Patent Publication Number: US-6334611-B1

Title: Paper discharging apparatus for printer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a paper discharging apparatus for a printer that transfers sheets of paper from an image printer to a plurality of paper discharging trays. 
     2. Description of the Related Art 
     In general, a printer such as a laser printer or a copier, as shown in FIG. 1, includes an image forming unit  3  for forming an image on a photoreceptor belt  2  and printing the formed image on a sheet of paper P. The paper P having a printed image is discharged to the outside of a printer body  1  by a paper discharging apparatus. 
     The paper discharging apparatus includes a plurality of discharge trays  4  installed in the exterior side of the printer body  1 , and a transfer means for selectively transferring the paper P from the image forming unit  3  to the discharge trays  4 . 
     The paper P is selectively discharged to one of the plurality of discharge trays  4  according to the printed image. For example, in the case where an identical image is printed onto a plurality of sheets, the sheets of printed paper are transferred to the respective discharge trays  4  to then be sorted. 
     The transfer means includes a pair of pulleys  5  rotatably installed in the upper and lower portions of the printer body  1 , a belt  6  supported by the pulleys  5 , a stepping motor  8  for driving the pulleys  5 , and an indexer  7  installed on the belt  6 , for clamping paper P printed and transferred. The indexer  7  is constituted by a pair of rollers  7   a  which rotate in contact with each other, and a motor  7   b  for rotating the rollers  7   a.    
     In the above-described configuration, the paper P printed in the image forming unit  3  is guided by a guide  9 , and then clamped between rollers  7   a  of the indexer  7 . As the belt  6  travels, the indexer  7  elevates to reach a selected discharge tray  4  as shown in phantom in FIG.  1 . Then, the paper P is discharged to the selected discharge tray  4  by rotation of the rollers  7   a.    
     Although such conventional devices are generally thought to be acceptably, they are not without shortcomings. In particular, paper discharge occurs at a rapid rate, and therefore the indexer  7  cannot properly clamp a subsequent sheet of paper. This phenomenon is especially problematic when paper is discharged to the lowermost discharge tray  4  because the movement speed of the indexer  7  cannot catch up with the paper discharge speed from the guide  9 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved paper discharging apparatus for a printer, which rapidly transfers successively discharged sheets of paper to discharge trays. 
     Accordingly, to achieve the above objective, a paper discharging apparatus for a printer includes a movement path having a first movement track and a second movement track for independently guiding paper printed in an image forming unit in a printer body. A means is provided for branching the movement path and allowing the printed paper to selectively enter the first or second movement track. A first indexer is elevatably installed in the printer body, for clamping a first sheet of paper that has passed through the first movement track and moving to a first selected discharge tray to discharge the paper thereto. A second indexer is elevatably installed in the printer body, for clamping a second sheet of paper that has passed through the second movement track and moving to a next selected discharge tray to discharge the paper thereto. A means is provided for elevating the first and second indexers, and a controller controls the driving of the elevating means and the first and second indexers. 
     Each of the elevating means preferably includes a pair of belts for supporting the corresponding indexer, pulleys installed in the upper and lower portions of the printer body to support the belts, and a stepping motor for rotating the pulleys. 
     The first indexer may include first brackets fixed on the belts, a pair of first clamping rollers rotatably mounted on the first brackets, for clamping the first sheet of paper and discharging the clamped paper to the first discharge tray, a first guide plate installed in the first brackets, for guiding the first sheet of paper discharged by the first clamping roller to the first discharge tray, and a first motor for driving the first clamping rollers. 
     The second indexer may include second brackets fixed on the belts, a pair of second clamping rollers rotatably mounted on the second brackets, for clamping the second sheet of paper and discharging the clamped paper to the second discharge tray, a second guide plate slidably installed in the second brackets so as to extend and retract toward and away from the discharge trays, for guiding the paper discharged from the second clamping rollers to the second discharge tray, a second motor for driving the second clamping rollers, and means for driving the second guide plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objective and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
     FIG. 1 is a schematic diagram illustrating a printer employing a conventional paper discharging apparatus; 
     FIG. 2 is a schematic diagram illustrating a printer employing a paper discharging apparatus according to an embodiment of the present invention; 
     FIG. 3 is a schematic perspective view illustrating a first indexer and elevating means shown in FIG. 2; and 
     FIG. 4 is a schematic perspective view illustrating a second indexer and elevating means shown in FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2, a paper discharging apparatus according to one embodiment of the present invention includes a movement path  14  along which paper P (on which an image is printed in an image forming unit  12 ) moves, a plurality of discharge trays  16  installed on the exterior side of a printer body  10 , first and second indexers  20  and  30 , respectively, elevatably installed in the printer body  10 , means for elevating the first and second indexers  20  and  30 , and a controller  40  for controlling the driving of the elevating means and the first and second indexers  20  and  30 . 
     The movement path  14  is branched off into a plurality of movement tracks, for example, first and second movement tracks  14   a  and  14   b , respectively. The first and second movement tracks  14   a  and  14   b  have ends at which the indexers  20  and  30  are correspondingly installed. A transfer roller  15   a  for transferring the paper P is installed at an entrance of the movement path  14 . If the movement path  14  is long, another transfer roller  15   b  may be installed in the middle of the movement path  14 . 
     A solenoid shutter  14   c  is provided at the branching part of the first and second movement tracks  14   a  and  14   b . The shutter  14   c  allows the printed paper P to selectively enter one of the first and second movement tracks  14   a  and  14   b  by the control of the controller  40 . 
