Abstract:
A recording medium discharging apparatus which can be mounted on top of the image forming apparatus includes a plurality of recording medium storers and a locking mechanism for locking the discharging apparatus to the image forming apparatus when the discharging apparatus is mounted on the image forming apparatus. The locking mechanism includes a release lever for unlocking the discharging apparatus by being manipulated to shift in the same direction as the discharging apparatus moves away from the image forming apparatus to be dismounted from it. The locking mechanism prevents the discharging apparatus from falling off the image forming apparatus even if external force is applied to the discharging apparatus mounted on the image forming apparatus. The release lever for unlocking the discharging apparatus makes it easy to dismount the discharging apparatus from the image forming apparatus.

Description:
This application is a continuation in part of U.S. patent application Ser. No. 09/253,551 filed on Feb. 22, 1999, which in-turn is a Continuation-in-Part of application Ser. No. 09/236,466 filed Jan. 25, 1999 and priority-based on Japanese patent applications No. 10-13686, No. 10-32471 and No. 10-40213. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a recording medium discharging apparatus and an image forming apparatus provided with the discharging apparatus. In particular, the invention relates to a recording medium discharging apparatus which can be mounted on top of an image forming apparatus such as a printer in order to receive, sort and store recording media on which images have been formed. 
     2. Description of Related Art 
     Conventionally known is a recording medium processor apparatus for receiving, sorting and storing or holding recording media such as sheets of paper on which images have been formed by an image forming machine such as a copying machine, a printer and a facsimile machine. A recording medium processor of this type is provided generally as an option for an image forming apparatus, and is sometimes called as “discharging apparatus”, “sorter”, “mail box” etc. The recording medium processor can be mounted detachably on top of the image forming apparatus so that a space over the image forming apparatus can be utilized for space saving. 
     The recording medium processor has an inlet formed at its bottom, through which recording media can enter it. The processor also has two legs protruding downward from its bottom each on one side. The image forming apparatus has an outlet formed at its top for discharging through it the recording media on which images have been formed. The image forming apparatus also has two slots formed at its top for receiving the respective legs. The processor can be mounted on top of the image forming apparatus with the legs inserted from above into the respective slots, and with the inlet and the outlet connected together. 
     The image forming apparatus originally includes a tray for storing or holding sheets of paper on which images have been formed by the image forming apparatus. When the recording medium processor is not mounted on the image forming apparatus, all the sheets are discharged to the tray. When the processor is mounted on the image forming apparatus, all or some of the sheets may be conveyed from the image forming apparatus to the processor. The image forming apparatus also includes a pivotable flapper for switching the conveyance of sheets to either the image forming apparatus tray or the processor inlet. 
     Because the flapper is required only when the recording medium processor is mounted on the image forming apparatus, the provision of the flapper may lead to a wasteful cost increase for the image forming apparatus itself (the first problem). 
     After dismounting the recording medium processor from the image forming apparatus, it is not possible to place the processor on only the two legs stably on a floor or the like. If the dismounted processor is placed on the legs, it may fall down and consequently be damaged. Therefore, the dismounted processor needs to be laid down on a floor, leaned against a wall or supported by a member. It is thus troublesome to dismount the processor from the image forming apparatus, keep the dismounted processor from damage, and mount the dismounted processor again on the image forming apparatus (the second problem). 
     The recording medium processor is mounted on the image forming apparatus simply with its legs inserted into the respective slots of the image forming apparatus. If external force is applied to the thus mounted processor, the processor may tilt and consequently result in defective operation. Even greater external force may cause the mounted processor to fall from the image forming apparatus and consequently be damaged (the third problem). 
     The recording medium processor might be screwed or bolted to the image forming apparatus. This would, however, be troublesome and/or time-consuming, and therefore prevent the processor from being mounted on and dismounted from the image forming apparatus simply or easily. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the present invention to provide a recording medium discharging apparatus and the image forming apparatus which can prevent wasteful cost increase for the image forming apparatus. 
     It is another object of the invention to provide a recording medium discharging apparatus which can be placed stably on a floor or the like even after dismounted from an image forming apparatus, and which is easy to mount on and dismount from the image forming apparatus. 
     It is still another object of the invention to provide a recording medium discharging apparatus which can be held securely or reliably on an image forming apparatus, and which is simple or easy to mount on and dismount from the image forming apparatus. 
     In accordance with a first aspect of the invention, an image forming machine is provided, which includes an image forming apparatus for forming images on recording media. The apparatus also includes a recording medium discharging apparatus which can be mounted on top of the image forming apparatus, the discharging apparatus including a plurality of recording medium storers. The apparatus further includes a locking mechanism for locking the discharging apparatus to the image forming apparatus when the discharging apparatus is mounted on the image forming apparatus. The locking mechanism includes a release lever for unlocking the discharging apparatus by being manipulated to shift in the same direction as the discharging apparatus moves away from the image forming apparatus to be dismounted from it. 
     As stated above, the image forming apparatus includes a locking mechanism for locking the recording medium discharging apparatus to the image forming apparatus when the discharging apparatus is mounted on the image forming apparatus. The locking mechanism prevents the discharging apparatus from falling off the image forming apparatus even if external force is applied to the discharging apparatus mounted on the image forming apparatus. The release lever for unlocking the discharging apparatus makes it easy to dismount the discharging apparatus from the image forming apparatus. This lever can be manipulated to shift in the same direction as the discharging apparatus moves away from the image forming apparatus to be dismounted from it. This makes it possible to drive the lever by utilizing the force applied by a user to dismount the discharging apparatus from the image forming apparatus. It is therefore possible to unlock the discharging apparatus by the operation of dismounting the discharging apparatus from the image forming apparatus. 
     The recording medium discharging apparatus may include a holding portion which can be held by a user&#39;s hand. In particular, by supporting the release lever on the holding portion, it is possible for a user to manipulate the lever while holding the holding portion to dismount the discharging apparatus from the image forming apparatus. The lever may be urged to protrude from the holding portion. In this case, when the user lifts the discharging apparatus from the image forming apparatus, his or her hand draws the lever until the lever retracts into the holding portion against the urging force. 
     The locking mechanism may include a locking member provided at one of the image forming apparatus and the recording medium discharging apparatus, and shiftable between a locking position and an unlocking position. This mechanism may also include an engaging portion provided at the other of the image forming apparatus and the discharging apparatus. When in the locking position, the locking member is in engagement with the engaging portion. In this case, the release lever moves to shift the locking member from the locking position to the unlocking position. 
     The recording medium discharging apparatus may include a pair of connectors provided on both sides thereof and extending toward the image forming apparatus. The image forming apparatus may include a pair of engaging portions for receiving the respective connectors. The holding portion may be formed substantially at the midpoint between the connectors. In this case, when a user lifts the discharging apparatus, its weight is balanced with respect to the holding portion. This enables the discharging apparatus to be dismounted safely. 
