Patent Publication Number: US-7594721-B2

Title: Sheet ejecting

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   The present application is related to co-pending U.S. patent application Ser. No. 11/263,130 filed on the same day herewith by Jason S. Belbey, Steve O. Rasmussen and Robert M. Yraceburu, and entitled MEDIA EJECTION SYSTEM, the full disclosure of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   Various systems may be utilized to separate media from a support surface once the media has been interacted upon. Such media ejection systems may be complex, space consuming and unreliable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of one example of a media ejection system illustrating the movement of a claw between an ejecting position and a non-ejecting position (shown in phantom) according to one example embodiment. 
       FIG. 2  is a schematic illustration of the media ejection system of  FIG. 1  illustrating a cam follower disengaged from a cam according to an example embodiment. 
       FIG. 3  is a schematic illustration of the media ejection system of  FIG. 1  illustrating the claw in a retracted position behind a shield according to an example embodiment. 
       FIG. 4  is a top perspective view of one example of a printing system including one example of the media ejection system of  FIG. 1  according to an example embodiment. 
       FIG. 5  is an enlarged view of the media ejection system of  FIG. 4  according to an example embodiment. 
       FIG. 6  is an enlarged perspective view of a claw assembly and lever of the media ejection system of  FIG. 5  according to an example embodiment. 
       FIG. 7  is a fragmentary enlarged perspective view of a portion of the claw assembly of  FIG. 6  according to an example embodiment. 
       FIG. 8  is a fragmentary exploded perspective view of a portion of the media ejection system of  FIG. 5  according to an example embodiment. 
       FIG. 9   a  is a sectional view of the media ejection system of  FIG. 4  illustrating a cam follower in a non-ejecting position in the ejection mode according to an example embodiment. 
       FIG. 9   b  is a sectional view of the media ejection system of  FIG. 4  illustrating a claw in a non-ejecting position during the ejection mode according to an example embodiment. 
       FIG. 10   a  is a sectional view of the media ejection system of  FIG. 4  illustrating the cam follower in an ejecting position during the ejection mode according to an example embodiment. 
       FIG. 10   b  is a sectional view of the media ejection system of  FIG. 4  illustrating the claw in the ejecting position during the ejection mode according to an example embodiment. 
       FIG. 11   a  is a sectional view of the media ejection system of  FIG. 4  illustrating the cam follower and cam in a withdrawn position according to an example embodiment. 
       FIG. 11   b  is a sectional view of the media ejection system of  FIG. 4  illustrating the claw in a withdrawn position during the ready mode according to an example embodiment. 
       FIG. 12   a  is a sectional view of the media ejection system of  FIG. 4  illustrating the cam follower and cam in a retracted position during the shielded mode according to an example embodiment. 
       FIG. 12   b  is a sectional view of the media ejection system of  FIG. 4  illustrating the claw in a retracted position during the shielded mode according to an example embodiment. 
       FIG. 13  is a top perspective view of another printing system including another embodiment of the media ejection system of  FIG. 4  according to an example embodiment. 
       FIG. 14  is an enlarged perspective view of the media ejection system of  FIG. 13  according to an example embodiment. 
       FIG. 15  is an enlarged fragmentary perspective view of a portion of the media ejection system of  FIG. 14  according to an example embodiment. 
       FIG. 16  is a sectional view of the printing system of  FIG. 13  illustrating a cam follower and cam in a non-ejecting position during the ejection mode according to an example embodiment. 
       FIG. 17  is a sectional view of the printing system of  FIG. 13  illustrating the cam follower and cam in the ejecting position during the ejection mode according to an example embodiment. 
       FIG. 18  is a sectional view of the printing system of  FIG. 13  illustrating the cam follower and cam withdrawn from one another during the ready mode according to an example embodiment. 
       FIG. 19  is a sectional view of the printing system of  FIG. 13  illustrating the cam follower and cam further retracted from one another during the shielding mode according to an example embodiment. 
   

   DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
     FIGS. 1-3  schematically illustrate one example of media ejection system  20 . System  20  is configured to separate a medium  22 , such as a sheet or piece of cellulose-based material, polymer-based material, metallic-based material or combinations thereof, and medium support surface  24  for ejection of the medium  22  from a media interaction system such as a printer, scanner, or other device configured to interact or modify the medium. As shown by  FIGS. 1-3 , media ejection system  20  generally includes shield  28 , claw  30 , cam  34 , cam follower  36 , arm  38 , actuation mechanism  40  and controller  41 . Shield  28  may comprise a structure extending opposite to medium support surface  24  configured to inhibit the physical contact of a person with claw  30  when claw  30  is in the position shown in  FIG. 3 . In one embodiment, shield  28  includes opening  42  through which claw  30  or a supporting structure coupled to claw  30  extends when claw  30  is in one of the positions shown in  FIG. 1  or  2 . As shown in  FIG. 3 , opening  42  facilitates retraction of claw  30  to a retracted position behind shield  28 . In the retracted or shielded position shown in  FIG. 3 , claw  30  is substantially out of the way, facilitating media jam clearance or other tasks. 
   Claw  30  may comprise a structure configured to engage and lift media  22  away from medium support surface  24 . In the particular embodiment illustrated, claw  30  has a tip  44  configured to extend below a medium  22  to facilitate separation of medium  22  from medium support surface  24 . In the particular example illustrated, claw  30  is configured such that tip  44  extends into a channel, divot, depression or groove  46  that is configured to extend below medium  22  to enhance the separation of medium  22  from surface  24 . In other embodiments, surface  24  may omit groove  46 . 
   As further shown by  FIG. 1 , claw  30  is configured to pivot about axis  50  between a media engaging ejecting position (shown in solid lines) in which tip  44  is positioned so as to extend beneath medium  22  and a raised non-ejecting position (shown in phantom) in which tip  44  is sufficiently raised above surface  24  by a distance such that medium  22  may pass beneath claw  30  without being engaged. 
   Cam  34  may comprise a surface associated with medium support surface  24  that is configured to contact and guide movement of cam follower  36  to control pivoting of claw  30  about axis  50  between the engaging and non-ejecting positions shown in  FIG. 1 . In one particular embodiment, cam  34  is coupled to medium support surface  24  so as to move with medium support surface  24  as medium support surface  24  moves medium  22 . In one particular embodiment, media support surface  24  may be provided by a drum, wherein cam  34  is formed along a surface of the drum or is coupled to an axial end of the drum so as to rotate with the drum. Because cam  34  moves with the movement of medium support surface  24 , cam  34  accurately and reliably controls timing of claw actuation between the ejecting and non-ejecting positions without undue complexity. 
   Cam follower  36  may comprise a structure operably coupled to claw  30  and configured to contact or otherwise engage cam  34  at one or more predetermined points along medium surface  24 , wherein such contact results in claw  30  pivoting about axis  50  from the non-ejecting position to the ejecting position. In other embodiments, cam  34  and cam follower  36  may alternatively be configured such that engagement of cam follower  36  with cam  34  causes claw  30  to pivot about axis  50  from the ejecting position to the non-ejecting position. In one particular embodiment, cam follower  36  may include a roller. In other embodiments, cam follower  36  may comprise other surfaces or structures. 
