Sheet folding apparatus and image forming system

A sheet folding apparatus including a conveying roller pair, first and second folding roller pairs, and a control unit. The control unit controls the apparatus such that a sheet conveying speed or a sheet conveying amount of the conveying roller pair is different from a sheet conveying speed or a sheet conveying amount of the first folding roller pair or the second folding roller pair when the folded part of the folded sheet is guided between the first folding roller pair and the second folding roller pair.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is based on and claims priority pursuant to 35 U.S.C. §119 from Japanese Patent Application No. 2013-098827, filed on May 8, 2013, in the Japan Patent Office, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present application generally relates to a sheet folding apparatus and an image forming system. Particularly, this application relates to a sheet folding apparatus which is used for a post-processing apparatus, for example, of a body of an image forming system such as a printing machine. Examples of printing machines include a copying machine, a printer, a facsimile apparatus, a plotter, an inkjet recording apparatus, a stencil printing apparatus, or a multi-functional machine having two or more functions thereof. This application further relates to an image forming system having mounted thereon a sheet folding apparatus.

BACKGROUND ART

In general, in an image forming apparatus capable of copying onto a large-sized sheet, such as A0, A1, etc., if such a large-sized sheet is stored as it is or if the large-sized sheet is handled as it is, the storage space required is large, or handling is inconvenient, and as such, normally, the sheet is folded for storing and handling.

However, if a sheet folding operation is performed manually, a significant amount of time is needed, so that a time required for folding a sheet may end up being longer than a time required for copying.

In light of the above, there is a system in which is arranged, in a sheet discharge path of an image forming apparatus, a sheet folding apparatus which can fold a sheet automatically, making it possible to automatically fold in succession large-sized sheets copied, as is discussed generally in JP 5-238635, JP 11-349218, JP 2004-67266, and JP 2006-335500.

In a sheet folding apparatus for use in such a system, there may be included a unit (an off-line operation) for folding a sheet which was inadvertently copied and discharged without folding in advance, or a large-sized sheet which was produced by a different image forming apparatus, as well as (an on-line operation of) automatically folding a sheet discharged from an image forming apparatus.

When paper folding is actually performed by such a system, for a standard-sized sheet such as A0, A1, etc., paper folding can be performed using a predetermined size for each face of a sheet to be folded. In an image forming apparatus capable of copying onto the large-sized sheet, copying may be performed onto a long sheet such that a length in a sub-scanning direction amounts to several meters, so that it is required to perform paper folding even for such a non-standard long sheet.

A paper folding apparatus disclosed in JP 5-238635 automatically adjusts a folded length of each folded portion to fold even a sheet other than one having a standard length to a specified dimension.

JP 11-349218 discloses a paper folding method and a paper folding mechanism that orderly form a folding edge in a desired folding mode.

JP 2004-67266 discloses a paper folding machine which ensures that unnecessary folds are not produced when a folded sheet is discharged.

JP 2006-335500 discloses a paper folding apparatus which reduces unevenness in a folding dimension even for a large-sized sheet having a curled tip.

FIG. 23is a schematic diagram showing an operation of a related-art sheet folding apparatus. InFIG. 23, the sheet folding apparatus1includes a conveying roller pair3; a first folding roller pair6and a second folding roller pair7that are arranged in an opposing manner to the left and the right of a lower portion thereof; a first sheet guiding member4and a second sheet guiding member5that selectively guide a sheet P conveyed from the conveying roller pair3in each folding roller pair direction; and a lower sheet face guide10which guides a lower face of the sheet P. The sheet P is fed by the conveying roller pair3and conveyed, and selectively guided to the first folding roller pair6or the second folding roller pair7by an operation of the first sheet guiding member4or the second sheet guiding member5. The guided sheet P is folded a predetermined number of times by being fed between the first folding roller pair6or the second folding roller pair7while sliding on an upper face of the lower sheet face guide10. This is accomplished by an operation of the first sheet guiding member4or the second sheet guiding member5in alignment with repetition of forward and reverse rotations of the first folding roller pair6and the second folding roller pair7.