     In accordance with a second aspect of the invention, a recording medium discharging apparatus is provided, which can be mounted on top of an image forming apparatus for forming images on recording media. This discharging apparatus includes a plurality of recording medium storers. The discharging apparatus also includes a locking mechanism for locking the discharging apparatus to the image forming apparatus when the discharging apparatus is mounted on the image forming apparatus. The locking mechanism includes a release lever for unlocking the discharging apparatus by being manipulated to shift in the same direction as the discharging apparatus moves away from the image forming apparatus to be dismounted from the image forming apparatus. 
     This recording medium discharging apparatus can be mounted on an image forming apparatus according to the first aspect, and may further include: 
     a recording medium introducing section for introducing the recording media with images formed thereon by the image forming apparatus; 
     a conveying device for conveying the media introduced into the introducing section; 
     a plurality of discharging devices for discharging to the respective recording medium storers the media conveyed from the conveying device; and 
     a switching device for guiding selectively to any of the discharging devices the media conveyed by the conveying device. 
     In accordance with a third aspect of the invention, another recording medium discharging apparatus is provided, which can be mounted on top of an image forming apparatus. This discharging apparatus includes a body including a recording medium storer. The discharging apparatus also includes at least three extensions extending downward from the body for mounting the body with them on the image forming apparatus. The bottoms of the extensions support the discharging apparatus on a horizontal plane when the discharging apparatus is dismounted from the image forming apparatus. 
     The extensions, with which the discharging apparatus body can be mounted on the image forming apparatus, function as supports for the discharging apparatus. Therefore, when dismounted from the image forming apparatus, the discharging apparatus can stand on the bottoms of the extensions stably on a floor. This prevents the discharging apparatus from being damaged by falling down. 
     The extensions may be two pairs of extensions, and each pair of them may extend downward from the discharging apparatus body on one side of the discharging apparatus. The four extensions can support the discharging apparatus more stably on a floor. In order to make the discharging apparatus more stable, it is preferable that the center of gravity of the discharging apparatus be positioned between two vertical planes each extending through one of the extensions of one pair and the adjacent extension of the other pair. It is more preferable that the center be positioned substantially at the midpoint between the planes. The image forming apparatus may include four engaging portions for receiving the respective extensions. 
     The discharging apparatus body may include a recording medium receiver which can be mounted on the image forming apparatus for receiving recording media from the image forming apparatus. The recording medium storer may be mounted on the receiver. The recording medium discharging apparatus may include a pair of connectors for mounting the storer with them on the receiver. The connectors may be fitted to either of the storer and the receiver. Each of the connectors may be positioned between the extensions of one pair. 
     The recording medium storer may include a plurality of bins. The recording medium discharging apparatus may include a conveying device for conveying the recording media received by the recording medium receiver. The discharging apparatus may also include a plurality of discharging devices for discharging to the respective bins the media conveyed from the conveying device. The discharging apparatus may further include a switching device for guiding selectively to any of the discharging devices the media conveyed by the conveying device. 
     In accordance with a fourth aspect of the invention, still another recording medium discharging apparatus is provided, which can be mounted on top of an image forming apparatus for forming images on recording media. This forming apparatus includes a discharging portion for discharging the media with images formed thereon. This discharging apparatus includes a plurality of recording medium storers. The discharging apparatus also includes a recording medium introducing section for introducing the media from the image forming apparatus into the discharging apparatus when the discharging apparatus is mounted on the image forming apparatus. The discharging apparatus further includes a switching device for guiding selectively to either of the discharging portion of the image forming apparatus and the introducing section the media with images formed thereon. 
     As stated above, this recording medium discharging apparatus can be mounted on top of an image forming apparatus. When the discharging apparatus is dismounted from the image forming apparatus, the image forming apparatus discharges recording media through its discharging portion. When the discharging apparatus is mounted on the image forming apparatus, the switching device can guide recording media to the recording medium introducing section of the discharging apparatus. The switching device is fitted to the discharging apparatus, not to the image forming apparatus. It is therefore possible to manufacture the image forming apparatus as an independent image forming apparatus without raising the costs for the image forming apparatus. 
     The switching device may include a flapper which can pivot between a first guide position where it guides recording media to the discharging portion of the image forming apparatus and a second guide position where it guides recording media to the recording medium introducing section. The switching device may also include a drive for driving the flapper. The recording medium discharging apparatus may include an urging device for urging the flapper toward the second guide position. The discharging apparatus may also include a transmitting device. When the discharging apparatus is mounted on the image forming apparatus, the transmitting device causes no urging force of the urging device to act on the flapper. When the discharging apparatus is dismounted from the image forming apparatus, the transmitting device causes the urging force of the urging device to act on the flapper. The discharging apparatus is thus constructed for the following reason. 
     The image forming apparatus may have a top opening through which recording media can be conveyed from the image forming apparatus to the recording medium discharging apparatus. The opening should be as small as possible to prevent dust, rubbish, etc. from entering the image forming apparatus. On the other hand, the discharging apparatus needs to be mounted smoothly on the image forming apparatus, with the flapper inserted into the opening without interfering with the opening. For this purpose, when the discharging apparatus is in the process of being mounted on the image forming apparatus, the transmitting device causes the flapper to be urged to the second guide position, where the flapper does not interfere with the opening. 
     Otherwise, when the recording medium discharging apparatus is mounted on the image forming apparatus, the urging force of the urging device might be applied to the flapper. This could cause the recording media to be conveyed from the image forming apparatus to the discharging apparatus when the discharging apparatus has been mounted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention is shown in the accompanying drawings, in which: 
     FIG. 1 is a schematic side view in cross section of a sorter embodying the invention and a laser printer, on which the sorter is mounted; 
     FIG. 2 is an enlarged schematic side view in cross section of the sorter; 
     FIG. 3 is a perspective view of the sorter; 
     FIG. 4 is a schematic side view in cross section of the sorter, showing how the sorter is mounted on the printer; 
     FIG. 5 is a schematic side view in cross section of the sorter mounted on the printer; 
     FIG. 6 is a schematic side view in cross section of the sorter placed on a floor; 
     FIGS. 7 and 8 are side views of the adapter of the sorter, but the left side cover of the casing of the adapter has been removed in order for the locking mechanisms of the sorter to be shown; 
     FIG. 9 is a partially broken side view of the sorter adapter mounted on the printer, but the right side cover of the adapter casing has been removed so that the selectively switching mechanism of the sorter can be shown; 
     FIG. 10A is another partially broken side view of the sorter adapter mounted on the printer, but the right side cover of the adapter casing has been removed so that the switching mechanism can be shown; 
     FIG. 10B is an enlarged view of the selecting flapper and the solenoid of the switching mechanism shown in FIG. 10A; 
     FIG. 11 is a partially broken side view of the sorter adapter dismounted from the printer, but the right side cover of the adapter casing has been removed in order for the switching mechanism to be shown; 
     FIG. 12 is a schematic side view in cross section of the sorter, showing how the sorting unit of the sorter is mounted on the adapter; 
     FIG. 13A is a schematic side view in cross section of the sorter. 
