Abstract:
A pick mechanism includes a hinged pick arm which moves between a retracted position and a varying, operating position. The pick arm is anchored about a pivot axis and hinged along its length. Rotation of a pick roller along the arm while in contact with a media sheet induces a moment on the pick arm causing the pick arm to pivot and hinge. A first stop limits the pivoting motion. A second stop limits the hinging motion, Such pivoting and hinging is desirable to create an effective normal force enabling reliable picking of thick media sheets. Such motions are limited to prevent the pick roller from translating too far from a media separation ramp. If the pick roller translates too far, undesirable media buckling may occur during the pick operation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. application Ser. No. 09/972,559 with the same title and filed Oct. 6, 2001 now U.S. Pat. No. 6,637,743 application Ser. No. 09/470,174 is a continuation in part of U.S. Pat. No. 6,322,065 with the same title and issued Nov. 27, 2001 on an application filed Dec. 22, 1999. 

   BACKGROUND 
   This invention relates generally to media sheet feed mechanisms, and more particularly, to a media sheet pick and feed system which operates effectively regardless of media tray content and which enables easy re-loading of the media tray. 
   Print recording devices, such as printers, fax machines and copy machines, and print scanning devices often include an input media tray. A media sheet is picked from the input tray and fed along a media path to receive print recording or to undergo print scanning. One common mechanism for picking and feeding a media sheet employs a D-shaped wheel. During rotation of the wheel the curved portion contacts and picks a media sheet. Subsequent to the pick action the flat portion of the D-shaped wheel is adjacent to the picked media sheet, but out of contact with the media sheet. The media sheet is fed from the media tray while the flat portion of the wheel is adjacent but out of contact with the media sheet. 
   Another known pick mechanism includes a drive gear mounted on a shaft which in turn is coupled to a drive motor. The drive motor turns the shaft and drive gear during a pick operation. The drive gear engages a driven gear to which is rigidly connected a pick roller. Thus, the drive motor rotates the pick roller. The pick mechanism is moved into and out of contact with a media sheet to be picked by the rotation of the drive gear. When the drive gear rotates in one direction the driven gear and pick roller move into contact with a media sheet. Continued rotation in such direction causes the media sheet to be picked and moved onto a media feed path. Typically, rotation in the opposite direction causes the drive gear and pick roller to move out of contact with the media sheet. A shortcoming of this mechanism is that a spring-loaded tray is needed to bias the media sheets toward the pick range of the pick roller. Further, the media tray needs to be removed during reloading (or alternatively a mechanism is needed during reloading to depress the spring-loading plate which raises a media sheet into the pick range). 
   In U.S. Pat. No. 5,547,181 issued Aug. 20, 1996 to Underwood for “Media Sheet Pick and Feed System,” Underwood discloses a clutch mechanism which allows the pick roller to remain in contact with the media sheet as the media 
   e media tray along the feed path. In particular, the clutch disengages the drive gear from the drive motor allowing the pick roller (along with the drive gear and driven gear) to “free” wheel. This approach eliminates the need for a spring-loaded media tray. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an exemplary host system for the pick arm mechanism. 
       FIG. 2  is a block diagram of a media transport assembly according to one embodiment. 
       FIG. 3  is a block diagram of a media transport assembly according t another embodiment. 
       FIG. 4  is a planar view of the pick arm assembly according to an embodiment of this invention, as shown with a frame and an input tray. 
       FIG. 5  is a partial view of a hinge point of the pick arm shown in FIG.  4 . 
       FIG. 6  is a view of a cam mechanism for retracting the pick arm of FIG.  4 . 
       FIG. 7  is a view of a cam contact points relative to the pick arm and input tray. 
       FIG. 8  is a diagram of a portion of the media transport assembly with the pick arm in a retracted position. 
       FIG. 9  is a diagram of a portion of the media transport assembly with the pick arm in a down position. 
       FIG. 10  is a diagram of a portion of the media transport assembly with the pick arm in an operative position and a media sheet being picked from a media stack. 
       FIG. 11  is a diagram of a portion of the media transport assembly with the pick arm in an operative position and a media sheet being picked from a smaller media stack. 
       FIG. 12  is a force diagram of the forces acting on a pick roller at a point where the pick roller contacts a media sheet. 
       FIG. 13  is a line diagram depicting the angles which the pick arm portions form. 
