Patent Publication Number: US-2011062059-A1

Title: Document sorting apparatus and document sorting method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Provisional U.S. Applications 61/243,000 filed on Sep. 16, 2009, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     An embodiment of the present invention relates to a document sorting apparatus and a document sorting method for reusing sheets that are printed on one side but are blank, that is, unused, on the other side. 
     BACKGROUND 
     Recently, in view of effective use of resources, it is increasingly important to use sheets that are printed on one side but are blank on the other side in copiers or the like. Document sorting systems for this purpose are developed. 
     In order to reuse sheets that are printed on one side in this manner, it is convenient for reuse that sheets are stored in a cassette or the like with their unused sides facing upward or downward, that is, aligned on one side. A paper supply system in an image forming apparatus which stores sheets with their non-image formed sides (blank sides) facing upward, for example, is known. 
     However, all sheets that are used once are not necessarily printed on one side alone. Moreover, even sheets that are printed on one side may contain important matters. Thus, documents containing sheets that are used once generally include various kinds of sheets. 
     An embodiment of the invention is a document sorting apparatus and a document sorting method for sorting various documents including confidential documents and printed sheets, without waste and with security maintained. Another embodiment of the invention is a document sorting apparatus and a document sorting method that enable flexible setting of confidentiality levels where documents are treated as confidential. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the structure of a document sorting apparatus according to a first embodiment of the invention. 
         FIG. 2  shows an exemplary configuration of a print detector according to the first embodiment. 
         FIG. 3  shows an exemplary configuration of a recognition comparison unit of the print detector shown in  FIG. 2 . 
         FIG. 4  shows a display position of a confidentiality level on a sheet and a detection range by the print detector. 
         FIG. 5  shows an exemplary electrical configuration according to the first embodiment. 
         FIG. 6  is a flowchart illustrating the operation according to the first embodiment. 
         FIG. 7  shows the structure of a second embodiment of the invention. 
         FIG. 8  shows an exemplary electrical configuration according to the second embodiment. 
         FIG. 9  shows the structure of a third embodiment of the invention. 
         FIG. 10  shows the relation between a fourth embodiment of the invention and an image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment of the invention, a document sorting apparatus includes: two print detection units which are provided facing both sides of a sheet, respectively, and detect presence or absence of a print on each side and presence or absence of an indication of a confidentiality level; a confidential sheet housing unit which houses the sheet when a confidentiality indication level detected at least on one side is higher than a preset setting level; and a reuse sheet housing unit which houses the sheet when a print on the sheet is detected only by one of the two print detection units and there is no indication of the confidentiality indication level. 
     Hereinafter, embodiments of the document sorting apparatus according to the invention will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  shows the configuration of a document sorting apparatus according to a first embodiment of the invention. Roughly speaking, this document sorting apparatus  10  has an apparatus body  11 , a sheet insertion tray  12 , print detectors  13   a  and  13   b  which detect the presence or absence of a print on the face side and the back side of a sheet P, respectively, inserted from the sheet insertion tray  12 , a reuse sheet cassette  14   a  which houses sheets printed on one side only, a disposal sheet cassette  14   b  which houses sheets printed on both sides, and a confidential sheet cassette  14   c  which houses sheets detected as confidential documents. 
     The sheets inserted in this document sorting apparatus  10  are classified into sheets having an indication that the sheets are confidential documents and sheets having no indication that the sheets are confidential documents. The sheets having no indication of confidential document include sheets printed on one side only and sheets printed on both sides. Sheets having no indication of confidentiality and printed on both sides are to be disposed of and housed in the disposal sheet cassette  14   b.    
     Sheets having no indication of confidentiality and printed on one side only are housed in the reuse sheet cassette  14   a  with their unused sides aligned for reuse. On the sheets having the indication that the sheets are confidential documents, a confidentiality level of 1 to 5 is indicated. An indicated confidentiality (indication) level DL is compared with a preset setting level SL. If the confidentiality indication level DL is higher than the setting level SL, the sheet is housed in the confidential sheet cassette  14   c.    
