Abstract:
A sheet processing apparatus which flattens a curled sheet includes: a water content control unit which controls a water content of a sheet to flatten the curled sheet; a decurling section which is provided downstream the water content control unit with respect to a conveyance direction of the sheet, and the decurling section bends the curled sheet to be flat by a bending force; and a conveyance route changing section which changes a conveyance route of the sheet to direct to the water content control unit or not.

Description:
[0001]    This application is based on Japanese Patent Application No. JP2006-110555 filed on Apr. 13, 2006, with the Japanese Patent Office, the entire content of which is hereby incorporated by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a sheet processing apparatus which flattens a curled sheet and an image forming system in which the same apparatus is provided. 
       BACKGROUND OF THE INVENTION 
       [0003]    As is well known, image formation conducted by an electro-photographic process incorporates the process in which toner image is formed via electrostatic charge, exposure and development, the formed toner image is transferred onto a recording sheet and the toner image transferred onto the sheet is fixed. 
         [0004]    In the fixing of this process, when toner is melted by heat and pressure to fix the image on the sheet, water evaporates from the sheet due to the heat. Further, after the fixing, the sheet is open to the outside air, and thereby absorbs water from the outside air. 
         [0005]    Since such evaporation and absorbance of water occur at a different rate between the front and reverse surfaces of the sheet, resulting in waving or curling on the sheet, which of course is a major problem. 
         [0006]    The waved or curled sheets cause troubles during conveyance, subsequent image processing and stacking, in the sheet processing apparatus combined to the image forming apparatus. Further, bundled sheets formed by a filing process increase the thickness due to this deformation, which results in disturbance during binding and storage. Accordingly, technologies which can decurl these sheets have been developed. 
         [0007]    That is, in Unexamined Japanese Patent Application Publication 4-338,060 and Unexamined Japanese Patent Application Publication 5-309,971, technology is proposed in which a mechanical bending force is given to the sheet in the conveyance route, to decurl the sheet. The former further proposes the technology in which the amount of decurl can be selected, based on the type of sheet and density of the image fixed on the sheet. 
         [0008]    Even if the decurling amount is selected to use based on the type of recording sheet, since there are various types of the sheets, it is to be understood that when only physical bending force is used, sometimes the sheet can not be decurled. 
         [0009]    That is, relatively thick sheets are decurled by strong force, but thin sheets can not be decurled when only physical bending force is used. Specifically, bond paper for printing work can not be decurled when only physical bending force is used. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one embodiment of the present invention, a sheet processing apparatus which flattens a curled sheet. The apparatus includes a water content control unit which controls a water content of a sheet; a decurling section which is provided downstream the water content control unit with respect to a conveyance direction of the sheet, and the decurling section bends the curled sheet to be flat by a bending force; and a conveyance route changing section which changes a conveyance route of the sheet to direct to the water content control unit or to the decurling section. 
         [0011]    In the present invention, after water is applied to the both surfaces of the sheet to reduce the elasticity of the fibers which form the sheet, the bending force is applied to the sheet to be flattened by the decurling section, and even thin sheets can be properly flattened, whereby problems during conveyance, image processing and stacking are resolved. 
     