     FIG. 13B is a schematic side view in cross section of the sorter, showing how two sorting units are mounted; 
     FIG. 14 is a schematic side view in cross section of the sorter, showing the two sorting units as mounted. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a laser printer  2  as an image forming apparatus, which is fitted with a sorter  1  as a recording medium processor according to the present invention. The sorter  1  is mounted removably on top of the printer  2 . 
     The printer  2  includes a sheet cassette  3  for storing in it sheets of paper as recording media, an image forming unit  4  for forming a toner image, a fixing unit  5  for fixing the toner image transferred onto a sheet of paper, discharge rollers  15  for discharging a sheet of paper with a toner image fixed on it, and a discharge tray  16  for storing or holding a sheet of paper discharged by the rollers  15 . The cassette  3 , the units  4  and  5 , the rollers  15 , and the tray  16  are arranged in order in the direction of sheet flow. 
     Sheets of paper are stacked in the sheet cassette  3 , which is positioned at the bottom of the printer  2 . The cassette  3  includes a support plate  10  for supporting the stacked sheets. One end of the plate  10  is urged upward by a compression spring  131 . Provided near the urged end of the plate  10  are a feed roller  11  and a frictional separation pad  132  for separating one of the stacked sheets at a time and feeding the separated sheets in order from the cassette  3  to the image forming unit  4 . 
     The image forming unit  4  and the fixing unit  5  are positioned over or above the sheet cassette  3  in the printer  2 . The image forming unit  4  includes a photosensitive drum  6 , a development processor (not shown) and a charger (not shown). After the drum  6  is charged, the image forming unit  4  forms a toner image by developing with toner an electrostatic latent image formed by scanning for exposure with a laser scanner  133 . Provided under the drum  6  is a transfer roller  7  for transferring onto a sheet of paper the toner image formed on the drum. The fixing unit  5  includes a heating roller  8  and a pressing roller  9  opposite it. A sheet of paper fed from the cassette  3  is fed to the nip between the photosensitive drum  6  and the transfer roller  7  of the image forming unit  4 , where a toner image is transferred onto the sheet. The sheet is moved from the image forming unit  4  to the nip between the heating roller  8  and the pressing roller  9  of the fixing unit  5 , where the transferred toner image is fixed. The sheet is moved from the fixing unit  5  to the discharge rollers  15 . 
     Formed downstream of the discharge rollers  15  are a first guide passage  18  and a second guide passage  19  for guiding to the discharge tray  16  and the sorter  1 , respectively, the sheets discharged from the rollers  15 . 
     The discharge tray  16  is positioned downstream of the first guide passage  18 . Sheets of paper discharged from the discharge rollers  15  can be received by and stacked on the tray  16 . The tray  16  is positioned in a recess formed in an upper portion of the printer  2 . The front end of the tray  16  is supported rotatably, and the rear end is urged upward by a compression spring  134 . As sheets of paper are stacked on the tray  16 , their increasing weight turns it gradually downward around its front end. This makes it possible to stack a large number of sheets in aligned condition. 
     Provided over or above the rear end of the discharge tray  16  is a level sensor  17  for detecting the tray being filled with stacked sheets of paper. The sensor  17  includes a pivotable detecting lever for contact by its own weight with the top one of the sheets stacked on the tray  16 . The sensor  17  detects the filled tray  16  when sheets of paper are stacked up to the position indicated by a phantom line F, and consequently the detecting lever does not pivot downward beyond this position. Provided in the first guide passage  18  are uncurling rollers  20  for uncurling a sheet of paper. 
     The printer  2  includes a manual feed tray  13  and a feed roller  14  for feeding a sheet of paper placed on this tray. With reference to FIG. 2, the sorter  1  includes an adapter or adapting unit or recording medium receiver  29  as an introducing section for introducing a sheet of paper with an image formed on it by the printer  2  into the sorter  1 . The sorter  1  also includes a sorting unit  28  as a processing unit, which is mounted removably on top of the adapter  29 . 
     The printer  2  includes a manual feed tray  13  and a feed roller  14  for feeding a sheet of paper placed on this tray. With reference to FIG. 2, the sorter  1  includes an adapter or adapting unit  29  as an introducing section for introducing a sheet of paper with an image formed on it by the printer  2  into the sorter  1 . The sorter  1  also includes a sorting unit  28  as a processing unit, which is mounted removably on top of the adapter  29 . 
     The adapter  29  has an introducing passage  21  formed through its casing  27 . This passage  21  is for introducing a sheet of paper. The adapter  29  includes in the casing  27  a count lever  31  for detecting a sheet of paper introduced into the passage  21 . The adapter  29  also includes uncurling rollers  30  for uncurling the introduced sheet. The adapter  29  is fitted with a selectively switching mechanism  58  as selectively switching device for guiding a sheet of paper selectively to the discharge tray  16  of the printer  2  or the introducing passage  21  of the sorter  1 . 
     As shown in FIG. 3, the adapter casing  27  includes a rectangular trunk or body  53  and side portions  51  and  52 . Each of these portions  51  and  52  extends forward from one end of the body  53 . Each of the side portions  51  and  52  generally takes the form of an inverted U in side view. These portions  51  and  52  each include a trunk or body  56 , a front leg  54  and a rear leg  55 . The rear leg  55  extends straight downward from the trunk  56 . The front leg  54  first extends downward and forward from the trunk  56 , and then extends downward. Provided in each of the side portions  51  and  52  is a support plate  57  (FIG.  7 ), which will be described below in detail. This plate  57  includes a front fitting portion  81  and a rear fitting portion  82  as fitting members for fitting on the printer  2 . 
     As shown in FIG. 2, the introducing passage  21  extends generally vertically through the adapter  29  so that a sheet of paper discharged from the discharge rollers  15  of the printer  2  can be conveyed through this passage to the sorting unit  28 . The nips between the uncurling rollers  30  are positioned in the passage  21 , which extends across the count lever  31 . This lever  31  is positioned upstream of the uncurling rollers  30 . 
     As described below in detail, the selectively switching mechanism  58  protrudes downward from the adapter  29 , and is inserted into the printer  2  when the adapter  29  is mounted on the printer. The switching mechanism  58  includes a selecting flapper  12  which can pivot between a first guide position as indicated by phantom lines in FIG. 1, where the flapper guides a sheet of paper toward the discharge tray  16 , and a second guide position as indicated by solid lines in FIG. 1, where the flapper guides a sheet of paper toward the introducing passage  21 . In accordance with the guide position of the flapper  12 , a sheet of paper from the discharge rollers  15  is guided selectively to one of the guide passages  18  and  19 . The flapper  12  is controlled by a CPU (not shown) and can be actuated by a solenoid  61  which will be described below. 