     The sheets hosed in the confidential sheet cassette  14   c  are also divided into two types, that is, sheets printed on one side only and sheets printed on both sides. The confidential sheets printed on one side only may be in two forms, that is, where the already printed sides (used sides) of the sheets face upward and where the used sides face downward. In this embodiment, it is assumed that when sheets are housed in the confidential sheet cassette  14   c , the used sides of the sheets are not aligned. 
     The sheets printed on both sides may have an indication of a confidentiality level on both sides. If different confidentiality levels are indicated on the two sides, the higher confidentiality indication level is compared with the setting level. Moreover, there are cases where a confidentiality level is indicated on one side but no confidentiality level is indicated on the other side. In such cases, the indicated confidentiality level is compared with the setting level. If the indicated confidentiality level is determined as being higher than the setting level, this sheet is treated as a confidential sheet and is housed in the confidential sheet cassette  14   c.    
     Although actually inserted sheets may include sheets that are not printed on either side, it is now assumed that sheets are always printed at least on one side. 
     The print detectors  13   a  and  13   b  are provided on the face side and the back side of the sheet insertion tray  12  and include, for example, light sources  13   ao  and  13   bo  which cast lights toward the sheet P, optical sensors  13   as  and  13   bs  which detect reflected lights from the sheet P of the lights cast from the light sources and have, for example, a linear shape, and recognition comparison units  13   ar  and  13   br  which recognize the reflected lights, as shown in  FIG. 2 . 
     Each of the recognition comparison units  13   ar  and  13   br  has a print line detection unit  13   rg , a confidentiality indication detection unit  13   rh , a confidentiality indication level recognition unit  13   ri , a confidentiality indication level setting unit  13   rj , and a confidentiality indication level comparison unit  13   rk , for example, as shown in  FIG. 3 . 
     The print line detection unit  13   rg  is a circuit to detect printed lines or the like. The confidentiality indication detection unit  13   rh  is a circuit to detect the presence or absence of a confidentiality indication. If a confidentiality indication is detected by the confidentiality indication detection unit  13   rh , the confidentiality indication level recognition unit  13   ri  recognizes the confidentiality indication level. The recognized confidentiality indication level is sent from the confidentiality indication level recognition unit  13   ri  to the confidentiality indication level comparison unit  13   rk.    
     Meanwhile, a preset confidentiality setting level is inputted to the confidentiality indication level comparison unit  13   rk  from the confidentiality indication level setting unit  13   rj . This setting level may be set, for example, to 3 as an initial value and then may be changed by ten keys provided on the top panel of the apparatus body  11  of the document sorting apparatus  10 . 
     It is also possible to change the confidentiality setting level every time a button is pressed. If the setting level for confidential documents can be changed or inputted from the top side of the apparatus body, there is an advantage that the range of documents that are treated as confidential documents can be changed easily and flexibly. 
     The confidentiality indication level comparison unit  13   rk  compares the confidentiality indication level inputted from the confidentiality indication level recognition unit  13   ri  with the setting level inputted from the confidentiality indication level setting unit  13   rj , and sends a comparison result signal indicating whether the confidentiality indication level is higher than the setting level or not, to an overall control unit  24  (see  FIG. 5 ) which will be described later. 
     Also a print presence or absence signal indicating whether the sheet is printed or not is sent to the overall control unit  24  from the print line detection unit  13   rg . When no confidentiality indication is detected, a control signal indicating that no confidentiality indication is detected is sent to the overall control unit  24  from the confidentiality indication detection unit  13   rh.    
       FIG. 4  shows the relation of the sheet P with the print detectors  13   a  and  13   b . On the sheet P inserted upside down, an area  19  represents a range where the light source  13   ao  of the print detector  13   a  casts light and the optical sensor  13   as  receives reflected light. Therefore, if a certain description such as letters is detected within this range, the print detector  13   a  recognizes that this side is printed. An area  20  represents, for example, a range where a confidentiality class is indicated. As for the print detector  13   b , the back side of the sheet P has areas at similar positions. 