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0012]      FIG. 1  is a sectional view of a sheet processing apparatus B in an embodiment of the present invention. 
           [0013]      FIG. 2  is an enlarged sectional view of water content control unit  110 . 
           [0014]      FIG. 3  is an enlarged sectional view of decurling sections  150  and  160 . 
           [0015]      FIG. 4  is a drawing for the explanation of the amount of curl. 
           [0016]      FIG. 5  shows the total structure of an image forming system relating to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    The present invention will now be detailed, while referring to the drawings, which however is not limited to the present embodiment. 
         [0018]      FIG. 1  is a sectional view of the sheet processing apparatus in the embodiment of the present invention. 
         [0019]    Sheet S carrying the image which was formed by an image forming apparatus (which is to be detailed later) is introduced to route HR 1  from entrance  101  of sheet processing apparatus B, after sheet S is conveyed through route HR 2  or HR 3  to be processed, sheet S is discharged from sheet processing apparatus B. 
         [0020]    In both a non-decurling mode in which sheet S is not reformed in sheet processing apparatus B and a first decurling mode in which sheet S is mechanically flattened but the water content is not controlled, sheet S is conveyed through routes HR 1  and HR 2 . 
         [0021]    On the other hand, in both a water content control mode in which only the water content is controlled and a second decurling mode in which sheet S is mechanically flattened and the water content is controlled, sheet S is conveyed through routes HR 1  and HR 3  and a portion of route HR 2 . Route HR 2  or HR 3  is selected by switching gate  102 . 
         [0022]    Mechanical decurling sections  150  and  160  are provided on route HR 2 . Mechanical decurling section  150  flattens concavely curled sheet S 2 , and mechanical decurling section  160  flattens convexly curled sheet S 1 . “Convex curl” means that the surface of the sheet is convex upward, being sheet S 1 , while “concave curl” means that the surface of the sheet is convex downward, being sheet S 2 , which are illustrated in  FIG. 3 . 
         [0023]    Water content control unit  110  is provided on route HR 3 . Water content control unit  110  can be withdrawn by an operator from sheet processing apparatus B, being guided by rails  120 A and  120 B. 
         [0024]    In route HR 1 , sheet S is conveyed by paired rollers R 1 , while in route HR 2 , sheet S is conveyed by paired rollers R 2 -R 5 . In route HR 3 , sheet S is conveyed by paired rollers R 6 -R 11 . 
         [0025]    Tank unit  130 , provided under water content control unit  110  to supply water to water content control unit  110 , can be withdrawn from sheet processing apparatus B, being guided by rails  130 A and  130 B. 
         [0026]      FIG. 2  shows an enlarged sectional view of water content control unit  110 . 
         [0027]    Sheet S is vertically conveyed from route HR 1  (shown in  FIG. 1 ) to route U-shaped route HR 3  (shown in  FIG. 2 ), and then turns upward at a U-shaped section. Water content control unit  110  is mounted to sandwich a portion of route HR 3  through which sheet S is conveyed upward. 
         [0028]    Water content control unit  110  is formed of paired water content control sections, which are left side water content control section  110 A and right side water content control section  110 B. Left side water content control section  110 A is structured of moisturizing roller  111 A, water supplying roller  112 A and water tank  114 A, while right side water content control section  110 B is structured of moisturizing roller  111 B, water supplying roller  112 B and water tank  114 B. Moisturizing rollers  111 A and  111 B are in contact with each other, and rotate as shown by arrows to convey sheet S and to supply water to sheet S. 
         [0029]    Water supplying roller  112 A is in contact with moisturizing roller  111 A, while water supplying roller  112 B is in contact with moisturizing roller  111 B. Water supplying roller  112 A is partially submerged in water W of water tank  114 A, and water supplying roller  112 B is partially submerged in water W of water tank  114 B. 
         [0030]    Control member  113 A squeezes water supplying roller  112 A to regulate the water content of water supplying roller  112 A, while control member  113 B squeezes water supplying roller  112 B to regulate the water content of water supplying roller  112 B. 
         [0031]    Moisturizing rollers  111 A and  111 B, as well as water supplying rollers  112 A and  112 B are formed of single layered or double layered elastic members, such as non-foamed solid rubber and foamed rubber, or formed of double layered rubbers on which a textile is wrapped. Moisturizing roller  111 A is structured of metallic core  111 Aa and rubber layer  111 Ab layered on the same, while moisturizing roller  111 B is structured of metallic core  111 Ba and rubber layer  111 Bb layered on the same. Water supplying roller  112 A is structured of metallic core  112 Aa and rubber layer  112 Ab formed on the same, while water supplying roller  112 B is structured of metallic core  112 Ba and rubber layer  112 Bb formed on the same. 
         [0032]    Control members  113 A and  113 B are round bars which rotate or do not rotate. Flat blades may also be used for control members  113 A and  113 B. 
         [0033]    Water W stored in tank unit  130  is pumped up to water tanks  114 A and  114 B by a pump which is not illustrated, and any overflow in each tank returns to tank unit  130  through overflow tube  116 , whereby water level in water tanks  114 A and  114 B are secured in the same. In addition, water tanks  114 A and  114 B are connected to each other, and water in each tank is controlled to remain at the same level. 
         [0034]    During the water supplying process, moisturizing rollers  111 A and  111 B, as well as water supplying rollers  112 A and  112 B rotate as shown by arrows to supply water to each side of sheet S. 
         [0035]    Moisturizing roller  111 A and water supplying roller  112 A are symmetrically arranged with moisturizing roller  111 B and water supplying roller  112 B with respect to route HR 3  as shown in  FIG. 1 . Therefore, the form and the length of the water supplying path from water tank  114 A to moisturizing roller  111 A is the same as those of a water supplying path from water tank  114 B to moisturizing roller  111 B. 
         [0036]    Accordingly, an equal amount of water is supplied to both sides of sheet S. Further, since sheet S is moisturized in vertical route HR 3 , an equal amount of water is supplied onto sheet S in the direction of the thickness of sheet S, which preferably maintains the flatness of sheet S. 