     The first indexer  20 , as shown in FIG. 3, includes first brackets  22  fixed on a pair of belts  54  at the same height with each other, a pair of first clamping rollers  24  rotatably mounted on the first brackets  22 , and a first guide plate  28  installed in the first brackets  22 , for guiding paper. Also, a first motor  26 , for driving the first clamping rollers  24  by a first interlocking gear  24   a , is installed on the first brackets  22 . 
     In this embodiment, when the second movement track  14   b  is located lower than the first movement track  14   a , the movement distance of the second indexer  30  is shorter than that of the first indexer  20 . 
     As shown in FIG. 4, the second indexer  30  includes second brackets  32  fixed on a pair of belts  64  at the same height with each other, a pair of second clamping rollers  34  rotatably mounted on the second brackets  32 , a second motor  36 , for driving the second clamping rollers  34  by a pair of second interlocking gears  34   a , a second guide plate  38  slidably installed in the second brackets  32  by a guide  31 , and means for driving the second guide plate  38 . 
     The second guide plate  38 , for guiding the paper clamped by the second clamping rollers  34  and discharged to the discharge trays  16 , is installed for movement toward and away from the discharge trays  16 . That is, the guide plate  38  is moveable in directions A and B, so as to avoid interfering with the first indexer  20 . 
     The driving means (for the second guide plate  38 ) includes a rack gear  38   a  formed on the bottom face of the second guide plate  38 , a pinion gear  39  rotatably installed on the second brackets  32  so as to be engaged to the rack gear  38   a , and a clutch  37  connected to a shaft  39   a  of the pinion gear  39 . The clutch  37  is controlled by the controller  40  and selectively transfers a driving force of the second motor  36  to the shaft  39   a.    
     As shown in FIGS. 3 and 4, the means for elevating the first and second indexers  20  and  30  includes stepping motors  52  and  62 , respectively, a pair of belts  54  and  64 , respectively, for supporting the first and second indexers  20  and  30 , pulleys  56   a ,  57   a  and  66   a ,  67   a , respectively, installed in the upper portion of the printer body  10 , and pulleys  56   b ,  57   b  and  66   b ,  67   b , respectively, installed in the lower portion of the printer body  10 . The pulleys support the belts  54  and  64 . Ends of the pulley shafts  58  and  68  are respectively coupled to rotation shafts of the stepping motors  52  and  62 . 
     The paper discharge apparatus according to this embodiment of the present invention operates as follows. 
     The paper P printed in the image forming unit  12  is transferred by the transfer roller  15   a  into the movement path  14 . The solenoid shutter  14   c  selectively opens or closes the first and second movement tracks  14   a  and  14   b  so that the paper P is introduced to one of the first and second movement tracks  14   a  and  14   b  according to the printing sequence. For example, as shown in FIG. 2, when a first sheet of paper P 1  (which is printed first) enters the movement path  14 , the solenoid shutter  14   c  is positioned (as shown in phantom) to open the first movement track  14   a  and close the second movement track  14   b . Thus, the first sheet of paper P 1  enters into the first movement track  14   a . Subsequently, when a second sheet of paper P 2  (which is printed second) enters the movement path  14 , the solenoid shutter  14   c  is repositioned (as shown in solid lines) to close the first movement track  14   a  and open the second movement track  14   b . Thus, the second sheet of paper P 2  enters into the second movement track  14   b.    
     The paper P 1 , having passed through the first movement track  14   a , is clamped between the first clamping rollers  24  of the first indexer  20  positioned at the end of the first movement track  14   a . In this state, the pulley  56   a  and  57   a  are rotated by the stepping motor  52  to lower the first indexer  20  fixed on the belt  54  to a selected discharge tray  16   a.    
     The first indexer  20  moves to the desired discharge tray  16   a  and stops. The first clamping rollers  24  are rotated to discharge the paper P 1  to the discharge tray  16   a  via the first guide plate  28 . Then, the stepping motor  52  is rotated in reverse to move the first indexer  20  to its original position. 
     The paper P 2 , having passed through the second movement track  14   b , is clamped between the second clamping rollers  34  of the second indexer  30 . Next, the pulleys  66   a  and  67   a  are rotated by the stepping motor  62 , to lower the second indexer  30  to a position corresponding to a selected discharge tray  16   b . Thus far, the second guide plate  38  remains retracted in the direction B (See FIG. 4) so as to avoid interfering with the first indexer  20 . 
     When the second indexer  30  reaches the selected discharge tray  16   b , the pinion gear  39 , rotated by the second motor  36  and the clutch  37 , advances the second guide plate  38  in the direction A so that the end of the second guide plate  38  is positioned to correspond to the discharge tray  16   b . Subsequently, the second clamping rollers  34  are rotated to discharge the clamped paper P 2  across the second guide plate  38  and into the discharge tray  16   b.    
     After the paper P 2  is discharged, the clutch  37  is driven to rotate the pinion gear  39  in a reverse direction so that the second guide plate  38  retracts in the direction B. Then, the second indexer  30  is restored to its original position. 
     According to the present invention, since printed paper is led via two movement tracks and clamped by first and second indexers which independently elevate to then be discharged to discharge trays, the printed paper can be rapidly discharged and sorted. 
     Also, only one of the first and second indexers may be used according to the printing speed or type. Although not shown, each indexer may be constructed such that it elevates by known means such as a guide rail, rather than a belt. 
     The above and other features of the invention including various and novel details of construction has been particularly described with reference to the accompanying drawings and pointed out in the following claims. It will be understood that the particular paper discharging apparatus embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention.