Abstract:
A sheet alignment apparatus includes: an aligning element for pushing a sheet supported on a sheet supporting face by moving in a direction perpendicular to a conveyance direction of the sheet, thereby aligning a position of the sheet; and a driving source for reciprocating the aligning element. An aligning face of the aligning element is arranged to be inclined with respect to the sheet supporting face.

Description:
[0001]     This application is based on Japanese Patent Application No. 2005-206853 filed on Jul. 15, 2005, which is incorporated hereinto by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a sheet alignment apparatus for aligning a sheet-like paper and a sheet finisher provided with the sheet alignment apparatus.  
         [0003]     For paper with an image formed thereon, an high-speed image forming apparatus such as an electrophotographic image forming apparatus is often used in combination with a sheet finisher that provides finishing operations such as stapling, punching, folding and shifting. The sheet finisher is commonly equipped with a sheet stacking apparatus for stacking a plurality of sheets are stacked to form a bundle of paper.  
         [0004]     In many cases, the sheet stacking apparatus is required to have a function of stacking sheets by aligning the edge of each sheet or a plurality of sheets being fed, in both the lateral and longitudinal directions. The sheet stacking apparatus has a sheet alignment apparatus for aligning the edges in the lateral and longitudinal directions, i.e. the edges in the conveying direction of the paper being introduced, and the edge across the width of paper.  
         [0005]     As disclosed in the Patent Document 1, the sheet alignment apparatus includes an aligning element for aligning the lateral edge of paper by making a reciprocating motion in the direction intersecting the conveying direction when paper is introduced into the sheet stacking apparatus and a stopper for receiving the leading edge of paper when it is introduced. It aligns the paper falling from a inclined supporting table, in the lateral and longitudinal directions.  
         [0006]     [Patent Document 1]: the Official Gazette of Japanese non-examined Patent Publication No. 10-297815.  
         [0007]     The following describes the conventional sheet alignment apparatus with reference to  FIG. 6 .  
         [0008]     The sheet alignment apparatus has a supporting table SD for supporting the sheet and aligning elements SG 1  and SG 2  for aligning the sheet. Sheets S are stacked on the supporting table SD. Every time the sheet S is introduced, the aligning elements SG 1  and SG 2  make a reciprocating motion opposite to each other in the X direction so as to align the lateral edges of the sheets S. When the stacked sheets are curled, the sheets S close to the bottom of the bundle of sheets S are formed flat due to the weight of sheets S. However, the sheets S on the upper portion are not pressed from the top, and therefore, the force for correcting the curl is reduced or the correcting force does not work, with the result that the curl of sheets S is kept uncorrected at the time of introduction.  
         [0009]     Thus, the apparent length Lb of the sheets on the upper portion is smaller than the apparent length La of the sheets closer to the bottom. To be more specific, the sheet contour line SRS formed by connecting the edges of the sheets S is inclined with respect to the aligning line SGS drawn on the aligning face of the aligning element SG 1 . The spacing between the aligning line SGS and sheet contour line SRS is greater at a higher position.  
         [0010]     As a result, alignment effects of the aligning elements SG 1  and SG 2  are reduced at a higher position. Thus, the alignment of the edges of sheets tends to become more difficult due to reduced alignment performances.  
         [0011]      FIG. 6  shows an example of an upward curl wherein the central portion of sheet S is curled upward. This is the same as the downward curl wherein the central portion of sheet S is curled downward, in that the apparent length of the sheet S is smaller as the degree of curling is greater. The sheet contour line SRS is more removed from the perpendicular aligning line SGS at a higher position.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention is characterized by one of the following structures:  
         [0013]     1. A sheet alignment apparatus comprising: an aligning element for pushing edges of a sheet supported on a sheet supporting face by moving in a direction perpendicular to a conveyance direction of the sheet, thereby aligning a position of the sheet; and a driving source for reciprocating the aligning element, wherein an aligning face of the aligning element is arranged to be inclined with respect to the sheet supporting face.  