         [0037]    Fans  117 A and  117 B blow dry air onto both surfaces of sheet S, which allow extra water in sheet S to evaporate just after the water supply so that parts mounted in the route, such as rollers, are prevented from covered with water. 
         [0038]      FIG. 3  is an enlarged sectional view of decurling sections  150  and  160 . 
         [0039]    Decurling section  150  is structured of small diameter roller  151  (having a radius of 7 mm, for example), paired belt driven rollers  152  and  153 , and belt  154  entraining about belt driven rollers  152  and  153 . Spring  156  is entrained about shaft  155  and small diameter roller  151 , and allows small diameter roller  151  to press against belt  154 . 
         [0040]    Changeover gate  157  switches the conveyance routes of sheet S. When changeover gate  157  exists at the dotted position in  FIG. 3 , route HR 21  is selected through which sheet S can not enter decurling section  150 , while when changeover gate  157  exists at the solid-line position, route HR 22  is selected through which sheet S enters decurling section  150 . 
         [0041]    Since route HR 21  has a large curvature radius, for example 60 mm, as shown in the figure, when sheet S passes through route HR 21 , no decurling operation is conducted. On the other hand, when sheet S passes through route HR  22  formed of small diameter roller  151  and belt  154 , sheet S is decurled by bending force generated by small diameter roller  151  and belt  154 . That is, a concavely curled sheet S 2  is returned to be a flat sheet state. 
         [0042]    Next, decurling section  160  is structured of small diameter roller  161  (having, for example, a radius of 7 mm), paired belt driven rollers  162  and  163 , and belt  164  entraining about belt driven rollers  162  and  163 . Coiled spring  166  is entrained about shaft  165  and small diameter roller  161 , and allows small diameter roller  161  to press against belt  164 . 
         [0043]    Changeover gate  167  switches the conveyance routes of sheet S. When changeover gate  167  exists as at the dotted-line position in  FIG. 3 , route HR 23  is selected through which sheet S does not enter decurling section  160 , while when changeover gate  167  exists as at the solid-line position, route HR 24  is selected through which sheet S enters decurling section  160 . 
         [0044]    Since route HR 23  has a large curvature radius for example, 60 mm, as shown in the figure, when sheet S passes through route HR 23 , no decurling is conducted. On the other hand, when sheet S passes through route HR  24 , sheet S is decurled by bending force generated by small diameter roller  161  and belt  164 . That is, convexly curled sheet S is returned to its original flat sheet state. 
         [0045]    Using sheet processing apparatus B, the operator can select an operation mode from among: a non-decurling mode which does not reform sheet S, a water content control mode which moisturizes sheet S, a first decurling mode which flattens sheet S using a bending force, but without moisturizing sheet S, and a second decurling mode which flattens sheet S using a bending force after moisturizing sheet S. 
         [0046]    In the non-decurling mode, route HR 2  is selected by changeover gate  102  as shown in  FIG. 1 , and routes HR  21  and HR 23  shown in  FIG. 2  are selected by changeover gates  157  and  167 , respectively, through which sheet S is conveyed. 
         [0047]    In the water content control mode, route HR  3  is selected by changeover gate  102  in  FIG. 1 , and routes HR  21  and HR 23  shown in  FIG. 2  are selected by changeover gates  157  and  167 , respectively. After sheet S passes through routes HR 1  and HR 3  in  FIG. 1 , sheet S is moisturized by water supplying device  110 , then sheet S enters route HR 2  between paired rollers R 2 , and further passes through routes HR 21  and HR 23  to be ejected out of sheet processing apparatus B. 
         [0048]    The first decurling mode, in which sheet S is mechanically decurled without water, includes decurling mode A which flattens the concavely curled sheet, and decurling mode B which flattens the convexly curled sheet. 
         [0049]    In decurling mode A, after route HR 2  is selected by changeover gate  102  shown in  FIG. 1 , route HR 22  is selected by changeover gate  157 , and route HR 23  is selected by changeover gate  167  shown in  FIG. 3 . 
         [0050]    Accordingly, concavely curled sheet S 2  passes through the selected routes which are HR 2 , HR 22  and HR 23 , and is reformed to the original flat sheet state by decurling section  150 , after which flattened sheet S is ejected out of sheet processing apparatus B. 
         [0051]    In decurling mode B, after route HR 2  is selected by changeover gate  102  shown in  FIG. 1 , route HR 21  is selected by changeover gate  157 , and route HR 24  is selected by changeover gate  167 . 
         [0052]    Accordingly, convexly curled sheet S 1  passes through the selected routes which are HR 2 , HR 21  and HR 24 , and is returned to its original flat sheet state by decurling section  160 , after which flattened sheet S is ejected out of sheet processing apparatus B. 
         [0053]    The second decurling mode in which sheet S is mechanically decurled and water content of the sheet is controlled, also includes decurling mode A and decurling mode B. 
         [0054]    In decurling mode A, after route HR 3  is selected by changeover gate  102  shown in  FIG. 1 , route HR 22  is selected by changeover gate  157 , and route HR 23  is selected by changeover gate  167  shown in  FIG. 3 . 
         [0055]    Accordingly, concavely curled sheet S 2  passes through route HR 3 , after which it is moisturized by water content control unit  110 , and is reformed to be its original flat sheet state by decurling section  150 , then flattened sheet S is ejected out of sheet processing apparatus B. 
         [0056]    In decurling mode B, after route HR 3  is selected by changeover gate  102  shown in  FIG. 1 , sheet S passes through route HR 2  and route HR 21  which is selected by changeover gate  157 , and further passes through route HR 24  which is selected by changeover gate  167  shown in  FIG. 3 . 
         [0057]    Accordingly, convexly curled sheet S 1  passes through route HR 3 , after which it is moisturized by water content control unit  110 , and is reformed to be its original flat sheet state by decurling section  160 , then flattened sheet S is ejected out of sheet processing apparatus B. 
         [0058]    Table 1 shows the effects of reformation of the various types of sheets. 
         [0000]    
       