     By fitting the switching mechanism  58  to the adapter  29 , it is possible for the sorter  1  to include all the members and/or parts for determining the direction of sheet discharge. This makes the printer  2  simpler in structure, thereby preventing wasteful cost increase for the printer. 
     The sorting unit  28  includes a casing  26 , which has an inlet  47  formed at its bottom. A sheet of paper from the introducing passage  21  of the adapter  29  passes through the inlet  47  into the sorting unit  28 . This unit  28  also includes a first bin  41 , a second bin  42 , a third bin  43 , a fourth bin  44  and a fifth bin  45  for storing or holding sheets of paper. The unit  28  includes, in its casing  26 , pairs of discharge rollers  22  as discharging devices for discharging sheets of paper to the respective bins  41 - 45 . The unit  28  also includes pairs of conveying rollers  24  as a conveying device for conveying, to the discharge rollers  22 , sheets of paper passing from the inlet  47 . The unit  28  further includes a first switching flapper  35 , a second switching flapper  36 , a third switching flapper  37 , a fourth switching flapper  38  and a fifth switching flapper  39  as direction switching devices for guiding, to the respective pairs of discharge rollers  22 , sheets of paper passing from the inlet  47 . The casing  26  has an outlet  46  formed at its top, through which a sheet of paper conveyed by the conveying rollers  24  can be discharged upward from the unit  28 . The unit  28  has a conveying passage  32 , which includes a vertical stem or trunk  33  and five branches  34 . The stem  33  is formed vertically through the unit  28 , and extends between the inlet  47  and the outlet  46 . The branches  34  extend from the stem  33  toward the respective pairs of discharge rollers  22 , and open to them. This passage  32  guides sheets of paper from the inlet  47  to the discharge rollers  22  and the outlet  46 . 
     As shown in FIG. 3, the casing  26  of the sorting unit  28  includes a rectangular trunk or body  50  and side portions  48  and  49 . These portions  48  and  49  each extend forward from one end of the body  50 . 
     Each of the bins  41 - 45  generally takes the form of a plate to receive and store or hold sheets of paper. Rear end portions of the bins  41 - 45  are supported by the body  50  and the side portions  48  and  49  of the casing  26 . The bins  41 - 45  extend forward and upward, and their front end portions protrude forward beyond the side portions  48  and  49 . The bins  41 - 45  are arranged in vertical alignment. 
     As shown in FIGS. 1 and 2, the pairs of discharge rollers  22  are positioned over or above the rear ends of the respective bins  41 - 45 . One of the discharge rollers  22  of each pair is driven, and the other roller follows the driven roller. 
     Each of the switching flappers  35 - 39  is supported pivotably on its horizontal axis positioned over the rear end of the associated branch  34  of the conveying passage  32 . Each of these flappers  35 - 39  can pivot between a third guide position (the position of the third flapper  37  in FIG.  2 ), where it guides a sheet of paper to the associated discharge rollers  22 , and a fourth guide position (the position of the switching flappers other than the third flapper  37  in FIG.  2 ), where it guides a sheet of paper vertically. In accordance with the guide positions of the flappers  35 - 39 , sheets of paper having entered the sorting unit  28  are guided from the vertical stem  33  to arbitrary branches  34  of the passage  32 . 
     The pairs of conveying rollers  24  for conveying sheets of paper vertically are positioned between the switching flappers  35 - 39  along the vertical trunk  33  of the conveying passage  32 . One of the conveying rollers  24  of each pair is driven, and the other roller follows the driven roller. 
     The sorting unit  28  includes a motor (not shown) as a motive power source for driving the discharge rollers  22  and the conveying rollers  24  through gear trains (not shown). This motor can also drive the uncurling rollers  30  of the adapter  29 , which includes no motor. 
     Sheets of paper discharged from the printer  2  can be stored by the bins  41 - 45  of the sorter  1  in the following manner. If the selecting flapper  12 , which has been inserted in the printer  2 , is switched to the second guide position (solid lines in FIG.  1 ), this flapper guides to the introducing passage  21  of the sorter adapter  29  a sheet of paper discharged by the discharge rollers  15  of the printer. The sheet in this passage  21  is uncurled by the uncurling rollers  30 , and then pushes the count lever  31 . Thereafter, the sheet passes through the inlet  47  into the conveying passage  32  of the sorting unit  28 . 
     Because the uncurling rollers  30  are provided in the adapter  29 , a sheet of paper is uncurled immediately before it is sorted and stored in the sorting unit  28 . The uncurled sheet smoothly enters the sorting unit  28 . This makes it possible to store sheets of paper in an orderly manner in the bins  41 - 45  and restrain sheets of paper from being jammed. 
     When the count lever  31  is pushed, a detection signal is output, causing the CPU (not shown) to judge that a sheet of paper has entered the sorter  1 . Thus, by providing this lever  31  in the adapter  29 , it is possible to determine whether a sheet of paper has entered the sorter  1 . Therefore, when a sheet of paper is jammed, it is easy to judge whether the sheet is jammed in the printer  2  or the sorter  1 . 
     A sheet of paper having entered the conveying passage  32  can be conveyed upward in the vertical passage stem  33  by the conveying rollers  24 . When the sheet reaches the switching flapper  35 ,  36 ,  37 ,  38  or  39  in the third guide position, this flapper guides the sheet to the associated discharge rollers  22 . In more detail, the flappers  35 - 39  are controlled by the CPU (not shown) and can each be actuated by a solenoid (not shown). When a sheet of paper should be discharged to one of the bins  41 - 45 , the associated flapper  35 ,  36 ,  37 ,  38  or  39  is turned to the third guide position, with the other switching flappers in the fourth guide position. 
     As shown in FIG. 2, there may be a case where sheets of paper should be discharged to the third bin  43 . In this case, only the third switching flapper  37  is in the third guide position, while the other switching flappers  35 ,  36 ,  38  and  39  are in the fourth guide position. After a sheet of paper enters the conveying passage  32 , the sheet is conveyed in the vertical passage stem  33  up to the third flapper  37  in the third guide position by the conveying rollers  24  below this flapper. This flapper  37  turns the sheet to the associated passage branch  34 . The turned sheet is then discharged by the associated discharge rollers  22  to the third bin  43 . 
     In the case shown in FIG. 2, a sheet of paper from the introducing passage  21  is conveyed without slowing down in the vertical passage stem  33  by the conveying rollers  24  below the third switching flapper  37  until the sheet reaches this flapper. After the sheet is turned by the third flapper  37  to the associated passage branch  34 , the sheet is completely discharged without slowing by the associated discharge rollers  22  to the third bin  43 . Therefore, the sorter  1  can reliably, at high speed, sort and store sheets of paper on which images have been formed by the printer  2 . 
