Abstract:
A sheet discharging device includes a guide member including a guide surface on which a conveyed sheet is guided, a plurality of sheet discharging rollers, which have an axis, arranged on a guide surface side of the guide member at intervals in a direction crossing a direction in which the sheet is conveyed, the sheet discharging rollers discharging the sheet guided on the guide surface, a sheet discharging tray on which sheets discharged by the sheet discharging rollers are stacked, and a plurality of projecting portions provided on the guide member and projecting from a plane on which the sheet discharging rollers contact the sheet, toward the axis of the sheet discharging rollers, to partly raise the sheet toward the axis of the sheet discharging rollers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-193028, filed Jun. 30, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a sheet discharging device mounted in, for example, an auto document feeder in an image forming apparatus to discharge each loaded sheet to a sheet discharging tray or the like, and to a sheet discharging method.  
         [0004]     2. Description of the Related Art  
         [0005]     Some image forming apparatuses such as copiers are provided with an auto document feeder (ADF). The auto document feeder takes out each of the documents (sheets) stacked in a sheet feeding tray and feeds it to a read position in the image forming apparatus. Then, after an image is read, the auto document feeder discharges the sheet to a sheet discharging tray. The auto document feeder is thus provided with a sheet feeding device that discharges the document from which the image has been read, to the sheet discharging tray. The sheet discharging device comprises a guide member that guides the conveyed document and a sheet discharging roller that discharges the document guided by the guide member, to the sheet discharging tray.  
         [0006]     A problem with the conventional sheet discharging device is that a variation in document discharging speed, document size, or the like suppresses the alignment of documents on the sheet discharging tray, that is, the alignment of discharged sheets. The main cause of the suppressed alignment of discharged sheets is that the leading end of a discharged document hangs down owing to gravity and comes into contact with the surface of the documents already discharged onto the sheet discharging tray, thus moving the documents on the sheet discharging tray.  
         [0007]     To solve this problem, a technique has been developed which provides a flange portion at one or both of the ends of the sheet discharging roller to corrugate documents. This enables corrugated documents to advance straight more properly when discharged. A discharged document thus first comes into contact with the surface of the documents on the sheet discharging tray at a position farther than the one achieved using a sheet discharging roller without any flange portion. This reduces the time for which and the area over which the discharged document contacts the surface of the documents on the sheet discharging tray. The alignment of discharged documents is thus improved.  
         [0008]     A disclosed technique for corrugating documents is adapted for sheet discharging in a fixer in an image forming apparatus (for example, Jpn. Pat. Appln. Publication Nos. 9-240900 and 2002-12355). This technique also uses a flange portion provided on a roller corresponding to a sheet discharging roller to corrugate documents.  
         [0009]     However, the manufacture costs of the sheet discharging roller increase when the sheet discharging roller is provided with the flange portion as in the prior art.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     The present invention provides a sheet discharging device and a sheet discharging method that can corrugate discharged sheets without increasing manufacture costs.  
         [0011]     An aspect of the present invention configures a sheet discharging device as described below.  
         [0012]     A sheet discharging device comprises a guide member comprising a guide surface on which a conveyed sheet is guided; a plurality of sheet discharging rollers, which have an axis, arranged on a guide surface side of the guide member at intervals in a direction crossing a direction in which the sheet is conveyed, the sheet discharging rollers discharging the sheet guided on the guide surface; a sheet discharging tray on which sheets discharged by the sheet discharging rollers are stacked; and a plurality of projecting portions provided on the guide member and projecting from a plane on which the sheet discharging rollers contact the sheet, toward the axis of the sheet discharging rollers, to partly raise the sheet toward the axis of the sheet discharging rollers.  
         [0013]     Another aspect of the present invention configures a method for discharging a sheet as described below.  
         [0014]     A method for discharging a sheet comprises guiding a conveyed sheet along a guide surface to a sheet discharging tray; and allowing projecting portions provided on the guide surface to raise at least a part of the guided sheet in a direction in which the sheet is separated from the guide surface.  
