles in the middle.

FIG. 2 and FIG. 3 are front view and side view diagrams of the lower unit 29. The sheet 4, which has been conveyed to the post-processing unit 15, is conveyed downward and the trailing end (trailing end in the direction of conveyance to the paper discharge tray from the post-processing unit 15) is received by a sheet receiving member (sheet conveying means) 18. The sheet receiving member 18 is mounted on a belt 52 which rotates on two rotating shafts 50, 51. The sheet receiving member 18 waits at a predetermined location in the direction of belt movement based on the size of the sheet being used. Furthermore, the upper end of the lower unit 29 has a rotating shaft 58, and another belt 60 revolves around this rotating shaft 58 and rotating shaft 50. This belt 60 has a protrusion 59 which presses on the lead edge of the sheet (lead edge in the direction of conveyance to the paper discharge tray 13) in order to align the sheets (Refer to FIG. 3).

The lower unit 29 has a pair of upper guides 53 and a pair of lower guides 54 arranged in line in the paper conveyance lateral direction (hereinafter defined as the direction orthogonal to the sheet discharge direction) in order to guide the sheet in the direction of conveyance. Both the pair of upper guides 53 and the pair of lower guides 54 are able to move symmetrically with regards to a centerline A in the paper conveyance lateral direction. A pair of double end support members 55 are established in line in the paper conveyance lateral direction between the upper guides 53 and the lower guides 54. The double end support members 55 receive the trailing end of the sheet bundle if stapling is to be performed, and have a near L-shaped receiving plate 56. The double end support members 55 are moved in conjunction with the corresponding lower guide 54 by an operating lever 57. If the length of the sheet in the conveyance direction is smaller than a predetermined sheet size, the pair of lower guides 54 will spread outward, the lower guides 54 will press on the operating lever 57, the double end support members 55 will be pushed down by the operating lever 57 and move to a base position which supports the trailing end of the sheet as shown by the line in FIG. 3. If the length of the sheet in the conveyance direction is longer than the predetermined sheet size, the pair of lower guides 54 will become narrow, the operating lever 57 will rotate freely, the double end support members 55 will push up on the operating lever 57, and will move to the retreated position shown by the broken line in FIG. 3.

In this manner, if the length of the sheet in the direction of conveyance is smaller than the predetermined sheet size, the multiple sheets 4 stacked in the post-processing tray 16 after being received by the sheet receiving member 18 are post-processed such as stapling or the like by the post-processing means 17 after moving the belt 60 downwards and lightly pushing the lead edge of the sheet to the sheet receiving member 18 side using a protrusion. This post-processing means 17 has 2 center binding staplers 17a and an angled binding stapler 17″ established on the right side of FIG. 2. If the length of the sheet in the conveyance direction is smaller than the predetermined sheet size, the double end support members 55 will be waiting at the base position, so the trailing end of the sheet bundle will be more stably supported by the sheet receiving member 18 and the double end support members 55.

If the length of the sheet in the conveyance direction is longer than a predetermined sheet size, the sheet receiving member 18 will move to the base position, and then the pair of lower guides will tighten, the double end support members 55 will rotate to the narrow position for the sheet receiving member 18 to move downward, and the trailing end of the sheet bundle will be supported only by the sheet receiving member 18. Furthermore, the plurality of sheets 4 which have been moved downward by the sheet receiving member 18 are lightly pressed on the lead edge of the sheet to the sheet receiving member 18 side by the protrusion 59 to arrange and align the lead edge of the sheets, and then the belts 52, 60 will simultaneously move upward, and the sheet receiving member 18 will return again to the base position before stapling will be performed.

At this time, in order to prevent the plurality of sheet bundles which have been discharged to the paper discharge tray 13 from stacking up to form an incline and falling off of the paper discharge tray 13, the stapled sheet bundles are alternately shifted in the paper conveyance lateral direction when discharged Therefore, the pair of upper guides 53 will alternately move to both ends of the shift positions (not shown in the drawings) so that the stapled sheet bundles will be discharged upward by the sheet receiving member 18 in that position.