         
               
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Amount of curl (average value at 4 
               
               
                   
                 corners of a single side copy) [mm] 
               
             
          
           
               
                   
                 After decurling operation 
               
             
          
           
               
                   
                   
                   
                 When water 
                   
               
               
                   
                   
                   
                 content is 
                 When water 
               
               
                   
                 Sheet 
                   
                 not 
                 content is 
               
             
          
           
               
                   
                 Basis 
                   
                 Before 
                 controlled 
                 controlled 
               
               
                   
                 weight 
                 Types of 
                 decurling 
                 [water 
                 [water 
               
               
                 Symbol 
                 [g/m 2 ] 
                 sheet 
                 operation 
                 content: 2%] 
                 content: 6%] 
               
               
                   
               
             
          
           
               
                 A 
                 64 
                 J paper 
                 5 
                 3 
                 3 
               
               
                   
                   
                 (sheet for 
               
               
                   
                   
                 plain paper 
               
               
                   
                   
                 copier) 
               
               
                 B 
                   
                 Kinmari-V 
                 12 
                 11 
                 4 
               
               
                   
                   
                 (bond paper) 
               
               
                 C 
                 81.4 
                 Kinmari-V 
                 14 
                 10 
                 3 
               
               
                   
                   
                 (bond paper) 
               
               
                 D 
                 128 
                 Kinmari-V 
                 16 
                 4 
                 4 
               
               
                   
                   
                 (bond paper) 
               
               
                 E 
                   
                 Connie Kent 
                 10 
                 2 
                 3 
               
               
                   
                   
                 (PPC) 
               
               
                 F 
                 209 
                 Connie Kent 
                 9 
                 −2 
                 2 
               
               
                   
                   
                 (PPC)) 
               
               
                 G 
                 262 
                 Connie Kent 
                 12 
                 −3 
                 3 
               
               
                   
                   
                 (PPC) 
               
               
                   
               
               
                 J-paper: KONICAMINOLTA HOLDINGS, INC. 
               
               
                 Kinmari-V: HOKUETSU PAPER MILLS, LTD. 
               
             
          
         
       