A first sensor8is arranged downstream of the first folding roller pair6in the sheet conveyance direction. The first sensor8senses the front end of the sheet folded by the first folding roller pair6. A second sensor9is arranged downstream of the second folding roller pair7in the sheet conveyance direction. The second sensor9senses the front end of the sheet folded by the second folding roller pair7. InFIG. 23, a number2denotes an inlet sensor.

Another known folding method is one in which crest folding is repeated. A folding finishing state shown in FIG.24A is a state in which an A0-sized sheet is folded, resulting in basic folding. In this case, crest folding is performed twice with a title column facing up. Moreover, in a similar manner, with respect to A0-sized bag folding, crest folding is performed twice with the title column facing up. This folding, which cannot be handled by the related-art sheet folding apparatus, is handled by performing crest folding and trough folding from the title column side as shown inFIG. 24B.

There are other folds which require finishing in which there are successive folds in the same direction. These are folds which are often used in notices, brochures, etc., including, for example, an inner three fold as shown inFIG. 24Cand a gate fold as shown inFIG. 24D. A Z-fold shown inFIG. 24Bis achieved by folding to successively perform trough folding or to successively perform crest folding.

However, the sheet folding apparatus1often causes displacement of the folded sheet shown inFIG. 23Cwhen the apparatus transfers the folded sheet between rollers.

FIG. 23Ashows a state in which a sheet is folded at first, the front end Pt of the folded sheet is guided to a conveying roller pair3by reversing the second folding roller pair7and with a second sheet guiding member5. In this state, a gap occurs between an aspect from the front end Pt to the folded part Pb of the folded sheet and another aspect of the sheet part after the folded part Pb.

The diagram shown inFIG. 23Bis a state in which the front end Pt of the folded sheet is inserted in the conveying roller pair3again in the state with the gap shown inFIG. 23A.

The diagram shown inFIG. 23Cis a state in which the folded part Pb of the folded sheet is guided from the second folding roller pair7to the first folding roller pair6. When the folded part Pb of the folded sheet is nipped and conveyed by the first folding roller pair6in this state. The folded part Pb of the folded sheet is formed to the displacement of the folded sheet.

SUMMARY

In light of the problems and circumstances as described above, a main object of the present application is to prevent forming displacement of the folded sheet when performing successive trough folding or performing crest folding.

According to an embodiment of the present application, a sheet folding apparatus includes: a conveying roller pair which feeds a sheet and a first folding roller pair and a second folding roller pair which fold the sheet fed from the conveying roller pair in turns. The first and second folding roller pairs are arranged at a predetermined gap with respect to each other. A sheet conveying speed or a sheet conveying amount of the conveying roller pair is different from a sheet conveying speed or a sheet conveying amount of the first folding roller pair or the second folding roller pair when the folded part Pb of the folded sheet is guided from the folding roller pair to another folding roller pair.

DETAILED DESCRIPTION

The embodiments of the present application are described in detail with reference to a plurality of embodiments and drawings. For elements (parts, components, etc.,) having the same function, shape, etc., in multiple embodiments or variations, the same reference numerals are used, so that repetitive explanations are omitted after having been explained once unless there is a possibility of confusion.

InFIG. 1, an image forming system100includes an image forming apparatus200and a sheet folding apparatus300.

In the image forming apparatus200, a conveying member210conveys a sheet P which is fed by a sheet feeding member209, an image forming unit220forms an image on the sheet P, and a discharge member230discharges the sheet P out of the image forming apparatus200.

A sheet inlet member21in the sheet folding apparatus300connected at the discharging outlet of the image forming apparatus200and receives the sheet P discharged out of the image forming apparatus200. A feeding unit20feeds the sheet P to a sheet folding unit1.

InFIG. 1, an inlet sensor2is a sheet detecting unit arranged between the conveying roller pair3and the feeding unit20. The inlet sensor2detects a tip of the sheet P which is conveyed from the feeding unit20. The inlet sensor2is a trigger signal for use in control of an operation of each member, motor, etc., at and after a timing of detecting thereof.

FIG. 2is a diagram showing in detail a sheet folding unit1. As shown inFIG. 4, the sheet folding unit1includes the inlet sensor2, a conveying roller pair3, a first folding roller pair6, a second folding roller pair7, a first sensor8, a second sensor9, a first sheet guiding member4, a second sheet guiding member5, and a lower sheet face guide10.