Structure of Pair of Discharge Rollers

FIG. 4 through FIG. 6 are diagrams which show the structure of the pair of discharge rollers 12 which are an embodiment of the present invention, and are block diagrams of the region shown by K in FIG. 1.

The pair of discharge rollers 12 are comprising a discharge upper guide 21 which is rotatably supported to the device body 20 side at the longitudinal center region, a plurality of upper discharge rollers 22 which are rotatably supported on one end 21a of the upper discharge guide 21, a lower discharge guide 23 which is rotatably supported to the device body 20 side at the longitudinal center region, and a plurality of lower discharge rollers 24 which are rotatably supported by the device body 20 side. These plurality of upper discharge rollers 22 and lower discharge rollers 24 are positioned at appropriate intervals in the paper conveyance lateral direction (direction orthogonal to the sheet discharge direction), and therefore any size of sheet which is subject to post-processing by the post-processing device can positively be conveyed.

The lower discharge guide 23 is rotatably supported to the frame 26 of the device body 20 in the longitudinal center region by a support pin 25. A lower discharge guide 23 is constructed such that a counterclockwise rotational moment on the fulcrum point (support pin 25) is generated by gravity. Furthermore, the lower discharge guide 23 is supported by a hooking member 27 formed in the frame 26 on the side of the device body 20 such that one end 23a of the lower discharge guide 23 on the lower discharge roller 24 side is further retracted than the outer surface of the lower discharge roller 24, when positioned in the closed state where a nip P is formed between the lower discharge roller 24 and the upper discharge roller 22.

Furthermore, a near U-shaped groove 30 with an opening towards the lead edge is formed on the other end 23b of the lower discharge guide 23. This U-shaped groove 30 is made to lock with play to a connecting pin 31 formed in the other end 21b of the upper discharge guide 21 which will be described later. The play between the connecting pin 31 and the U-shaped groove 30 is formed to create a maximum separation dimension between the lower discharge roller 24 and the upper discharge roller 22. Incidentally, the lower discharge guide 23 is formed to guide movement of the sheet by the sheet guide plate 23c.

The upper discharge guide 21 is rotatably supported in the longitudinal center region by a support pin 25 which is used in common with the lower discharge guide 23. The longitudinal center region of the upper discharge guide 21 has a bias force applied by a spring 37 in a direction such that the upper discharge roller 22 is pushed to the lower discharge roller 24 side, and on the other end 21b, a bias force is applied by a solenoid 40 (driving means) in the direction which separates the upper discharge roller 22 from the lower discharge roller 24. Furthermore, the solenoid 40 is turned on and off by a controlling means not shown in the drawings. The upper discharge guide 21 is attached such that the connecting pin 31 on the other end 21b which locks with play into the U-shaped groove 30 of the lower discharge guide 23 protrudes from the side surface.

The frame 26 on the side of the device body 20 is comprising a solenoid 40, a lever 42 which is rotatably supported to the frame 26 by a support pin 41, and a wire or the like connecting ring 44 which connects one end 42a of the lever 42 to an operating rod 43 of the solenoid 40. Furthermore, when the solenoid 40 is turned on, the lever 42 is pulled by the operating rod 43 of the solenoid 40, the lever 42 rotates in a clockwise direction, the other end (lead edge) 42b of the lever 42 pushes the other end 21b of the upper discharge guide 21, and causes the upper discharge guide 21 to rotate (in the clockwise direction) around the support pin 25.

If sheets which are not to have post-processing are discharged onto the paper discharge tray 13 by the pair of discharge rollers 12, the upper discharge guide 21 will be pushed by the spring force of the spring 37 and the upper discharge roller 22 will apply pressure to the lower discharge roller 24 through the upper discharge guide 21. Thereby the connecting region between the upper discharge roller 22 and the lower discharge roller 24 will be in the closed state wherein a nip P is formed, and the sheet will be conveyed by the pair of discharge rollers 12 onto the paper discharge tray 13.