     Each of the recognition comparison units  13   ar  and  13   br  has a built-in comparison circuit which recognizes an electrical signal acquired from the reflected light from the light sensor, then recognizes whether the corresponding side is printed and an indication of a confidentiality level of a confidential document, for example, a QR code, on the corresponding side, and compares the confidentiality indication level with a preset confidentiality level. 
     There are, for example, five confidential levels 1 to 5. Level 1 is the highest confidentiality level. Level 5 is the lowest confidentiality level. A sheet having no indication that the sheet is a confidential document is much lower in confidentiality. The indication that the sheet is a confidential document can be omitted if there is an indication of a confidential level. 
     Here, the indication that the sheet is a confidential document is omitted. The QR code is usually shown in the form of barcode. However, in  FIG. 4 , its content (level 2) is shown so that the content can be easily understood. 
       FIG. 5  shows an exemplary configuration of an electric control block in the document sorting apparatus  10  according to this embodiment. This document sorting apparatus  10  includes the print detector  13   a  which detects the presence or absence of a print on the face side of the sheet P, the print detector  13   b  which detects the presence or absence of a print on the back side of the sheet P, a sheet carrying control unit  21  which controls the rotation of each roller and thus controls the carrying and housing of the sheet P into each cassette, a gate control unit  22  which controls a gate G, a reverse roller control unit  23  which controls the rotation and the direction of rotation of reverse rollers  18   a  and  18   b , and the overall control unit  24  which controls each of these units. 
     The overall control unit  24  receives information whether the face side and the back side of the sheet P are printed and whether there is an indication of a confidential class, from the recognition comparison units  13   ar  and  13   br  of the print detectors  13   a  and  13   b.    
     In response to the result, the overall control unit  24  drives the sheet carrying control unit  21  and controls the rotation of carrying rollers  15   a ,  15   b ,  16   a ,  16   b , housing rollers  17   a ,  17   b , and the reverse rollers  18   a ,  18   b . The following control is carried out by the overall control unit  24 . 
     The sheet P inserted from the sheet insertion tray  12  is carried along a carrying path formed by the several pairs of carrying rollers  15   a ,  15   b  and  16   a ,  16   b . The sheet P is then housed in the reuse sheet cassette  14   a , the disposal sheet cassette  14   b  or the confidential sheet cassette  14   c  by the pair of housing rollers  17   a ,  17   b  in accordance with the type of the sheet to be housed. Which sheet cassette the sheet is housed in is decided in accordance with the circumstance where a print is detected by the print detectors  13   a  and  13   b.    
     Moreover, the pair of reverse rollers  18   a  and  18   b  are provided near the carrying rollers  15   a  and  15   b  at the positions close to the sheet insertion tray  12 , and a sheet reverse carrying path is thus formed. For example, it is now assumed that a sheet printed on the back side only is inserted in the sheet insertion tray  12 . In this case, no print on the sheet is detected by the print detector  13   a  which detects a print on the face side of the sheet P, and a print is detected by the print detector  13   b  which detects a print on the back side of the sheet P. 
     The sheet P, inserted from the sheet insertion tray  12  and passed the first carrying rollers  15   a  and  15   b , is carried once to the left in  FIG. 1  by forward rotation of the pair of reverse rollers  18   a  and  18   b  as the gate G is controlled. After that, the sheet P is moved in a switchback-like manner by reverse rotation of the rollers  18   a  and  18   b , then carried again and housed in the reuse sheet cassette  14   a  by the housing rollers  16   a  and  16   b . The sheet P is housed in the reuse sheet cassette  14   a  with the printed side facing downward. 
     If the sheet P has an indication of a confidentiality level, and this confidentiality level is recognized as being higher than a predetermined confidentiality level, for example, level 3, the sheet P is housed in the confidential sheet cassette  14   c.    