   Arm  38  may comprise an elongated structure having a first portion pivotally coupled to claw  30  for pivotal movement about axis  50  and a second portion configured to pivot about axis  52 . As shown by  FIGS. 2 and 3 , pivoting of arm  38  about axis  52  results in claw  30  also being rotated about axis  52 . In one particular embodiment, axis  50  of claw  30  may also rotate about axis  52  in response to rotation of arm  38  about axis  52 . Arm  38  is configured such that pivotal movement of arm  38  about axis  52  moves claw  30  to the withdrawn position in which cam follower  36  is also spaced from cam  34  such that cam  34  may pass beneath cam follower  36  without engaging cam follower  36  and without causing pivotal movement of claw  30  about axis  50 . As a result, medium support surface  24  may transport medium  22  past claw  30  without claw  30  being actuated to the ejecting position and without interference from claw  30 . When cam follower  36  is spaced from cam  34 , medium  22  may be interacted upon multiple times before being separated from medium support surface  24 . For example, in particular embodiments, medium  22  may be moved past claw  30  multiple times for multi-pass printing. 
   As shown by  FIG. 3 , further pivoting of arm  38  about axis  52  causes claw  30  to be further moved to a retracted position in which tip  44  of claw  30  is spaced further from medium support surface  24 . In one particular embodiment, when claw  30  is in the retracted position, tip  44  is retracted to a position so as to inhibit the physical contact with tip  44 . In one particular embodiment, in the retracted position, tip  44  of claw  30  is retracted within opening  42  of shield  28 . In the particular embodiment illustrated, tip  44  is retracted behind shield  28  in the retracted position. Because physical contact of a person with tip  44  is inhibited while tip  44  is in the retracted position, jams may be more easily cleared. 
   Actuation mechanism  40  may comprise a mechanism operably coupled to arm  38  and configured to pivot arm  38  about axis  52 . In one particular embodiment, actuation mechanism  40  is configured to pivot arm  38  in either direction about axis  52 . In one embodiment, actuation mechanism  40  may include a source of torque, such as a rotary actuator, operably coupled to arm  38  by one or more motion transmitting structures such as gear trains, belt and pulley arrangements, chain and sprocket arrangements, links and the like. 
   Controller  41  may comprise a processing unit configured to generate control signals directing operation of actuation mechanism  40 . For purposes of this disclosure, the term “processing unit” shall mean a presently developed or future developed processing unit that executes sequences of instructions contained in a memory. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described. Controller  41  is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit. 
   In operation, controller  41  generates control signals directing actuation mechanism  40  to appropriately position claw  30  and cam follower  36  relative to medium support surface  24  based at least in part upon a status of interaction with medium  22 , such as the status of printing upon medium  22 . As shown in  FIGS. 1-3 , controller  41  generates control signals which cause actuation mechanism  40  to move claw  30  between an ejecting position (shown in  FIG. 1 ), a withdrawn position (shown in  FIG. 2 ) and a retracted position (shown in  FIG. 3 ).  FIG. 1  illustrates system  20  in an ejection state or mode. In the ejection mode, arm  38  is appropriately pivoted about axis  52  by actuation mechanism  40  such that cam follower  36 , coupled to claw  30 , is in engagement with cam  34 . Movement of medium support surface  24  in the direction indicated by arrow  56  results in cam  34  interacting with follower  36  to position tip  44  of claw  30  within groove  46 , facilitating the engagement of tip  44  of claw  30  with an underside of medium  22  to lift and separate medium  22  from support surface  24 . As indicated in phantom, appropriate engagement of cam  34  with cam follower  36  also results in claw  30  being pivoted about axis  50  to a non-ejecting position. 
     FIG. 2  illustrates system  20  in a ready mode. In the ready cam disengaged mode, controller  41  generates control signals to direct actuation mechanism  40  to pivot arm  38  about axis  52  in the direction indicated by arrow  60 . As a result, claw  30  is raised above medium transport surface  24  and cam follower  36  is elevated or spaced from cam  34 . As a result, all portions of cam  34  may pass cam follower  36  without claw  30  being lowered to position tip  44  in groove  46 . Thus, medium  22  may be transported by surface  24  past claw  30  multiple times such as when multi-pass printing is desired. 
     FIG. 3  illustrates system  20  in a shielded mode. In the shielded mode, controller  41  generates control signals directing actuation mechanism  40  to pivot arm  38  further in the direction indicated by arrow  62  about axis  52 . As shown in  FIG. 3 , this results in claw  30  being moved even further away from medium transport surface  24  so as to position tip  44  within opening  42  of shield  28  so as to inhibit physical contact with tip  44 . Because physical contact of a person with tip  44  is inhibited while tip  44  is in the retracted position, jams may be more easily cleared. 
     FIG. 4  illustrates printing system  100  which includes media ejection system  120 , one example embodiment of media ejection system  20  shown and described with respect to  FIGS. 1-3 . In addition to media ejection system  120 , printing system  100  also includes media transport drum  102 , rotary actuator  104 , frame  106 , media input  108 , printing mechanism  110 , media output  112  and controller  114 . Media transport drum  102  may comprise a large generally cylindrical member configured to be rotatably driven about axis  122  and including medium support surface  124 . Medium support surface  124  may comprise a generally circumferential surface upon which one or more sheets of medium, such as paper and the like, may be held during printing and/or other interaction. In one particular embodiment, medium support surface  124  includes elongated circumferential grooves or depressions, such as grooves  46  shown in  FIG. 1 , to facilitate separation of sheets from surface  124 . In particular embodiments, medium support surface  124  may additionally include perforations or other openings through which a vacuum may be applied to selectively retain one or more sheets against surface  124 . In other embodiments, electrostatic charges may be created along surface  124  to retain one or more sheets against surface  124 . In the particular embodiment illustrated, support surface  124  is configured to retain at least three 8½×11 sheets of a medium. In other embodiments, surface  124  may be configured to support a fewer or greater number of the same sheets or larger or smaller sheets. 
   Rotary actuator  104  may comprise a device configured to rotatably drive drum  102  about axis  122  to move the one or more sheets from media input  108  to printing mechanism  110  and ultimately to media ejection system  120  and media output  112 . In one embodiment, rotary actuator  104  may comprise an electric motor operably coupled to drum  102  by a transmission or other power train. In other embodiments, rotary actuator  104  may comprise other devices configured to provide torque to rotate drum  102 . 
   Frame  106  may comprise one or more structures proximate to drum  102  that are configured to support the components of printing system  100  relative to drum  102 . As shown by  FIG. 4 , frame  106  supports media ejection system  120  relative to drum  102 . In particular embodiments, frame  106  may also be configured to support at least portions of media input  108  and printing mechanism  110  relative to drum  102 . Although illustrated as including two parallel plates, frame  106  may have various other sizes and configurations and may support fewer or additional components of printing system  100 . 
   Media input  108  (schematically shown) may comprise a mechanism configured to supply and transfer sheets of media to drum  102  of printing system  100 . In one embodiment, media input  108  may include a media storage volume, such as a tray, bin and the like, one or more pick devices (not shown) configured to pick a sheet of media from the storage volume and one or more media transfer mechanisms configured to transfer the media to drum  102 . Media input  108  may have a variety of sizes and configurations. 
   Printing mechanism  110  (schematically shown) may comprise a mechanism or device configured to print or otherwise form an image upon sheets of media held by drum  102 . In one embodiment, printing mechanism  110  may be configured to eject fluid ink onto sheets of media held by drum  102 . In one embodiment, printing mechanism  110  may include one or more printheads carried by a carriage that are configured to be scanned across sheets of media held by drum  102  in directions generally along axis  122 . In other embodiments, printing mechanism  110  may include printheads which substantially extend across a width or a dimension of sheets of media held by drum  102  such as with a page-array printer. In still other embodiments, printing mechanism  110  may comprise other printing devices configured to deposit ink, toner or other printing material upon sheets of media held by drum  102  in other fashions. 
   Media output  112  may comprise a mechanism or device configured to transport sheets of media that have been separated from drum  102  by media ejection system  120  to one or more locations for further interaction with such removed sheets or for output to a user of printing system  100 . For example, in one embodiment, media output  112  may be configured to transport such ejection sheets of media to a duplexer and back to media input  108  for two-sided printing. In still another embodiment, media output  112  may be configured to transport such ejected sheets to an output tray or bin for receipt by a user of printing system  100 . 
   Controller  114  may comprise one or more processing units configured to generate control signals directing the operation of rotary actuator  104 , media input  108 , printing mechanism  110 , media output  112  and media ejection system  120 . For purposes of this disclosure, the term “processing unit” shall mean a presently developed or future developed processing unit that executes sequences of instructions contained in a memory. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described. Controller  114  is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit. 
   In operation, controller  114  generates control signals directing rotary actuator  104  to rotatably drive drum  102  about axis  122 . Controller  114  further generates control signals directing media input  108  to pick or otherwise supply a sheet of media to drum  102 . Drum  102  transfers a sheet to printing mechanism  110 . In response to control signals from controller  114 , printing mechanism  110  prints or otherwise forms an image upon the sheet. Thereafter, drum  102  transports the printed upon sheet to media ejection system  120 . If printing mechanism  110  is to perform an additional printing pass over the sheet of media, controller  114  generates control signals so as to move or maintain media ejection system  120  in a ready cam disengaged mode as shown in  FIGS. 11   a  and  11   b  as will be described in greater detail hereafter. In such a cam disengaged mode, media ejection system  120  permits the sheet of media to pass beneath system  120  to printing mechanism  110  once again. 
   Alternatively, if the printed upon sheet is ready for separation from drum  102 , controller  104  generates control signals directing actuation mechanism  140  to move or actuate media ejection system  120  to the ejection mode shown in  FIGS. 9   a ,  9   b ,  10   a  and  10   b , as will be described in greater detail hereafter, prior to drum  102  moving the printed upon sheet to media ejection system  120 . Once the drum  102  sufficiently rotates to position the printed upon sheet proximate to ejection system  120 , the printed upon sheet will be separated from drum  102  as shown in  FIG. 10   b . Thereafter, in response to control signals from controller  114 , media output  112  will transfer the sheets separated from drum  102  to another location for further printing or manipulation of the printed upon sheet or for receipt by a user printing system  100 . 
   Upon shutdown or idle mode of printing system  100  or in those circumstances in which printing system  100  experiences a media jam or should be repaired or cleaned, controller  114  may additionally generate control signals causing actuation mechanism  140  to actuate media ejection system  120  to a retracted or shielded mode shown in  FIGS. 12   a  and  12   b  as will be described in greater detail hereafter. 
     FIGS. 5-8  illustrate media ejection system  120  of printing system  100  in more detail. System  120  generally includes shield  128  (shown in  FIG. 4 ), claw assembly  130 , spring  131 , cam  132  (shown in  FIG. 4 ), cam  134 , lever  135 , cam follower  136 , cam follower  137 , arms  138 , pivot shaft  139 , and actuation mechanism  140 . Shield  128 , shown in  FIG. 4 , may comprise an elongated structure extending axially across drum  102  and spaced above drum  102  by frame  106 . Shield  128  includes multiple apertures  160  along its length through which portions of claw assembly project into engagement with sheets of media when ejection system  120  is in the ejection mode shown in  FIGS. 9   a ,  9   b ,  10   a  and  10   b , or when media ejection system is in the ready or cam disengaged mode shown in  FIGS. 11   a  and  11   b . Apertures  160  further permit portions of claw assembly  130  to be retracted within or behind shield  128  when ejection system  120  is in the shielded mode shown in  FIGS. 12   a  and  12   b . As a result, shield  128  inhibits physical contact of a user with portions of claw assembly  130  while media ejection system  130  is in the shielded mode. 
   Claw assembly  130  may comprise that portion of media ejection system  120  configured to physically contact or engage sheets of media to separate the sheets of media from drum  102  (shown in  FIG. 4 ).  FIGS. 6 and 7  illustrate claw assembly  130  in more detail. As shown by  FIGS. 6 and 7 , claw assembly  130  generally includes support shaft  161 , support  162 , claws  164  and claw retainers  166 . Support shaft  161  may comprise an elongated shaft to which support  162  and claws  164  are mounted. As shown in  FIG. 8 , in one embodiment, support shaft  161  includes knurled portions  168  and substantially smooth portions  170 . Knurled portions  168  engage support  162  such that rotation of shaft  161  also results in rotation of support  162 . Smooth portions  170  are configured to be received within and to engage portions of claws  164 , enabling claws  164  to rotate about shaft  161  relative to support  162 . In other embodiments, support shaft  161  may be coupled to support  162  and claws  164  in other fashions. 
   Support  162  (sometimes referred to as a holder or paw) may comprise an elongated structure configured to extend into contact with multiple claws  164  so as to enable claws  164  to be uniformly and simultaneously moved in a first direction  172  about axis  174  and so as to uniformly limit and control movement of claws  164  in a direction  176  about axis  174 . Support  162  further enables multiple individual claws  164  to be connected to support  162  as a single assembly, further facilitating pre-assembly of claw assembly  130  and efficient connection of claws  164  to support post  160 . 
   As shown by  FIGS. 6 and 7 , support  162  generally includes collar  180 , platform  182  and clips  184 . Collar  180  may comprise that portion of support  162  configured to connect support  162  to support shaft  161 . In one embodiment, collar  180  is molded about shaft  161 . In other embodiments, connection of collar  180  to shaft  161  may be achieved in other fashions. Collar  180  includes openings  186  through which claws  164  may partially encircle smooth portions  170  (shown in  FIG. 8 ) of support shaft  160 . In other embodiments, openings  186  may be omitted where support  162  itself includes a shaft or other bearing structure configured to facilitate rotational movement of claws  164  about axis  174 . 
   Platform  182  may comprise an elongated blade, bar or other structure extending from collar  180  generally below claws  164 . Platform  182  supports clips  184  and includes datum surfaces  188 . Datum surfaces  188  engage opposite datum pads or surfaces  190  of an associated claw  164  to control the angular positioning of claw  164  about axis  174 . Because a single support  162  provides such datums  188  for each of claws  164 , claws  164  may be more reliably located at the same position with respect to axis  174 . 
   Clips  184  may comprise structures extending from platform  182  that are configured to retain claw retainers  166  in place with respect to claws  164  and with respect to support  162 . In the particular example shown, clips  184  extend on opposite sides of each claw  164  and engage opposite ends of a claw retainer  166 . In other embodiments, clips  184  may have other configurations and may have other locations depending upon the configuration of claws  164  and the configuration of claw retainers  166 . In some embodiments, clips  184  may be omitted. 
   Claws  164  may comprise elongated pins, fingers or other structures configured to extend towards a surface of drum  102  (shown in  FIG. 4 ) so as to engage and separate a sheet of media from drum  102 . In the particular embodiment illustrated, each claw  164  is integrally formed as a single unitary body from a high strength-to-weight ratio material such as magnesium. The reduced weight of each claw  164  reduces bouncing of claw  164  on drum  102 . In the particular example illustrated, each claw  164  is further coated with a material such as a ceramic coating to reduce wear. In other embodiments, each claw  164  may be formed from other materials, may be formed from multiple portions welded, bonded or otherwise fastened to one another and may include other wear coatings or may omit such wear coatings. 
   As shown by  FIG. 7 , each claw  164  generally includes a knuckle portion  192 , an intermediate portion  194  including datum pad  190 , and a tip  196 . Knuckle  192  may comprise an elongated downwardly extending V- or C-shaped portion configured to partially extend about smooth portion  170  of shaft  161  (shown in  FIG. 8 ). As a result, claws  164  may be positioned about support shaft  161  after support  162  has been connected to support shaft  161 . In other embodiments, knuckle  192  may have other configurations that pivotally connect claw  164  to support shaft  161  or support  162 . 
   Intermediate portion  194  extends between knuckle  192  and tip  196  along a top portion of platform  182  of support  162 . Intermediate portion  194  has an underside including datum pad  190 . As noted above, datum pad  190  is configured to contact datum surface  188  on platform  182  to control the positioning of claw  164  and its tip  196  with respect to drum  102  and any media being separated. In the particular example illustrated in which tip  196  is spaced from axis  174  (shown in  FIG. 6 ) by a linear distance D, contact pad  190  is spaced from axis  174  by a distance of at least 0.1D and nominally at least about 0.5D. In the particular embodiment illustrated, datum pad  190  is spaced from axis  174  by a distance of about 25.4 mm. Because datum pad  190  is spaced from axis  174  by a distance of at least 0.1D, angular misalignment of tips  196  with respect to one another about axis  174  may be reduced, enabling more precise positioning of claws  164 . 
   Tip  196  extends at an end of claw  164  and is configured to project between sheets of media and drum  102 . In the particular example illustrated, tip  196  is pointed to enhance insertion of tip  196  between sheets of media and drum  102  (shown in  FIG. 4 ). In other embodiments, tip  196  may have other shapes. 
   Spring retainers  166  may comprise one or more structures configured to resiliently bias datum pads  190  against the datum surfaces  188 . In the particular embodiment illustrated, spring retainers  166  are further configured to retain their respective claws  164  relative to support shaft  161  and support  162 . In other embodiments, claws  164  may be retained relative to support shaft  161  by claws  164  snapping about support shaft  161  or other retention structures. In the particular example illustrated, spring retainers  166  may comprise torsion springs mounted to support  162  by clips  166  and extending over intermediate portion  194  of each claw  164 . In the particular example illustrated, each retainer  166  further retains claw  164  to support  162  as an assembly. Although claw assembly  130  is illustrated as including an individual retainer  166  for each claw  164 , in other embodiments, a retainer  166  may resiliently retain more than one claw  164  relative to support  162 . Although retainers  166  are illustrated as structures distinct from support  162 , in other embodiments, retainers  166  may be integrally formed as part of support  162 . 
   As shown by  FIG. 5 , spring  131  may comprise a structure configured to resiliently bias support shaft  161 , support  162  and claws  164  about axis  174  in the direction indicated by arrow  176  in  FIG. 6 . Such bias force urges claw assembly  130  about axis  174  until either cam follower  136  is against cam  132  or until cam follower  137  is against cam  134 . In the particular example illustrated, spring  131  may comprise a torsion spring having one end coupled to arm  138  and having another end connected to support  162 . In other embodiments, spring  131  may comprise other spring mechanisms and may be at other locations. 
   Cam  132  (shown in  FIG. 4 ) may comprise a surface configured to interact with cam follower  136  so as to control the positioning of lever  135  and claws  164  of claw assembly  130  in response to rotation of drum  102 . In the particular example illustrated, cam  132  may comprise an annular or circumferential member secured to an axial end of drum  102 . Cam  132  includes surface portions  200  and  202 . Surface portions  200  may comprise surfaces configured such that when in engagement with cam follower  136 , claw assembly  130  is positioned with tips  196  of claws  164  elevated above medium support surface  124  of drum  102  in a non-ejecting position. The locations of portions  202  are positioned to correspond with pre-determined locations of leading edges of media. 
   Surface portions  202  may comprise surfaces configured such that when in engagement with cam follower  136 , claw assembly  130  is moved towards surface  124  of drum  102  such that tips  196  of claws  164  extend between surface  124  of drum  102  and an upcoming sheet of media carried by drum  102  in an ejecting position. In the particular example illustrated, surface portions  202  may comprise concavities or depressions such that cam follower  136  and lever  135  dip into surface portions  202  to lower claws  164  into a position for separating a sheet of media from drum  102 . In the particular example illustrated, cam  132  includes three spaced surface portions  202 , permitting drum  102  to simultaneously support three sheets of media. In other embodiments, cam  132  may include a greater or fewer number of such surface portions  202 . In still other embodiments, cam  132  may include surface portions  202  having other configurations. 
   Cam  134  may comprise a structure configured to interact with cam follower  137  to selectively reposition lever  135  and cam follower  136  with respect to drum  102 . In the particular example illustrated, cam  134  is supported by frame  106  (shown in  FIG. 4 ) proximate to cam follower  137 . As shown by  FIG. 8 , cam  134  includes sloped or inclined surfaces  206  and  208 . Surface  206  is configured to engage cam follower  137  so as to move cam follower  136  out of engagement with cam  132 . In particular, surface  206  engages cam follower  137  to move cam follower  136  from an ejecting position (shown in  FIGS. 9   a  and  9   b ) to a withdrawn position (shown in  FIGS. 11   a  and  11   b ). Surface  208  is configured to engage cam follower  137  to move lever  135  and cam follower  136  to the retracted position (shown in  FIGS. 12   a  and  12   b ). Although surfaces  206  and  208  are illustrated as being generally linear, surfaces  206  and  208  may have other shapes and relative positions. 
   Lever  135  may comprise an elongated rigid structure fixedly coupled to support shaft  161  so as to rotate with support shaft  160 . As shown by  FIG. 8 , in the particular example illustrated, lever  135  has a generally non-circular opening  210  configured to receive a non-circular end portion  212  of support shaft  161 . In other embodiments, lever  135  may be coupled to support shaft  161  in other manners so as to rotate with rotation of support shaft  161 . Lever  135  supports cam followers  136  and  137 . 
   Cam follower  137  may comprise a structure configured to bear against surfaces  206  and  208  of cam  134  during movement of lever  135  and cam follower  136  between the ejection, cam disengaged and shielded modes shown in  FIGS. 9A ,  9 B,  10   a  and  10   b ,  FIGS. 11   a  and  11   b , and  FIGS. 12A and 12B , respectively. In the particular example illustrated, cam follower  137  may comprise a wheel or roller rotatably supported at midpoint of lever  135  generally opposite to cam  134 . In other embodiments, cam follower  137  may comprise other movable or immovable structures mounted or otherwise coupled to lever  135  at an appropriate location. 
   As shown by  FIGS. 5 and 8 , arms  138  may comprise elongated members having a first portion  216  pivotally connected to claw assembly  130  and lever  135  and a second portion  218  fixedly coupled to pivot shaft  139 . As shown by  FIG. 8 , portion  216  of each of arms  138  has a generally cylindrical bore  220  which is rotatably positioned about a cylindrical bushing  222  through which end  212  of support shaft  161  extends. As further shown by  FIG. 8 , portion  216  of arm  138  is captured on bushing  222  by head portion  224  of bushing  222  and by spring  226  and washer  228 . In other embodiments, portion  216  of arm  138  may be rotatably or pivotally connected to support shaft  161  and/or lever  135  in other fashions. Although ejection system  120  is illustrated as including two opposite arms  138 , in other embodiments, ejection system  120  may include fewer or greater of such arms coupled to claw assembly  130  and fever  135 . 
   Pivot shaft  139  (shown in  FIG. 5 ) may comprise an elongated shaft extending between and fixedly coupled to both of arms  138 . Pivot shaft  139  may comprise a biasing torsional interconnection between arms  138  such that arms  138  may pivot about pivot axis  220  in substantial unison to maintain claw assembly  130  and surface  124  of drum  102  substantially parallel. The biasing interconnection allows both arms  138  to engage stops  296  as shown in  FIGS. 9   a  and  10   a . In other embodiments, other structures may be utilized to interconnect arms  138 . 
   Actuation mechanism  140  may comprise a mechanism configured to selectively pivot shaft  139  about axis  220  so as to also pivot arms  138  about axis  220 . Pivoting of arms  138  about axis  220  results in cam follower  137  being moved relative to cam  134  to move lever  135  and cam follower  136  relative to surface  124  of drum  102  (shown in  FIG. 4 ) to actuate system  120  between the ejection, cam disengaged and shielded modes. Actuation mechanism  140  generally includes rotary actuator  240  and pivot drive  242 . Rotary actuator  240  may comprise a source of torque. In one embodiment, rotary actuator  240  may comprise an electric motor such as a DC motor with an encoder. In yet another embodiment, motor  240  may comprise a stepper motor. In still other embodiments, other motors may be utilized. In some embodiments, actuation mechanism  140  may additionally include one or more sensors configured to sense the angular positioning of structures corresponding to the angular position of arms  138  or pivot shaft  139  to facilitate control of torque supplied by rotary actuator  240 . 
   Pivot drive  242  may comprise one or more structures configured to transmit torque from rotary actuator  240  to pivot shaft  139  with an appropriate amount of torque and an appropriate amount of speed. In the particular example illustrated, pivot drive  242  includes a first gear train portion  244 , a toothed pulley  246  and an intermediate belt  248 . Gear train portion  244  receives initial torque from rotary actuator  240  and terminates at toothed pinion  250  which is in engagement with belt  248 . Belt  248  extends from toothed pinion  250  and encircles toothed pulley  246 . Belt  248  is maintained in tension by belt tensioner  252  and transmits torque to pulley  246  to rotate pivot shaft  139  in either direction about axis  220 . In other embodiments, pivot drive  242  may comprise other transmission or drive train assemblies. For example, in one embodiment, pivot drive  242  may alternatively include chain and sprocket assemblies or may utilize gear trains extending from rotary actuator  240  to pivot shaft  139 . In other embodiments, pivot drive  242  may be operably coupled to a rotary actuator that also supplies torque to other components of printing system  100  (shown in  FIG. 4 ). 
     FIGS. 9   a - 12   b  illustrate actuation of media ejection system  120  between various modes of operation.  FIGS. 9   a - 10   b  illustrate media ejection system  120  in a media ejection mode in which cam follower  136  rides upon cam  132 . To move cam follower  136  into engagement with cam  132 , actuation mechanism  140  (shown in  FIG. 5 ) pivots shaft  139  downward in the direction indicated by arrow  264  about axis  220  as seen in  FIG. 5  until arm  138  contacts or abuts datum stop  296 . Datum stop  296  may comprise a structure that is fixed or stationary with respect to drum  102  and with respect to arm  138 . In one embodiment, datum stop  296  may comprise a projection extending from frame  106  (shown in  FIG. 4 ). As a result, cam follower  137  is rolled along surface  208  and down surface  206  of cam  134  until cam follower  136  is in engagement with cam  132  as shown in  FIG. 9   a . As seen in  FIG. 9   b , this also results in claws  164  being lowered through openings  160  of shield  128  towards media support surface  124  of drum  102 . 
   During rotation of drum  102  in the direction indicated by arrow  260 , cam follower  136  rolls along surface portion  200  until engaging surface portion  202  shown in  FIG. 10   a . As shown in  FIG. 10   a , surface portion  202  causes cam roller  136  to clip into the depression of surface portion  202 . As shown in  FIG. 10   b , this results in claw assembly  130  and claws  164  also being lowered to position tips  196  below a bottom of the sheet of media  22  to be separated from drum  102 . In one particular embodiment, surface  124  may include channels, grooves, concavities and the like, into which tips  196  may project further below a bottom of the sheet  22  to be separated from drum  102 . Once the sheet has been separated from drum  102 , continued rotation of drum  102  results in cam follower  136  rolling out of the depression of surface portion  202  and back up onto a succeeding surface portion  200  which results in claws  164  once again rising above surface  124 . In particular embodiments, such rising may occur while claws  164  are in engagement with a bottom of a sheet to further facilitate separation of the sheet from surface  124  of drum  102 . 
     FIGS. 11   a  and  11   b  illustrate ejection system  120  in a ready or cam disengaged mode. To actuate media ejection system  120  from the ejection mode to the ready mode, actuation mechanism  140  rotates pivot shaft  139  about axis  220  in the direction indicated by arrow  266 . As a result, cam follower  137  is moved into engagement with surface  206  and is rolled up to surface  206  onto surface  208  to the position shown in  FIG. 11   a . Consequently, cam follower  136  is withdrawn from cam  132 . In the ready mode, cam follower  137  rests upon surface  208  of cam  134  proximate to surface  206 . As a result, lever  135  is raised to support cam follower  136  out of engagement with cam  132  of drum  102 . As a result, drum  102  may continue to be rotated in the direction indicated by arrow  260  so as to move surface portion  202  of cam  200  past cam follower  136  without surface portion  202  engaging cam follower  136 , without claw  164  (shown in  FIG. 11   b ) dipping below sheet  22  of media (shown in  FIG. 11   b ), allowing media sheet  22  to move past media ejection system  120 . Because media sheet  22  may be moved past media ejection system  120 , drum  102  may position sheet  22  opposite printing mechanism  110  (shown in  FIG. 4 ) once again for multi-pass printing or at other stations. 