Furthermore, if a sheet bundle which has had post-processing is discharged onto the paper discharge tray 13 by the pair of discharge rollers 12, the solenoid 40 will be turned on, and the solenoid 40 will rotate the lever 42 in the clockwise direction, and the lead edge 42b of the lever 42 will apply pressure on the top surface of the other end 21b of the upper discharge guide 21, and the upper discharge guide 21 will be made to rotate in the clockwise direction with the support pin 25 as a fulcrum point. Thereby the upper discharge roller 22, which is rotatably supported on one end 21a of the upper discharge guide 21, will separate from the lower discharge roller 24. When the upper discharge guide 21 rotates in a clockwise direction with the support pin 25 as a fulcrum point, the connecting pin 31, which is connected to the other end 21b of the upper discharge guide 21, will contact the bottom edge of the U-shaped groove 30 of the lower discharge guide 23. The position where the connecting pin 31 contacts the bottom edge of the U-shaped groove 30 on the lower discharge guide 23 is the maximum separation position for the upper discharge roller 22 and the lower discharge roller 24. Incidentally, the maximum dimension for the separation between the upper discharge roller 22 and the lower discharge roller 24 is set to be the approximate dimension where a bundle of 50 sheets of approximately A4 size copy paper with an average paperweight of 80 g/m2 can pass through.

When one end 23a of the lower discharge guide 23 separates from the locking member 27 on the side of the device body 20, rotates together with the upper discharge guide 21 in the clockwise direction with the support pin 25 as the center of rotation, and the one end 23a rotates to a position which protrudes past the outer surface of the lower discharge roller 24, the solenoid 40 will continue to function and the position will be maintained. In this manner, the bottom sheet (back surface side) of the sheet bundle discharged from the post-processing unit 15 by the sheet receiving member 18 will not come in contact with the outer surface of the lower discharge roller 24, and the lead edge side of the sheet bundle will smoothly pass through the gap between the lower discharge roller 24 and the upper discharge roller 22 without catching, because one end 23a of the lower discharge guide 23 protrudes past the outer surface of the lower discharge roller 24. Incidentally, the pair of discharge rollers 12 are made to be in the separated state even if the sheet size of the sheet bundle for post-processing is large so that the lead edge of the sheet in the direction of conveyance exceeds the nip P between the lower discharge roller 24 and the upper discharge roller 22 and must protrude externally when the sheet bundle is discharged during the aligning operation for the sheets in the post-processing unit 15. Thereby the aligning operation can smoothly be performed for large sized sheet bundles.

Sheet Bundle Discharge Operation by the Post-processing Device

With this embodiment, when the sheet bundle is discharged from the post-processing unit 15 by the sheet receiving member 18, the power to the solenoid 40 will be turned off after a predetermined period of time when passage of the lead edge of the sheet bundle in the direction of conveyance is detected by a detecting sensor 47, or the power to the solenoid will be turned off after a predetermined period of time when the sheet bundle lifting operation (conveyance operation) by the sheet receiving member 18 begins. By turning off the power to the solenoid 40, the sheet bundle which has been conveyed to the discharge port will be grasped by the closing of the lower discharge roller 24 and the opening discharge roller 22, and will be conveyed onto the paper discharge tray 13.