     If a print is detected on both sides by the print detectors  13   a  and  13   b  and no indication of confidentiality level is detected, the sheet P is housed in the disposal sheet cassette  14   b . If a print is detected on one side by the print detector  13   a  or the print detector  13   b  and no indication of confidentiality level is detected, the sheet is housed in the reuse sheet cassette  14   a  with the printed side facing downward. 
     Next, the operation of the document sorting apparatus according to this embodiment will be described with reference to the flowchart shown in  FIG. 6 . 
     In ACT  501 , it is first checked whether an indication of a confidentiality level can be recognized. In the print detectors  13   a  and  13   b , lights from the internal light sources  13   ao  and  13   bo  are cast toward the sheet P and their reflected lights are received by the optical sensors  13   as  and  13   bs . Each of the received lights is converted to an electrical signal. Depending on whether there is a fluctuation in the electrical signal, it is detected whether there is a print. The presence or absence of an indication of a confidentiality level is also recognized and the confidentiality indication level is recognized where this indication exists. 
     When this confidentiality indication is not recognized, the confidentiality level can be level 1 or 2 in the worst case scenario. Thus, if no indication of confidentiality level is recognized in  FIG. 6  (N in ACT  501 ), the sheet is carried toward the confidential sheet cassette  14   c  and housed in this cassette in ACT  502 . 
     On the other hand, when it is recognized that there is an indication of a confidentiality level, the processing shifts to ACT  503  and it is checked whether there is an indication of a confidentiality indication level. If the confidentiality indication level is recognized, the confidentiality indication level is compared with the setting level in ACT  504 . 
     If the confidentiality indication level is higher than the setting level in the subsequent ACT  505  (Y in ACT  505 ), the processing shifts to ACT  502  and the sheet is carried toward the confidential sheet cassette  14   c  and housed in this cassette. 
     Meanwhile, if the confidentiality indication level is equal to or lower than the setting level in ACT  505  (N in ACT  505 ), the processing shifts to ACT  506 . In ACT  506 , the recognition comparison units  13   ar  and  13   br  examine whether a print is detected by the print detector  13   a  and the print detector  13   b . In this case, the sheet is a confidential document but has a low confidentiality level and the sheet is printed on both sides. This sheet is sent to the disposal sheet cassette  14   b.    
     If it is recognized that there is no indication of confidentiality level in ACT  503  (N in ACT  503 ), the processing similarly shifts to ACT  506  and it is examined whether a print is detected by the print detectors  13   a  and  13   b , that is, whether the sheet is printed on both sides. If the sheet is printed on both sides (Y in ACT  506 ), the processing shifts to ACT  507  and the sheet is carried toward the disposal sheet cassette  14   b  and housed in this cassette. 
     On the other hand, if a print is not detected by the print detector  13   a  and the print detector  13   b  (N in ACT  506 ), it is checked whether a print is detected by the print detector  13   b  in ACT  508 . 
     If a print is detected by the print detector  13   b  (Y in ACT  508 ), it means that the sheet P is printed on its back side only. Thus, in the subsequent ACT  509 , the sheet P is reversed. That is, the overall control unit  24  sends a control signal to the gate control unit  22  and causes the gate G shown in  FIG. 1  to operate in such a manner that the sheet P is carried to the reverse rollers  18   a  and  18   b . Then, the sheet printed on the back side is carried to the left in  FIG. 1  (the direction of an arrow  18   f ) by forward rotation of the reverse rollers  18   a  and  18   b.    
     After a rear end of the sheet P is released from the carrying rollers  15   a  and  15   b , the reverse rollers  18   a  and  18   b  are rotated backward and the sheet P is carried in the direction of an arrow  18   r  via the carrying rollers  16   a  and  16   b . After that, the sheet P with its printed side facing downward is housed in the reuse sheet cassette  14   a  by the housing rollers  17   a  and  17   b  (ACT  510 ). 
     If no print is detected by the print detector  13   b  in ACT A 508  (N in ACT  508 ), it is a case where a print is detected by the print detector  13   a . In this case, the sheet P is printed on its face side. In this case, the sheet P is carried by the carrying rollers  16   a  and  16   b  from the carrying rollers  15   a  and  15   b  and housed in the reuse sheet cassette  14   a  by the housing rollers  17   a  and  17   b . In this case, too, the printed side of the sheet P is the side facing downward. 
