Patent Publication Number: US-8109501-B2

Title: Sheet feeding device with guide member

Description:
This application is based on Japanese Patent Application No. 2008-083128 filed on Mar. 27, 2008 in Japanese Patent Office, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a sheet feeding device that separates a sheet from a plurality of stacked sheets one sheet by one sheet and conveys to an image forming section or to an image reading section, in an image forming apparatus or an image reading apparatus. 
     As the sheet feeding device of this kind, those each being composed of a pickup roller, a feed roller and a retarding roller as is disclosed in, for example, Unexamined Japanese Patent Application Publication No. 5-43073, are widely used. 
     In this sheet feeding device, a sheet located at the outermost position of stacked sheets is caused to receive conveyance force by a pickup roller to be fed out and is conveyed after being separated from others by a feed roller and a retarding roller. 
     In the Unexamined Japanese Patent Application Publication No. 5-43073, between the pickup roller and the feed roller, there are provided guide members wherein a distance between the guide members arranged to interpose a sheet conveyance path between them becomes narrower gradually toward the downstream side from the upstream side in the sheet conveyance direction. 
     The sheet feeding device described in the Unexamined Japanese Patent Application Publication No. 5-43073 has a problem that conveyance of a thick sheet is not smooth, and sheet feeding failure tends to be caused. 
     Problems generated in the case of a thick sheet will be described as follows, referring to  FIGS. 1  ( a ) and  1  ( b ). 
     When sheet S is left under low humidity environment for a long time, moisture evaporates from the sheet, and an amount of evaporation on a peripheral portion of the sheet is more than that on the central portion, resulting in occurrence of a curvature whose form is close to that of a part of a spherical surface on a surface of sheet S. As a result, when a sheet S is placed on a sheet feeding table, a lift that is shown with K is formed on each of both end portions of the sheet S. 
       FIG. 1  ( b ) shows a phenomenon that takes place in the sheet feeding for curved sheet S shown in  FIG. 1  ( a ). 
     As is shown in  FIG. 1  ( b ), leading edges K on both lifted end portions of the sheet S hit an inclined guide surface of the guide member  110 , when Y represents the direction of conveyance for a sheet in sheet feeding. In the case of a thick sheet, the sheet S that hits the guide surface does not bend along the guide surface because stiffness of the sheet S is high, and thus, a leading edge of the sheet S is blocked by the guide member  110 , which stops conveyance of the sheet S. 
     In the case of a thin sheet whose stiffness is low, a stop of conveyance of this kind hardly takes place, but when stiffness is high as in the case of a thick sheet, a stop of conveyance that is called no-feed tends to take place. 
     An objective of the invention is to solve the aforesaid problem in a conventional sheet feeding device, and thereby to provide a sheet feeding device that can feed sheets stably even in the case of a thick sheet. 
     SUMMARY 
     The objective of the invention is attained by the following invention. 
     Item  1 . 
     A sheet feeding device which includes a pickup device which feeds a sheet by rotating while the pickup device comes in contact with a sheet located at an outermost position of a loaded stack of sheets, and a separation device which separates the sheet fed by the pickup device from another sheet and conveys the sheet with the separation device having a conveying device for conveying the sheet in a conveyance direction and a removing device for providing conveyance resistance on a lower surface of the sheet with the sheet feeding device further including a guide member for guiding the sheet from a point upstream of the separation device to a point downstream of the separation device in the conveyance direction, wherein the guide member comprises a sloping guide surface which is a slope so as to form a conveyance gap which is wider on an upstream side and narrower on a downstream side in the conveyance direction and wherein the sloping guide surface is formed so that an uppermost stream point of the slope is positioned on an upstream side of a separation point which is formed by the conveying device and the removing device in the conveyance direction and a lowermost stream point of the slope is positioned on a downstream side of the separation point in the conveyance direction. 
     Item  2 . 