For instance, in FIG. 2 and FIG. 3, if the sheet receiving member 18 is moved such that the sheet bundle is moved to the base position for performing the post-processing and the sheet bundle is to be stapled, stapling will be performed after moving the sheet bundle to the staple position in the paper conveyance lateral direction. For instance, if staples are to be in symmetric locations with regards to the center of the sheet, the pair of upper guides 53 will be moved in the paper conveyance lateral direction, and stapling will be performed by a center binding stapler 17′. Furthermore, if stapling is to be done in one corner of the sheet bundle, the pair of upper guides 53 will be moved to the right edge (FIG. 2) in the paper conveyance lateral direction and stapling will be performed by an angle binding stapler 17″. Next, the first stapled sheet bundle will be moved to a first shift position (bundle lifting position), and the sheet bundle will be lifted and discharged by the sheet receiving member 18. The sheet receiving member 18 is attached to the belt 52, and therefore the sheet bundle will be lifted out by the sheet receiving member 18 to the location of the rotating shaft 50 shown in FIG. 3, and thereafter will be transferred to the protrusion 59 and discharged to the pair of discharge rollers 12 by the protrusion 59. The protrusion 59 moves the back side of the tray in conjunction with the counterclockwise rotation of the belt 60 when the conveyance upper end is reached, and is then returned to the original position. Furthermore, the second stapled sheet bundle is moved to the other shift position (bundle lifting position) in the paper conveyance lateral direction, and the sheet bundle is lifted up and discharged by the sheet receiving member 18. Therefore, if there are a plurality of sheet bundles, the shift position will be alternately changed when discharging. Incidentally, if the sheet bundles are not to be stapled, the shift position is similarly alternately changed for each sheet bundle, and the sheet bundles are lifted up and discharged by the sheet receiving member 18.

Incidentally, when considering bundle staggering and alignment problems, the timing for cutting (nip) the power to the solenoid 40 will should be such that the trailing end of the sheet in the direction of conveyance is as close as possible to the stapling position. However, when the sheet bundle is raised by the sheet receiving member 18, as shown in FIG. 2, problems will not occur from the start of lifting the sheet bundle until passing through the top end of the upper guide 53, but after passing the upper guide 53, a guide will not be present on both sides in the lateral direction and therefore, if the center of gravity in the lateral direction of the sheet bundle protrudes past the sheet receiving member 18, the sheet bundle will be inclined and unstable during conveyance, and there is a possibility that conveyance defects such as catching or the like could occur. To illustrate, if a sheet bundle is discharged while shifted in the lateral direction of the sheet, the center of gravity in the lateral direction of the sheet will protrude past the sheet receiving member 18, and there is a possibility that the sheet bundle will become inclined during conveyance and that conveyance defects will occur. Therefore, with this embodiment, nipping will be performed in the appropriate position of the sheet bundle in order to prevent bundle staggering and alignment defects during nipping.

For instance, if the stapled sheet bundle is A4 vertical or smaller, the sheet detection sensor 47 will detect the lead edge of the sheet bundle, and when one third of the sheet size in the direction of conveyance has passed after the lead edge, the power to the solenoid 40 will be cut off, and nipping will be performed. For instance, for the case of A4 lateral, nipping will occur at approximately 70 mm which is one third of the total length from the lead edge of the sheet in the direction of conveyance, and for the case of A4 vertical, nipping will occur at approximately 100 mm which is ⅓ of the total length from the lead edge of the sheet in the direction of conveyance. In this manner, nipping will be performed at a position one third of the total length from the lead edge of the sheet in the direction of conveyance, so the sheet bundle will not become inclined or the like even after passing through the upper guide 53. Furthermore, the nipping will be performed at a point one third of the total distance from the lead edge of the sheet in the direction of conveyance, so damage caused by nipping smaller sheet bundles after stapling can be prevented.

