Sheet conveying apparatus and image forming apparatus

The sheet conveying apparatus includes a first member configured to convey a sheet along a predetermined conveying path while holding the sheet, a second member configured to convey a sheet along the predetermined conveying path while holding the sheet, and a changing unit configured to change a first state in which the first member and the second member convey the same sheet along the predetermined conveying path and a second state in which the first member and the second member convey different sheets in the predetermined conveying path according to a length of a sheet along the predetermined conveying path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet conveying apparatus for conveying sheets and to an image forming apparatus.

2. Description of the Related Art

Conventionally, an apparatus body of an image forming apparatus selected from the group consisting of a photocopier, a printer and the like for forming an image onto a sheet occasionally conveys a sheet where an image is formed with an apparatus body and includes a sheet stacking apparatus (stacker) for stacking a large amount of the conveyed sheets. Such a stacker is described in Japanese Patent Application Laid-Open No. 2006-124051. A stacker100inFIG. 8is described in Japanese Patent Application Laid-Open No. 2006-124051.

A sheet discharged from the apparatus body of an image forming apparatus is conveyed to an inlet roller pair101and is guided upward by a flapper102. A sheet is further guided upward and is discharged into a sample tray109above a stacker. Even if the sheet is guided upward, in the case where the sheet is conveyed in a normal state, the sheet passes a conveying path103to be conveyed further from outlet roller pair104to a post processing apparatus (not illustrated in the drawing) in the downstream. In addition, in the case where the sheet is guided to a downward path by the flapper102, the sheet is discharged and stacked on a stacking tray106by a discharging roller105. The stacking tray106moves up and down with an elevating apparatus not illustrated in the drawing and is adjusted in height so that the height on the upper plane of the stacking sheet is always kept constant with a sheet plane detecting lever110.

However, in that stacker, the stacking tray106is horizontal. Therefore, in the case of a sheet such as an easily bending thin sheet, the sheet is discharged from the outlet roller pair104so that the tip of the sheet droops and rubs against already stacked sheets to occasionally result in jamming.

Therefore, the stacker100illustrated inFIG. 8conveys the tip of the sheet discharged from a discharging roller105being gripped by grippers107aand107bon a belt108. The tip of the sheet is urged to the stopper114and the sheet is disengaged from the grippers107aand107b. Thereby, the sheet drops onto the stacking tray106and is stacked. The belt108is hung by a drive pulley111and a driven pulley112to circulate in the direction of an arrow A. The grippers107aand107bare provided with a common interval on the belt108.

However, in the stacker100adapted as described above, if grippers are arranged so as to be capable of conveying and stacking sheets with half sheet sizes A4, B5 and the like at an occasion of conveying a sheet with large sheet sizes A3, B4 and the like, there are present grippers107aand107bwhich do not grip the sheet. The grippers which do not grip a sheet will hamper conveyance of a sheet to occasionally damage an image while an image is formed on the sheet.

Therefore, in a sheet conveying apparatus in conventional stacker, grippers are arranged in an interval to allow a sheet of the maximum length to be stacked to be conveyed. However, when the grippers are thus arranged, the distance for conveying a sheet gets long to make sheet conveying efficiency worse when a short sheet in length in the sheet conveying direction is conveyed. In that case, when a short sheet in length in the sheet conveying direction is conveyed, acceleration of the circulation velocity of the belt is conceivable. However, a change in the circulation velocity of the belt based on sheet length gives rise to another problem that structure and controls get complicated.

In addition, in an apparatus disclosed in Japanese Patent Application Laid-Open No. S61-174058, a pair of drive shafts provided at a predetermined spaces and four sprockets913being present in each of those drive shafts are axially arranged in a position so as to face each other as illustrated inFIG. 9AandFIG. 9B. The four sprockets913are divided into two outer sprockets913arranged in both ends of the drive shaft and two units are arranged inside the outer sprockets913. Four roller chains914are respectively attached to those sprockets913in mesh with each other and rotate corresponding with rotation of respective sprockets913. The roller chains914consist of two chains put on the inner sprockets913respectively and other two chains put on the outer sprockets913respectively. The two chains arranged inside and two chains arranged outside come into communication with a plurality of tie bars915and916mounted on chains914respectively to form pair structure. The distance between two roller chains914brought into communication with the tie bars915and916substantially corresponds with the width of a sheet (length in the direction perpendicular to the conveying direction) in the sheet size A3. Each sprocket913on the side of the respective drive shaft is axially connected to those two sets of roller chains914through a clutch917and can, therefore, rotate independently. Relative positions of a plurality of tie bars915fixed on the roller chains914and a diaper916is freely variable in the direction of movements of the roller chains914. Tie bars915and916are provided on the outer surface thereof with a gripper918capable of gripping the tip of the sheet.

