Abstract:
A discharge system for printed media sheets which includes a tray having a surface for supporting the media sheets; and rotating transport elements forming a discharge nip for discharging the sheets onto the tray, wherein at least one driven transport belt is arranged to engage a trailing edge of the sheet that has left the discharge nip and to exert a driving force towards the tray surface.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a discharge system for printed media sheets, including: a tray having a surface for supporting the media sheets; and rotating transport elements forming a discharge nip for discharging the sheets onto the tray.  
         [0002]     In printers and copiers, printed media sheets are frequently collected on one or more trays. The media sheets may be supplied, for example, from a stack of cut sheets, or may be continuously supplied from a reel and then cut into sheets. When the media sheets are supplied from a reel, they are often slightly curled. This effect becomes even more pronounced when the end of the reel is reached and the radius of curvature of the reel becomes smaller. Also, for example, when the media sheets are supplied from a stack of cut sheets, they may become curled during the printing process.  
         [0003]     When the printed media sheets are collected on the tray, curled edges of deposited sheets may prevent subsequent sheets from being properly stacked and collected on the tray. For example, when a sheet on the tray is curled upwards at its leading and trailing edges, the space on the tray is used inefficiently, leading to a reduced capacity of the tray. Moreover, curled edges of previously collected sheets might block the discharge nip.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the present invention to provide a discharge system that ensures that upwardly curled media sheets are neatly collected on a tray while avoiding the problems mentioned above. It is also an object of the present invention to provide a printer containing such a discharge system.  
         [0005]     According to the present invention, this object is achieved by a discharge system of the type indicated above, wherein at least one driven transport belt is arranged to engage a trailing edge of the sheet that has left the discharge nip and to exert a driving force towards the tray surface.  
         [0006]     If a sheet curls upwards after it has left the discharge nip, the trailing edge will engage the transport belt and will be frictionally entrained towards the tray surface. Thus, a subsequent sheet may be neatly deposited on the previous sheet. In this way, a relatively large number of printed media sheets can be neatly stacked on the tray surface, and the discharge nip will not become blocked by the trailing edges of upwardly curled sheets. The transport belt may have two functions: pushing down the trailing edges of printed media sheets, and assisting in transporting the sheets onto the tray.  
         [0007]     The tray surface may slope downward towards the discharge nip. In this case, when the sheet has been discharged from the discharge nip, it falls onto the tray and may slide down the slope of the tray until its trailing edge is caught either by the transport belt or, if the sheet is not curled, by a stop formed at the lower edge of the tray.  
         [0008]     The tray system of the present invention is especially advantageous when media sheets are supplied from a reel and a media transport line is arranged such that a surface of a sheet which has been outwardly oriented on the reel comes to lie towards the tray surface. The media sheets may be, for example, continuously supplied from the reel and then cut into sheets.  
         [0009]     In a preferred embodiment, the transport belt forms one of the transport elements defining the discharge nip. For example, the transport belt is mounted on two pulleys, and the second transport element may be another roller that is positioned adjacent to one of the pulleys. Thus, the sheet that is to be discharged is held between said roller and the transport belt. For example, the transport belt may be positioned below the roller. It the sheet is guided to the discharge nip along a curved guide plate making approximately a half turn around the roller and the drive belt so as to reverse the sheet before it is discharged, then the transport belt may also help to guide the leading edge of the sheet to the discharge nip, especially when the sheet is strongly curled.  
         [0010]     The number of transport belts may be larger than one and will be adapted to the maximum width of the sheets to be discharged. Also, there may be more than one further roller, these rollers rotating round a common axis. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     A preferred embodiment of the present invention will now be described in conjunction with the drawings in which:  
         [0012]      FIG. 1  is a schematic partial cross-sectional view of a printer; and  
         [0013]      FIG. 2  shows details of a sheet discharge system of the printer shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     As is shown in  FIG. 1 , an ink jet printer comprises a platen  10  which is intermittently driven to rotate in order to advance a sheet  12 , e.g. a sheet of paper, in a direction indicated by an arrow A over the top surface of a sheet support plate  14 . A number of transport rollers  16  are rotatably supported in a cover plate  18  and form a transport nip with the platen  10  so that the sheet  12 , which is supplied from a reel  19  via a guide plate  20 , is paid out through a gap formed between an edge of the cover plate  18  and the surface of the sheet support plate  14 .  