   

   DETAILED DESCRIPTION 
   Overview 
   The pick arm mechanism of this invention is implemented in a print recording system or a print scanning system, such as a printer, a fax machine, a copy machine, or an optical scanning device. Referring to  FIG. 1 , such a system  10  includes an operative device  12 , such as a print recording device or a print scanning device, along with an operations controller  14  and a media transport assembly  16 . The system  10  responds to commands input at a user interface panel (not shown) or input from a host device (e.g., a computer) to which the system  10  is coupled. In response to the command, the operations controller  14  generates signals which are sent to the media transport system  16  to move a media sheet into position for an operation (e.g., print recording; media scanning) by the operative device  12 . 
   Typically the system  10  includes an input tray including a stack of media sheets. A media sheet is picked from the stack and then fed along a feed path. Accordingly, the media transport assembly  16  includes mechanisms for a pick function  18  and mechanisms for a feed function  20 . 
   Referring to  FIG. 2 , in one embodiment the media transport assembly  16  includes one or more feed rollers  22  driven by a feed drive motor  24  through a feed transmission  26 . The transmission  26  typically includes a gear chain for mechanically coupling the feed rollers  22  to the drive motor  24 . The media transport assembly  16  also includes a pick roller  30  driven by a pick drive motor  32  through a pick transmission  33 . The feed drive motor  24  and the pick drive motor  32  respond to signals received from the operations controller  14 . In addition, sensors  34  are included which provide information to the operations controller  14  to allow desired control of operations. For example, a media position sensor is often included which enables the operations controller  14  to determine when to signal one of the drive motors  24 ,  32  to stop or reverse directions. 
   Referring to  FIG. 3 , in an alternative embodiment the pick roller  30  is driven by the same drive motor  24  as the feed rollers  22 . In such embodiment a transmission  26 ′ links both the feed rollers  22  and the pick roller  30  to the common drive motor  24 . 
   Hinged Pick Arm 
   Referring to  FIG. 4 , a pick arm assembly  40  is shown mounted to a frame  42  which also supports an input tray  44 . The pick arm assembly  40  includes one or more pick rollers  46 , the pick drive motor  32  and the pick transmission  33 , mounted to a distal portion  48  of a hinged pick arm  50 . Wires (not shown) or other signal transport medium couple the motor  32  to the operations controller  14 . 
   The pick arm assembly  40  is mounted to the frame  42  at an axle  52  which extends along a transverse section  54  of the assembly  40 . In one embodiment the pick arm assembly  40  is free to rotate about the axle  52  within a given rotational range of motion. In another embodiment the axle  52  may be coupled to a transmission which also is coupled to the pick rollers  46 . The pick arm  50  includes a first portion  55  (also referred to as the proximal portion) located proximal to the transverse section  54  and a second portion  48  (also referred to as the distal portion) located distally from the transverse section  54 . 
   The pick arm  50  is hinged at a hinge axis  56 . The distal portion  48  moves with one degree of freedom relative to the proximal portion  55  about the hinge axis  56 . In other embodiments additional degrees of freedom are implemented to also allow the distal portion to slide or translate longitudinally relative to the proximal portion  55 . In a preferred embodiment the distal portion  48  is spring-biased to maintain the distal portion  48  at a first orientation relative to the proximal portion  55 . In the best mode embodiment the first orientation is straight, although an angular orientation may be implemented instead. Various spring-like mechanisms may be used to implement the spring biasing. Referring to  FIG. 5 , in one embodiment a torsion spring  60  provides the bias to maintain the hinged pick arm  50  in the first orientation. In other embodiments, a compression spring, tension spring, leaf spring or sheet metal spring may be used. Still other known spring-like mechanisms may be used instead. 
   Pick Arm Movement Between Retracted Position and Operative Position 
   Referring again to  FIG. 5 , the hinged pick arm  50  rotates about an axis defined by the axle  52 . The pick arm  50  moves into an operative position adjacent to a media sheet  58  during a pick operation. It also is desirable that the pick arm  50  be retracted when the input tray  44  is removed, so that the tray  44  does not bump the pick arm  50  upon re-insertion. There are various known methods for moving a pick am between a retracted position and an operative position. Referring to  FIGS. 4 ,  6 ,  7 ,  8 , and  9 , in one embodiment, a cam  61  is included to control the retraction of the pick arm  50 . The cam  61  is biased (see  FIG. 8 ) to maintain the pick arm  50  in a retracted position  64 . The cam  60  moves about an axis  62  and includes two contact points  66 ,  68 . One contact point  66  enters physical communication with the pick arm assembly  40  at an area  70  as the cam  60  is biased to move the pick arm into the retracted position  64 . The other contact point  68  receives physical communication from the input tray  44  along a rail  72  when the input tray is inserted into frame  42 . In some embodiments the cam  60  is spring-biased as shown in  FIGS. 8 and 9 . In other embodiments the cam  61  is biased into the retracted position  64 , instead, by having a balance point away from axis  62 . 
   As the input tray  44  is inserted, the rail  72  contacts the point  68  of the cam  60 . The rail  72  has an inclined portion  74  where contact first occurs. As the tray  44  is pushed into the frame  42 , the point  68  moves up the inclined portion  74  of the rail  72 , then along a flat portion  76 . As the contact point  68  moves up the incline  74 , the cam  60  rotates about axis  62  in direction  67 . Cam  60  is a rigid structure so contact point  66  rotates with the cam  60  moving the contact point  66  in a direction away from the pick arm  50 . The pick arm  50  under its own weight falls, or more specifically rotates about axle  52 , to stay supported by the contact point  66 . During the rotation of the cam  60 , the pick arm  50  eventually rotates enough for the pick roller  46  to make contact with the media sheet  58 . The pick arm  50  is entering an operative position. As rotation of the cam  60  continues, the contact point  66  separates from the portion  70 , as shown in FIG.  9 . While the tray  44  remains installed the contact point  66  is kept away from the pick arm. In some embodiments the pick arm section  70  rotates back into contact with the contact point  66  with the picking of the last media sheet from the input tray  44 . As a result, the normal force applied by the pick roller  46  on the empty tray  44  is reduced. This avoids damage to the pick arm and pick roller  46  in the event that a pick operation is attempted while the input tray is empty. In other embodiments a sensor is used to signal that the tray  44  is empty, so that a pick operation does not occur. 
   Upon removal of the input tray  44 , the cam  60  rotates in direction  69  which causes the contact point  66  to contact section  70  and left the pick arm into the extracted position. The cam  60  is biased to rotate in the direction  68  either by a spring or another biasing method (e.g., relative weights of cam links about the axis  62 ). 
   Hinging of the Pick Arm 
   During the pick operation, the operations controller  14  signals the pick drive motor  32  to rotate the pick roller  46  in a pick direction  78  (see FIG.  10 ). When the pick roller begins to move, it applies a translation force to the media sheet. Ignoring acceleration of the roller, this translation force is resisted by equal and opposite forces consisting of a separation force and the friction between the sheet being picked and the sheet below it. The separation force, in the example described, is a force acting on the leading edge of the sheet being picked, applied by the separation ramp when the sheet runs into it. The translation force applied by the roller will continue to increase until the sheet bends at the ramp, allowing it to picked out of the tray. Referring to  FIG. 12 , horizontal and vertical components, R x  and R y , of a reaction force act upon the roller  46  at roller bearings. These forces are reaction forces balancing the forces N and f applied by the sheet  58  to the roller  46 . 
   The resisting forces, applied by the sheet to the roller induce a moment at the pivot point  52 . When the moment exceeds the spring force that biases the pivot arm  50  into the first orientation, the distal portion  48  and proximal portion  55  hinge at the hinge axle  56 , as shown in FIG.  10 . Because the pick arm is fixed at the axle  52 , the proximal portion  55  rotates about the axle  52  in the direction  82 . As a result the pick roller  46  translates slightly in the direction  84  away from a media separation ramp  86 . When the input tray  44  is filled with media sheets the proximal portion  55  rotates in the direction  82  until it reaches a mechanical stop  88 . In one embodiment the mechanical stop  88  is positioned so as to allow the proximal portion  55  to return to the same place as when the entire arm  50  is retracted. In one embodiment this is a position which extends generally parallel to the media sheet  58 . Due to the hinging at hinge point  56 , however, the pick arm has a second orientation different than the first orientation, in which the distal portion  48  is out of the retracted position.  FIG. 10  shows the pick arm  50  in an operative position for picking a media sheet  58 . 
   Referring to  FIG. 13 , an angle α is defined as 180 degrees minus the angle formed between the proximal portion  55  and the distal portion  48 . Angle β is defined as the angle formed between the distal portion  48  and the media sheet  58 . In an embodiment in which the mechanical stop  88  is positioned to keep the proximal portion  55  parallel to the media sheet  58 , angle α equals angle β as long as the proximal portion  55  is in contact with the mechanical stop  88 . 
   In some embodiments the angle α is limited by another stop mechanism  90  (see FIG.  5 ). The distal portion  48  can only rotate to a limited angle relative to the proximal portion  55  before being stopped by stop mechanism  90 . 