The conveying roller pair3is the conveying rotating pair member which conveys the sheet P. The first folding roller pair6and the second folding roller pair7are arranged, with a predetermined gap therebetween, in an opposing manner at the left and the right in a lower portion of the conveying roller pair3. Those are the first folding rotating member pair and the second folding rotating member pair which folds the sheet P. A first sensor8is a first sheet detecting unit which detects a sheet P edge (including a sheet P edge portion and a folding edge portion) on the first folding roller pair6side. A second sensor9is a second sheet detecting unit which detects a sheet P edge on the second folding roller pair7side. A first sheet guiding member4is a first sheet guiding member which can undergo fluctuating displacement and operation to guide, to the first folding roller pair6, the sheet P which is fed by the conveying roller pair3. A second sheet guiding member5is a second sheet guiding member which can undergo fluctuating displacement and operation to guide, to the second folding roller pair7, the sheet P which is fed by the conveying roller pair3. A lower sheet face guide10is a lower sheet face guiding member which guides the sheet P guided by the first sheet guiding member4or the second sheet guiding member5to a nip portion between the respective rollers6aand6bof the first roller pair6or the respective rollers7aand7bof the second roller pair7.

The conveying roller pair3, the first folding roller pair6, and the second folding roller pair7are supported by the apparatus body via an axle respectively such that they can undergo forward and reverse rotations. The first sheet guiding member4or the second sheet guiding member5is also a member which selectively guides, to the respective folding roller pairs6and7directions, the sheet P which is conveyed from the conveying roller pair3.

The sheet P is conveyed by the conveying roller pair3and selectively guided to the first folding roller pair6or the second folding roller pair7by a displacement operation of the first sheet guiding member4or the second sheet guiding member5. If it is guided to the first folding roller pair6side, a tip or a folding edge of the sheet P is detected by the first sensor8and, with this detected time as a reference, the first folding roller pair6undergoes a reverse rotation after being conveyed for a required distance. If it is guided to the second folding roller pair7side, a tip or a folding edge of the sheet P is detected by the second sensor9. With this detected time as a reference, the second folding roller pair7undergoes a reverse rotation after being conveyed for a required distance. In alignment with this reverse rotation, the first sheet guiding member4is caused to undergo a displacement operation at a time of conveying to the first folding roller pair6and the second sheet guiding member5is caused to undergo a displacement operation at a time of conveying to the second folding roller pair7. Then, being guided by the first sheet guiding member4or the second sheet guiding member5from inside a sheet folded portion Pb of the sheet P, a lower face of the sheet P is folded a predetermined number of times by being slid on an upper face of the lower sheet face guide10and fed to the first folding roller pair6or the second folding roller pair7toward which there is a conveying direction.

As shown inFIG. 3, a driving system for the first sheet guiding member4includes a sheet guiding member driving arm33a, a first sheet guiding member operating pivotal axle34, a sheet guiding member driving pulley32a, a sheet guiding member driving belt31a, and a first sheet guiding member driving motor30.

A driving system for the second sheet guiding member5includes a sheet guiding member driving arm33b, a second sheet guiding member operating pivotal axle35, a sheet guiding member driving pulley32b, a sheet guiding member driving belt31b, and a second sheet guiding member driving motor36.

The driving system of the first sheet guiding member4and the driving system of the second sheet guiding member5are configured to be generally the same, so that explanations are given below with the driving system of the first sheet guiding member4being represented.

The first sheet guiding member4is fixed to the arm33a. The pulley32ais supported to be able to turn, or in other words, to fluctuate within a predetermined angular range to one of side plates (the side of the side plate which is arranged on the front side of a sheet face) that is an immobile member (not shown) on the apparatus body side. The arm33ais fixed to the pulley32awith the operating pivotal axle34. A motor30, which is fixed to the side plate, is arranged in the vicinity of the pulley32a. A belt31ais stretched between a motor pulley which is fixed to an output axle of the motor30and the pulley32a, so that the motor30, the pulley32a, and the arm33aare in a driving force transmitting relationship. With the driving system of the above-described configuration, the driving force of the motor30is transmitted to the arm33aand a position of the first sheet guiding member4is changed to allow a displacement operation, making it possible to guide from inside a sheet folded portion Pb and a tip Pt of a sheet P (seeFIGS. 4 and 5).

For the second sheet guiding member5, a displacement operation which is similar to that for the first sheet guiding member4is performed, so that guiding is performed from inside the sheet folded portion Pb and the tip Pt of the sheet P. However, operations of the first sheet guiding member4and the second sheet guiding member5need to be performed independently. Therefore, the displacement operation of the second sheet guiding member5is performed by driving of the second sheet guiding member driving motor36, which is independent of the first sheet guiding member driving motor30. The pulley32band the arm33bare fixed to the operating pivotal axle34, which is supported to be able to fluctuate to the other of side plates (the side of the side plate which is arranged on the back side of a sheet face) not shown.

InFIG. 3, a position of the first sheet guiding member4which is fixed to the arm33a(that is shown in a solid line) and a position of the second sheet guiding member5which is fixed to the arm33b(that is shown in a solid line) are respective home positions. Also shown is a position at which the first and second sheet guiding members4and5(shown in a long dashed double-short dashed line), which are fixed in a corresponding manner to arms33aand33b, undergo a displacement operation via a fluctuating displacement and operation of each arm33aand33bby driving of the respective motors30and36.

FIGS. 4 to 13are schematic diagrams which show how trough folding is mainly performed in a successive manner.

As shown inFIG. 4, in a home position state in which the first sheet guiding member4and the second sheet guiding member5are arranged in parallel such that they oppose each other, a tip Pt of the sheet P, which is conveyed by the conveying roller pair3, which is rotating in a direction shown by the arrow, is guided by a displacement operation of the first sheet guiding member4. Then, as the sheet P is guided to the first folding roller pair6, which is rotating in a direction shown by the arrow, and as conveying of the sheet P is continued, the sheet P enters a nip portion of the first folding roller pair6, so that the sheet P is placed therebetween and conveyed. After this, the tip Pt of the sheet P is detected by the first sensor8. Before or after this operation, the first sheet guiding unit4undergoes a displacement operation and returns to an original home position.

Next, as shown inFIG. 5, after conveying for a required distance with a detected timing of the first sensor8as a reference, the first folding roller pair6undergoes a reverse rotation. Then, the sheet folded portion Pb of the sheet P is guided from inside the sheet folded portion Pb by a displacement operation of the second sheet guiding member5and guided to the second folding roller pair7, which is arranged in an opposing manner. As shown inFIG. 6, as conveying is continued, the sheet P enters a nip portion of the second folding roller pair7and is placed therebetween and conveyed, so that folding is formed. The folding edge formed is detected by the second sensor9. Before or after this operation, the second sheet guiding member5undergoes a displacement operation and returns to an original home position.

Then, as shown inFIG. 7, after conveying for a required distance with a detected timing of the second sensor9as a reference, the second folding roller pair7undergoes a reverse rotation. Then, the sheet folded portion Pb of the sheet P is conveyed toward the first folding roller pair6. At that time, the second sheet guiding member5operates from the state inFIG. 7to the state inFIG. 8. The operation guides the tip Pt of the sheet P, and prevents the tip Pt of the sheet P from moving to the first folding roller pair6. In the state inFIG. 8, the second folding roller pair7conveys the sheet P to the first folding roller pair6as shown inFIG. 9.

Thereafter, the sheet P is guided to the first folding roller pair6and is placed therebetween and conveyed as shown inFIG. 10by an operation of the first sheet guiding member4, and the sheet P is detected by the first sensor8.

Then, as shown inFIG. 12, after conveying the sheet P for a required distance with a detected timing of the first sensor8as a reference, the first folding roller pair6undergoes a reverse rotation. Then, the portion of the sheet P in which a second folding is carried out is guided from inside the sheet folded portion Pb by a displacement operation of the second sheet guiding member5and guided to the second folding roller pair7, which is arranged in an opposing manner. It enters the second folding roller pair7and is placed therebetween and conveyed by continued conveying, so that the second folding is formed. An edge of the second folding formed is detected by the second sensor9. With this detection by the second sensor9as a reference, the following operation is selected, making it possible to successively perform trough folding and successively perform crest folding.