In the case where that apparatus conveys a sheet919with a sheet size A3, as illustrated inFIG. 9A, two sets of roller chains914are provided so that they are changed in their relative positions by the clutch917to move the gripers918of both chains so as to come substantially closer to each other. The tip of the sheet919with a sheet size A3 is gripped by grippers918(grippers provided in the outer roller chain inFIG. 9A) located on the delayed side in the sheet moving direction and is conveyed. At that occasion, the grippers of the inner roller chain do not hold a sheet and enter a rotary or non-rotary state in cooperation with outside roller chain.

In the case of conveying a sheet920with the sheet size A4, the relative positions of the two sets of roller chains914are changed as illustrated inFIG. 9B. That is, the positions of the tie bars915and916are moved so that the tie bars915of the inner roller chain914come in substantially center position of two tie bars916and916provided in the outer roller chain914. The distance between the mutually adjacent tie bars915and916is set to the length of the sheet with the sheet size A4. Thus, once the relative positions of the two sets of roller chains914are set subjected to displacement in the longitudinal direction of the roller chain, then both of the roller chains914and914start rotating in cooperation with each other to convey the sheet920with the gripper918of both of the roller chains914and914.

In the case of conveying a sheet920with the sheet size A4, the relative positions of the two sets of the roller chains914are changed as illustrated inFIG. 9B. That is, the positional relation of the tie bars915and916is adjusted so that the tie bar915of the inner roller chain914is arranged in the substantially center position of the two tie bars916provided in the outer roller chain914. The distance between the mutually adjacent tie bars915and916is set to the sheet length of a sheet with the sheet size A4. Thus, when the relative positions of the two sets of roller chains914are set, then both of the roller chains914start rotating in cooperation with each other to convey the sheet920with the grippers918of both of roller chains914.

In an apparatus disclosed in that Japanese Patent Application Laid-Open No. S61-174058, a gripper holding no sheet at an occasion of conveying a sheet with a sheet size A3 is located in the position in the vicinity of the gripper918which conveys the sheet. That is, at an occasion of conveying a sheet with the sheet size A3, the gripper918conveying the sheet and the gripper conveying no sheet will be in an aligned state in the sheet conveying direction. Here, in order to prevent the grippers holding no sheet refrains from contacting the sheet to be conveyed to damage the sheet, the space for the grippers holding no sheet has to be secured in the direction of conveying the sheet. Accordingly, the distance among a plurality of grippers gripping a sheet has to be lengthened for the space secured for the grippers regaining no sheet. Accordingly, it is necessary to lengthen the distance between the grippers for conveying the sheet and, therefore, sheet conveyance efficiency is not good.

SUMMARY OF THE INVENTION

A purpose of the present invention is to provide a highly efficient apparatus in conveying a sheet.

Another purpose of the present invention it to provide a highly processing-efficient apparatus.

A further purpose of present invention is to provide a sheet conveying apparatus including a first member configured to convey a sheet along a predetermined conveying path while holding the sheet, a second member configured to convey a sheet along the predetermined conveying path while holding the sheet and a changing unit configured to change a first state in which the first member and the second member convey the same sheet along the predetermined conveying path and a second state in which the first member and the second member convey different sheets in the predetermined conveying path according to a length of a sheet along the predetermined conveying path.

A further purpose of present invention is to provide a sheet conveying apparatus including a first member configured to convey a sheet along a predetermined conveying path while holding the sheet a second member configured to convey a sheet along the predetermined conveying path while holding the sheet and a changing unit configured to change a first state in which the first member conveys a sheet along the predetermined conveying path and the second member is retracted from the predetermined conveying path and a second state in which the second member conveys a sheet along the predetermined conveying path according to a length of a sheet along the predetermined conveying path.

DESCRIPTION OF THE EMBODIMENTS

A sheet stacking apparatus of embodiments of the present invention and an image forming apparatus including that sheet stacking apparatus will be described below based on the drawings.

FIG. 1is a section of an image forming apparatus of an embodiment of the present invention along a sheet conveying direction. An image forming apparatus900includes an apparatus body900A provided with a sheet stacking apparatus51(hereinafter to be referred to as “stacker”). The stacker51is optionally connected to the apparatus body900A but can be incorporated inside the apparatus body900A. A controller922controls operations of the image forming apparatus900.

The apparatus body900A includes an image reader951and an original paper auto-feeding apparatus950in the upper portion. A sheet set in a sheet feeding cassettes902ato902eis conveyed to reach resist roller pair910with sheet feeding rollers903ato903eand conveying roller pair904. Here, in the sheet feeding cassettes902aand902b, sheets S1with the half sheet size are stored and sheets S2with the large sheet size are stored in sheet feeding cassettes902cand902d.

On the other hand, a photosensitive drum906as an image forming unit is exposed to light by an exposure portion908in the state charged by a primary charger907to form digital original data of an original read with an image reader951as an electrostatic latent image. A developing device909develops the photosensitive drum906with toner to make a toner image from the electrostatic latent image.

Positioning with the toner image, a sheet is delivered by the registration roller pair910to the space between the photosensitive drum906and the transferring device905. The transferring device905transfers a toner image from the photosensitive drum906onto the sheet. Foreign matter such as residual toner attached to the photosensitive drum906without having been transferred onto the sheet is scratched off with the blade of a cleaning apparatus921. Consequently, the photosensitive drum906is cleaned to get ready for next image forming.

The sheet on which a toner image has been transferred is conveyed to a fixing device912by a conveying belt911and is sandwiched by a heat roller and a pressure roller of the fixing device912to get heated and pressed so that a toner image is fixed. The sheet on which a toner image has been fixed is directly conveyed to the stacker51by the sheet discharging roller pair914and otherwise conveyed to a duplex device901by the flapper915so that a toner image is formed again on the plane of the opposite side.

The image forming apparatus900includes an operating portion920aoperated by a user for various kinds of setting on the image forming apparatus900. A controller920controls the image forming apparatus based on inputs to the operating portion920a.

Next, a stacker will be described. Like reference characters designate the same or similar parts throughout the figures thereof to appropriately omit duplicated description.

FIG. 2AandFIG. 2Billustrate the case of stacking sheets with the half sheet sizes A4 and B5 and the like (hereinafter to be referred to as “half sheet”).FIG. 2Ais a schematic section along the sheet conveying direction of a sheet stacking apparatus in the midst of stacking half sheets.FIG. 2Bis a perspective view of belts of the sheet stacking apparatus in the case of conveying the half sheet.

FIG. 3AandFIG. 3Bare diagrams at stacking sheets with the large sheet sizes A3, B4 and the like (hereinafter to be referred to as “large sheet”.FIG. 3Ais a schematic section along the sheet conveying direction of a sheet stacking apparatus in the midst of stacking large sheets.FIG. 3Bis a perspective view of belts of the sheet stacking apparatus.

(Schematic Description on Stack Apparatus Operation)

In the case where a user provides an inputs to designate a sample tray9into an operating portion920a, the tips of the flappers2and10rotate downward. A sheet is conveyed from the apparatus body900A to an inlet roller pair1of the image forming apparatus900(FIG. 1). The sheet is guided by the flappers2and10, conveyed to the sample tray9and discharged.

In addition, in the case where a user designates post processing apparatus not illustrated in the drawing connected to the downstream with an input to the operating portion920a, the flapper2rotates downward and the flapper10rotates upward. Then, the sheet is guided to the conveyance path3and sent from an outlet roller pair4into the post processing apparatus not illustrated in the drawing.

Moreover, in the case where a user designates a stacker tray6as a stacking unit with an input to the operating portion920a, the sheet is guided to a sheet discharging roller pair5by the flapper2and the tip thereof is gripped by one of all and any of grippers7ato7dof a first belt8ato a third belt8cas a circulating body. The sheet is gripped by the grippers and conveyed onto a stacker6. When the tip of the sheet gripped by the grippers is brought into contact with a tip stopper14, the sheet falls off the grippers and drops on the stacker tray6. Accordingly, the position of the tip stopper14comes to a releasing position for releasing the grippers from holding sheets.