   As the media sheets are picked from the input tray  44 , the height of the media stack decreases. While the stack is high, the angle a increases as the media stack height decreases. Eventually angle a reaches a maximum angle where the mechanical stop  90  prevents further increases in angle a As the media stack continues to be reduced in height, the pivot arm  50  then rotates about the axle  52  keeping angle a fixed at the maximum angle. In other embodiments the spring constant for the spring  60  biasing the hinge point  56  is selected so as to overcome the moment exerted on it by the translation force when angle α reaches a prescribed angle. In such embodiment the spring  60  serves as the stop mechanism  90  which limits angle α to some maximum angle. 
   An advantage of hinging the pick arm  50  is that picking becomes more effective as angle a is increased to some maximum angle. Referring to  FIGS. 10 and 12 , the normal force N acting on the pick roller  46  increases as angle a increases. As the normal force increases, the available pick force (μN) also increases. Accordingly, as the normal force N acting on the pick roller  46  increases, it becomes easier to pick heavier media sheets. Stated another way, picking of heavier media sheets is more effective as the normal force N increases. Correspondingly, picking of heavier media sheets is more effective as angle α increases. 
   There is also a trade-off, however. As the angle α increases the pick roller  46  translates away from the media separation surface  86 . As the pick roller gets farther from the media separation surface  86  there is more likelihood of undesirable media sheet buckling. Accordingly, it is desirable to limit the amount of translation. One manner of doing so is to limit the angle α to a maximum angle using the angle stop mechanism  90  or by appropriately selecting a spring constant for spring  60 . Once the maximum of angle α is reached, the pick arm no longer hinges at axle  56 , but instead pivots at axle  52 . As a result, there is relatively less translation of the pivot roller  46  per unit drop in height while the media stack continues to decrease in height toward an empty input tray  44 . 
   In an alternative embodiment the translation is minimized not by limiting angle α but instead by limiting angle β. To do so, a stop mechanism is mounted to stay in the same horizontal position relative to the input tray while dropping vertically by the same amount as the paper stack decreases in height. Thus, regardless of the stack height, the stop mechanism limits angle β to a maximum angle. 
   Method for Picking a Media Sheet 
   In one embodiment the pick arm  50  is lowered adjacent to a media sheet  58  when the media input tray  44  is inserted into frame  42 , as shown in  FIGS. 8 and 9 . With the pick arm  50  in the position shown in  FIG. 9 , the operations controller  14  signals the pick drive motor  32  to rotate the pick roller  46 . In an alternative embodiment the driving of the pick roller causes the pick arm to lower into position to begin a pick operation. In such alternative embodiment, the pick arm retracts after the pick operation (or after the media sheet is fed along the media path). 
   With the pick roller rotating while in contact with the media sheet  58 , the translation force applied by the roller to the media sheet causes the media sheet to move in direction  27  toward a media separation ramp  86 . The separation ramp resists the motion of the sheet, causing the translation force to increase and allowing only the top sheet to be picked. The top media sheet moves into contact with a feed roller  22  and a pinch roller  23 . When the leading edge of the media sheet  58  is captured between the feed roller  22  and pinch roller  23 , the media sheet is pulled out of the input tray  44  onto a media path  25 . The media sheet  58  then is driven along the media path by one or more feed rollers  22 . 
   As the pick roller  46  rotates while in contact with the media sheet  58 , the forces applied by the media sheet to the roller, opposing the translational force, cause a moment to act upon the pick arm  50  which causes the pick arm  50  to hinge at hinge point  56 . As a result the arm pivots about axle  52  and hinges about hinge point  56  until the proximal portion  55  of the arm  50  reaches a mechanical stop  88 . As the media stack gets lower (see FIG.  11 ), a second mechanical stop  90  limits the angle formed between the proximal portion  55  and the distal portion  48 . As a result, the proximal portion  55  rotates away from the mechanical stop  88  as the weight of the arm  50  acts to keep the pick roller  46  in contact with the media sheet  58 . 
   In some embodiments the pick arm is retracted after a picking operation. In the embodiment illustrated, the pick arm  50  remains in contact with the media stack until the input tray  44  is removed (see FIG.  8 ). 
   Meritorious and Advantageous Effects 
   One advantage of the invention is that media sheets of varying weights are effectively picked from a media sheet stack without media buckling. 
   Although a preferred embodiment of the invention has been illustrated and described, various alternatives, modifications and equivalents may be used. Therefore, the foregoing description should not be taken as limiting the scope of the invention which are defined by the appended claims.