     An image forming apparatus provided with the sheet feeding device of Item  1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Each of  FIG. 1  ( a ) and  FIG. 1  ( b ) is a diagram illustrating no-feed that is caused in sheet feeding for curved thick sheets. 
         FIG. 2  is a diagram showing overall composition of an image forming apparatus in which a sheet feeding device relating to the embodiment of the invention is incorporated. 
         FIG. 3  is a front sectional view of sheet feeding device  100  relating to the embodiment of the invention. 
         FIG. 4  is a top view of sheet feeding device  100  shown in  FIG. 3 . 
         FIG. 5  ( a ) and  FIG. 5  ( b ) are diagrams illustrating positional relationships between a guide member and a separation device, respectively in the central portion and an end portion in the width direction of a sheet. 
       Each of  FIG. 6  ( a ) and  FIG. 6  ( b ) is a diagram showing a sheet feeding testing instrument. 
       Each of  FIG. 7  ( a ) and  FIG. 7  ( b ) is a diagram showing an amount of curve. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     [Image Forming Apparatus] 
       FIG. 2  is a diagram showing overall composition of an image forming apparatus in which a sheet feeding device relating to the embodiment of the invention is incorporated. 
     Image forming apparatus A is an apparatus for forming an image on sheet S through a well-known electrophotographic system, and the image forming apparatus A has thereon automatic document feeder DF. Further, the image forming apparatus A is equipped with image reading section  1 , image processing section  2 , image forming section  3 , sheet storage section  4 , sheet feeding section  100  and reversal and sheet-ejection device  6 . 
     The automatic document feeder DF is an apparatus that separates documents placed on a document table (having no symbol) into a single sheet one by one, then, conveys it to an image reading position, and ejects it to sheet ejection tray (having no symbol). This automatic document feeder DF is also constructed to be capable of reversing a document upside down after conveying it to an image reading position, then, conveying again to the image reading position, to be ejected on a sheet ejection tray, and thus, it is possible to cause image reading section  1  described later to read only one side or both sides of the document. Incidentally, the automatic document feeder DF is made up so that a document may travel on an image reading position, and so that image reading section  1  which will be described later may read an image on a traveling document. However, it is also possible to constitute so that a document in transport is stopped temporarily, and the document that is at a standstill is read. 
     The image reading section  1  is a device that reads an image on a document to obtain image data and it is a device that reads an image on a document that is conveyed by the automatic document feeder DF. Namely, a document conveyed by the automatic document feeder DF is converted into image signals, on a photoelectric basis, by CCD (image sensor)  1 A representing an image pickup device, through an optical system (having no symbol) that is at a standstill. In addition, as stated above, it is also possible to constitute to obtain image data from a document that is at a standstill, while moving an optical system. Further, though image forming apparatus A is equipped with image reading section  1 , in the present embodiment, the image forming apparatus may also be one that obtains image data from an outer equipment through a network and thereby forms an image based on the image data. 
     Image processing section  2  conducts analog processing, A/D conversion, shading correction and image compression processing for analog signals converted by CCD image sensor  1 A on a photoelectric basis. After image processing by the image processing section  2 , signals are sent to image writing section  31  of image forming section  3  through a storing device (memory) AM that stores image data as occasion demands. 
     The image forming section  3  is one that forms an image on sheet S, and it forms an image through an electrophotographic system. The image forming section  3  has therein image writing section  31 , image forming unit  32  and fixing section  33 . The image writing section  31  is a device that gives exposure to a photoconductor drum (having no symbol) of image forming unit  32  which will be described later, based on the image data which have been read by image reading section  1  and have been image-processed by image processing section  2 , and forms a latent image of an image. In other words, light outputted from semiconductor laser (having no symbol) based on the image data is applied on a photoconductor drum of image forming unit  32 , and a latent image is formed. On the image forming unit  32 , there are conducted charging, exposure and development for the photoconductor drum, and a toner image is formed on the photoconductor drum. The toner image is transferred onto sheet S conveyed toward the image forming unit  32 . The photoconductor drum after transferring will be cleaned. 