Furthermore, if the stapled sheet bundle is larger than A4 vertical (such as B4 or A3 or the like), in order to prevent damage or the like to the sheet bundle, first the sheet bundle is shifted by the lower discharge roller 24 without contacting the outer surface of the lower discharge roller 24 while the lower discharge roller 24 and the upper discharge roller 22 are in the opened state, and then the bundle will be lifted by the sheet receiving member 18. Furthermore, the timing when the power to the solenoid 40 is turned off and the lower discharge roller 24 and the upper discharge roller 22 are closed, is set to be the moment where ⅖ of the sheet bundle has passed since the lead edge in the conveyance direction after the bundle has started being raised by the sheet receiving member 18. For instance, for the case of B4 vertical, nipping will occur at approximately 145 mm which is ⅖ of the total length from the lead edge of the sheet in the conveyance direction, and for the case of A3 vertical, nipping will occur at approximately 167 mm which is ⅖ of the total length from the lead edge of the sheet in the conveyance direction. In this manner, nipping will occur at a position ⅖ of the total length from the lead edge of the sheet in the direction of conveyance, so similar to when the size is smaller than A4 vertical, the sheet bundle will not become inclined or the like after passing the upper guide 53. Therefore, for sizes which are smaller than A4 vertical as well as for sizes which are larger than A4 vertical such as B4, or A3 or the like, the sheet position where the lower discharge roller 24 and the upper discharge roller 22 close will moved toward the trailing end as the sheet size increases (timing will be delayed).

Furthermore, with the present embodiment, the timing for turning off the power to the solenoid 40 is delayed as the number of sheets in the sheet bundle increases, so nipping will be performed to the trailing end side. For instance, if the lower discharge roller 24 and the upper discharge roller 22 close (nip) when half of the sheet size in the conveyance direction passes after the lead edge in the conveyance direction when the number of sheets in the sheet bundle is 50 or higher, bundle staggering will increase because the nipping force will be weaker as the number of sheets in the sheet bundle increases, even though the timing for nipping is the same. Therefore, the timing for nipping is changed for every 10 sheets in the sheet bundle, and as the number of sheets in the sheet bundle increases, the timing for closing the lower discharge roller 24 and the upper discharge roller 22 will be delayed. For instance, for 10 or fewer sheet bundles, nipping will occur 50 ms after the sheet detection sensor 47 is turned on.

For 20 or fewer sheets, nipping will occur 100 ms after the sheet detection sensor 47 is turned on.

For 30 or fewer sheets, nipping will occur 150 ms after the sheet detection sensor is 47 turned on.

For 40 or fewer sheets, nipping will occur 200 ms after the sheet detection sensor 47 is turned on.

For 50 or fewer sheets, nipping will occur 250 ms after the sheet detection sensor 47 is turned on.

Furthermore, in order to perform nipping at the same sheet position from the lead edge in the sheet conveyance direction, the timing for turning off the power to the solenoid 40 should be faster as the discharge speed of the sheet bundles increases. For instance, if nipping at a position 60 mm from the detection of the lead edge of the sheet (position ⅓ from the lead edge of the sheet in the conveyance direction), nipping is performed 150 ms from the moment the sheet detection sensor 47 is ON if the discharge speed is 400 mm/sec.

If the discharge speed is 500 mm/sec, nipping is performed 120 ms after the sheet detection sensor is ON.

If the discharge speed is 600 mm/sec, nipping is performed 100 ms after the sheet detection sensor is ON.

However, as the discharge speed increases, a staggering force which is created in the vertical direction of the sheet bundle will act on the staple region and damage will easily occur, so with this embodiment, the nipping location should be on the trailing end of the sheet. For instance, for the case of an A4 vertical sheet bundle, nipping is performed at a position 100 mm from the lead edge of the sheet when the discharge speed is 400 mm/sec.

Nipping is performed at a position 150 mm from the lead edge of the sheet when the discharge speed is 500 mm/sec.

Nipping is performed at a position 200 mm from the lead edge of the sheet when the discharge speed is 600 mm/sec.

The post-processing device and image processing device of the present invention can be used in combination with an image reading device such as a scanner, or can be used for performing post-processing on a sheet bundle after reading an image.

Any terms of degree used herein, such as “substantially”, “about” and “approximately”, mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

This application claims priority to Japanese Patent Application No. 2004-364148. The entire disclosure of Japanese Patent Application No. 2004-364148 is hereby incorporated herein by reference.