Here, the operation of the stacker51is controlled by a controller30, which exchanges information with a controller920which controls the image forming apparatus900in its entirety. Here, one of both of the controllers920and30can be incorporated in the other.

(Description on Stack Apparatus Structure)

InFIG. 2BandFIG. 3B, a first belt8aand a third belt8cas first rotary bodies on both sides are hung over a drive pulley11fixed on a drive shaft17and a driven pulley12provided on a driven shaft24in a freely rotary manner. The first belt8aand the third belt8ccirculate in the direction of an arrow B in receipt of rotary driving power by gears22and23from a drive motor16. The respective grippers7cand7das a first member provided in the first belt8aand the third belt8care provided at an equal space in the circulating direction (sheet conveying direction) of the belt so as to circulate in a synchronized manner. A third belt8cis provided on its sides with a detection sensor19for detecting positions of the grippers7cand7d.

The drive shaft17is provided with a clutch pulley18capable of switching ON/OFF of drive linkage of the drive motor16.

A second belt8bin the center as a second rotary body is hung over the clutch pulley18and a driven pulley12provided on a driven shaft24in a freely rotary manner. Therefore, the second belt8bis activated by the clutch pulley18to circulate and stop. Here, the first belt8aand the third belt8ccan be respectively driven and controlled by separate motors.

The second belt8bis provided with the grippers7aand7bas second member at an equal space in the circulating direction of the belt. The second belt8bis also provided on its sides with a detection sensor20for detecting positions of the grippers7aand7b.

A sheet conveying apparatus41is adapted to include the first belt8a, the third belt8c, the second belt8band the rippers7ato7dprovided in the respective belts.

The tip stopper14is movable corresponding with the size (length) of sheets stacked on the stacker tray6.

The respective grippers7ato7das a holding portion are adapted to include a pair of opening and closing piece provided with a spring property. The tip of the sheet is pushed into the opening and closing piece thereof. In addition, each gripper can be provided with an elastic member such as sponge inside the respective V-shaped members so that the tip of a sheet is pushed in between the elastic members thereof. Thus, being capable of gripping a sheet, the gripper damages the sheet little since the sheet rapidly falls off when the sheet comes into contact to the tip stopper14.

In addition, instead of a gripper, as holding portion, there can be an apparatus suctioning the sheet with air and static electricity. Also in such a case, the gripper damages the sheet little since the sheet rapidly falls off when the sheet comes into contact to the tip stopper14.

The controller30of the stacker51obtains information on the sheet type through the controller920of the image forming apparatus900based on an input from the operating portion920a. Information on sheet type is selected from the group consisting of sheet sizes, sheet orientations, sheet material, information on sheet discharge destinations and the like. The sheet orientation refers to which of the longer line or the shorter line is headed for the sheet conveying direction. Accordingly, the sheet length information is obtainable based on the sheet size information and the sheet orientation information. Here, the sheet length information can be input by a user directly and otherwise by outside information apparatus such as a personal computer. Moreover, the sheet conveying route can be provided with a sensor to obtain the information based on operations of the sensor.

From the controller920of the apparatus body900A, the controller30of the stacker51obtains information that the sheet is a half sheet. Here, the controller30moves, to the position of the half sheet, the position of the tip stopper14as a matching member for determining the position of the sheet tip.

The first belt8aand the third belt8crotates at the same velocity as the discharge velocity of the sheet discharged from the sheet discharging roller pair5in the direction of the arrow B.

The first half sheet S1discharged from the discharging roller pair5is gripped by each gripper7con the first belt8aand the third belt8ccirculated by the drive motor16and is conveyed onto the stacker tray16. The half sheet S1contacts the tip stopper14, is released from the gripper7c, drops onto the tray6and is stacked.

The rotary position of the second belt8bis positioned in advance by the detection sensor20and the clutch pulley18.

Each belt at the time of the half sheet conveyance is positioned so that the distance between the gripper7aand the gripper7cin the circulating direction, the distance between the gripper7cand the gripper7bin the circulating direction, the distance between the gripper7band the gripper7din the circulating direction and the distance between the gripper7dand the gripper7ain the circulating direction come into all equal relation. In addition, the respective grippers7cand7don the first belt8aand the third belt8care aligned in the direction perpendicular to the belt circulating direction so as to be capable of concurrently gripping the half sheet tip.