         [0015]     A carriage  22  which includes a number of ink jet print heads (not shown) is mounted above the sheet support plate  14  so as to reciprocate in a direction that is perpendicular to the plane of the drawing across the sheet  12 . In each pass of the carriage  22 , a number of pixel lines are printed on the sheet  12  by means of the print heads which eject droplets of ink onto the sheet in accordance with image information supplied to the print heads. For the sake of simplicity, guide and drive means for the carriage  22 , ink supply lines and data supply lines for the print heads, and the like, have not been shown in the drawing.  
         [0016]     As is shown in  FIG. 1  and, in a more detailed view, in  FIG. 2 , the printed sheet  12  is further transported by transport means formed by rollers  110  defining a transport nip that is positioned in the media transport line behind the sheet support plate  14 . The rollers  110  advance the sheet along a curved guide member  112  that turns the sheet upside down and reverses the transport direction of the sheet  12 .  
         [0017]     The sheet  12  is then fed to a discharge nip  114  formed between a plurality of discharge rollers  116  and a plurality of rubber-coated transport belts  118  which are each passed around a pair of pulleys  120  and  122 . The direction of movement of the transport belts  118  is indicated by arrows. The discharge rollers  116  are mounted on a common axle  116   a , and the pulleys  120  and  122  are also mounted on common axles  120   a  and  122   a , respectively. While the sheet  12  is guided by the guide member  112  around the pulleys  122 , the transport belts  118  may also serve to guide a leading edge of the sheet  12  towards the discharge nip  114  in the case where the leading edge of the sheet  12  bends down towards the transport belts  118 .  
         [0018]     From the discharge nip  114 , the sheet  12  is discharged onto a tray  124 . The tray  124  has a top surface  126  for supporting the media sheets. The top surface  126  rises from a lower edge  128  near the discharge nip  114  and the transport belts  118  to an upper edge  130  ( FIG. 1 ). At the lower edge  128 , finger-like stops  132  rise perpendicularly to the tray surface  126  towards the transport belts  118 . In a direction perpendicular to the plane of the drawing in  FIG. 2 , the transport belts  118  and the stops  132  are arranged at intervals, and in a side view of  FIG. 2 , the stops  132  intersect a straight section  134  of the transport belt  118  which passes through gaps between the stops. The straight section  134  is inclined by, for example, approximately 55° with respect to the stops  132 , and moves towards the tray surface  126 .  
         [0019]     Beginning at the discharge nip  114  and ending at the line where the transport belts  118  intersect the stops  132 , the sections  134  of the transport belts  118  form guide and drive means for the trailing edge  12   a  of a sheet  12  that has just left the discharge nip. The belt section  134  first pushes the sheet  12  onto the tray  124  and then comes into frictional engagement with the trailing edge  12   a  of the sheet and pushes it towards the tray surface  126  and towards the lower edge  128  of the tray  124 . Thus, the sheet  12  is neatly deposited on the tray  124 , even if its trailing edge  12   a  is curled upwards as indicated in  FIG. 2 .  
         [0020]     Like the platen  10 , the rollers  110  and the transport belts  118  are intermittently driven in order to advance the sheet  12  step-wise. A discharge sensor  136  is arranged near the discharge nip  114  to indicate when the trailing edge  12   a  of the sheet  12  has been discharged from the discharge nip  114  and has been guided towards the tray surface  126 . The discharge sensor  136  is of conventional design and comprises an arm that is pivotable about an axis.  
         [0021]     A top frame member  138  of the tray  124  carries a tray-full sensor  140  which is also of a conventional design comprising an arm that is pivotably mounted on the frame member  138 .  
         [0022]     By means of the transport belts  118 , the printed sheets  12  are neatly deposited on the tray  124 . Thus, the upwardly curled edge  12   a  of the sheet  12  will not interfere with the discharge sensor  136 , and the tray-full sensor  140  will allow the full capacity use of the tray  124 .  
         [0023]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.