     With reference to FIGS. 3-6, the sorter  1  can be mounted on and dismounted from the printer  2  as follows. In FIGS. 4-6, locking mechanisms are not shown, which will be described below. As shown in FIGS. 3-6, the front fitting portion  81  of the support plate  57  of each side portion  51  or  52  of the adapter casing  27  protrudes downward from the front leg  54  of the side portion. Likewise, the rear fitting portion  82  of each side portion  51  or  52  protrudes downward from the rear leg  55  of the side portion. The fitting portions  81  and  82  are substantially rectangular, and each include a thin bottom portion. Each front fitting portion  81  has a flat bottom surface for surface contact with another surface. The bottom portion of each rear fitting portion  82  is bifurcated and has round bottom surfaces for surface contact with another surface. The bottom surfaces of the fitting portions  81  and  82  are substantially in horizontal alignment. These portions  81  and  82  surround the center of gravity (dotted line  85  in FIG. 6) of the sorter  1 . 
     The printer  2  includes a pair of front holding plates  83  and a pair of rear holding plates  84 , all of which are provided in its upper portion. The front holding plates  83  are located for engagement with the respective front fitting portions  81  of the support plates  57  of the sorter  1 . The rear holding plates  84  are located for engagement with the respective rear fitting portions  82 . 
     With the front fitting portions  81  engaging with and positioned by the respective front holding plates  83 , these portions can be held by these plates. With the rear fitting portions  82  engaging with and positioned by the respective rear holding plates  84 , these portions can be held by these plates. By inserting each of the fitting portions  81  and  82  from above into the associated holding plate  83  or  84 , as shown in FIG. 4, and engaging them, as shown in FIG. 5, it is possible to mount the sorter adapter  29  on the printer  2 . In FIG. 5, each of the fitting portions  81  and  82  is positioned by the associated holding plate  83  or  84 . This makes the sorter  1  mounted stably in an upright or standing position on the printer  2 . 
     It is possible to dismount the sorter  1  from the printer  2  by lifting the adapter  29  in an upright position to pull each of the fitting portions  81  and  82  out of the associated holding plate  83  or  84 . The sorter  1  may be dismounted from the printer  2  with a user&#39;s hands holding the trunks  56  of the side portions  51  and  52  of the adapter casing  27 . Because the trunks  56  are positioned substantially on a vertical plane extending through the center of gravity  85  of the sorter  1 , the sorter can be lifted in balance. 
     When the sorter  1  is placed on a floor, as shown in FIG. 6, the bottoms of the fitting portions  81  and  82  are substantially in horizontal alignment. These portions  81  and  82  surround the center of gravity  85  of the sorter  1 . It is preferable that, as shown in FIG. 6, the center  85  be positioned substantially at the midpoint between a vertical plane extending through the front fitting portions  81  and a vertical plane extending through the rear fitting portions  82 . It is also preferable that the center  85  be positioned substantially at the midpoint between two vertical planes each extending through the fitting portions  81  and  82  on one side. Therefore, the sorter  1  can rest on the floor stably, without toppling or falling down, substantially in the same upright position as it is mounted on the printer  2 . Therefore, it is not necessary to lay the sorter  1  down on a floor, lean it against a wall and support it with a member, and it is easy to dismount the sorter  1  from the printer  2 , store the dismounted sorter and mount the dismounted sorter again on the printer. Because the sorter  1  can contact with the floor with the bottom surfaces of the fitting portions  81  and  82 , it is possible to well keep the sorter  1  mounted stably on the floor. 
     The fitting portions  81  and  82 , which are provided as fitting members used when the sorter  1  is mounted on the printer  2 , function as legs when the sorter is dismounted from the printer and placed on a floor. Therefore, there is no need to provide special or extra legs other than the fitting portions  81  and  82 , with which to place the sorter  1  stably on a floor. This simplifies the structure of the sorter  1  and reduces the number of parts of the sorter. 
     The sorter  1  is mounted in an upright position on the printer  2 . After the sorter  1  is dismounted from the printer  2 , the sorter is placed still in an upright position on a floor. In other words, the sorter  1  is mounted and dismounted substantially in the same position. Therefore, the sorter  1  can be dismounted from the printer  2  by being lifted in an upright position, and then be placed still in the same position on a floor. Likewise, the sorter  1  placed in the upright position on the floor can be lifted still in the same position, and then be mounted still in this position from above on the printer  2 . It is therefore easier to mount the sorter  1  on and dismount it from the printer  2 . 
     FIGS. 7 and 8 are left side views of the sorter adapter  29 , but the side cover (not shown) of the left side portion  52  of the adapter casing  27  is removed. With reference to FIGS. 7 and 8, the sorter  1  includes two locking mechanisms  101  (only one shown in FIGS. 7 and 8) for keeping it mounted on the printer  2 . These mechanisms  101  are provided in the respective side portions  51  and  52  of the casing  27 . 
     With reference to FIG. 7, each of the support plates  57  of the sorter adapter  29  includes a trunk or body  59  integrally connecting the tops of the associated fitting portions  81  and  82 . Each of the locking mechanisms  101  is provided on the trunk  59  and a top portion of the rear fitting portion  82  of the associated support plate  57 . Each locking mechanism  10  includes a lever  102 , a pivot or swing member  103  as first engaging portion, a compression spring  104  as an urging device, and a link  105 . The pivot member  103  interlocks or works with the lever  102 . The link  105  links the lever  102  and the pivot member  103  together. 
     The lever  102  is supported pivotably by the associated support plate  57  in such a manner that it can be positioned partially under the trunk  56  of the associated side portion  51  or  52  of the adapter casing  27 . The lever  102  includes an operating portion  106  for manual operation or manipulation, a horizontal support pin  107 , a spring shoe or seat  108  and a connector  109 . The operating portion  106 , the pin  107 , the shoe  108  and the connector  109  are formed integrally. The pin  107  is supported rotatably on the trunk  59  of the support plate  57  so that the operating portion  106  can pivot up and down around the pin. The pin  107  is positioned at the top of the lever  102  and near the rear end of the lever. The shoe  108  is positioned above and in the rear of the pin  107 , and bears one end of the spring  104 ,the other end of which is fixed to the trunk  59 . The connector  109  extends downward and backward from the pin  107 , and is connected to the pivot member  103 . 
     Part of the operating portion  106  is positioned under the trunk  56  of the associated side portion  51  or  52  of the adapter casing  27 . Through the operating portions  106  of the side portions  51  and  52  extends a vertical plane on which the center of gravity  85  of the sorter  1  is positioned. The spring  104  downward urges the front end of the associated operating portion  106 , which is positioned opposite the associated spring shoe  108  with respect to the associated support pin  107 . 
     The pivot member  103  includes a connector  110  as a portion for receiving motive power, a pawl  111 , and a horizontal pivot pin  112 . This pin  112  is supported rotatably on the top of the rear fitting portion  82  of the support plate  57  in such a manner that the pivot member  103  can pivot around this pin. The connector  110  extends upward and forward from the pin  112  toward the trunk  59  of the plate  57 . The pawl  111  extends downward from the pin  112 . 
