Abstract:
In one embodiment, a sheet media input tray comprises a base and opposing sidewalls. The base includes a first feature configured to support sheet media lying flat in the tray and a second feature intersecting the first feature across the width of the tray. The intersection between the first feature and the second feature defines an elongated fulcrum along which media sheets can bend when pressed against the base. In another embodiment, a sheet media input tray comprises a first elevated sheet supporting surface, a depression portion immediately adjacent to and downstream from the first sheet supporting surface, and a second elevated sheet supporting surface immediately adjacent to and downstream from the depressed portion. The depression portion spans the full width of sheet media that may be supported in the tray and the second sheet supporting surface lies in the same plane as the first sheet supporting surface.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to an input tray for printers and other sheet media processing devices.  
         BACKGROUND  
         [0002]    A swing arm type pick mechanism is used in some printers to feed sheets of paper or other print media into the printer. In a swing arm type pick mechanism, the feed roller is mounted to the end of a swing arm that pivots or “swings” above the media input tray. The pick roller rests on top of the stack of media sheets in the tray. A biasing spring applies a small force urging the swing arm down to keep the pick roller in contact with the top of the stack as sheets are used and the stack gets smaller. The swing arm pivot is located upstream (rearward) from the pick roller so that the pick roller will pull itself into the stack as it picks the top sheet and feeds it into the printer, rather than push itself away from the stack. The swing arm provides the force pressing down against the stack to create friction between the pick roller and the top sheet in the stack. The friction helps the pick roller grip the top sheet and move it off the stack. This pressing force is often called a “normal” force because the direction of the force is normal (perpendicular) to the stack. The rotating pick roller, by contrast, provides a force directed along the top sheet to move the sheet forward off the stack.  
           [0003]    One advantage of a swing arm type pick mechanism is the self-adjusting relationship between the pick load and the pick force. The swing arm pivot above and behind the pick roller allows the pick force exerted by the pick roller to increase automatically as the pick load (the top sheet&#39;s resistance to movement) increases. For example, heavier media increases the top sheet&#39;s resistance to movement. Heavy media, therefore, creates a higher pick load. Consequently, a larger pick force is necessary to move the top sheet off the stack. As the pick load increases, however, the force of the pick roller against the unmoving top sheet drives the swing arm down and presses the pick roller harder against the stack, increasing the normal force, to automatically increase the pick force. This effect becomes more pronounced as the stack gets smaller. Unfortunately, as the pick roller presses harder against the stack, the friction between the sheets increases which, in turn, increases the pick load. The increased pick load negates some of the self-adjusting effect of the swing arm pick mechanism.  
           [0004]    The present invention was developed in an effort to reduce the pick load in a swing arm type mechanism, particularly for heavy, stiff and other higher friction print media. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a perspective view of an inkjet printer.  
         [0006]    [0006]FIG. 2 is a perspective view of an inkjet printer such as the one shown in FIG. 1 with the cover and other parts of the housing removed.  
         [0007]    [0007]FIG. 3 is a side elevation and partial section view of an inkjet printer such as the one shown in FIG. 2 with a conventional media tray and pick mechanism.  
         [0008]    [0008]FIG. 4 is a perspective view showing in more detail the media tray and pick mechanism of the printer of FIG. 3.  
         [0009]    [0009]FIGS. 5 and 6 are side elevation and partial section views of the media tray and pick mechanism of FIG. 4.  
         [0010]    [0010]FIG. 7 is a side elevation and partial section view of an inkjet printer such as the one shown in FIG. 2 with a media tray and pick mechanism constructed according to one embodiment of the invention.  
         [0011]    [0011]FIG. 8 is a perspective view showing the media tray and pick mechanism of FIG. 7.  
         [0012]    [0012]FIGS. 9-11 are side elevation and partial section views showing in sequence the operation of the media tray and pick mechanism of FIGS. 7 and 8.  
         [0013]    [0013]FIG. 12 is a perspective view showing a media tray and pick mechanism according to an alternative embodiment of the invention.  
         [0014]    [0014]FIGS. 13 and 14 are side elevation and partial section views showing the media tray and pick mechanism of FIG. 12. 