The second half sheet is gripped at its tip by the gripper7bon the second belt8balmost without any interval after the first half sheet, conveyed onto the stacker tray6and is discharged. At that occasion, the signal of the detection sensor20of the second belt8bis used for controlling the position in order to bring the gripper7band the half sheet tip into matching.

Moreover, the third half sheet is gripped by respective grippers7don the first belt8aand the third belt8c, conveyed onto the stacker tray6and is discharged.

Thus, in the present stacker51, the distance in the conveying direction between the respective grippers of the first to third belts8a,8band8cis positioned so as to match the half sheet size. Therefore, sheets can be stacked on the stacker tray6with the conveying interval between the half sheets being kept constant and shorter than in the conventional cases. The stacker tray6freely moves up and down and descends corresponding with the sheet stacking amount subjected to detection of the upper plane of the sheet by a sensor not illustrated in the drawing so that the upper plane of the sheet gets to the constant height.

Accordingly, the present stacker51can improve the stacking efficiency of the sheet with the half sheet size than the conventional one. Here, in the case where the circulation velocity of the first to third belts8a,8band8cgets uneven, the stacker51can be adjusted to make the circulation velocity constant.

InFIG. 3A, the controller30of the stacker51obtains, from the controller920of the apparatus body900A, information that the sheet is a large sheet. Here, the controller30causes the position of the tip stopper14of the stacker51to move from the half sheet position to the direction of the arrow B to stand by in the large sheet position.

Thereafter, the controller30drives the drive motor16to activate the clutch pulley18in the state where the first to third belts are circulated and to displace the position of the second belt8bfrom the first belt8aand the third belt8cby length equivalent to the semiperimeter of the belts. Then the grippers7band7aon the second belt8band the grippers7dand7con the first belt8aand the third belt8ccome to the state of being aligned in the direction perpendicular to the belt circulating direction.

In that state, the large sheet S2conveyed firstly is gripped concurrently by the three grippers7d,7band7don the first to third belts and conveyed onto the stacker tray6. The large sheet S2contacts the tip stopper14, is released from the gripper7c, drops onto the tray6and is stacked.

The second sheet is gripped concurrently by the three grippers7c,7aand7con the first to the third belts, conveyed onto the stacker tray6and stacked. The third large sheet is conveyed onto the stacker tray6by the three grippers7d,7band7dlikewise the first large sheet and stacked.

A large sheet is long in length in the sheet conveying direction (discharging direction). Therefore, a conventional stacker buckles to occur jamming. However, the present stacker will occur little jamming since the sheet is pulled and conveyed by the grippers. Moreover, the large sheet is gripped and conveyed by three grippers and therefore is conveyed and stacked in the more certain manner to occur little jamming.

Here, the case of the half sheet was exemplified by a mode where the relative positions of the grippers7aand7bto the grippers7cand7din the belt circulating direction is moved to the positions corresponding with the length of the half sheet so as to cope with two types of sheets of the large sheet and the half sheet respectively. However, the present invention is not limited to cope with the two types. That is, more belts are provided separately so as to cope with sheets of three or more types. And in the constitution, at an occasion of conveying sheets with shorter length, the relative positions of the grippers on the separately provided belt to the grippers7cand7din the belt circulating direction is set to the position corresponding with the length of the sheet. Such a constitution is acceptable.

That is, in the case of a large sheet, the present stacker51can convey the large sheet only with the first belt8aand the third belt8con both sides as illustrated inFIG. 4AandFIG. 4B. In that case, the controller30controls the clutch pulley18to cause the grippers7aand7bof the second belt8bin the center to withdraw to retracted positions so as not to hamper large sheet conveyance of the first belt8aand the third belt8cso that the rotary power of the drive motor16is not transmitted to the second belt8b. At that occasion, the retracted positions of the grippers7aand7bof the second belt8bin the center are positions outside the conveyance region of the sheet gripped by the grippers7cand7dprovided to the first belt8aand the third belt8con both sides.

