Abstract:
In one embodiment, a device for moving print media in a printer includes: a rotatable shaft extending lengthwise along an axis of rotation and a hub. The hub is operatively and pivotally connected to the shaft at a connection such that the hub rotates with the shaft about the axis of rotation and so that the hub may tilt on the shaft relative to the axis of rotation. The device also includes a pick tire or other feature on the hub on each side of the connection to move print media when the shaft rotates the hub. In another embodiment, a method for moving print media in a printer includes: applying a force to a sheet of print media at two locations spaced apart across the sheet; and, simultaneously with the act of applying, equalizing the force applied at the two locations.

Description:
BACKGROUND 
       [0001]    Reliably feeding different sizes of paper and other print media straight into the printer presents significant design challenges in an inexpensive printer. In one conventional technique for feeding print media into the printer, a movable width adjuster is used to register and guide different size media along a stationary registration wall and a single pick tire is placed close to the registration wall to pick and feed media sizes from 3″×5″ to A4 and letter size. Although this technique is inexpensive, additional guidance and skew control is needed to get all media sizes straight in the print zone because the pick tire is asymmetric to most media sizes. A second conventional technique uses movable guides in the input tray to position the print media at the center of the tray with one or more pick tires placed symmetrically about the tray centerline. This techniques works well for feeding media straight into the printer but it is more expensive than the edge justified technique and it requires sensors or other edge detectors to avoid unacceptable variations in printed margins. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]      FIG. 1  is a block diagram illustrating one example of an inkjet printer in which embodiments of the present disclosure may be implemented. 
           [0003]      FIG. 2  is a perspective view illustrating an inkjet printer according to one embodiment of the disclosure. 
           [0004]      FIG. 3  is a section view of the printer shown in  FIG. 2 . 
           [0005]      FIGS. 4 and 5  are perspective views illustrating one example of a print media pick/feed mechanism for the printer shown in  FIGS. 2 and 3 . The perspective of  FIG. 4  is viewed from the front of the printer with a media stack. The perspective view of  FIG. 5  is viewed from the rear of the printer without a media stack. 
           [0006]      FIG. 6  is a detail perspective view of a portion of the pick/feed mechanism shown in  FIGS. 4 and 5 . 
           [0007]      FIG. 7  is a detail elevation view of the drive shaft and hub assembly in the pick/feed mechanism shown in  FIGS. 4 and 5 . 
           [0008]      FIGS. 8 and 9  are section views of the drive shaft and hub assembly taken along the lines  8 - 8  and  9 - 9 , respectively, in  FIG. 7 . 
           [0009]      FIG. 10  is an exploded partial section view of the drive shaft and hub assembly shown in  FIG. 7 . 
           [0010]      FIG. 11  is a perspective partial cut-away view of the drive shaft and hub assembly shown in  FIG. 7 . 
           [0011]      FIGS. 12 and 13  are partial section views of the drive shaft and hub assembly shown in  FIG. 7 . In  FIG. 12 , the hub is straight relative to the axis of rotation of the drive shaft. In  FIG. 13 , the hub is tilted relative to the axis of rotation of the drive shaft. 
           [0012]      FIG. 14  is an elevation view illustrating one example configuration for the pick tires in the drive shaft and hub assembly shown in  FIG. 7  relative to the registration wall and separation blocks in the pick/feed mechanism of  FIGS. 4 and 5 . 
       
    
    
       [0013]    The same numbers are used throughout the figures to designate the same or similar parts. 
       DESCRIPTION 
       [0014]    The example drive shaft and hub assembly shown in the figures and described below was developed for an inexpensive printer in an effort to help reliably feed different sizes of paper and other print media straight into the printer. The example embodiment described below should not be construed to limit the scope of this disclosure, which is defined in the claims that follow the description. 
         [0015]      FIG. 1  is a block diagram illustrating one example of an inkjet printer in which embodiments of the present disclosure may be implemented. Referring to  FIG. 1 , printer  10  includes a print cartridge  12 , a carriage  14 , a print media transport mechanism  16 , an input/output device  18 , and a printer controller  20  connected to each of the operative components of printer  10 . Print cartridge  12  includes one or more ink holding chambers  22  and one or more printheads  24 . A print cartridge is sometimes also referred to as an ink pen or an ink cartridge. Printhead  24  represents generally a small electromechanical part that contains an array of miniature thermal resistors or piezoelectric devices that are energized to eject small droplets of ink out of an associated array of nozzles. A typical thermal inkjet printhead, for example, includes a nozzle plate arrayed with ink ejection nozzles and firing resistors formed on an integrated circuit chip. Each printhead is electrically connected to printer controller  20  through external electrical contacts. In operation, printer controller  20  selectively energizes the firing resistors through the electrical contacts to eject a drop of ink through a nozzle on to media  22 . 