In embodiment 1 of the present application, as shown inFIG. 9, a tension state of the sheet P between a nip of the second folding roller pair7and the first sheet guiding unit becomes loose. Then the present application prevents formation of displacement of the folded sheet P as shown inFIG. 23C.

FIGS. 14A-14Cillustrate an operation in the sheet folding apparatus1and show an operation followingFIG. 9.FIG. 14Ais a diagram showing that a state of the sheet P inFIG. 9is slacked. InFIG. 14A, a part P1of the sheet P and another part P2of the sheet P are slacked each, and the tip Pt of the sheet P is conveyed to the conveying roller pair3in a state with the gap between the part P1of the sheet P and another part P2of the sheet P.

FIG. 14Bshows a state of the tip Pt of the sheet P conveyed in a state that is slacked and with the gap inFIG. 14Areaches to the conveying roller pair3.FIG. 14Cshows a state of the tip Pt of the sheet P conveyed more by a state inFIG. 14B, and enters in the conveying roller pair3.

The sheet P is conveyed with a gap of a sheet conveying speed (a sheet conveying amount) between the conveying roller pair3and the first folding roller pair6or the second folding roller pair7, when the sheet folded portion Pb of the sheet P is guided from one folding roller pair (6or7) to another folding roller pair (6or7), which is arranged in an opposing manner. In other words, the sheet conveying speed (the sheet conveying amount) of the conveying roller pair3is different from that of the first folding roller pair6or the second folding roller pair7.

In that way the slack of the sheet P, between the conveying roller pair3and the first folding roller pair6or the second folding roller pair7, is able to be removed. Therefore, formation of displacement of the folded sheet when the sheet is folded is prevented.

Embodiment 1 of the present application is explained as a case to successively perform trough folding, or to successively perform crest folding, as well as to alternately perform crest folding and trough folding.

As shown inFIG. 14, Embodiment 2 is an example that the conveying roller pair3conveys the sheet P faster than does the first folding roller pair6or the second folding roller pair7dose. Thus, the slack of the sheet P, between the conveying roller pair3and the first folding roller pair6or the second folding roller pair7, is able to be removed, as shown inFIG. 14C.

On the other hand, the conveying roller pair3conveys the sheet P more than does the first folding roller pair6or the second folding roller pair7. Thus, the slack of the sheet P is able to be eliminated similarly.

In addition to an effect of embodiment 1, embodiment 2 has the following effect: The slack of the sheet P is able to be removed while the first folding roller pair6or the second folding roller pair7is conveying the sheet P to the conveying roller pair3.

FIGS. 15A-15Cillustrate an operation in the sheet folding apparatus1, which show embodiment 3. The sheet P is capable of causing to be slacked, by changing the relative operation of the conveying roller pair3, the first folding roller pair6and the second folding roller pair7, during a series operation ofFIG. 14shown in embodiment 2. Therefore, an operation of embodiment 3 is changing the conveying speed.

InFIG. 15A, conveying amount of the sheet P is reduced by stopping temporarily to convey the sheet P with the first folding roller pair6and the second folding roller pair7, during a series operation shown inFIG. 14. Therefore, the sheet conveying amount with the conveying roller pair3is larger than the sheet conveying amount with the first folding roller pair6and the second folding roller pair7. Thus, the slack of the sheet P is able to be removed, and the operation prevents formation of displacement of the folded sheet when the sheet is folded.

InFIG. 15B, the conveying amount of the sheet P is reduced by slowing down the conveying speed with the first folding roller pair6and the second folding roller pair7, during a series operation shown inFIG. 14. Therefore, the sheet conveying amount with the conveying roller pair3is larger than the sheet conveying amount with the first folding roller pair6and the second folding roller pair7. As such, the slack of the sheet P is able to be removed, and the operation prevents formation of displacement of the folded sheet when the sheet is folded.

InFIG. 15C, the conveying amount of the sheet P is increased by speeding up the conveying speed with the conveying roller pair3, during a series operation shown inFIG. 14. Therefore, the sheet conveying amount with the conveying roller pair3is larger than the sheet conveying amount with the first folding roller pair6and the second folding roller pair7. As such, the slack of the sheet P is able to be removed without lowering productivity, and the operation prevents formation of displacement of the folded sheet when the sheet is folded.