         [0014]     2. A sheet finisher comprising: an aligning element for pushing edges of a sheet supported on a sheet supporting face by moving in a direction perpendicular to a conveyance direction of the sheet, thereby aligning a position of the sheet position; a driving source for reciprocating the aligning element; and a supporting table having the sheet supporting face being inclined by 60° or more with respect to a horizon, wherein an aligning face of the aligning element is arranged to be inclined with respect to the sheet supporting face. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is an overall block diagram representing an image forming apparatus incorporating a sheet alignment apparatus and sheet finisher as an embodiment of the present invention;  
         [0016]      FIG. 2  is a diagram showing the major portions of the sheet finisher as an embodiment of the present invention;  
         [0017]      FIG. 3  is a plan of the sheet alignment apparatus as an embodiment of the present invention;  
         [0018]      FIG. 4  is a cross sectional view showing an example of the aligning element;  
         [0019]      FIG. 5  is a cross sectional view showing another example of the aligning element; and  
         [0020]      FIG. 6  is a cross sectional view of a conventional aligning element. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     The following describes the present invention with reference to the embodiments shown in the drawings, without the present invention being restricted thereto.  
         [0000]     &lt;Image Forming Apparatus&gt; 
         [0022]      FIG. 1  is an overall block diagram representing an image forming apparatus incorporating a sheet finisher as an embodiment of the present invention.  
         [0023]     The image forming apparatus main body A has an image forming section GK in which a charger  2 , an imagewise exposing unit  3 , a developing unit  4 , a transfer unit SA, a discharger SB, a separation claw  5 C and a cleaning unit  6  are arranged around a photoreceptor  1 . After the surface of the photoreceptor  1  has been uniformly charged by the charger  2 , a latent image is formed by exposure based on the image data obtained by reading the document Ge to be copied by the light beam of the imagewise exposing unit  3  or the image data received from the outside through a network. The latent image is subjected to reversal development by the developing unit  4 , whereby a toner image is formed on the surface of the photoreceptor  1 .  
         [0024]     The recording-sheet RS fed from the sheet feed tray  7 A as a sheet feeding and storing unit is fed to the transfer position, where the toner image is transferred onto the recording sheet RS by the transfer unit  5 A. Then the electric charge on the back side of the recording sheet RS is removed by the discharger  5 B. The recording sheet RS is removed from the photoreceptor  1  by the separation claw  5 C, and is conveyed by the intermediate conveyance unit  7 B. Then the recording sheet RS is subjected to the process of fixing by a fixing unit  8 , and is ejected by an ejection roller  7 C.  
         [0025]     When an image is formed on one side of the recording sheet RS, a conveyance path switching board  7 D as one of the sheet conveyance units is switched over to the position indicated by a dotted line.  
         [0026]     Downstream of the separation claw  5 C, the remaining developer, i.e. toner is removed by the cleaning unit  6  from the surface of the photoreceptor  1  subsequent to image formation, thereby creating a required environment for next image formation.  
         [0027]     When an image is formed on both sides of the recording sheet RS, the conveyance path switching board  7 D is switched over to the position indicated by the dotted line. Then the recording sheet RS having been heated and fixed by the fixing unit  8  is conveyed downward and is switched back by the sheet reversing and conveying unit  7 E so that the recording sheet RS is reversed. After that, a new toner image is transferred on the back face at the transfer position.  
         [0028]     As will be described later, when punching, folding, binding and others operations are performed, the conveyance path switching board  7 D is switched to the position indicated by the solid line, whereby the recording sheet RS having been heated and fixed by the fixing unit  8  is fed downward and is switched back by the sheet reversing and conveying unit  7 E so that the recording sheet RS is reversed. After that, the sheets are fed upward with the trailing edges becoming the leading edges, and are ejected by the ejection roller  7 C.  
         [0029]     The recording sheet RS ejected from the ejection roller  7 C is fed to the first sheet finisher FS 1 .  
         [0030]     An operation display unit  9  capable of selecting and setting various forms of modes such as an image formation mode and sheet finishing mode is arranged on the stop front side of the image forming apparatus main body A. An image reading apparatus B as an image reading unit equipped with an automatic document conveyance apparatus G is mounted on the upper portion of the image forming apparatus main body A. The image data obtained from reading by the image reading apparatus B and the image data received from outside by facsimile machine or network communication are stored in the storage apparatus (not illustrated).  
         [0031]     The first sheet finisher FS 1  is a sheet finishing apparatus for punching and folding. The second sheet finisher FS 2  is a sheet finishing apparatus for shifting and binding.  
         [0032]     The first sheet finisher FS 1  has a punching unit  12  and a folding unit  14 . The recording sheet RS ejected from the image forming apparatus main body A and the cover HS supplied from the cover feed tray  11  are subjected to the process of punching and folding at the inlet.  10 .  
         [0033]     As illustrated, the folding unit  14  has several branched conveyance paths. Folding in two or folding in three can be performed by proper selection of branched conveyance paths.  
         [0034]     A fixed ejection tray  30  used a sub-tray is arranged in the upper tray of the second sheet finisher FS 2 . A shifting unit  50  and ejecting unit  60  are provided along an approximately horizontal conveyance path h 2 . A binding unit  70  and a folding unit  80  are provided in the lower tray of the second sheet finisher FS 2 .  
         [0035]     A main tray  90  for loading the shifted sheets and stapled bundles of paper is arranged on the left inside the second sheet finisher FS 2 . A lower tray  91  is mounted on the lower left, and folded sheets are ejected in this tray.  
         [0036]     The following describes the structure of the second sheet finisher FS 2  with reference to  FIGS. 1 through 4 .  FIG. 2  is a diagram showing the major portions of the second sheet finisher FS 2 .  FIG. 3  is a plan of the sheet alignment apparatus as an embodiment of the present invention, and  FIG. 4  is a cross sectional view showing an example of the aligning element. In the following description, the recording sheet RS and cover HS will be collectively called the sheet S.  
         [0037]     The sheet S ejected from the first sheet finisher FS 1  is led to the inlet  20  of the second sheet finisher FS 2 .  
         [0038]     A sheet branching unit composed of switching gates G 1  and G 2  is provided downstream of the inlet  20 . Driven by a solenoid (not illustrated)., the switching gates G 1  and G 2  selects one of the three conveyance paths, i.e. a first conveyance path h 1  for the upper tray ejection, a second conveyance path h 2  for the middle tray ejection and a third conveyance path h 3  for the lower tray ejection.  
         [0039]     In the image formation on a small number of sheets, the switching gate G 1  opens only the first conveyance path h 1 , closing the second conveyance path h 2  and third conveyance path h 3 . The sheets S are fed along the first conveyance path h 1 . Gripped by the conveyance roller  31  located downstream, the sheets S go upward, and are ejected by an ejection roller  32 . They are then stacked on the sub tray  30  sequentially.  
         [0040]     The sub tray  30  has a storage capacity of accommodating a maximum of  200  sheets S.  
         [0041]     In a large volume image formation mode where stapling is not performed, the switching gate G 1  blocks the first conveyance path h 1 . The switching gate G 2  closes the third conveyance path h 3 , and opens the second conveyance path h 2  to allow the sheet S to be fed. Guiding the sheet S, it allows the sheet S to be ejected to the main tray  90 . In the mode wherein the sheet S is ejected to the main tray  90  through the second conveyance path h 2 , the sheet S can be shifted by the shifting unit  50 . The shifting unit  50  applies processing of shifting, whereby the ejection position of the sheet S is shifted across the width every predetermined number of sheets. The main tray  90  is lowered when a large number of sheets S are to be stacked. A maximum of 3000 sheets can be stored in the case of A4-sized or B5-sized paper.  
         [0042]     A sheet sensor PS 1  for sensing the passage of the sheet S ejected to the main tray  90  is provided in the vicinity of the ejection roller  61  constituting the ejecting unit  60 .  
         [0043]     The sheet S ejected from the first sheet finisher FS 1  is fed along the third conveyance path h 3  by the conveyance rollers  22  and  23 . The sheet S is fed upward on the left over an intermediate stacker  71  by a stacker ejection roller  24 . The trailing edge of the sheet S passes through the stacker ejection roller  24 . The sheet S is detached from the stacker ejection roller  24  and is dropped onto the intermediate stacker  71  by gravity.  
         [0044]     The intermediate stacker  71  is a supporting table for support the sheets S. A sheet supporting face of the supporting table is inclined by angle θ with respect to the horizontal line HL. To improve the performance of aligning the leading edge of the sheet S and to downsize the apparatus, the angle is preferably θ≧60°.  
         [0045]     When the bottom edge of the sheet S has reached the stopper  72 , a pair of aligning elements  73 A and  73 B make a reciprocating motion across the width intersecting the conveying direction of the sheet S, i.e. in the X direction, whereby the sheets S are aligned across the width ( FIGS. 3 and 4 ). Further, the lower ends of the sheets S are aligned by the stopper  72 .  
         [0046]     The aforementioned processing is applied on a continuous basis to the sheets S supplied to the intermediate stacker  71 . A predetermined number of aligned sheets S are stacked on the intermediate stacker  71 .  
         [0047]     When a predetermined number of sheets S have been stacked, the binding unit  70  operates to bind a bundle of sheets S.  