     In this manner, according to this embodiment, a confidential document having a confidentiality level exceeding the setting level is housed in the confidential sheet cassette  14   c . A sheet that is printed on both sides and has no confidentiality indication and a sheet that is printed on both sides and has a low confidentiality level are housed in the disposal sheet cassette  14   b.    
     A sheet that is printed on one side and has no confidentiality indication and a sheet that is printed on one side and has a low confidentiality level are housed in the reuse sheet cassette  14   a  with the printed side facing downward. 
     According to this embodiment, sheets are reversed by forward rotation and reverse rotation of the reverse rollers and unused sides of the sheets can be aligned to one side. 
     This embodiment has an advantage that even a sheet having a confidentiality indication can be reused if the confidentiality level is equal to or lower than a predetermined level, that is, the degree of confidentiality is low. Moreover, since the confidentiality setting level can be set from outside, there is an advantage that confidential documents that should not be reused and should be treated as confidential can be flexibly changed. 
     Second Embodiment 
     In the first embodiment, if the printed side of a sheet printed on one side is its back side, the sheet is reversed by the reverse mechanism (switchback mechanism). However, the sheet can be reversed by another mechanism. In this second embodiment, sheets having a print detected on different sides are carried through different paths and the unused sides can be thus aligned to one side. 
       FIG. 7  shows the configuration of this embodiment. The reference numerals and symbols  70  to  77   b  in a document sorting apparatus  70  according to this embodiment represent similar units to those denoted by the reference numerals and symbols  10  to  17   b  in the apparatus according to the first embodiment shown in  FIG. 1 . However, in this embodiment, a reuse sheet cassette  74   a  is set in the second stage of an apparatus body  71 , and a disposal sheet cassette  74   b  is set in the first stage. This document sorting apparatus  70  roughly includes the apparatus body  71 , a sheet insertion tray  72 , print detectors  73   a  and  73   b  which detect the presence or absence of a print on the face side and the back side of a sheet P, respectively, inserted from the sheet insertion tray  72 , the reuse sheet cassette  74   a  which houses sheets printed on one side only, the disposal sheet cassette  74   b  which houses sheets printed on both sides, and a confidential sheet cassette  74   c  which houses sheets detected as confidential documents. 
     In this embodiment, a carrying path formed by a pair of carrying rollers  76   c  and  76   d  is formed as well as a carrying path formed by a pair of carrying rollers  76   a  and  76   b . The reuse sheet cassette  74   a  and the confidential sheet cassette  74   c  can house sheets not only from the right in  FIG. 7  but also from the left by housing rollers  77   c  and  77   d.    
     The print detectors  73   a  and  73   b  are similar to those shown in  FIG. 2 . The direction in which a sheet is carried is controlled by a gate G 2  in accordance with the print-detected side of the sheet, and a carrying path is thus selected.  FIG. 8  shows the electrical control configuration according to this embodiment. 
     In this case, a carrying path control unit  83  is provided instead of the reverse roller control unit  23 . This carrying path control unit  83  is a circuit to control whether to send the sheet to the carrying path formed by the carrying rollers  76   a  and  76   b  or to send the sheet to the carrying path formed by the carrying rollers  76   c  and  76   d . Other parts of the configuration, that is, a sheet carrying control unit  81 , a gate control unit  82  and an overall control unit  84  are similar to those shown in  FIG. 5 . 
     As the print detectors  73   a  and  73   b , print detectors having the same configuration as the print detectors  13   a  and  13   b  shown in  FIG. 5  may be used. 
     A sheet P having a print detected on its face side by the print detector  73   a  is carried by the carrying rollers  76   a  and  76   b  and is housed in the reuse sheet cassette  74   a  by housing rollers  77   a  and  77   b  from the right. 
     A sheet P having a print detected on its back side by the print detector  73   b  is carried by the carrying rollers  76   c  and  76   d  and is housed in the reuse sheet cassette  74   a  by the housing rollers  77   c  and  77   d  from the left. 
     If a sheet P having a confidentiality indication but has a confidentiality level equal to or lower than a predetermined confidentiality level is inserted from the sheet insertion tray  72 , since the degree of confidentiality is low, the sheet printed on one side is housed in the reuse sheet cassette  74   a.    
     If a sheet P having an indication of a confidentiality level higher than a setting level is printed on one side only, switching is carried out as to whether to carry the sheet via the carrying path formed by the carrying rollers  76   a  and  76   b  or to carry the sheet via the carrying path formed by the carrying rollers  76   c  and  76   d . This carrying path switching control is carried out by the carrying path control unit  83 . 
     In the second embodiment, sheets which are printed on one side only and have a high degree of confidentiality can be housed in the confidential sheet cassette  74   c  with their printed sides aligned, for example, facing downward. 
     In the second embodiment, for sheets printed on one side only, the carrying paths are changed and the unused sides thus aligned. Therefore, though two carrying paths need to be formed, there is an advantage that a so-called switchback mechanism to return sheets at a halfway part of the carrying process is not required. 
     This embodiment also has an advantage that the printed sides of sheets which have a higher confidentiality level than the setting level and are printed on one side only can be aligned. Therefore, there is an advantage that confidential sheets housed in the confidential sheet cassette, particularly, confidential sheets printed on one side only, can be taken out and read easily. 
     Third Embodiment 
     In the document sorting apparatuses according to the first and second embodiments, sheets which are unused on one side are housed in the reuse sheet cassette, with their unused sides aligned. 
     However, it is also possible to provide a reuse sheet cassette which houses sheets with the unused sides facing upward, and a reuse sheet cassette which houses sheets with the unused sides facing downward. By doing so, it is no longer necessary to provide a reverse mechanism or switch carrying paths in order to align the unused sides. 
       FIG. 9  shows such a configuration according to a third embodiment. A document sorting apparatus  90  shown in  FIG. 9  has an apparatus body  91 , a sheet insertion tray  92  in which a sheet P is inserted, print detectors  93   a  and  93   b  which detect the presence or absence of a print on the face side and the back side of the sheet inserted in the sheet insertion tray, a reuse sheet cassette  94   a   1  which houses reuse sheets with the upper sides unused, a reuse sheet cassette  94   a   2  which houses sheets with the lower sides unused, a disposal sheet cassette  94   b  which houses sheets printed on both sides, a confidential sheet cassette  94   c  which houses sheets having a higher confidentiality level than a setting level, plural pairs of carrying rollers  96   a  and  96   b  which carry sheets to these cassettes, and a pair of housing rollers  97   a  and  97   b  to house sheets in each cassette. 
     Although not shown, the print detectors  93   a  and  93   b  in this embodiment have the configuration as shown in  FIG. 2 . That is, lights from light sources are cast on the sheet P. Reflected lights are received by optical sensors and each of them is converted to an electrical signal. Based on the electrical signal, it is detected whether light-cast side of the sheet P is printed or not. After that, it is detected whether there is an indication of a confidentiality level as a confidential document. If there is an indication of a confidentiality level, it is detected whether the confidentiality indication level is higher than a preset setting level. 
     A confidential document having an indication of a higher level than the setting level is housed in the confidential sheet cassette  94   c . A sheet P which has no indication of confidentiality level or has an indication of a lower confidentiality level than the setting level, if any, and has a print detected by both the print detectors  93   a  and  93   b , is housed in the disposal sheet cassette  94   b  because the sheet is printed on both sides. 
     Meanwhile, a sheet P which has no indication of confidentiality level or has a lower confidentiality level than the setting level, if any, and has its lower side used and upper side unused, is housed in the reuses sheet cassette  94   a   1 . A sheet P which has no indication of confidentiality level or has a lower confidentiality level than the setting level, if any, and has its upper side used and lower side unused, is housed in the reuses sheet cassette  94   a   2 . 