Here, the apparatus can be constituted so that it can cope with three or more types of sheet. That is, further additional belts and grippers on the belts are provided. At the occasion of conveying a shorter sheet, the positions of the grippers to the grippers7cand7dare set to the position in the belt circulating direction corresponding with length of the sheet. At an occasion of conveying a long sheet, those grippers are positioned in the retracted positions in advance.

Here, in order to convey a large sheet only with the first belt8aand the third belt8con both sides, a lever21withdraw the second belt8bin the center upward as in the stacker52illustrated inFIG. 5. Rotation of the second belt8bis caused to stop in the state where the grippers7aand7bare positioned in the retracted positions so as not to hamper large sheet conveyance. Thereby, the large sheet can be conveyed only by the first belt8aand the third belt8c. That is, the second belt8bis moved to withdraw the grippers7aand7bprovided in the second belt8bfrom the conveyance region of the sheet conveyed by the grippers7cand7d.

Here, the driven shafts24supporting the driven pulleys12of the three belts are separated respectively. In addition, in the case of stacking half sheets with that stacker52, the second belt8bin the center is caused to descend to convey and stack the half sheet onto the stacker tray6in the state likewiseFIG. 2.

The sheet conveying apparatus42is adapted to include the first belt8a, the third belt8c, the second belt8bcapable of going up and down and the grippers7ato7dprovided in the respective belts.

Here, the first belt8aand the third belt8ccan be caused to stop to convey the sheet with the second belt8bin the center.

Thus, in the case where a plurality of belts is present to convey one sheet and large sheets are stacked, the belt to cause to circulate is made less abundant in number to enable decrease of drive load and the working sound.

The constitution can cope with three or more types. That is, further additional belts and grippers on the belts are provided. At the occasion of conveying a shorter sheet, the positions of those separately provided grippers to the grippers7cand7dare set to the position in the circulating direction corresponding with length of the sheet. At an occasion of conveying a long sheet, the belts are moved so that those grippers are positioned in the retracted positions.

(Stacker of Another Embodiment)

The stacker53illustrated inFIG. 6A,FIG. 6B,FIG. 7AandFIG. 7Bcan be designed to be capable of conveying a half sheet only with the second belt8din the center and conveying both of a half sheet and a large sheet with the first belt8aand the third belt8don both sides. Length of the second belt8din the center as a second circulating member is a half of length of the first belt8aand the third belt8don both sides.

The sheet conveying apparatus43is adapted to include the first belt8a, the third belt8c, the second belt8band the grippers7ato7dprovided in the respective belts.

FIG. 6AandFIG. 6Bare diagrams in the case where half sheets are stacked. The grippers7aon the second belt8dis adjusted in position by a clutch pulley18in the direction perpendicular to the gripper7cof the other belts8aand8cin the circulating direction (correspondent in the orthogonal direction).

The first half sheet S1is gripped by three grippers7c,7aand7cand conveyed. The second half sheet is gripped by the gripper7bon the second belt in the center and conveyed. The third half sheet is gripped by three grippers7d,7aand7dand conveyed. The fourth half sheet is gripped by the gripper7bon the second belt in the center and conveyed. Thereafter likewise operations are repeated so that the half sheets are conveyed and stacked.

In the case of conveying a large sheet S2, as illustrated inFIG. 7AandFIG. 7B, the second belt8din the center withdraws to a retracted position with the clutch pulley18so that the grippers7aand7bwill not hamper large sheet conveyance.

Accordingly, the sequentially conveyed large sheet is sequentially gripped in the tip by the grippers7cand7don the belts8aand8con both sides, conveyed onto the stacker tray16and stacked.

Here, clutch pulleys can be arranged in the belts on both sides. Then at an occasion of conveying a large sheet, the belts on both sides are stopped so that the sheet can be conveyed only by the belt in the center.

Thus, use of shorter belts can enhance compactness and lightness of the stacker.

The present embodiment was described with an example to cope with two types of sheets different in length but will not be limited thereto. By further providing short belts, three or more sizes can be coped with. Also in that case, at an occasion of conveying a short sheet, the position of the grippers on the further provided belts to the grippers7cand7din the belt circulating direction can be set in the position corresponding with the size. At an occasion of conveying a long sheet, the grippers are positioned in the retracted positions in advance.

This application claims the benefit of Japanese Patent Application No. 2006-243471, filed Sep. 7, 2006, which is hereby incorporated by reference herein in its entirety.