         [0048]     When the binding has terminated, the stopper  72  is fed upward by the belt  74  driven by the motor Ml obliquely to the left in  FIGS. 1 and 2 , whereby the bundle of sheets S is pushed upward and is ejected to the main tray  90 .  
         [0049]     The bundle of sheets S stacked in the intermediate stacker  71  is again fed obliquely to the bottom. The sheets S are folded by the folding unit  80  and are ejected to the lower tray  91 .  
         [0000]     &lt;Alignment of Sheet&gt; 
         [0050]     The alignment of sheets will be described with reference to  FIGS. 2 through 5 .  FIG. 5  is a cross sectional view showing another example of the aligning element.  
         [0051]     The aligning elements  73 A and  73 B are fixed to the belt  74  driven by the motor M 2  as a driving source. They makes a reciprocating motion in the direction opposite to each other caused by the forward and reverse rotation of the motor M 2 , whereby the sheets S are aligned.  
         [0052]     As shown in  FIG. 4 , the aligning element  73 A is U-shaped, and is composed of an upper plate unit  73 A 1 , a side plate unit  73 A 2  and a lower plate unit  73 A 3 . The aligning element  73 B is also U-shaped and is composed of an upper plate unit  73 B 1 , a side plate unit  73 B 2  and a lower plate unit  73 B 3 . The left side of the side plate unit  73 A 2  and the right side of the side plate unit  73 B 2  are used to align the lateral edge of the sheet S as aligning faces. The side plate unit  73 A 2  and side plate unit  73 B 2  are brought into contact with the lateral edge of the sheets S, whereby the sheets S are aligned.  
         [0053]     The intermediate stacker  71  as a supporting table for supporting the sheet S constitutes the sheet supporting face JS that supports the sheet S. The sheets S are stacked on the intermediate stacker  71  and are loaded approximately parallel to the sheet supporting face JS. When a large number of sheets S have been loaded, the sheets S are loaded in a flat form on the lower portion by gravity, but the upper portion of the sheets is curled as illustrated. In this case, the sheets S are stacked in a curled form.  
         [0054]     The aligning surface of the side plate unit  73 A 2 , i.e. the left surface of the side plate unit  73 A 2  is formed to be deviated by an inclined angle of α 1  toward the sheet from the direction PJS orthogonal to the sheet supporting face JS. The inclined angle α 1  is formed along the sheet contour line SRS which is formed by a large number of curled sheets S.  
         [0055]     The sheet contour line SRS assume varied angles depending on the degree of the curl of the sheet S. The inclined angle α 1  is set to the average value of various angles or a value close thereto.  
         [0056]     In the similar manner, the side plate unit  73 B 2  is formed in such a way that the aligning surface, i.e. the right side of the side plate unit  73 B 2  is deviated by an inclined angle of α 2  toward the sheet from the direction PJS orthogonal to the sheet supporting face JS.  
         [0057]     The inclined angles α 1  and α 2  are preferably 0.5° through 1.5°.  
         [0058]     If the inclined angles α 1  and α 2  are smaller than 0.5°, the performance of aligning the curled paper will be reduced. If the inclined angles α 1  and α 2  are greater than 1.5°, then a sheet bending force will be applied to the sheets if they are flat and uncurled. This will cause the sheets to be bulged, and alignment performance will be reduced.  
         [0059]     If the side plate units  73 A 2  and  73 B 2  are formed as described above, both curled and uncurled sheets are aligned correctly.  
         [0060]      FIG. 5  is a cross sectional view showing another example of the aligning element.  
         [0061]     As shown in  FIG. 5 , the aligning surfaces of the side plate units  73 A 2  and  73 B 2  are positioned at right angles with the sheet supporting surface JS, on the lower portion. On the upper portion, they are inclined toward the sheet S. The example shown in  FIG. 5  exhibits excellent alignment performances for the curled sheets.  
         [0062]     The aforementioned embodiments provide a sheet alignment apparatus characterized by excellent alignment performance, especially for curled sheets. This sheet alignment apparatus ensures excellent alignment of the paper, independently of the presence or absence of curling or the degree of curling.  
         [0063]     The aforementioned embodiments provide a sheet alignment apparatus characterized by excellent alignment performance and compact structure.  
         [0064]     The aforementioned embodiments provide a sheet finisher capable of producing a booklet characterized by preferably aligned edges of sheets.  
         [0065]     The aforementioned embodiments allow the process of binding to be applied to the bundle of sheets with aligned edges, thereby ensuring an improved quality of bound documents.