         [0016]    Print cartridge  12  may include a series of stationary cartridges or printheads that span the width of print media  26 . Alternatively, cartridge  12  may include one or more cartridges that scan back and forth on carriage  14  across the width of media  26 . Other cartridge or printhead configurations are possible. Media transport  16  advances print media  26  lengthwise past cartridge  12  and printhead  24 . For a stationary cartridge  12 , media transport  16  may advance media  26  continuously past printhead  12 . For a scanning cartridge  12 , media transport  16  may advance media  26  incrementally past printhead  24 , stopping as each swath is printed and then advancing media  26  for printing the next swath. Controller  20  may communicate with external devices through input/output device  18 , including receiving print jobs from a computer or other host device. Controller  20  controls the movement of carriage  14  and media transport  16 . By coordinating the relative position of cartridge  12  and printhead  24  with media  26  and the ejection of ink drops, controller  20  produces the desired image on media  26 . 
         [0017]      FIG. 2  is a perspective view illustrating an inkjet printer  10  according to one embodiment of the disclosure.  FIG. 3  is a section view of the printer  10  shown in  FIG. 2 . Referring to  FIGS. 2 and 3 , printer  10  includes an external housing  28 , an input tray  30  for holding a sheet or stack of sheets of paper or other print media, and an output tray  32  for holding printed media. For an inexpensive printer, such as printer  10 , the most common print media is paper. Thus, for convenience, reference is made to paper throughout the remainder of this description. As best seen in  FIG. 3 , a paper path  34  extends from input tray  30  to output tray  32 .  FIG. 3  shows a sheet of paper  26  moved along path  34 , as indicated by direction arrow  36 , at the urging of input rollers  38 , intermediate transport rollers  40 , and output rollers  42 . (Only one roller in each set of rollers  38 ,  40 , and  42  is visible in  FIG. 3 .) Printer  10  also includes a user control panel  44 , a print engine (not shown) and a controller (not shown) housed in housing  30 . A print engine for printer  10  may include, for example, a set of print cartridges  12  and a carriage  14  from  FIG. 1 . 
         [0018]      FIGS. 4 and 5  are perspective views illustrating one example of a print media pick/feed mechanism  46  for printer  10 . The perspective of  FIG. 4  is viewed from the front of printer  10  with a paper stack  48  and the perspective view of  FIG. 5  is viewed from the rear of the printer without the paper stack  48 . Referring to  FIGS. 4 and 5 , pick/feed mechanism  46  is used to pick the top sheet of paper from stack  48  and feed it into printer  10  toward a print zone where ink is applied. Pick/feed mechanism  46  includes a drive shaft  50 , a hub  52  mounted to drive shaft  50 , and a pair of pick tires  54   a  and  54   b  mounted to hub  52 . Each pick tire  54   a  and  54   b  grips the top sheet of print media in the stack to pick the sheet from the stack and feed it into the printer. (Pick tires  54   a ,  54   b  rotating with hub  52  form input rollers  38  described above with reference to  FIG. 3 .) Drive shaft  50  and hub  52  are referred to collectively as drive shaft and hub assembly  53 . 
         [0019]    Drive shaft  50  is driven by a motor  56  through a drive train  58  that includes a gear  60  mounted on one end of drive shaft  50 . Hub  52  is supported on a chassis  62  as described in detail below with reference to  FIGS. 6 and 7 . Pick/feed mechanism  46  also includes load stops  64  that prevent loading paper stack  48  too far into printer  10 , a pair of sheet separator blocks  66   a  and  66   b  that help separate a top sheet from other sheets in stack  48  as the top sheet is fed into printer  10 , and a registration wall  67  ( FIG. 4 ). A movable width adjuster (not shown) is used to hold one edge of the paper close to registration wall  67  to help guide the paper straight into printer  10  during pick/feed operations. 
         [0020]      FIG. 6  is a detail perspective view of a portion of pick/feed mechanism  46  and  FIG. 7  is a detail elevation view of drive shaft and hub assembly  53 . Referring to  FIGS. 6 and 7 , assembly  53  is supported by chassis  62  at the middle part  68  of hub  52 . Chassis  62  is stationary with respect to hub  52 . As shown in  FIG. 6 , a cradle  70  in chassis  62  cradles hub  52  at middle part  68  to support hub  52  while allowing hub  52  to rotate with drive shaft  50  and to tilt on drive shaft  50 , as described below. Thus, cradle  70  acts both as a bearing surface on which hub  52  rotates during a pick/feed operation and as a pivot allowing  52  to tilt on drive shaft  50 . In the embodiment shown, cradle  70  is configured as a flange or multiple flange parts that are thin in the lengthwise direction (parallel to axis of rotation  71  of drive shaft  50  in  FIGS. 12 and 13 ). Hub  52  fits loosely in cradle  70  between a pair of rings  72  that define a recess  74  and constrain movement of hub  52  lengthwise along drive shaft  50 . The loose fit and thin cradle  70  allows hub  52  to tilt on drive shaft  50 . 