         [0015]     The present invention enables discharged sheets to be corrugated without increasing the manufacture costs.  
         [0016]     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0017]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0018]      FIG. 1  is a front view showing a digital copier according to an embodiment of the present invention;  
         [0019]      FIG. 2  is a sectional view showing the internal structure of an auto document feeder according to the embodiment of the present invention;  
         [0020]      FIG. 3  is a schematic diagram showing a sheet discharging portion according to the embodiment as viewed from a downstream side in a direction in which the documents are conveyed; and  
         [0021]      FIG. 4  is a schematic diagram showing the sheet discharging portion according to the embodiment as viewed from the front of the auto document feeder. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     An embodiment of the present invention will be described below in detail with reference to the drawings.  
         [0000]     (Configuration of a Digital Copier)  
         [0023]      FIG. 1  is a front view showing a digital copier in accordance with an embodiment of the present invention. As shown in  FIG. 1 , the digital copier comprises an auto document feeder (ADF)  10 , a scanner unit  20 , and a printer engine section  30 .  
         [0024]     The auto document feeder  10  loads and supplies each document D to a read position R (described later).  
         [0025]     The scanner unit  20  optically reads an image from the document D supplied by the auto document feeder  10  or manually to convert the image into image data.  
         [0026]     The printer engine section  30  comprises a charger, a laser unit, a photosensitive drum, a developing device, a transfer roller, and a fixing device (none of them are shown). The charger charges a surface of the photosensitive drum to a predetermined potential. The laser unit forms an electrostatic latent image on the surface of the photosensitive drum on the basis of image data from the scanner unit  20 . The developing device develops the electrostatic latent image on the photosensitive drum using toner. The transfer roller transfers the toner image formed on the photosensitive drum to a sheet. The fixing device fixes the toner image transferred to the sheet. In this configuration, the printer engine section  30  copies the document image read by the scanner unit  20  to the sheet.  
         [0000]     (Configuration of the Auto Document Feeder  10 )  
         [0027]      FIG. 2  is a sectional view showing the internal structure of the auto document feeder  10  in accordance with the embodiment of the present invention. As shown in  FIG. 2 , the auto document feeder  10  is composed of a sheet feeding tray  11  on which a plurality of documents D are placed, a conveying device  12  that takes each of the documents D out of the sheet feeding tray  11  to convey the document D along a conveying path C (described later), and a sheet discharging tray  13  that accommodates a plurality of documents D discharged by the conveying device  12 .  
         [0028]     The conveying device  12  comprises a first and second guide members  121  and  122 . The first and second guide members  121  and  122  comprise smooth guide surfaces  121   a  and  122   a , respectively, inside. The U-shaped conveying path C is provided in the gap between the guide surfaces  121   a  and  122   a  so that the document D can be conveyed along the conveying path C.  
         [0029]     The conveying path C connects the sheet feeding tray  11  and the sheet discharging tray  13  together. A read position R is provided in a portion of the conveying path C which is closest to the scanner unit  20 ; a document image is read at the read position R.  
         [0030]     The first guide member  121  is placed outside the second guide member  122 . The first guide member  121  has a rectangular opening  121   b  formed in its area corresponding to the read position R. This allows the document D conveyed along the conveying path C to be located opposite the scanner unit  20  on passing through the read position R.  
         [0031]     The conveying path C has a pickup roller  123 , a separate roller  124 , a registration roller  125 , a first conveying roller  126   a , a second conveying roller  126   b , a stabilizing roller  127 , a third conveying roller  126   c , and a sheet discharging roller  128  which are arranged in this order from an upstream side in a direction in which the document D is conveyed.  