In addition, the operation of conveying with the conveying roller pair3, the first folding roller pair6, and the second folding roller pair7is changed, in a state where the tip Pt of the sheet enters in the conveying roller pair3, and the part P1and the part P2of the sheet P is conveyed with the conveying roller pair3, the first folding roller pair6, and the second folding roller pair7, as shown inFIG. 15A.

FIGS. 16A-16Cillustrate an operation in the sheet folding apparatus1, which show embodiment 4.

FIGS. 16A and 16Bshow that a conveying speed and force of the conveying roller pair3is larger than those of the first folding roller pair6or the second folding roller pair7. Therefore, the slack of the sheet P is able to be removed. Then a gap of the conveying speed is absorbed by a conveying slip of the second folding roller pair7.

FIG. 16Cshows that a conveying speed of the conveying roller pair3is larger than that of the first folding roller pair6or the second folding roller pair7, and a conveying force of the first folding roller pair6or the second folding roller pair7is larger than those of the conveying roller pair3.

As such, the slack of the sheet P is able to be removed. Then a gap of the conveying speed is absorbed by a conveying slip of the conveying roller pair3.

Embodiment 4 is the operation in a state where the tip Pt of the sheet enters in the conveying roller pair3, and the part P1and the part P2of the sheet P is conveyed with the conveying roller pair3, the first folding roller pair6, and the second folding roller pair7. Therefore, the operation is able to remove the slack of the sheet P, and prevents formation of displacement of the folded sheet.

The operation of embodiment 4 carried out when the sheet P is conveyed from the first folding roller pair6or the second folding roller pair7to the conveying roller pair3as shown inFIG. 14AtoFIG. 14C.

FIG. 17shows a driving operation of the conveying roller pair3, the first folding roller pair6, and the second folding roller pair7in the sheet folding apparatus, according to embodiment 6.

InFIG. 17, a rotational driving force of a motor50for driving a conveying roller is transmitted to a pulley51for driving a conveying roller through a belt58for driving a conveying roller, and to a pulley53afor driving a pressing roller through a belt52afor driving a pressing roller. The rotational driving force transmitted to the pulley53afor driving a pressing roller drives the conveying roller pair3.

A rotational driving force of a motor60for driving a folding roller is transmitted to a pulley61for driving a folding roller through a belt68for driving a folding roller, and to a pulley63afor driving a pressing roller through a belt62afor driving a pressing roller. The rotational driving force transmitted to the pulley63afor driving a pressing roller drives the first folding roller pair6and the second folding roller pair7.

On the other hand, the conveying roller pair3includes a pressing roller3aand a conveying roller3b. The pressing roller3aand the conveying roller3bare each pressure-contacted by a spring54for pressing a conveying roller. The first folding roller pair6includes a pressing roller6aand a folding roller6b. The pressing roller6aand the conveying roller6bare each pressure-contacted by a spring64for pressing a folding roller. The first folding roller pair7includes a pressing roller7aand a folding roller7b. The pressing roller7aand the conveying roller7bare each pressure-contacted by a spring64for pressing a folding roller.

InFIG. 17, for example, a conveying force gap between the conveying roller pair3and the first folding roller pair6or the second folding roller pair7is caused by setting it so that a pressing force of the spring54is different from that of the spring64.

FIG. 18is an enlarged perspective view showing a driving operation of a pressure roller constituted by a conveying roller pair in the sheet folding apparatus according to embodiment 7. A torque limiter70is attached with a driving shaft in the pulley53afor driving a pressing roller shown inFIG. 17. A rotary driving force with more than a torque set in the torque limiter70isn't transmitted from the pulley53afor driving a pressing roller to the pressing roller3a.

A torque limiter70is attached with a driving shaft in one lowering the conveying force among the conveying roller pair3, the first folding roller pair6and the second folding roller pair7. Therefore, the conveying force gap between the conveying roller pair3and the first folding roller pair6or the second folding roller pair7is caused. At that time, the torque limiter70is able to absorb the gap of the conveying speeds. Therefore, the displacement of the folded sheet is prevented without damaging to the sheet with slip between the sheet P and the conveying roller pair3or the first folding roller pair6or the second folding roller pair7.