     
    
     DETAILED DESCRIPTION  
       [0015]    Embodiments of the invention will be described with reference to the inkjet printer shown in FIGS. 1 and 2. The invention, however, is not limited to use with inkjet printers. Embodiments of the invention may be implemented in any printer or other sheet media processing device in which it is necessary or desirable to reduce the pick load of media sheets picked from the sheet input tray. While the invention is not limited to use with inkjet printers, it is expected that various embodiments of the invention will be particularly useful in printers with a U-shaped media path typical of many inkjet printers in which the print media is fed at a steep angle from a horizontal tray.  
         [0016]    [0016]FIG. 1 illustrates an inkjet printer  10 . FIG. 2 shows inkjet printer  10  with cover  12  (FIG. 1) and other parts of housing  14  removed. FIG. 3 is a side elevation and partial section view of an inkjet printer  10  such as the one shown in FIGS. 1 and 2 with a conventional sheet media tray  16  (FIG. 2). A conventional sheet media tray is discussed first along with the other components of printer  10  to better distinguish the various embodiments of the sheet media tray of the present invention. FIGS. 3-7 show a conventional tray. FIGS. 8-13 show a new tray.  
         [0017]    Referring to FIGS. 1-3, printer  10  includes a cover  12  and a housing  14 . A sheet media tray  16  is positioned at the bottom of printer  10  along an opening  18  in housing  14 . Paper or other print media sheets  32  (FIG. 3) are stacked in tray  16  for input to printer  10  and printed sheets are output back through opening  18  over tray  16 . A supporting surface  20  helps suspend the trailing edge of the printed sheets over tray  16 .  
         [0018]    Printer  10  includes a chassis  22  that supports the operative components of printer  10 . Chassis  22  represents generally those parts of housing  14  along with other structurally stable elements in printer  10  that support the operative components of printer  10 . A printhead carriage  24  is driven back and forth along a guide rail  26  mounted to chassis  22 . Any suitable drive mechanism may be used to move carriage  24 . A reversing motor (not shown) coupled to carriage  24  through a belt and pulley system (not shown), for example, is one carriage drive mechanism commonly used in inkjet printers.  
         [0019]    Carriage  24  has stalls for holding one or more printheads  28 . In the printer shown in FIGS. 1-3, carriage  24  carries two printheads  28 —one printhead containing color ink for color printing and one printhead containing black ink for monochrome printing. Printheads  28  are also commonly referred to as print cartridges or ink cartridges. As best seen in FIG. 3, printheads  28  are positioned along media path  30  such that each sheet of print media  32  passes directly under printheads  28  at print zone  34 . The bottom  36  of each printhead  28 , which faces media sheet  32 , includes an array of nozzles through which drops of ink are ejected onto media sheet  32 .  
         [0020]    An electronic printer controller  38  receives print data from a computer, scanner, digital camera or other image generating device. Controller  38  controls the movement of carriage  24  back and forth across media sheet  32  and the advance of media sheet  32  along media path  30 . Printer controller  38  is also electrically connected to printheads  28  through, for example, a flexible ribbon cable  40 . As carriage  24  carries printheads  28  across media sheet  32 , printer controller  38  selectively activates ink ejection elements in printheads  28  according to the print data to eject ink drops through the nozzles onto media sheet  32 . By combining the movement of carriage  24  across media sheet  32  with the movement of sheet  32  along media path  30 , controller  38  causes printheads  28  to eject ink onto media sheet  32  to form the desired print image.  
         [0021]    [0021]FIG. 4 is a perspective view of the forward part of a conventional input tray  16  and components of the media sheet pick mechanism. FIGS. 5 and 6 are side elevation and partial section views showing conventional tray  16  and pick/feed mechanism components along media path  30 . FIG. 5 shows a stack  42  of media sheets  32  in tray  16  and a top sheet being fed along media path  30 . In FIG. 6, tray  16  is empty. Referring first to FIGS. 4 and 5, top sheet  32  is “picked” from a stack  42  of media sheets in tray  16  and fed along media path  30 . A pick roller  44 , mounted on a swing arm  46 , rests on top sheet  32 . When a sheet is needed for printing, pick roller  44  is driven clockwise at the direction of controller  38  to grab top sheet  32  and feed it along media path  30  toward transport roller  48 . Transport roller  48  bears against idler roller  50  to form a nip that moves sheet  32  along toward output roller  52 . Output roller  52  bears against idler arm  54  to form a nip that moves sheet  32  onto sheet output supporting surface  20 .  