     FIGS. 12   a  and  12   b  illustrate media ejection system  120  in a shielded mode. As shown in  FIG. 12   a , in the shielded mode, cam follower  137  is positioned at a rear of surface  208  of cam  134 . Actuation of media ejection system  120  from the ready mode shown in  FIG. 11   a  to the shielded mode shown in  FIG. 12   a  is achieved by actuation mechanism  140  (shown in  FIG. 5 ) further rotating pivot shaft  139  about axis  220  in the direction indicated by arrow  266  until arm  138  contacts or abuts datum stop  298 . Datum stop  298 , like datum stop  296 , may comprise a projection or other surface that is fixed or stationary with respect to drum  102  and with respect arm  138 . In one embodiment, datum stop  298  may comprise a projection extending from frame  106 . As a result, cam follower  137  rolls from the withdrawn position shown in  FIG. 11   a  along surface  208  to the retracted position shown in  FIG. 12   a . As shown in  FIG. 12   b , this results in claws  136  being retracted through openings  160  behind shield  128 . In this position, shield  128  inhibits physical contact with the potentially sharp tips  196  of claws  164  to facilitate clearing of media jams, repair or maintenance activities. 
   As discussed above, media ejection system  120  is actuated between the ejection mode (shown in  FIGS. 9   a ,  9   b ,  10   a  and  10   b ), the ready mode (shown in  FIGS. 11   a  and  11   b ) and the retracted or shielded mode (shown in  FIGS. 12   a  and  12   b ) based upon torque supplied by rotary actuator  240  (shown in  FIG. 5 ). The duration for which rotary actuator  240  supplies torque, the amount of torque and the speed is in part based upon data obtained during a start-up calibration routine and continuous operation calibration routines. Upon start-up or initialization, which may occur after power cycling, or after a media jam has been cleared, controller  114  (shown in  FIG. 4 ) presumes that the components of media ejection system  300  are in some unknown, arbitrary position. 
   To calibrate, home and precisely move media ejection system  120  to a known position, controller  114  generates control signals directing rotary actuator  240  to supply a low level of torque at a low speed for a predetermined period of time to ensure that a lower range of motion for media ejection system  120  is reached such as when arm  138  engages datum stop  296 . Because movement of media ejection system  120  to this lower range of motion occurs at a lower motor torque and low speed, arm  138  is not moved into contact with datum stop  296  with a destructively high amount of energy. 
   Once this lower range of motion has been established and detected (such as by an encoder of rotary actuator  240 ), controller  114  (shown in  FIG. 5 ) generates control signals directing rotary actuator  240  to supply a high amount of torque at a high speed to rapidly move components of media ejection system  120  approximately 90% of the particular distance from the lower limit in which arm  138  contacts datum stop  296  as shown in  FIGS. 9   a  and  10   a  to an upper limit of the estimated range of motion such as when arm  138  contacts datum stop  298  as seen in  FIG. 12   a . During this movement, high torque facilitates winding of spring  131  (shown in  FIG. 5 ) and overcomes high loads due to lifting of claw assembly  132  to the retracted position. 
   For the final 10% of the predicted move from the lower limit of the range of motion to the upper limit of the range of motion, controller  114  generates control signals directing rotary actuator  240  to supply a medium level of torque at a medium speed for a predetermined time to cover the remaining estimated distance to the upper limit of the range of motion. The medium level of torque supplied by rotary actuator  240  reduces likelihood of arm impacting stop  298  with a destructively high amount of energy. 
   Each of the aforementioned steps is repeated to further stabilize motions and normalize deflections. During such movement, travel distance between the upper range of motion and the lower range of motion is measured by an encoder and saved by controller  114 . The upper range of motion location is defined as the retracted position, the lower range of motion is defined as the ejecting position and a predefined fraction of distance between the upper limit of the range of motion and the lower limit of the range of motion is defined as the cam disengaged position. Using such information, controller  114  may generate control signals to reliably position media ejection system  120  in one of the three positions. The aforementioned process enables rotary actuator  240  to employ an inexpensive, relatively course, low accuracy single-channel encoder. 
   During operation of printing system  100 , controller  114  (shown in  FIG. 4 ) may continuously calibrate media ejection system  120  each time the system moves from the ready mode (shown in  FIGS. 11   a  and  11   b ) to the ejection mode (shown in  FIGS. 9   a ,  9   b ,  10   a  and  10   b ). To move ejection system  120  from the ready mode to the ejection mode, controller  114  generates control signals directing rotary actuator  240  to provide a high level of torque at a relatively high speed for a duration so as to move the components of media ejection system  120  approximately 95% of the estimated distance from the current withdrawn position of cam follower  136  in the ready mode to the lower limit of the estimated range of motion such as when arm  138  contacts datum stop  296 . 
   For the remaining approximately 5% of the move to the lower range of motion, controller  114  (shown in  FIG. 13 ) generates control signals directing rotary actuator  240  to supply a low level of torque for a sufficient duration to provide a gentle but definite contact between arm  138  and datum stop  296 . The lower level of torque reduces destructive impact forces against datum stop  296  and establishes or zeroes the eject position for ejection system  120 . 
   Subsequent return of ejection system  20  to the withdrawn position is achieved by controller  114  generating control signals directing rotary actuator  240  to supply a high level of torque for a high speed based upon the new zero location established for the lower range of motion. Since this calibration process is repeated for every sheet during printing, system  120  is continuously calibrated, enabling the use of inexpensive, relative course, electronically noisy and low accuracy single-channel encoders as part of rotary actuator  240 . 
   Overall, media ejection system  120  offers several benefits. Media ejection system  120  utilizes a dual-pivot rotational motion against cam  134  to place system  120  in one of three operating states, allowing sheets to pass multiple times through and relative to printing mechanism  110 . Because ejecting system  120  permits claws  164  to be moved to a retracted position within or behind shield  128 , repair, maintenance and clearance of media jams is facilitated. Because system  120  employs a single claw holder or support  162  to position all claws  164 , claw tip location variation is reduced. In addition, assembly time and part count is also reduced. A media ejection system  120  further facilitates use of a start-up calibration routine and a continuous calibration routine that facilitates accurate positioning of the components utilizing a simple and relatively inexpensive motor and single channel encoder. 
     FIGS. 13-19  illustrate printing system  300 , another embodiment of printing system  100  shown in  FIG. 4 . Printing system  300  is similar to printing system  100  except that printing system  300  includes media ejection system  320  in lieu of media ejection system  120 . For ease of illustration, those remaining elements or components of printing system  300  which correspond to elements of printing system  100  are numbered similarly. 
   Media ejection system  320 , shown in  FIGS. 13 and 14 , is similar to media ejection system  120  except that media ejection system  320  includes lever  335 , cam follower  336 , and linkage assembly  342  in lieu of cam  134 , lever  135 , cam followers  136 ,  137 , and pivot drive  242 . Those remaining elements of media ejection system  320  which correspond to elements of media ejection system  120  are numbered similarly. 
   Lever  335  may comprise an elongated member having a first end  337  fixedly coupled to support shaft  161  such that lever  335  rotates or pivots about axis  174  with support shaft  161  and a second opposite end  338  rotatably supporting cam follower  336 . Cam follower  336  may comprise a wheel, roller and the like, rotatably supported by lever  335  and configured to engage cam  132  (shown in  FIG. 13 ) when media ejection system  320  is in the ejecting position as shown in  FIGS. 16 and 17 . Cam follower  336  rolls along surface portions  200  to maintain claws  164  in a non-ejecting position spaced from surface  124  of drum  102  as shown in  FIG. 16 . Upon cam follower  336  engaging a surface portion  202 , cam follower  336  dips into surface portion  202  causing claws  164  to also dip or drop towards surface  124  for engagement with a sheet of media field by drum  102 . Although cam follower  136  is illustrated as a roller, in other embodiments, cam follower  336  may alternatively comprise other movable or immovable structures coupled to lever  335  and configured to bear against cam  132  during rotation of drum  102 . 
   Link assembly  342  may comprise an arrangement of links extending between rotary actuator  240  and pivot shaft  139  as well as lever  335 . Link assembly  342  generally includes links  350 ,  352 ,  354  and  356 . Link  350  may comprise a member fixedly coupled to an output shaft  360  of gear train  244  described above with respect to pivot drive  242  (shown in  FIG. 5 ). Gear train  244  is coupled to an output shaft of rotary actuator  240  and transmits torque to link  350  via its output shaft  360 . Link  350  rotates about axis  362  of output shaft  360  in response to torque supplied by rotary actuator  240 . 
   Link  352  may comprise an elongated member having a first end  364 , a second end  366  and an intermediate tab  368 . First end  364  is pivotally connected to link  350  so as to pivot relative to link  350  about axis  370 . End  366  pivotally connected to an intermediate portion of lever  335  such that link  352  and lever  335  may pivot or rotate relative to one another about an axis  372 .  FIG. 15  is an enlarged view illustrating end  366  connected to lever  335  in more detail. As shown by  FIG. 15 , end  366  includes an elongated slot  374  through which a boss  376  extends and is coupled to lever  335 . Boss  376  and slot  374  cooperate to pivotally connect lever  335  and link  352 . Slot  374  further enables axis  372  about which lever  335  and link  352  are pivoted to move within slot  374 . Movement of boss  376  within slot  374  facilitates movement of claw assembly  130  between multiple states or positions as will be described in greater detail hereafter. Although boss  376  is illustrated as being coupled to lever  335  while slot  374  is formed in end  366  of link  352 , in other embodiments, boss  376  may alternatively be coupled to end  366  of link  352  while slot  374  is formed in lever  335 . 
   Tab  368  extends between ends  364  and  366  and is configured to be received within a corresponding aperture  380  in link  354 . Tab  368  and aperture  380  and link  354  cooperate to control relative movement of links  352  and  354  and to transmit force between links  352  and  354  during movement of links  352  and  354 . As with slot  374  and boss  376 , tab  368  and aperture  380  facilitate movement of linkage assembly  342  to selectively position claw assembly  130  in one of multiple positions or states. Although tab  368  is illustrated as extending from link  352  and aperture  380  is illustrated as being provided in link  354 , in other embodiments, tab  368  may alternatively extend from link  354  while aperture  380  is provided in link  352 . 
   Link  354  may comprise an elongated linkage or member having an end  382  on a first side of aperture  380  and an opposite end  384  on a second opposite side of aperture  380 . End  382  is pivotally connected to link  350  about axis  370 . End  384  is pivotally connected to link  356  for pivotal movement about axis  386 . As shown by  FIG. 14 , end  384  additionally includes an elongated slot  388  through which a boss  390  extends into connection with link  356  to pivotally connect end  388  of link  354  to link  356 . Slot  388  enables axis  386  about which links  354  and  356  pivot relative to one another to move. Slot  388  further enables linkage assembly  342  to move to various positions or states so as to appropriately position claw assembly  130  in one of various states or positions. Although end  384  of link  354  is illustrated as including slot  388  and boss  390  is illustrated as being coupled to link  356 , in other embodiments, slot  388  may alternatively be formed in link  356  while boss  390  extends through slot  388  and is connected to link  354 . In still other embodiments, other mechanisms may be employed that facilitate pivotal connection of links  354  and  356  while permitting the axis of the pivotal connection to move. 
   Link  356  may comprise an elongated member having a first end portion  392  pivotally connected to link  354  as described above and a second end portion  394  fixedly coupled to pivot shaft  139  and arm  138 . Link  356  transmits force from linkage assembly  342  to arm  138  so as to move arms  138  about pivot shaft axis  220  for positioning of claw assembly  130 . 
     FIGS. 16-19  illustrate operation of media ejection system  320  to manipulate linkage assembly  342  so as to move lever  335 , cam follower  336  and claw assembly  130  (shown in  FIG. 14 ) between the ejection mode (shown in  FIGS. 16 and 17 ), a ready, cam disengaged mode (shown in  FIG. 18 ) and a retracted, shielded mode (shown in  FIG. 19 ). 
     FIGS. 16 and 17  illustrate media ejection system  320  in a media ejection mode. In the ejection mode, rotary actuator  240  (shown in  FIG. 14 ) supplies torque in a direction so as to rotate link  350  to the position shown until link  352  contacts datum stop  396  and until arm  138  contacts datum stop  398 . Datum stops  396  and  398  comprise structures that are fixed or stationary with respect to drum  102  and with respect to linkage assembly  342 . In one embodiment, datum stops  396  and  398  comprise projections extending from frame  106  (shown in  FIG. 13 ). In the position shown in  FIG. 16 , link  354  is held in compression with boss  390  moved within slot  388  to shorten the effective length of link  354 . At the same time, boss  376  is free to move within slot  374 , allowing lever  335  to pivot about axis  174  in response to engagement of cam follower  336  with portions  200  and  202  of cam  132 . In particular, as shown in  FIG. 16 , engagement of cam follower  336  with portion  200  of cam  132  results in boss  376  moving within slot  374  away from drum  102 . As a result, claw assembly  130  is also moved away from drum  102  as shown in  FIG. 16 . 
   As shown in  FIG. 17 , in response to cam follower  336  in engagement with portion  202  of cam  132 , boss  376  moves within slot  374  towards drum  102 . As a result, claw assembly  130  and claws  164  are moved towards drum  102  such that tips  196  extend between media and drum  102  for separating the media from drum  102  as seen in  FIG. 17 . 
     FIG. 18  illustrates media ejection system  320  actuated to the ready state in which cam follower  336  is out of engagement with cam  132 . To actuate media ejection system  320  to the cam disengaged mode shown in  FIG. 18 , rotary actuator  240  applies torque in appropriate directions so as to pivot link  350  to the position shown in  FIG. 18 . To actuate media ejection system  320  from the ejection mode shown in  FIGS. 16 and 17 , link  350  is pivoted about axis  362  in the direction indicated by arrow  402 . When system  320  is in the ready mode withdrawn position shown in  FIG. 18 , boss  376  is in engagement with an end of slot  374  as shown. As a result, link  352  is placed in tension and lever  335  is pivoted about axis  174  until cam follower  336  is disengaged and withdrawn from cam  132 . At the same time, link  350  is positioned such that boss  390  is moved within slot  388  such that link  354  is also in tension and is at its longest effective length. 
     FIG. 19  illustrates ejection system  320  in the retracted shielded mode in which claw assembly  130  (shown in  FIG. 14 ) is retracted away from drum  102  to such an extent so as to inhibit physical contact with tips  196  of claws  164 . To actuate media ejection system  320  to the shielded mode, rotary actuator  240  supplies torque in an appropriate direction so as to pivot link  350  to the position shown in  FIG. 19 . To actuate media ejection system  320  from the ready mode shown in  FIG. 18  to the shielded mode shown in  FIG. 19 , rotary actuator  240  (shown in  FIG. 14 ) pivots link  350  in the direction indicated by arrow  404 . In the retracted position, tab  368  is moved within aperture  380  until engaging an opposite end of aperture  380  as compared to the withdrawn position shown in  FIG. 18 . The opposite end  406  of aperture  380  serves as a hard stop for pivotal movement of link  350  in the direction indicated by arrow  404 . As shown by  FIG. 19 , when link  350  is in the position shown, lever  335 , cam follower  336  and claw assembly  130  (shown in  FIG. 14 ) are moved further away from drum  102  and are also moved in the direction indicated by arrow  408  such that tips  196  of claws  164  are retracted within or behind shield  128  as seen in  FIG. 12   b.    
   As discussed above, media ejection system  320  is actuated between the ejection mode (shown in  FIGS. 16 and 17 ), the ready mode (shown in  FIG. 18 ) and the retracted or shielded mode (shown in  FIG. 19 ) based upon torque supplied by rotary actuator  240  (shown in  FIG. 14 ). The duration for which rotary actuator  240  supplies torque, the amount of torque and the speed is in part based upon data obtained during a start-up calibration routine and continuous operation calibration routines. Upon start-up or initialization, which may occur after power cycling or after a media jam has been cleared, controller  114  (shown in  FIG. 13 ) presumes that the components of media ejection system  300  are in some unknown, arbitrary position. To calibrate, home and precisely move media ejection system  320  to a known position, controller  114  generates control signals directing rotary actuator  240  to supply a low level of torque at a low speed for a predetermined period of time to ensure that a lower range of motion for media ejection system  320  is reached such as when arm  138  engages datum stop  398 . Because movement of media ejection system  320  to this lower range of motion occurs at a lower motor torque and low speed, arm  138  is not moved into contact with datum stop  398  with a destructively high amount of energy. 
   Once this lower range of motion has been established and detected (such as by an encoder of rotary actuator  240 ), controller  114  (shown in  FIG. 13 ) generates control signals directing rotary actuator  240  to supply a high amount of torque at a high speed to rapidly move components of media ejection system  320  approximately 90% of the particular distance from the lower limit in which arm  138  contacts datum stop  398  as shown in  FIGS. 16 and 17  to upper limit of the estimated range of motion such as when tab  368  contacts end  406  of aperture  380  as seen in  FIG. 19 . During this movement, high torque facilitates winding of spring  131  (shown in  FIG. 14 ) and overcomes high loads due to lifting of claw assembly  132  to the retracted position. 
   For the final 10% of the predicted move from the lower range of motion to the upper range of motion, controller  114  generates control signals directing rotary actuator  240  to supply a medium level of torque at a medium speed for a predetermined time to cover the remaining estimated distance to the upper limit of the range of motion. The medium level of torque supplied by rotary actuator  240  reduces likelihood of tab  368  impacting end  406  of apertures  380  with a destructively high amount of energy. 
   Each of the aforementioned steps is repeated to further stabilize motions and normalize deflections. During such movement, travel distance between the upper range of motion and the lower range of motion is measured by an encoder and saved by controller  114 . The upper range of motion location is defined as the retracted position, the lower range of motion is defined as the ejecting position and a predefined fraction of distance between the upper range of motion and the lower range of motion is defined as the withdrawn position. Using such information, controller  114  may generate control signals to reliably position media ejection system  320  in one of the three positions. The aforementioned process enables rotary actuator  240  to employ an inexpensive, relatively course, low accuracy single-channel encoder. 
   During operation of printing system  300 , controller  114  (shown in  FIG. 13 ) may continuously calibrate media ejection system  320  each time the system moves from the ready mode (shown in  FIG. 18 ) to the ejection mode (shown in  FIGS. 17 and 18 ). To move ejection system  320  from the ready mode to the ejection mode, controller  114  generates control signals directing rotary actuator  240  to provide a high level of torque at a relatively high speed for a duration so as to move the components of media ejection system  320  approximately 95% of the estimated distance from the current withdrawn position of cam follower  336  in the ready mode to the lower limit of the estimated range of motion such as when arm  138  contacts datum stop  398 . 
   For the remaining approximately 5% of the move to the lower range of motion, controller  114  (shown in  FIG. 13 ) generates control signals directing rotary actuator  240  to supply a low level of torque for a sufficient duration to provide a gentle but definite contact between arm  138  and datum stop  398 . The lower level of torque reduces destructive impact forces against datum stop  398  and establishes or zeroes the eject position for ejection system  320 . 
   Subsequent return of ejection system  320  to the withdrawn position is achieved by controller  114  generating control signals directing rotary actuator  240  to supply a high level of torque for a high speed based upon the new zero location established for the lower range of motion. Since this calibration process is repeated for every sheet during printing, system  320  is continuously calibrated, enabling the use of inexpensive, relative course, electronically noisy and low accuracy single-channel encoders as part of rotary actuator  240 . 
   Overall, media ejection system  320  offers several benefits. Like system  120 , system  320  facilitates use of a continuous calibration which enables a simple and inexpensive electric motor and single channel encoder to initiate and home itself at power up and to precisely position the media ejection system  320  during printing. Like system  120 , system  320  utilizes a single piece claw holder or support  162  to ensure accurate positioning and datuming of claws  164 . Media ejection system  320  also reduces excessive backlash that would be present in an extended gear train, enabling faster transitions and greater positioning accuracy between the ejecting, withdrawn and retracted positions. 
   In addition, system  320  offers other benefits. System  320  reduces tension adjustment that would otherwise be required for a belt drive system, facilitating assembly and enhancing system reliability. Ejection system  320  also reduces the stress and deflection in components by reducing the amount of torque and gear reduction. The use of slots and links by media ejection system  320  forms three separate 4-bar linkages using only 4 links, reducing part count and assembly time. 
   Although systems  120  and  320  are illustrated as including claw assembly  130  in which a single claw support  162  (also known as a holder or a paw) supports multiple claws  164 , in other embodiments, systems  120  and  320  may alternatively utilize other claw mounting arrangements. For example, in other embodiments, systems  120  and  320  may alternatively have claws  164  individually mounted to support shaft  161  without support  162 . Although systems  120  and  320  are illustrated as being actuatable between an ejecting position, a withdrawn position and a retracted position, in other embodiments, system  120  or system  320  may alternatively be configured to move between fewer such positions or additional positions. 
   Although the present disclosure has been described with reference to example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.