     The fixing section  33  is a device that fixes a toner image transferred onto sheet S by image forming unit  32 . 
     Sheet storing section  4  is a device to store sheets S on which an image will be formed by image forming section  3 , and it has therein trays  41 ,  42  and  43  as well as manual bypass tray  44 . 
     Sheet feeding device  100  is a device that feeds out sheet S one by one from a plurality of trays  41 - 43 , and feeds a sheet to image forming section  3 . This sheet feeding device  100  is provided to correspond to each of trays  41 - 43  to feed sheets S placed in trays  41 - 43 . 
     Sheet S fed out of the sheet feeding device  100  is conveyed to registration roller  55  through conveyance section  5 . 
     Sheet S fed through the manual feeding tray  44  is supplied to the registration roller  55  by sheet feeding device  50 . 
     Reversal and sheet-ejection device  6  includes a sheet ejection device that ejects sheet S on which a toner image is fixed from image forming apparatus A, a reversing and ejecting device that reverses and ejects sheet S and a reversing device that reverses sheet S and conveys it again to image forming section  3 . 
     The reversal and sheet-ejection device  6  has therein sheet ejection roller  61  for ejecting a sheet from image forming apparatus A, sheet reversing section  62  that reverses sheet S upside down, switching section  63  that switches a path to convey sheet S coming out of fixing section  33  to the sheet ejection roller  61  side or to the reversing section  62  side and conveyance section  64  that conveys sheet S reversed at the sheet reversing section  62  to the image forming section  3  again. Then, when ejecting the sheet S on which a toner image is fixed as it is, the sheet S is guided to the sheet ejection roller  61  side by the switching section  63  to be ejected out of image forming apparatus A. 
     When ejecting the sheet S on which a toner image is fixed after reversing the sheet upside down, the sheet S is guided to the sheet reversing section  62  side by the switching section  63  to be conveyed temporarily, then, the advancing direction of the sheet is reversed, and the sheet is conveyed to the sheet ejection roller  61  side, to be ejected out of image forming apparatus A. 
     Further, when forming an image on a surface of sheet S being opposite to the side of sheet S on which a toner image has been fixed, the sheet S is guided to the reversing section  62  side to be conveyed, then, the advancing direction for the sheet is reversed, and the sheet is conveyed by conveyance section  64  toward the upstream side of registration roller  55  in the conveyance direction, thus, an image is formed on the opposite side. 
     [Sheet Feeding Device] 
     The sheet feeding device relating to the embodiment of the present invention will be described as follows, referring to  FIGS. 3-5  ( a ) and  FIG. 5  ( b ).  FIG. 3  is a front sectional view of sheet feeding device  100  relating to the embodiment of the invention,  FIG. 4  is a top view of sheet-feeding device  100  shown in  FIG. 3 , and  FIG. 5  ( a ) and  FIG. 5  ( b ) are diagrams illustrating positional relationships between a guide member and a separation device, respectively in a central portion and an end portion in the width direction of a sheet (direction perpendicular to conveyance direction for the sheet). 
     The sheet-feeding device  100  has therein pickup roller  102  representing a pickup device, feed roller  103  representing a conveyance device that constitutes a separation device and retarding roller  104  representing a removing device that constitutes the aforesaid separation device. 
     Feed roller  103  and retarding roller  104  are supported respectively on fixed shafts to be rotated. 
     The pickup roller  102  is supported on swing lever  101  that is supported by a rotary shaft for the feed roller  103 , and it is displaced vertically by swinging of the swing lever  101 . 
     The pickup roller  102  is caused by its own weight to be in contact with pressure on the top surface of sheet S. 
     Each of the pickup roller  102  and the feed roller  103  is driven by the same driving source (not shown) to rotate respectively in the direction of an arrow, and stacked sheets S are conveyed by these pickup roller  102  and feed roller  103  toward the left side (Y direction), beginning with an uppermost sheet. 