         [0022]    Each sheet  32  is guided from tray  16  toward transport roller  48  along guide ramps  56 . One or more guide ramps  56  are fitted with a separator pad  58 . Separator pad  58  is typically constructed as an elastomeric strip that protrudes from the face of ramp  56 . Separator pad  58  resists the forward motion of sheets in the stack  42 . The force of pick roller  44  on top sheet  32  is sufficient to overcome the resistance of separator pad  58  while the next to top sheet  60 , which is dragged along with only a much smaller sheet-to-sheet friction force, is stopped by pad  58 . That is to say, pad  58  separates next to top sheet  60  from top sheet  32 . A stack ramp  62  is also sometimes provided to elevate the leading edge of sheets in the stack  42  to reduce the force need to feed top sheet  32  past separator pad  58 .  
         [0023]    Media tray  16  includes a base panel  64  extending between sidewalls  66  and  68 . Media tray  16  typically includes a mechanism to adjust the width of the tray to accommodate different width media. In the printer  10  illustrated in the figures, left sidewall  66  is integral to a slider  70  that slides along a slot  72  in a recess  74  in base panel  64  to adjust for differing width media. Base panel  64  and slider  70  define media support surfaces  76 ,  78  and  80 .  
         [0024]    Swing arm  46  is mounted to chassis  22  at a swing arm pivot  47  located upstream and above pick roller  44  such that pick roller  44  swings down counter-clockwise against stack  42 . An idler roller  82  is recessed into base panel  64  directly below pick roller  44 . When tray  16  is empty, pick roller  44  rests on idler roller  82  as shown in FIG. 6. In the event pick roller  44  is activated when tray  16  is empty, pick roller  44  will turn on idler roller  82  and, therefore, avoid any damage to pick roller  44  or other pick mechanism components.  
         [0025]    One advantage of a swing arm type pick mechanism, such as the one shown in the figures, is the self-adjusting relationship between the pick load and the pick force. The swing arm pivot  47  above and behind the contact point between pick roller  44  and top sheet  32  allows the pick force exerted by pick roller  44  to increase automatically as the pick load (the top sheet&#39;s resistance to movement) increases. For example, heavier media increases the resistance to movement of top sheet  32 . Heavy media, therefore, creates a higher pick load. Consequently, a larger pick force is necessary to move top sheet  32  off stack  42 . As the pick load increases, however, the force of pick roller  44  against the unmoving top sheet drives swing arm  46  down and presses pick roller  44  harder against stack  42  to automatically increase the pick force. This effect becomes more pronounced as stack  42  gets smaller and swing arm  46  swings further down because more of the pick force is applied as a pivoting force to drive swing arm  46  down and press pick roller  44  even harder against stack  42 . A biasing spring  84  urges swing arm  46  down to maintain contact between pick roller  44  and top sheet  32  in stack  42 .  
         [0026]    Unfortunately, as pick roller  44  presses harder against stack  42 , the friction between the sheets increases which, in turn, increases the pick load. The increased pick load negates some of the self-adjusting effect of the swing arm pick mechanism. The present invention was developed in an effort to reduce the pick load, particularly for heavy, stiff and other higher friction print media.  
         [0027]    Carriage  24  and printheads  28  along with other hardware components necessary to deliver ink to the print media are referred to collectively as print engine  83 . Rollers  44 / 82 ,  48 / 50  and  52 / 54  along with other hardware components necessary to transport the print media through printer  10  are referred to collectively as pick/feed mechanism  85 . Controller  38  includes the programming, processor and associated memory and electronic circuitry necessary to control print engine  83  and pick/feed mechanism  85 . The components of printer  10  described above are all conventional components well known to those skilled in the art of inkjet printing. Therefore, additional structural and operational details of these components are omitted except as noted below for tray  16  and pick/feed mechanism  85 .  