FIG. 19is a diagram showing a driving operation of the conveying roller pair3, the first folding roller pair6, and the second folding roller pair7in the sheet folding apparatus according to embodiment 8. A drive system inFIG. 19also drives a roller and a counter roller among roller pair.

InFIG. 19, a rotational driving force of a motor50for driving a conveying roller is transmitted to pulleys51for driving conveying rollers respectively through a belt58for driving a conveying roller. In addition, the rotational driving force is transmitted to a pulley53afor driving a pressing roller and a pulley53bfor driving a conveying roller through a belt52afor driving a pressing roller and a belt52bfor driving a conveying roller. Then the rotational driving force transmitted drives both the pressing roller3aand the conveying roller3b, that is the conveying roller pair3.

A rotational driving force of a motor60for driving a folding roller is transmitted to a pulley61for driving a folding roller through a belt68for driving a folding roller. In addition, the rotational driving force is transmitted to a pulley63afor driving a pressing roller and a pulley63bfor driving a folding roller through a belt62afor driving a pressing roller and a belt62bfor driving a folding roller. The rotational driving force transmitted to the pulleys63afor driving a pressing roller and to the pulleys63bfor driving a folding roller drive the pressing roller6aand the folding roller6bcomposed of the first folding roller pair6, and the pressing roller7aand the folding roller7bcomposed of the second folding roller pair7.

FIG. 20is a diagram illustrating an operation in effect according to embodiment 8.

InFIG. 20A, the slack of the sheet part P1is equal with that of the sheet part P2, and only one side of the roller pair3,6,7is driven. Therefore both slacks of the sheet part P1and the sheet part P2are removed.

InFIG. 20B, the slack of the sheet part P1is larger than that of the sheet part P2, and only one side of the roller pair3,6,7is driven. The sheet part P1is maintained and the displacement of the folded sheet is caused because the pressing roller3acan't convey the sheet part P1when the slack of the sheet part P2is removed.

InFIG. 20C, the slack of the sheet part P1is larger than that of the sheet part P2, and both sides of the roller pair3,6,7are driven. Therefore, the slack of the sheet part P1is also removed by conveying with the conveying roller3bregardless of the state of the slacked sheet, as shown inFIG. 20B.

FIG. 21is an enlarged perspective view showing a driving operation of the pressure roller constituted by the conveying roller pair3in the sheet folding apparatus1, according to embodiment 9. The driving system of the conveying roller pair3, the first folding roller pair6, and the second folding roller pair7is shown inFIG. 19.

Two torque limiters70are attached with a driving shaft in the pulley53afor driving a pressing roller and another driving shaft in the pulley53bfor driving a conveying roller respectively.

A rotary driving force with more torque than a torque set in the torque limiters70isn't transmitted from the pulley53afor driving a pressing roller and the pulley53bfor driving a conveying roller to the pressing roller3aand the conveying roller3b, respectively.

Torque limiters70are attached with a driving shaft in one lowering the conveying force among the conveying roller pair3, the first folding roller pair6and the second folding roller pair7. Therefore, a conveying force gap between the conveying roller pair3and the first folding roller pair6or the second folding roller pair7is caused. At that time, the torque limiter70is able to absorb the gap of the conveying speeds regardless of slack of the sheet P1or the sheet P2. Therefore, the displacement of the folded sheet is prevented without damaging the sheet with slip between the sheet P and the conveying roller pair3or the first folding roller pair6or the second folding roller pair7.

On the other hand,FIG. 22is a block diagram showing a control configuration of an image forming system which shows the present application including embodiments 1-8.

A control unit400of a sheet folding apparatus includes CPU401, ROM402, RAM403, SERIAL I/F404and TIMER405, and controls the sheet folding apparatus300.

The image forming apparatus200and the sheet folding apparatus300transmit and receive commands to control for conveying a sheet and folding a sheet through SERIAL I/F415and404. A CPU401of the sheet folding apparatus300conducts various controls which include for a sheet folding processing with the conveying roller pair3, the first folding roller pair6, the second folding roller pair7, the first sheet guiding member4and the second sheet guiding member5, and for causing the gap of the sheet conveying speed or the sheet conveying amount between the conveying roller pair3and the first folding roller pair6or the second folding roller pair7.