     
         [0059]    In Table 1, PPC paper represents paper for the plain paper copier, while bond paper represents paper for printing. The amount of curl represents the average of differences h 1  to h 4  measured between the height of center and the height of four corners of A4 sized sheet S, as shown in  FIG. 4 . 
         [0060]    As shown by Table 1, curled sheets A and D-G are effectively flattened by the bending force of the mechanical decurling section without a water supplying process, while curled sheets B and C are not. However, curled sheets B and C are effectively flattened by the bending force of the decurling section after the water supplying process. 
         [0061]    Accordingly, based on the present embodiment, when the bending force is applied to a curled sheet by the mechanical decurling section after water is supplied, the various types of sheets are effectively flattened, though they are conventionally very difficult to be flattened by only the mechanical bending force. 
         [0062]    In addition to the above flattening effects, the present embodiment can also be used like below. 
         [0063]    That is, due to the water supplying process, some types of sheet may be curled or excessively curled. Such phenomena occur on sheets having coating layers, because the material of the sheet is not uniform, in view of the thickness direction. 
         [0064]    In such a case, after flat sheet S is curled by water content control unit  110 , it can be flattened to its original state by decurling section  150  or  160 . 
         [0065]      FIG. 5  shows a total structure of an image forming system, including image forming apparatus A, sheet processing apparatus B and book binding apparatus C (which is a sheet post-processing apparatus), relating to the embodiment of the present invention. 
         [0066]    Image forming apparatus A incorporates an image forming section which includes: charging section  2 , image exposure section  3  (which is a writing section), developing section  4 , transfer section  5 A, discharging section  5 B and cleaning section  6 , all of which are mounted around image carrier  1 . In the image forming section, after the surface of image carrier  1  is evenly charged by charging device  2 , which is scanned by laser beam generated by image exposure device  3  based on the image data which are read from the document, whereby latent images are formed on the surface of image carrier  1 . The latent images are developed by developing section  4 , and form the reversal toner image on the surface of image carrier  1 . 
         [0067]    Sheet S, which is supplied from sheet accommodating section  7 , is conveyed to a transfer position. At the transfer position, the above toner images are transferred by transfer section  5 A onto sheet S. After electrical charges on the reverse side of Sheet S are neutralized by discharging section  5 B, sheet S carrying the toner images separates from image carrier  1 , and is conveyed to conveyance section  7 B, further, sheet S is heat-fixed by fixing section  8 , and then ejected by paired ejecting rollers  7 C into sheet processing apparatus B. 
         [0068]    In addition, fixing section  8  includes heat roller  8 A, pressure applying roller  8 B to press against heat roller  8 A, and heater  8 C. The unfixed toner images are heated by heat roller  8 A, which is heated by heater  8 C, whereby deposited toner for forming the toner images is melted and fixed on sheet S. 
         [0069]    In the case of the double-sided image formation on sheet S, which has been heat-fixed by fixing section  8 , sheet S is branched from an ordinal ejecting route by route changeover plate  7 D, sheet S is flipped over in reverse conveyance section  7 E, and again conveyed to the image forming section. After images are formed on the reverse side of sheet S, sheet S is re-conveyed to fixing section  8 , and ejected by paired ejecting rollers  7 C from image forming apparatus A into sheet processing apparatus B. 
         [0070]    Concerning image carrier  1 , after the images are processed, any remaining toner on its surface is removed by cleaning section  6 , and image carrier  1  stands-by for the next image formation. 
         [0071]    In sheet processing apparatus B, sheet S is controlled based on the selected mode, such as the non-decurling mode which does not reform sheet S, the water content control mode which moisturizes sheet S, the first decurling mode which flattens sheet S using bending force without supplying water to sheet S, and the second decurling mode which flattens sheet S using bending force after sheet S is moisturized. 
         [0072]    The operator selects any of these modes using an operation section (which is not illustrated) of image forming apparatus A, or instructions sent via a network from an outer apparatus can be used to select the mode. 
         [0073]    Book binding apparatus C, as the sheet post-processing apparatus, is structured of sheet conveyance section  210 , sheet ejecting section  220 , cover supplying section  230 , printed sheets accommodating section  240 , printed sheets conveyance section  250 , pasting section  260 , cover attaching section  270 , cover folding section  280 , and book ejecting section  290 , all of which are vertically oriented in book binding apparatus C. 
         [0074]    When sheets S are to be ejected without being bound, the route directing to printed sheets accommodating section  240  is closed, and the route directing to sheet ejecting section  220  is opened. 
         [0075]    When printed sheets S are to be bound, sheets S are sequentially stacked on a predetermined position of printed sheets accommodating section  240 , whereby a stack of the printed sheets S is formed, which includes predetermined number of pages. The stack of the printed sheets S on sheets accommodating section  240  is conveyed to stacked sheets supporting section  250 , and section  250  rotates and stands vertically, then glue is applied onto the edge of the stacked sheets by pasting section  260 . 
         [0076]    Next, a cover sheet is supplied from cover supplying section  230  to be attached onto the stack by cover attaching section  270 , and the cover is folded by cover folding section  280  to become a book. 
         [0077]    The book is then ejected by book ejecting section  290  from book binding apparatus C. 
         [0078]    Additionally, book binding apparatus C is further detailed in JPA 2003-209,869.