         [0028]    One embodiment of the invention will now be described with reference to FIGS. 7-11. FIG. 7 is a side elevation and partial section view of a printer  10  incorporating a media tray  16  constructed according to a first embodiment of the invention. FIG. 8 is perspective view of tray  16  and components of the media sheet pick mechanism. FIGS. 9-11 are side elevation and partial section views showing in sequence the operation of media tray  16  and pick mechanism of FIGS. 7 and 8.  
         [0029]    Referring first to FIGS. 7 and 8, a depression  86  is formed in base panel  64  under pick roller  44  across the full width of media support surface  76 . Idler roller  82  is recessed into the bottom of depression  86  directly below pick roller  44 . Depression  86  represents a discontinuity that divides forward media support surface  76  into parts  76 A and  76 B.  
         [0030]    [0030]FIGS. 9 and 10 show media stack  42  being added to an empty tray  16 . The leading edge of stack  42  pushes pick roller  44  up onto the top of stack  42  as stack  42  passes over depression  86 . Separator pad  58  blocks stack  42  at the front of tray  16  and helps prevent the user from pushing stack  42  too far into printer  10 . As shown in FIG. 10, the forward part of stack  42  rests on surfaces  76 A and  76 B and spans depression  86  when the pick mechanism is not operating. Referring to FIG. 11, as pick roller  44  is driven to pick top sheet  32 , depression  86  allows the normal force pressing down on stack  42  to deflect stack  42 . As stack  42  is deflected into depression  86 , the forward edge  88  of depression  86  acts as a fulcrum to raise the leading edge of media sheets in stack  42  more into alignment with media path  30 .  
         [0031]    Deflecting or bending the media sheets in this way has several advantages. First, the leading edge of each sheet is released from immediate contact with separator pad  58  to reduce resistance to movement. Second, the leading edge of the sheets are more closely aligned with media path  30 . Third, each sheet bends a bit differently from adjacent sheets, reducing sheet-to-sheet contact and friction. For top media sheet  32 , the degree and duration of release depends on the media&#39;s resistance to movement. As top sheet  32  bends and is released from contact with separator pad  58 , the sheet has less resistance to movement. Eventually, pick roller  44  will overcome this resistance and feed top sheet  32  into and up along separator pad  58  toward transport roller  48 .  
         [0032]    When tray  16  is full and stack  42  is high, the normal force pressing down on stack  42  is low and stack  42  does not deflect or bend, at least not much. As stack  42  gets smaller and smaller and swing arm  46  swings down to press pick roller  44  harder against stack  42 , stack  42  bends more and more. The media sheet shape change is self-regulating—the greater the normal force pressing down on stack  42 , the greater the deflection of stack  42 .  
         [0033]    In a second embodiment of the invention, shown in FIGS. 12-14, a pivot plate  90  recessed into base panel  64  is used to more consistently redirect the leading edge of the sheets toward media path  30 . Referring to FIGS. 12-14, plate  90  is positioned in a depression  92  in base panel  64  under pick roller  44  across the full width of media support surface  76 . Plate  90  pivots on a pin/axis  94 . Axis  94  is located forward of pick roller  44  along a middle portion of plate  90 . A biasing spring  96  positioned rearward of axis  94  provides enough resistance to generate a normal force sufficient to move top sheet  32  off stack  42  but still allow plate  90  to pivot and redirect the leading edge of the sheets toward media path  30 .  
         [0034]    When the normal force of pick roller  44  pressing down on stack  42  is high, rear portion  90 A of plate  90  is depressed and front portion  90 B is raised as plate  90  pivots on axis  94 . The movement of plate  90  causes stack  42  to deflect into depression  92  while the leading edge of sheets in stack  42  is raised more into alignment with media path  30 . As with the first embodiment, the shape change in stack  42  lowers the resistance of top sheet  32  to the pick force, making it easier for pick roller  44  to feed top sheet  32  along media path  30 .  
         [0035]    The exemplary embodiments shown in the figures and described above illustrate but do not limit the invention. Other forms, details, and embodiments may be made and implemented. Hence, the foregoing description should not be construed to limit the spirit and scope of the invention, which is defined in the following claims.