     The retarding roller  104  is given a rotary power in the direction of an arrow by a driving source (not shown). This direction of the rotary power is opposite to the direction of a rotary power given to the feed roller  103  as is illustrated, at a point of contact with the feed roller  103 . 
     The retarding roller  104  has a torque limiter  104 A. Therefore, when the feed roller  103  rotates in the direction of the arrow, the retarding roller  104  is driven by the feed roller  103  to rotate under prescribed resistance. 
     Each of numerals  105  and  106  is a guide member that guides sheet S at the downstream side of a point of separation for the sheet, and the numeral  107  is a guide member that guides sheet S at the upstream side of a point of separation for the sheet. As is illustrated, each of guide members  105  and  106  has a guide surface wherein a width thereof is broader at the upstream side in conveyance direction Y for sheet S and a width thereof is narrower at the downstream side and has a parallel guide surface extending from the aforesaid guide surface. 
     Incidentally, the expression of aforesaid upstream and downstream sides is based on the conveyance direction for sheet S. 
     The numeral  111  represents a sensor that detects the uppermost surface of stacked sheets S. The uppermost surface of the stacked sheets S is controlled to be at a fixed height constantly, based on detection signals of the sensor  111 , and this controlling method is widely known. 
     Next, guide member  110  will be describe as follows. 
     The guide member  110  has sloping guide surface  110 C representing a slope whose upstream side in the conveyance direction Y for sheet S is positioned to be higher and the downstream side is positioned to be lower as shown in  FIGS. 5  ( a ) and  5  ( b ). 
     Owing to the sloping guide surface  110 C of the guide member  110 , a leading edge of sheet S is not caught at an entrance and sheet S is guided to the separation point, namely, to a nipping portion between the feed roller  103  and the retarding roller  104 . 
     As shown in  FIG. 4 , the guide member  110  is composed of guide member  110 A and guide member  110 B which are substantially symmetrical about a center line in width direction X. 
     As illustrated, each of the guide members  110 A and  110 B is extending obliquely toward the downstream side from the center portion in the width direction X to an end portion. 
       FIG. 5  ( a ) shows a sectional view along line D 2 -D 2  at the center portion in the width direction in  FIG. 4 , while,  FIG. 5  ( b ) is a sectional view along line D 1 -D 1  at an end portion in the width direction in  FIG. 4 . 
     As shown in  FIG. 5  ( a ) and  FIG. 5  ( b ), the guide surface  110 C of the guide member  110  is a guide surface on which each sectional portion from a central part up to an end portion has the same slope. 
     A position of the sloping guide surface  110 C on the central portion is shifted from that of the sloping guide surface  110 C on the end portion. 
     Namely, on the end portion shown in  FIG. 5  ( b ), uppermost stream point P 2  (a point to start tilting) on the guide surface  110 C of the guide member  110  is positioned to be at the upstream side of separation point P 1 , and lowermost stream point (a point to finish tilting) P 3  is positioned to be at the downstream side of separation point P 1 . 
     Meanwhile, the separation point P 1  is the point of intersection of a line connecting the rotation center of feed roller  103  with the rotation center of retarding roller  104  with a line on which both rollers  103  and  104  are in contact with each other. 
     On the central part shown in  FIG. 5  ( a ), uppermost stream point P 2  and lowermost stream point P 3  on the guide surface  110 C of the guide member  110  are positioned to be at the upstream side of separation point P 1 . 
     Meanwhile, as shown in  FIG. 5  ( b ), the guide member  110  has guide surface  110 D that is in parallel with conveyance surface F for sheet S on the upstream side of sloping guide surface  110 C. 
     The guide member  110 A and the guide member  110 B are in a shape which is substantially symmetrical about a center line in the width direction, and they have respectively the aforesaid sloping guide surface  110 C and guide surface  110 D that is in parallel with conveyance surface F. 
     On the central part in the width direction, sheet S is guided by guide member  110  to be conveyed to separation point P 1  as shown in  FIG. 5(   a ). 
     In other words, owing to the sloping guide surface  110 C of the guide member  110 , a leading edge of sheet S advances toward separation point P 1 . 
     On the upstream side of the separation point P 1 , the uppermost sheet S is not separated completely from sheet S that is immediately under the uppermost sheet S, whereby, plural sheets S are conveyed by conveyance power of pickup roller  102  toward separation point P 1  with the uppermost sheet S leading the other sheet S. 
     In  FIG. 5  ( b ), the guide member  110  having sloping guide surface  110 C is in a shape wherein uppermost stream point P 2  of guide surface  110 C is at the upstream side of separation point P 1  and lowermost stream point P 3  of guide surface  110 C is at the downstream side of separation point P 1 . 
     When sheet S is guided by the guide surface  110 C of this kind, a leading edge of sheet S that is caused to touch the guide surface  110 C of guide member  110  because of the curve of the sheet, touches feed roller  103  after touching the guide surface  110 C before it arrives at separation point P 1 . The sheet S that has touched the feed roller is conveyed by feed roller  103 . 
     Therefore, plural sheets S are prevented from being crammed into a narrow space on the upstream side of separation point P 1 . 
     Not only a thin sheet, as a matter of course, but also a thick sheet having high stiffness can be conveyed smoothly to separation point P 1  by the sheet guide of this kind. 
     Guide surface  110 D that is in parallel with conveyance surface F is formed at the upstream side of sloping guide surface  110 C, on the end portion in the width direction shown in  FIG. 5  ( b ). 
     A thick sheet can be guided more securely by this parallel guide surface  11 D. 
     Thus, at separation point P 1 , uppermost sheet S only is conveyed by feed roller  103 , and lower sheets S other than the uppermost sheet S are held by retarding roller  104 . 
     In this way, sheet feeding in which a single sheet among sheets S is separated from the others and conveyed is carried out smoothly. 
     Further, as shown in  FIG. 5  ( a ), there is formed guide member  110  so that uppermost stream point P 2  and lowermost stream point P 3  of guide surface  110 C of guide member  110  may be positioned at the upstream side of separation point P 1 , on the central portion in the width direction. 
     As shown in  FIG. 1  ( a ), both end portions of curved sheet S are in the lifted form, but the central portion thereof does not exceed greatly the height regulated by pickup roller  102 . Therefore, in the central portion, separation and conveyance of the sheet can be carried out smoothly even in the case of curved and thick sheet S. 
     By using guide member  110 A and guide member  110 B which have sloping guide surfaces and are arranged obliquely to be substantially symmetrical about a center line in width direction as shown in  FIGS. 4 ,  5  ( a ) and  5  ( b ), smooth and stable sheet feeding can be carried out without occurrence of conveyance troubles such as no-feed, for various types of sheets S as stated above. 
     EXAMPLE 
     As shown in  FIGS. 6  ( a ) and  6  ( b ), sheet feeding table  120  is arranged to face sheet feeding device  100 , and side guide  121  that regulates the side of sheet S is positioned on each of both sides of the sheet feeding table  120 . 
     Further, for the purpose of curving sheet S, spacer member  122  is caused to adhere to the sheet feeding table  120  to be fixed at each of both end positions close respectively to side guides  121 . 
     As the spacer member  122 , an object wherein plate-like members each having a thickness of 1 mm are superposed was used so that a height may be adjusted in millimeters. 
     Sheets were stacked on sheet feeding table  120  so that the total thickness may be about 10 mm. 
     As a sheet, a thick sheet having basis weight of 314 g/m 2  was used. 
     In the Example, a sheet feeding device shown in each of  FIGS. 3 and 4  was used, and in the Comparative Example, there was used a sheet feeding device having a guide member whose cross section on a plane parallel to the conveyance direction is shown in  FIG. 5  ( a ) and which is parallel to the width direction. 
     Sheet feeding tests for feeding a single sheet from stacked sheets S was conducted and an occasion where no-feed occurred during a period of sheet feeding for 5 sheets was ranked to be rejection “B” and an occasion where no-feed did not occur during a period of sheet feeding for 5 sheets was ranked to be acceptance “A.” 
     Table 1 shows the results of the tests. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                   
                 Amount of lift on end portion 
               
               
                   
                 Height of upper 
                 (mm) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 limit detection 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Com- 
                 Standard ± 0 mm 
                 A 
                 A 
                 A 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
               
               
                 parative 
                 Standard + 1 mm 
                 A 
                 A 
                 A 
                 A 
                 B 
                 B 
                 B 
                 B 
                 B 
               
               
                 Example 
               
               
                 Example 
                 Standard ± 0 mm 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 B 
               
               
                   
                 Standard + 1 mm 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 B 
               
               
                   
               
            
           
         
       
     
     Table 1 shows an occasion wherein the upper limit of sheet S established by sensor  111  is made to be standard±0 mm and an occasion wherein the upper limit of sheet S established by sensor  111  is made to be standard±1 mm, both with respect to “Height of upper limit detection”. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Amount of curve (h − g) (mm) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Sheet type 1 
                 Sheet type 2 
                 Sheet type 3 
                 Sheet type 4 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 After 3 
                 5.0 − 1.7 = 
                 6.0 − 1.7 = 4.3 
                 3.0 − 0.0 = 3.0 
                 2.7 − 0.0 = 2.7 
               
               
                 hours 
                 3.3 
               
               
                 After 4 
                 9.5 − 5.0 = 
                 9.3 − 4.7 = 4.6 
                 3.5 − 0.0 = 3.5 
                 2.7 − 0.0 = 2.7 
               
               
                 days 
                 4.5 
               
               
                 After 9 
                 9.5 − 5.5 = 
                 8.3 − 5.3 = 3.0 
                 4.5 − 0.0 = 4.5 
                 1.0 − 0.0 = 1.0 
               
               
                 days 
                 4.0 
               
               
                   
               
            
           
         
       
     
     Table 2 shows results of the investigation of an amount of curve (degree of curvature) under the condition that four typical types of sheets available on the current market were left in low humidity environment. 
     As shown in  FIG. 7  ( a ) and  FIG. 7  ( b ), an amount of curve is difference amount of the lifts of sheet S (h−g) in the case where the sheet S is left on a flat plate. 
     SA in  FIG. 7  ( b ) shows a section of sheet S along center line L 1  in the width direction X, and SB shows a section of sheet S along edge line L 2  in the width direction X. 
     Since sheet S left under the condition of low humidity environment is curved as shown in  FIG. 1  ( a ) and  FIG. 1  ( b ) and described earlier, the sheet S is lifted on both ends r 1  and r 2  in the conveyance direction even at the central portion in the width direction X. 
     The amount of lift g at the central portion is an amount of lift for the higher end among both ends r 1  and r 2 . 
     With respect to end portions in the width direction, both ends in the conveyance direction r 3  and r 4  as well as r 5  and r 6  are lifted. 
     The amount of lift h of the end portion is an amount of lift that is the highest among those for r 3 , r 4 , r 5  and r 6 . 
     An amount of curve is defined by the following expression.
 
Amount of curve= h−g  
 
     As is apparent from Table 2, an amount of curve of the sheet is within a range of 5 mm. 
     Table 1 shows that rejection started to occur on a spacer member having a thickness of 4 mm in Comparative Example, and that spacer members up to thickness of 8 mm were accepted in Example, and conveyance troubles including no-feed were prevented sufficiently for sheets in the range to be used. 
     When a guide member having a sloping guide surface is used, there is a possibility that buckling occurs on a sheet in sheet feeding for thin sheets and an edge portion is folded. 
     For the purpose of investigating sheet feeding capability for thin sheets for the sheet feeding device relating to the invention, following tests were conducted. 
     Sheet feeding tests were conducted on the sheet feeding device used in the aforesaid Example and Comparative Example by using a sheet having basis weight of 64 g/m 2  and by curving the sheet so that an amount of curve may become 20 mm. 
     As a result of sheet feeding conducted by stacking 100 sheets on the sheet feeding table, no sheet folding due to buckling or the like occurred, resulting in smooth sheet feeding, for both Example and Comparative Example. 
     Owing to these tests, it was possible to confirm that a sheet feeding device on which the measures for no-feed for thick sheets have been taken can feed sheets smoothly and stably even for thin sheets. 
     In the present invention, guide members are provided so that the uppermost stream point of the sloping guide surface may be positioned at the upstream side of a separation point formed by a conveyance device and a removing device constituting a separation device, and the lowermost stream point may be positioned at the downstream side of the aforesaid separation point, as stated above. 
     Owing to these guide members, a leading edge of the curved sheet can be guided to the separation point and conveyed by the aforesaid separation device even in the case of a curved thick sheet. 
     Therefore, even in the case of curved thick sheets, the sheet can be separated smoothly to one sheet to be conveyed.