     Each of the rear holding plates  84  of the printer  2  includes an engaging portion  113  as a second engaging portion formed at its top. The pivot member  103  can pivot between an engaging position, where its pawl  111  engages with the associated engaging portion  113 , and a disengaging position, where the pawl disengages from the engaging portion  113 . The connectors  110  and  109  of the pivot member  103  and the lever  102 , respectively, are linked together by the link  105 . The engaging portion  113  protrudes toward the pawl  111  so that it can engage with the pawl. When the sorter  1  is mounted on the printer  2 , the engaging portion  113  is positioned in front of the pawl  111 . The pawl  111  includes a slope  114  for sliding on the engaging portion  113  to guide the engagement of the pawl with the engaging portion when the sorter  1  is in the process of being mounted on the printer  2 . 
     FIG. 7 shows the sorter  1  as mounted on the printer  2  and locked by the locking mechanisms  101 . The spring  104  of each locking mechanism  101  urges the front end of the operating portion  106  of the associated lever  102  downward and the connector  109  of the lever upward. The upward urged connector  109  turns the connector  110  of the associated pivot member  103  upward through the associated link  105 , moving the associated pawl  111  forward to the engaging position, where the pawl engages with the associated engaging portion  113  of the printer  2 . 
     FIG. 8 shows the sorter  1  as unlocked in the process of being dismounted from the printer  2 . It is possible to unlock the sorter  1  by pushing upward the operating portions  106  of the levers  102  of the locking mechanisms  101 . Specifically, when each operating portion  106  is pushed upward against the urging force of the associated spring  104 , the associated lever connector  109  turns downward. This turns the connector  110  of the associated pivot member  103  downward through the associated link  105 , moving the associated pawl  111  backward to the disengaging position, where the pawl disengages from the associated engaging portion  113  of the printer  2 . 
     When a user mounts the sorter  1  on the printer  2 , he or she basically holds the trunks  56  of the side portions  51  and  52  of the adapter casing  27  with both his or her hands, as stated above. Therefore, with a user&#39;s hands holding and raising the levers  102  of the side portions  51  and  52 , the sorter  1  can be mounted from above on the printer  2 . By thus mounting the sorter  1  with the levers  102  held by a user&#39;s hands, it is possible for the levers to be turned upward relative to the support plates  57  naturally by the weight of the sorter. The upward turning of each lever  102  moves the associated pawl  111  to the disengaging position, in which the pawl is kept during the mounting operation. This allows the pawl  111  to be inserted smoothly without contacting with the associated engaging portion  113  of the printer  2 . When the mounting operation ends, the hands are moved out of contact with the levers  102 , causing the urging force of the springs  104  to move the pawls  111  to the engaging position. As a result, as shown in FIG. 7, the pawls  111  engage with the engaging portions  113 . 
     Consequently, while the sorter  1  is mounted on the printer  2 , the springs  104  keep the pawls  111  in engagement with the engaging portions  113  of the printer  2 , thereby keeping the sorter locked. This fixes the mounted sorter  1  securely to the printer  2 . Even if external force is applied to the mounted sorter  1 , the sorter hardly tilts or falls from the printer  2 . It is therefore possible to hold the sorter  1  reliably on the printer  2 . 
     Otherwise, the sorter  1  may be mounted on the printer  2  without the levers  102  being held. If the sorter  1  is mounted without the levers  102  being operated, the pawls  111  come into engagement with the engaging portions  113 . Then, the pawls  111  move against the urging force of the springs  104  to the disengaging position, where they disengage from the engaging portions  113 . When the slopes  114  of the pawls  111  disengage from the engaging portions  113 , the pawls return to the engaging position, where they are caused by the springs  104  to engage with the engaging portions  113 . It is therefore possible to lock the sorter  1  with the locking mechanisms  101  even without operating the levers  102  during the mounting operation. 
     When a user dismounts the sorter  1  from the printer  2 , he or she lifts the sorter with both his or her hands holding the levers  102 . In this situation, because the sorter  1  and the levers  102  are moved in the same direction, naturally the levers are turned upward relative to the sorter by the weight of the sorter. The upward turned levers  102  move the pawls  111  to the disengaging position, where the pawls disengage from the engaging portions  113 . This makes it possible to unlock the sorter  1  and dismount it from the printer  2  at a time by only holding the levers  102  with a user&#39;s hands. It is therefore easy to dismount the sorter  1  from and mount it on the printer  2 . 
     The levers  102  are positioned partially under the trunks  56  of the side portions  51  and  52  of the adapter casing  27 . As stated above, a user holds the trunks  56  with his or her hands when he or she mounts the sorter  1  on and dismounts it from the printer  2 . When a user dismounts the sorter  1  from the printer  2 , he or she holds the levers  102  as well as the trunks  56 . That is to say, it is possible to carry out the holding for removal and the lever operation by holding the same parts. This makes it possible to dismount the sorter  1  more efficiently. 
     The operating portions  106  of the levers  102  are positioned partially under the respective trunks  56  of the side portions  51  and  52  of the adapter casing  27 . Through the operating portions  106  extends a vertical plane on which the center of gravity  85  of the sorter  1  is positioned. Therefore, when the sorter  1  is lifted with the levers  102  held by a user&#39;s hands, it can be held in balance. Therefore, by mounting and dismounting the sorter  1  with the levers  102  held by a user&#39;s hands, it is possible to hold the sorter in balance. This enables the sorter  1  to be mounted on and dismounted from the printer  2  stably. 
     When the connectors  110  of the pivot members  103  turn upward, these members pivot so that their pawls  111  can engage with the engaging portions  113  of the rear holding plates  84 . There may be a case where external force is applied to pull upward the sorter  1  mounted on the printer  2 . This may turn the connectors  110  of the pivot members  103  upward. In this case, the pawls  111  do not disengage from the engaging portions  113 , rather engage more firmly or strongly with them. Therefore, even if external force is applied to the sorter  1  mounted on the printer  2 , the pawls  111  do not disengage accidentally from the engaging portions  113 . This makes it possible to more reliably or securely hold the sorter  1  mounted on the printer  2 . 
     As stated before, when the sorter  1  is mounted on the printer  2 , the pawls  111  of the pivot members  103  are moved to the engaging position, where they engage with the engaging portions  113  of the printer. This makes it possible to securely hold the sorter  1  mounted on the printer  2 . Therefore, even if external force is applied to the sorter  1 , the sorter hardly tilt or fall from the printer  2 . It is consequently possible to keep the sorter  1  operating in good condition, and prevent or restrain the sorter from being damaged by falling down. 
     As also stated, when the sorter  1  is in the process of being dismounted from the printer  2 , the sorter is lifted in an upright position with a user&#39;s hands holding the levers  102  of the locking mechanisms  101 . This moves the pawls  111  of the pivot members  103  to the disengaging position, where the pawls disengage from the engaging portions  113  of the printer  2 . The disengagement allows the sorter  1  to be dismounted easily from the printer  2 . 