         [0032]     The pickup roller  123  picks up each of the documents D in the sheet feeding tray  11  and loads it into the conveying path C of the conveying device  12 . When a plurality of documents D are loaded by the pickup roller  123 , the separate roller  124  passes only the uppermost document D through, while blocking the passage of the remaining documents D. The registration roller  125  registers the document D the passage of which is not blocked by the separate roller  124 . The first to third conveying rollers  126   a  to  126   c  convey the document D registered by the registration roller  125 , along the conveying path C. The stabilizing roller  127  stabilizes the behavior of the document D conveyed by the first to third conveying rollers  126   a  to  126   c . The sheet discharging roller  128  discharges the document D conveyed by the first to third conveying rollers  126   a  to  126   c , from the conveying path C.  
         [0033]     Each of the rollers  123  to  128  has a plurality of (in the present embodiment, four) roller pieces around a horizontally supported drive shaft at predetermined intervals. When each of the drive shafts is rotated, all roller pieces provided around the drive shaft rotate concurrently.  
         [0034]     Pinch rollers  129  are arranged immediately below the respective sheet discharging roller pieces  128 . Each of the pinch rollers  129  is rotatably disposed in a groove portion  121   b  of the first guide member  121  (lower guide member  121   c  described later). Each of the pinch rollers  129  is contacted with an outer peripheral surface of the sheet discharging roller  128  under pressure by elastic means such as a leaf spring.  
         [0035]     The separate roller  124 , registration roller  125 , first to third conveying roller  126   a  to  126   c , and sheet discharging roller  128  constitute respectively roller pairs together with driven rollers arranged opposite them across the conveying path C. For example, the separate roller  124  constitutes a separate roller pair together with a corresponding driven roller.  
         [0036]     That portion of the first guide member  121  which lies downstream of the read position R is located below that portion of the second guide member  122  which lies downstream of the read position R. Thus, in the description below, the portion of the first guide member  121  located downstream of the read position R is called a lower guide portion  121   c . The portion of the second guide member  122  located downstream of the read position R is called an upper guide portion  122   c.    
         [0037]      FIG. 3  is a schematic diagram showing the sheet discharging portion  120  according to the embodiment as viewed from a downstream side in the direction in which the document D is conveyed.  FIG. 4  is a schematic diagram showing the sheet discharging section  120  in accordance with the embodiment as viewed from the front of the auto document feeder.  
         [0038]     As shown in  FIGS. 3 and 4 , the lower guide portion (guide member)  121   c  has a guide surface  121   d  located below the lowermost portion of the sheet discharging roller  128 . It is noted that the guide surface  121   d  is a part of the guide surface  121   a . The lower guide portion  121   c  comprises a plurality of (in the present embodiment, four) projecting portions  130  located substantially immediately below its drive shaft of the sheet discharging roller  128 . The number of projecting portions  130  is not particularly limited.  
         [0039]     The projecting portions  130  are disposed so that two of the four sheet discharging roller pieces  128  arranged at the opposite ends of the sheet discharging roller are each sandwiched between the projecting portions  130 . The upper end of the each projecting portion  130  projects upward from the lowermost portion of the sheet discharging roller  128 .  
         [0040]     Each projecting portion  130  comprises a first inclined surface  130   a  on its side surface located upstream in the conveying direction of the document D; the first inclined surface  130   a  becomes higher as it approaches its downstream end in the conveying direction. Each projecting portion  130  also comprises a second inclined surface  130   b  on its top surface which becomes higher as it approaches its downstream end in the conveying direction and which is gentler than the first inclined surface  130   a.    
         [0041]     Thus, when the document D reaches the projecting portions  130 , parts of the document D which correspond to the projecting portions  130  are scooped up by the first inclined surface  130   a  and run onto the second inclined surfaces  130   b . On the other hand, parts of the document D which are corresponding to the roller pieces of the sheet discharging roller  128  are guided by the upper and lower guide portions  121   c  and  122   c  as they are and then advance between the sheet discharging roller  128  and the pinch roller  129 .  
         [0042]     As described above, the document D from which a document image has been read is guided by the lower guide portion  121   c . The document D is then discharged onto the sheet discharge tray  13  by the sheet discharging roller  128 . The lower guide portion  121   c  (including the projecting portions  130 ), sheet discharging roller  128 , and sheet discharging tray  13  thus constitute a sheet discharging portion (sheet discharging device)  120  that discharges the document D from the conveying path C of the conveying device  12 . In the present embodiment, a common contact plane P for the sheet discharging roller  128  and pinch roller  129  corresponds to the contact plane between the sheet discharging roller and the sheet in accordance with the present invention.  
         [0000]     (Configuration of the Scanner Unit  20 )  
         [0043]     As shown in  FIG. 2 , the scanner unit  20  comprises a glass plate (not shown) at a position corresponding to the read position R. The glass plate  21  is colorless and transparent and has a reader (not shown) provided on its scanner unit  20  side. The reader comprises a first carriage, a second carriage, an image forming lens, and a CCD sensor (none of them are shown).  
         [0044]     The first carriage is provided with an exposure lamp (not shown) that irradiates the document D passing on a surface of the glass plate, and a first mirror that reflects reflected light from the document surface in a predetermined direction. A second and third mirrors (not shown) are attached to the second carriage to reflect the reflected light from the first mirror in a predetermined direction.  
         [0045]     The light emitted from the exposure lamp passes through the glass plate to the surface of the document D passing through the read position R. Then, the light reflected off the document surface passes through the glass plate back to the scanner unit  20 . The light is reflected by the first to third mirrors and then guided to the image forming lens. The light converged by the image forming lens is detected by the CCD sensor. The detection signal is used to create image data.  
         [0046]     A document glass board (not shown) is provided on the top surface of the scanner unit  20  so that the document D is manually placed on the document glass board. The document glass board is used to read a document image without the use of the auto document feeder  10 .  
         [0000]     (Operation of Discharging the Document D)  
         [0047]     The document D from which the document image has been read is conveyed to the sheet discharging roller  128  while being guided by the upper and lower guides  121   c  and  122   c . Once the conveyed document D reaches the projecting portions  130  of the lower guide portion  121   c , parts of the document D which correspond to the projecting portions  130  are scooped up by the first inclined surface  130   a  and run onto the second inclined surfaces  130   b . However, parts of the document D which are corresponding to the roller pieces of the sheet discharging roller  128  are guided by guide surfaces  121   d  and  122   d  of the upper and lower guide portions  121   c  and  122   c  as they are and then advance between the sheet discharging roller  128  and the pinch roller  129 .  
         [0048]     This causes the parts of the document D discharged onto the sheet discharging tray  130  to advance in different directions. The document D discharged to the sheet discharging tray  13  has a locally substantially S-shaped cross section, that is, the document is corrugated. Corrugated documents D are sequentially stacked on the sheet discharging tray  13 .  
         [0049]     An alternate long and short dash line (A) in  FIG. 3  shows the advancing direction of the parts of the document D which are corresponding to the projecting portions  130 . An alternate long and two short dashes line (B) in  FIG. 3  shows the advancing direction of the parts of the document D which are corresponding to the roller pieces of the sheet discharging roller  128 .  
         [0050]     The document D having run onto the projecting portions  130  is in contact only with the second inclined surface  130   b  until it is discharged to the sheet discharging tray  13 . Thus, the first inclined surface  130   a  is used to scoop up the leading end of the document D when it reaches the projecting portions  130 .  
         [0000]     (Comparison of Alignment of Discharged Documents)  
         [0051]     [Table 1] indicates the misalignment of documents D discharged onto the sheet discharging tray  13  with respect to the conveying direction. [Table 2] indicates the misalignment of the documents D discharged onto the sheet discharging tray  13  with respect to a lateral direction of the documents D, that is, a direction orthogonal to the conveying direction.  
         [0052]     In [Table 1] and [Table 2], LT, LT-R, LG, LD, and ST-R denote the sizes of the documents D. The numerical values in [Table 1] and [Table 1] represent the levels of misalignment of the documents D. A larger numerical value indicates a higher level of misalignment. A smaller numerical value indicates a lower level of misalignment. In the present comparison, the speed at which the document D is conveyed is about 210 mm/sec.  
                                                 TABLE 1                                   Size   Present embodiment   Prior art                                        LT   30   68           LT-R   5   22           LG   6   18           LD   23   34           ST-R   25   58                      
 