         [0021]    Referring now also to  FIGS. 8-13 , hub  52  is connected to drive shaft  50  at a connection  76  at hub center part  68 . Connection  76  is configured to allow hub  52  to rotate with drive shaft  50  and to tilt on drive shaft  50 . Connection  76  includes a spline end  78  on drive shaft  50  extending through a mating disc shaped coupler  80  on hub  52 . In the embodiment shown, coupler  80  is configured as an annular protrusion with grooves matching the splines on shaft end  78 . Spline shaft  78  fits loosely in coupler  80 . Coupler  80  is thin in the lengthwise direction (parallel to the axis of rotation  71  of drive shaft  50  shown in  FIGS. 12 and 13 ). The loose fit and thin coupler  80  allows hub  52  to tilt on drive shaft  50 , as indicated by direction arrows  82  in  FIGS. 12 and 13 . In  FIG. 12 , hub  52  is straight on drive shaft  50 . In  FIG. 13 , hub  52  is tilted on drive shaft  50 . Thus, coupler  80  acts both as the operative connection for hub  52  to drive shaft  50  during a pick/feed operation and as a pivot allowing hub  52  to tilt on drive shaft  50 . In the embodiment shown, connection  76  is aligned with recess  74  and cradle  70  so that hub  52  pivots in cradle  70  at the same location hub  52  is operatively connected to and pivots on drive shaft  50 . 
         [0022]    “Loose” and “thin” in this context mean there is sufficient separation between the parts to allow the desired degree of tilt without also negating the operative connection between the parts. In one example configuration that has been shown to work effectively, coupler  80  is 2 mm long (parallel to the axis of rotation  71  of drive shaft  50 ) with a 0.25 mm gap (on average) between the inside of coupler  80  and the outside of drive shaft spline end  78 , allowing hub  52  to tilt at least 3° with respect to axis  71 . 
         [0023]      FIG. 14  is an elevation view illustrating one example configuration for positioning pick tires  54   a  and  54   b . Referring to  FIG. 14 , pick tires  54   a  and  54   b  are spaced equally on either side of hub/shaft connection  76  (d 1 =d 2  in  FIG. 14 ) and connection  76  is located at the center of a larger size print media. Thus, pick tires  54   a  and  54   b  will engage the larger print media symmetrically about the centerline of the larger media. For example, if the most popular large print media is A4 size, then connection  76  is positioned 105 mm from the registration wall. This position for pick tires  54   a  and  54   b  helps feed the larger media symmetrically along registration wall  67  straight into the printer. Inside pick tire  54   a  is positioned a distance from the registration wall equal to one half the width of a smaller size print media. For example, if the most popular small media for printer  10  is 4″×6″ color photo paper, then pick tire  54   a  is positioned 2″ from the registration wall. This position for pick tire  54   a  helps feed the smaller media symmetrically along registration wall  67  straight into the printer. 
         [0024]    Each pick tire  54   a  and  54   b  is spaced approximately equally from an adjacent separator block  66   a ,  66   b  (d 3 ≈d 4  in  FIG. 14 ). The reaction force of separation block  66   a  (adjacent to pick tire  54   a ) on the leading edge of smaller print media when fed into the printer creates a moment relative to the force of pick tire  54   a  that drives the smaller media into registration wall  67  ( FIG. 4 ). After the leading edge passes separator block  66   a , pick tire  54   a  then drives the media straight along wall  67 . As noted above, in the embodiment shown in  FIG. 14 , the spacing of pick tire  54   a  from registration wall  67  is determined by the centerline of a smaller media. In this embodiment, the spacing of separator block  66   a  from pick tire  54   a  (distance d 3  in  FIG. 14 ) is affected by the capacity of the smaller media to be driven against registration wall  67  without buckling. A larger distance d 3  creates a greater force driving the top sheet into wall  67  but may result in the top sheet buckling. Thus, distance d 3  is selected to create a sufficient moment to drive the top sheet into wall  67  but without also buckling the sheet. The distance d 4  between pick tire  54   b  and separator block  66   b  is approximately equal to d 3  to help maintain symmetry in feeding larger print media with both pick tires  54   a  and  54   b.    
         [0025]    To help deliver the normal force necessary to pick different size print media, hub  52  is allowed to pivot at its centerline to tilt with respect to the drive shaft axis or rotation  71 . A tilt-able hub  52  reduces the influence of part variation on the symmetric contact of pick rollers  54   a  and  54   b  with the print media. Without the tilt-able hub, part variation could prevent the two pick tires  54   a ,  54   b  from contacting the media with equal force, thereby losing the benefits of positioning pick tires  54   a  and  54   b  symmetrically across the print media. In addition, equalizing the normal force exerted by each pick tire  54   a ,  54   b  lowers the overall normal force needed to help ensure a reliable pick/feed. 
         [0026]    As noted at the beginning of this Description, the exemplary embodiment shown in the figures and described above illustrates but does not limit the disclosure. Other forms, details, and embodiments may be made and implemented. Therefore, the foregoing description should not be construed to limit the scope of the disclosure, which is defined in the following claims.