     Thus, by moving the pawls  111  of the pivot members  103  between the engaging and disengaging positions, it is possible to securely hold the sorter  1  mounted on the printer  2 , while it is easy or simple to mount the sorter on and dismount it from the printer. 
     FIGS. 9-11 are right side views of the sorter adapter  29 , but the right side cover (not shown) of the right side portion  51  the adapter casing  27  is removed. FIGS. 9 and 10A show the sorter  1  as mounted on the printer  2 . FIG. 10B is an enlarged view of the selecting flapper and the solenoid of the switching mechanism, and parts near them shown in FIG.  10 A. FIG. 11 shows the sorter  1  as dismounted from the printer  2 . 
     With reference to FIG. 9, the selectively switching mechanism  58  includes the selecting flapper  12  as a switching device, the solenoid  61 , a first tension spring  62  as an urging device and a link  63  as a transmitting device for transmitting urging force. The solenoid  61  can move the flapper  12  between the first and second guide positions. The spring  62  can urge the flapper  12  toward the second guide position. When the sorter  1  is mounted on the printer  2 , the link  63  causes no urging force of the spring  62  to act on the flapper  12 . When the sorter  1  is not mounted on the printer  2 , the link  63  causes the urging force of the spring  62  to act on the flapper  12 . 
     The selecting flapper  12  includes a horizontal shaft (not shown), a number of flap members  64  and a flapper swinger  66  which are formed integrally. This shaft has an axis  65 , extends through the trunk  53  of the adapter casing  27  longitudinally of it, and is supported rotatably between the side portions  51  and  52  of this casing. The flap members  64  are formed on this shaft at intervals along it, protrude downward from the casing trunk  53 , and can pivot or swing between the first and second guide positions. The swinger  66  is formed on the right end of this shaft and positioned in the right side portion  51  of the casing  27 . 
     The flapper swinger  66  includes a rear connector  68 , a front engaging portion  69  and a middle connector  70 . The rear connector  68  and the front engaging portion  69  are positioned opposite each other with respect to the shaft axis  65 . The middle connector  70  is positioned above and in front of the axis  65 , and between the rear connector  68  and the engaging portion  69 . The rear connector  68  is connected to one end of a second tension spring  67 , the other end of which is anchored above the swinger  66 . This spring  67  urges the selecting flapper  12  toward the first guide position, but is weaker than the first tension spring  62 . 
     The solenoid  61  is positioned in the right side portion  51  of the adapter casing  27 , and above and in the rear of the selecting flapper  12 . The middle connector  70  of the flapper swinger  66  is connected to a plunger  71 . If the solenoid  61  is energized or excited, it retracts the plunger  71 . 
     When the sorter  1  is mounted on the printer  2 , the link  63  is out of engagement with the front engaging portion  69  of the flapper swinger  66 , as described below. In this situation, if the solenoid  61  is not energized, the second tension spring  67  pulls the rear connector  68  of the swinger  66  upward. This turns the selecting flapper  12  around the axis  65  clockwise in FIG. 9, moving this flapper to the first guide position, which is shown in FIG.  9 . If the solenoid  61  is energized, the plunger  71  retracts, pulling the middle connector  70  of the swinger  66  backward. This turns the flapper  12  around the axis  65  counterclockwise in FIG. 9 against the force of the spring  67 , moving the flapper to the second guide position, which is shown in FIGS. 10A and 10B. 
     The link  63  is positioned in front of the selecting flapper  12 , and includes a body  73 , a first protrusion  74  as a connector, a second protrusion  75  as a second engaging portion, and an engaging portion  76  as a first engaging portion. The link body  73  has a horizontal shaft  72 . The protrusions  74  and  75  protrude from one side of the body  73 , and are spaced angularly from each other. The engaging portion  76  protrudes from the side of the body  73  opposite the protrusions  74  and  75  with respect to the shaft  72 . The body  73  and the parts  72 ,  74 ,  75  and  76  are formed integrally. When the sorter  1  is mounted on the printer  2 , as shown in FIGS. 9 and 10, the first protrusion  74  is oriented upward and backward, and the second protrusion  75  is oriented downward and backward, while the engaging portion  76  is oriented downward. 
     The shaft  72  of the link  63  is supported rotatably in the right side portion  51  of the adapter casing. The first protrusion  74  is connected to one end of the first tension spring  62 , the other end of which is anchored above and in front of the link  63 . This spring  62  urges the link  63  to turn around its shaft  72  clockwise in FIG. 11 so that the second protrusion  75  of the link  63  can engage with the front engaging portion  69  of the flapper swinger  66 . 
     When the sorter  1  is not mounted on the printer  2 , as shown in FIG. 11, the first tension spring  62  pulls the first protrusion  74  of the link  63  forward. This turns the link  63  around the shaft  72  clockwise in FIG. 11 to a second engaging position, where the second protrusion  75  of the link  63  pushes the front engaging portion  69  of the flapper swinger  66 . The pushing turns the selecting flapper  12  around the shaft axis  65  against the force of the second spring  67  counterclockwise in FIG. 11 to the second guide position, where the flap members  64  are oriented substantially downward. 
     When the sorter  1  is mounted on the printer  2 , as shown in FIGS. 9 and 10, the engaging portion  76  of the link  63  rests on the upper frame  77  of the printer. This turns the link  63  around the shaft  72  against the force of the first tension spring  62  counterclockwise in FIGS. 9 and 10 to a first engaging position, where the second protrusion  75  of the link  63  disengages from the front engaging portion  69  of the flapper swinger  66 . The disengagement allows the second tension spring  67  to urge the selecting flapper  12  toward the first guide position, which is shown in FIG. 9, where the flap members  64  are oriented slightly outward or backward. Only if the solenoid  61  is energized, the flapper  12  is turned against the force of the second spring  67  to the second guide position, which is shown in FIGS. 10A and 10B, where the flap members  64  are oriented downward. 
     When the sorter  1  is in the process of being mounted on the printer  2 , and when the sorter is dismounted from the printer, the sorter is not mounted on the printer, as shown in FIG.  11 . In this situation, the second protrusion  75  of the link  63  is in engagement with the front engaging portion  69  of the flapper swinger  66 . This allows the urging force of the first tension spring  62  to act through the link  63  on the selecting flapper  12 . This force keeps the flapper  12  in the second guide position, where the flap members  64  are oriented substantially downward. It is therefore possible to mount the sorter  1  on the printer  2  smoothly without the printer interfering with the flap members  64 . This avoids the sorter damage which would be caused if the printer  2  interfered with the flap members  64 . Even when the sorter  1  is dismounted from the printer  2 , no external force is liable to damage the flap members  64 , which are kept in a substantially downward oriented position. It is therefore possible to improve the durability of the sorter  1 . 