     In this manner, reuse sheets with the upper sides unused are housed in the reuse sheet cassette  94   a   1  and reuse sheets with the lower sides unused are housed in the reuse sheet cassette  94   a   2 . 
     According to this embodiment, while two reuse sheet cassettes are required, it is not necessary to provide a mechanism to reverse sheets at a halfway part of the carrying process or to change the paths. Therefore, there is an advantage that the document sorting apparatus can be reduced in size. This embodiment also has an advantage that confidentiality levels can be set flexibly and easily. 
     Fourth Embodiment 
     In the first, second and third embodiments, the document sorting apparatus is described as an independent apparatus. However, the document sorting apparatus can also be connected to an image forming apparatus. A fourth embodiment of the invention in such a configuration will now be described.  FIG. 10  shows the overall configuration of a system including a document sorting apparatus, an image forming apparatus and a finisher apparatus according to this embodiment. 
     A document sorting apparatus  100  has a sheet insertion tray  101  provided on the top, a reuse sheet cassette  104   a  which houses sheets P unused on one sides, a disposal sheet cassette  104   b  which houses sheets printed on both sides, a confidential sheet cassette  104   c  which houses sheets having a higher confidentiality level than a setting level, carrying rollers  106   a  and  106   b  which carry each sheet, reverse rollers  108   a  and  108   b  to return sheets, for example, in a switchback-like manner in order to align the unused sides, and so on. 
     This document sorting apparatus  100  is similar to the first embodiment shown in  FIG. 1  except for the following point. The reuse sheet cassette  104   a  on the lowermost stage in the document sorting apparatus  100  can supply sheets to a reuse sheet cassette  114   a  provided on the lowermost stage in an image forming apparatus  110 , which will be described hereinafter. For example, if a reuse sheet supply button (not shown) provided on the top of the document sorting apparatus  100  is pressed, a sheet is supplied from the reuse sheet cassette  104   a  to the reuse sheet cassette  114   a  with the unused side facing upward. 
     The image forming apparatus  110  has, for example, the reuse sheet cassette  114   a  provided on the lowermost stage, plural sheet cassettes  114   b  and  114   c  provided above the cassette  114   a , a mechanism to form an electrostatic latent image on four photoconductive drums  115 , a transfer belt  116  to develop the latent image and transfer the developed image to a sheet P by superimposition, a fixing unit  117  which fixes the transferred image, a discharge roller mechanism  118 , and the like. 
     The sheet P to which an image is fixed, that is, printed, is put into a finisher apparatus  120  installed near the image forming apparatus. The sheet P is then directly discharged to a discharge tray  121 . Alternatively, after plural sheets are aligned and finishing such as stapling by a stapler  122  is carried out, the sheets are discharged onto a discharge tray  123 . 
     In the fourth embodiment, the document sorting apparatus is provided as an option for the image forming apparatus. 
     According to this embodiment, the reuse sheet housed in the reuse sheet cassette  104   a  in the document sorting apparatus  100  is automatically housed into the cassette in the image forming apparatus by the pressing of a button or the like. Therefore, there is an advantage that the operator need not take out the reuse sheet from the reuse sheet cassette in the document sorting apparatus and supply the reuse sheet to the cassette in the image forming apparatus. 
     Also in this embodiment, it is possible to reuse a sheet having a lower confidentiality level than the setting level and having an unused side. Moreover, since the confidentiality setting level can be set from outside, it is possible to easily and flexibly prevent the reuse of a confidential document having a predetermined confidentiality level. 
     In each of the above embodiments, if the confidentiality level is higher than the setting level, the sheet is housed in the confidential sheet cassette as a confidential sheet. However, it is also possible to house the sheet in the confidential sheet cassette if the confidentiality level is equal to or higher than the setting level. 
     In each of the above embodiments, sheets are housed in the cassettes. However, the units to house sheets in the invention are not limited to cassettes and sheet housing units can be generally used. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms: furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.