While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Claims

1. A post-processing device, comprising:

a post-processing tray for stacking sheets;

post-processing means for performing post-processing on sheet bundles comprising a plurality of sheets which have been stacked in the post-processing tray;

sheet conveying means for alternately shifting each sheet bundle post-processed by the post-processing means in a direction orthogonal to a conveyance direction, and conveying each of the shifted sheet bundles to a discharge port;

a pair of discharge rollers for discharging sheet bundles which have been conveyed by the sheet conveying means from the discharge port, having an upper discharge roller and an opposing lower discharge roller which freely open and close in order to achieve a closed state where the sheet bundle can be grasped and discharged and an open state where the rollers are mutually separated;

a sheet discharging tray for receiving sheet bundles discharged by means of the pair of discharge rollers;

driving means for switching the upper discharge roller and the opposing lower discharge roller between the closed state and the open state; and

controlling means for controlling the timing for switching the lower discharge roller and the upper discharge roller between the open state and the closed state in response to the paper size or the number of sheets.

2. The post-processing device according to claim 1, wherein the controlling means switches from the open state to the closed state after a fixed period of time from the moment the lead edge of the sheet bundle in the conveyance direction reaches the pair of discharge rollers.

3. The post-processing device according to claim 1, wherein the controlling means switches from the open state to the closed state after a fixed period of time from the moment sheet bundle conveyance by the sheet conveying means begins.

4. The post-processing device according to claim 1, wherein the controlling means controls the timing for switching between the open state and the closed state in order to nip the trailing end side of the sheet bundle in the conveyance direction as the size of the sheet bundle increases.

5. The post-processing device according to claim 1, wherein the controlling means controls the timing for switching between the open state and the closed state in order to nip the trailing end side of the sheet bundle in the conveyance direction as the number of pages in the sheet bundle increases.

6. An image forming device, comprising:

an image forming unit for forming an image on a sheet;

a post-processing device for performing post-processing on a sheet onto which an image is formed by the image forming unit;

the post-processing device comprising:

a post-processing tray for stacking sheets;

post-processing means for performing post-processing on sheet bundles comprising a plurality of sheets which have been stacked in the post-processing tray;

sheet conveying means for alternately shifting each sheet bundle post-processed by the post-processing means in a direction orthogonal to a conveyance direction, and conveying each of the shifted sheet bundles to a discharge port;

a pair of discharge rollers for discharging sheet bundles which have been conveyed by the sheet conveying means from the discharge port, having an upper discharge roller and an opposing lower discharge roller which freely open and close in order to achieve a closed state where the sheet bundle grasped and discharged and an open state where the rollers are mutually separated;

the sheet discharging tray for receiving sheet bundles discharged by means of the pair of discharge rollers;

driving means for switching the upper discharge roller and the opposing lower discharge roller between the closed state and the opened state; and

controlling means for controlling the timing for switching the lower discharge roller and the upper discharge roller between the opened state and a closed state in response to the paper size or the number of sheets.

7. The image forming device according to claim 6, wherein the controlling means switches from the open state to the closed state after a fixed period of time from the moment the lead edge of the sheet bundle in the conveyance direction reaches the pair of discharge rollers.

8. The image forming device according to claim 6, wherein the controlling means switches from the opened state to the closed state after a fixed period of time from the moment sheet bundle conveyance by the sheet conveying means begins.

9. The image forming device according to claim 6, wherein the controlling means controls the timing for switching between the opened state and the closed state in order to nip the trailing end side of the sheet bundle in the conveyance direction in response to the size of the sheet bundle.

10. The image forming device according to claim 6, wherein the controlling means controls the timing for switching between the opened state and the closed condition in order to nip the trailing end side of the sheet bundle in the conveyance direction as the number of pages in the sheet bundle increases.