     When the sorter  1  is mounted on the printer  2 , as shown in FIGS. 9 and 10, the second protrusion  75  of the link  63  is out of engagement with the front engaging portion  69  of the flapper swinger  66 . This prevents the urging force of the first tension spring  62  from acting through the link  63  on the selecting flapper  12 . Therefore, the actuation of the solenoid  61  can switch the flapper  12  selectively between the first and second guide positions. 
     When the sorter  1  is not mounted on the printer  2 , that is to say, when the sorter is in the process of being mounted on the printer, and when the sorter is dismounted from the printer, the first tension spring  62  keeps the selecting flapper  12  in the second guide position, resulting in no electric power consumption. When the sorter  1  is mounted on the printer  2 , the solenoid  61  is energized only if the flapper  12  needs to be in the second guide position for guiding a sheet of paper to the introducing passage  21  of the sorter. Electric power is consumed only for the energization of the solenoid  61 . Thus, no electric power for switching the flapper  12  is consumed, not only when the sorter  1  is dismounted, but also if the sorter is not used even when it is mounted on the printer  2 . This saves electric power. 
     When the sorter  1  is mounted on the printer  2 , and when the sorter is dismounted from the printer, the link  63  is turned between the engaging positions. This, securely with simple structure, either allows the urging force of the first tension spring  62  to act on the selecting flapper  12  or prevents this force from acting on the flapper. It is therefore possible to simplify the sorter structure and reduce production costs. The sorting unit  28  of the sorter  1  can be fitted to the adapter  29  of the sorter as follows. 
     With reference to FIGS. 7-12, the support plate  57  in each side portion  51  or  52  of the adapter casing  27  includes a third fitting portion  86  and a fourth fitting portion  87  which are formed integrally. These portions  86  and  87  protrude upward from the top of the casing  27  so as to be fitted into the sorting unit  28 . 
     With reference to FIGS. 3 and 12, each side portion  48  or  49  of the casing  26  of the sorting unit  28  includes a fitting plate  88  protruding downward from its bottom so as to be fitted into the adapter  29 . 
     By inserting the third fitting portion  86  and the fourth fitting portion  87  of the support plate  57  into the sorting unit  28 , and inserting the fitting plate  88  of the sorting unit into the adapter  29 , as shown in FIG. 6, it is possible to mount this unit in positioned condition on the adapter. 
     During such fitting, whether the sorting unit  28  is mounted on the adapter  29  or not, as shown in FIGS. 6 and 12, the adapter is placed stably in an upright position without falling down. It is therefore possible to produce the sorter  1  by placing the adapter  29  on a floor and then fitting the sorting unit  28  to the adapter. This makes it possible to fit the sorting unit  28  well to the adapter  29  during the production, and to thereby improve the productivity. 
     As shown in FIGS. 13 and 14, one or more additional sorting units may be mounted on the sorting unit  28 . An additional sorting unit  128  is identical with the sorting unit  28 , and these units can be mounted on each other. The additional unit  128  includes five switching flappers  25  corresponding to the respective flappers  35 - 39  of the unit  28  and five bins  23  corresponding to the respective bins  41 - 45  likewise. Each of the units  28  and  128  includes a removable top lid or cover  127 . In FIGS. 13 and 14, the lid (not shown) of the unit  28  is removed, and the additional unit  128  is mounted on the unit  28 . 
     By inserting the fitting plates  88  of the additional sorting unit  128  into the top of the sorting unit  28 , as shown in FIG. 14, it is possible to mount the additional unit  128  on the unit  28  in stacked condition. The outlet  46  of the unit  28  is connected to the inlet  47  of the additional unit  128  mounted on the unit  28 . The top of the upper sorting unit  128  is covered with its lid  127 . 
     If all the switching flappers  35 - 39  of the sorting unit  28  mounted on the adapter  29  are in the fourth guide position, a sheet of paper can pass through this unit into the sorting unit  128  mounted on the unit  28 . It is therefore possible to sort and store sheets of paper with the units  28  and  128  combined together. 
     In particular, if only one of the sorting units  28  and  128  were used always, its top flapper  39  would not need to be pivotable, but might be fixed to the third guide position. Because the top flapper  39  of each unit  28  or  128  can pivot between the first and second guide positions like the other switching flappers  35 - 38  can, the unit can discharge a sheet of paper from its outlet  46 . This makes it possible to combine two or more sorting units. 
     It is therefore possible to add one or more sorting units depending on the number of bins needed by the users. This makes it possible to easily provide, without specially designing, a sorter  1  having an optimum number of bins for the users. Because the sorting units are stacked upward, the mounting area for the sorter  1  does not change even if a number of sorting units are stacked. This makes it possible to provide in a small mounting space a sorter  1  having a number of bins. 
     Even if one or more sorting units are added, the center of gravity  85  of the sorter  1  does not change substantially, as shown in FIGS. 6 and 14. Even in this case, the center of gravity  85  is positioned substantially at the midpoint between the vertical plane extending through the front fitting portions  81  and the vertical plane extending through the rear fitting portions  82 . Likewise, the center  85  is positioned substantially at the midpoint between the two vertical planes each extending through the fitting portions  81  and  82  on one side. This makes it possible to place the sorter  1  on a floor stably, without falling down, in substantially the same upright position in which the sorter is mounted on the printer  2 . 
     It is therefore possible to mount or dismount the additional sorting unit  128  with the adapter  29  placed on a floor. This makes it easier to mount or dismount the unit  128 . More specifically, if the additional unit  128  needed mounting or dismounting with the sorter  1  mounted on the printer  2 , it would be difficult to mount or dismount this unit at the high position over the sorter on the printer. By contrast, it is easier to mount or dismount the unit  128  with the sorter  1  placed on a floor. This greatly improves the working efficiency. 
     As shown in FIG. 3, the front legs  54  of the side portions  51  and  52  of the adapter casing  27  protrude forward or are positioned in front of the side portions  48  and  49  of the casing  26  of the sorting unit  28 . The front fitting portions  81  of the support plates  57  are positioned in the respective front legs  54 . Therefore, even if one pushes the back of the sorting unit  28  mounted on the adapter  29 , these fitting portions  81  securely support this unit so that the unit  28  may not fall down. This makes it possible to place the adapter  29  stably even with the unit  28  mounted on the adapter. 
     With reference to FIG. 14, each of the sorting units  28  and  128  is provided with a motor for driving it. Otherwise, only one of the units  28  and  128  might be provided with a motor for driving them. In such a case, the drive systems in the units  28  and  128  might be coupled together by one or more gears. Instead of the sorting unit  28 , the adapter  29  might be provided with a motor. 
     The recording medium processor (discharging apparatus) according to the invention is not limited to the sorter  1 , the processing unit of which is the sorting unit  28 . The recording medium processor may instead be a stapler, a puncher, a cutter, a laminator or any other processor. In such a case, the processing unit of the processor is a stapling unit, a punching unit, a cutting unit, a laminating unit or any other unit.