         [0053]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
               
               
                   
                 Size 
                 Present embodiment 
                 Prior art 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 LT 
                 18 
                 45 
               
               
                   
                 LT-R 
                 20 
                 5 
               
               
                   
                 LG 
                 8 
                 5 
               
               
                   
                 LD 
                 18 
                 18 
               
               
                   
                 ST-R 
                 5 
                 23 
               
               
                   
                   
               
             
          
         
       
     
         [0054]     As shown in [Table 1], the auto document feeder  10  according to the present embodiment is far more excellent in the alignment of the discharged documents D than a conventional auto document feeder that uses a flange portion provided on the sheet discharging roller to corrugate the documents.  
         [0055]     As shown in [Table 2], the auto document feeder  10  according to the present embodiment is far more excellent, for most document types, in the alignment of the discharged documents D than the conventional auto document feeder that uses the flange portion provided on the sheet discharging roller to corrugate the documents.  
         [0056]     [Table 3] indicates the misalignment of the documents D discharged onto the sheet discharging tray  13  with respect to the conveying direction. [Table 4] indicates the misalignment of the documents D discharged onto the sheet discharging tray  13  with respect to the lateral direction of the documents D, that is, the direction orthogonal to the conveying direction.  
         [0057]     In [Table 3] and [Table 4], A3, A4, and A4-R denote the sizes of the documents D. The numerical values in [Table 3] and [Table 4] represent the levels of misalignment of the documents D. A larger numerical value indicates a higher level of misalignment. A smaller numerical value indicates a lower level of misalignment.  
                                                                   TABLE 3                                       Basis weight                Size   60 g/m 2     64 g/m 2     80 g/m 2                              A3   23   8   3           A4   30   15   10           A4-R   5   5   15                      
 
         [0058]    
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                   
               
               
                   
                 Basis weight 
               
             
          
           
               
                   
                 Size 
                 60 g/m 2   
                 64 g/m 2   
                 80 g/m 2   
               
               
                   
                   
               
               
                   
                 A3 
                 18 
                 13 
                 18 
               
               
                   
                 A4 
                 18 
                 18 
                 16 
               
               
                   
                 A4-R 
                 20 
                 15 
                 13 
               
               
                   
                   
               
             
          
         
       
     
         [0059]     As shown in [Table 3] and [Table 4], the misalignment generally falls within a narrow range even with a small variation in misalignment depending on the weight of the document D.  
         [0060]     The above results indicate that the auto document feeder  10  according to the present embodiment significantly improves the alignment of the discharged documents D than the conventional auto document feeder that uses the flange portion provided on the sheet discharging roller to corrugate the documents.  
         [0000]     (Effects of the Present Embodiment)  
         [0061]     The lower guide portion  121   c  according to the present embodiment comprises the plurality of projecting portions  130 , which project upward from the lowermost portion of the sheet discharging roller  128 . The document discharged to the sheet discharging tray  13  thus has an S-shaped cross section, that is, the document is corrugated. This allows the discharged documents D to advance straight more properly.  
         [0062]     The present embodiment thus reduces the time for which a document D discharged later rubs against documents D already stacked on the sheet discharging tray  13 . The present embodiment also reduces the area over which the document D discharged later comes into frictional contact with the documents D already stacked on the sheet discharging tray  13 . This makes the documents D on the sheet discharging tray  13  difficult to move, thus improving the alignment of the documents D on the sheet discharging tray  13 .  
         [0063]     Furthermore, the projecting portions  130  according to the present embodiment are provided on the lower guide portion  121   c . This drastically reduces the manufacture costs compared to the conventional technique of providing a flange portion at one or both ends of the sheet discharging roller  128 .  
         [0064]     Moreover, each projecting portion  130  comprises the first inclined surface  130   a  on its side surface located upstream in the conveying direction of the document D; the first inclined surface  130   a  becomes higher as it approaches its downstream end in the conveying direction. This reduces a possible load on the document D running onto the projecting portions  130 . The document D is thus prevented from being damaged.  
         [0065]     The lower guide portion  121   c  has the guide surface  121   d  disposed below the lowermost portion of the sheet discharging roller  128 . This allows the parts of the document D corresponding to the projecting portions  130  to rise high on running onto the projecting portions  130 . The document D is thus significantly corrugated.  
         [0066]     Moreover, the auto document feeder  10  according to the present embodiment significantly improves the alignment of the discharged documents D than the conventional auto document feeder that uses the flange portion provided on the sheet discharging roller to corrugate the documents.  
         [0067]     The sheet discharging portion  120  is applicable not only to the auto document feeder but also to, for example, a fixer.  
         [0068]     The present invention is not limited to the above embodiments proper. In implementation, the components of the embodiments can be varied without departing from the spirit of the present invention. Further, various inventions can be formed by properly combining a plurality of components disclosed in the above embodiments. For example, some of the components shown in the embodiments can be deleted. Moreover, components of the different embodiments may be properly combined.  
         [0069]     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.