Patent Publication Number: US-8113504-B2

Title: Media sheet feeding method for overcoming at least one media handling failure mode

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to a media handling device in an image forming machine and, more particularly, to a media sheet feeding method for overcoming at least one media handling failure mode. 
     2. Description of the Related Art 
     A high capacity media handling device of an image forming machine typically includes a pick mechanism that feeds media a sheet at a time from pick positions to a downstream media process, such as printing, copying and the like, and an elevator that lifts a stack of media sheets so as to place the top of the stack at a selected pick position relative to the pick mechanism. The pick mechanism includes a pick arm pivotally mounted at one end and having a pick roll mounted at its free end that contacts a top sheet of a media stack. The pick roll includes a friction surface, oftentimes in the form of one or more tires. The pick positions may be at any of a plurality of levels that intersect an inclined surface on a wear or restraint dam of an input tray between the upper and lower ends of the dam. The pick mechanism is able to feed media a sheet at a time most reliably when the top of the stack is at any one of the pick positions. When the media sheets are picked one at a time from the stack to supply the media process, the level of the top of the stack decreases and potentially could go below the lowest level of the pick positions. The main function of the elevator is to return the top of the stack toward the upper limit of the pick positions before it goes below the lower limit thereof which may be the same as the lower end of the inclined surface of the dam. 
     It is generally the case that the timing for lifting the stack by the elevator should be such that the stack is not lifted when the pick mechanism is feeding sheets of media from the stack. It is understood that doing both at the same time could introduce adverse forces on the stack since the pick mechanism is pressing downward on the stack as the elevator is lifting the stack upward. As a result, heretofore the pick mechanism has been the only prime mover that acts on the top media sheet when it is being first moved from the stack and separated from the next sheet below it. The pick mechanism also includes a gear train supported by the pick arm and operable to transmit both a rotational force and a downward or normal force to the pick roll. The amount of the downward or normal force applied through the pick roll impacts the amount of frictional force created between the pick roll and the top most sheet. 
     In many media handling devices, the pick mechanism assumes a near horizontal orientation relative to the top of the media stack when the top of the stack is at the upper limit of the pick positions. In the near horizontal orientation, the normal force exerted by the pick mechanism on the stack by rotation of the pick roll may be too low to create the frictional force necessary to overcome both the friction between the top most sheet, the next sheet directly beneath it and the force necessary to buckle the top sheet up the dam. This is termed a ‘fails to feed’ failure mode. Also, in many media handling devices, the pick mechanism assumes a maximum downward sloped orientation relative to the top of the media stack when the top of the stack is at the lower limit of the pick positions. In the maximum downward sloped orientation, the normal force exerted by the pick mechanism on the stack by rotation of the pick roll may be too high, creating so much friction that it may cause what is termed a ‘sheet feed stall’ failure mode to occur. 
     Thus, there is a need for an innovation that will overcome these failure modes due to creation of frictional forces that are too high when the pick mechanism is at the lower limit or too low when the pick mechanism is at the upper limit of the pick position. 
     SUMMARY OF THE INVENTION 
     The present invention meets this need by providing an innovation that allows the top most sheet of the media stack to be acted upon by both the pick mechanism and the stack elevator at the same time or in close unison with one another to move the top most sheet off the media stack, without advancing the next sheet in the stack, in response to sensing the occurrence of a corresponding one of these media handling failure modes. 
     Accordingly, in an aspect of the present invention, a media sheet feeding method for overcoming at least one media handling failure mode includes supporting a media stack on a generally vertically movable elevator, initiating operation of a pick roll in conjunction with a top most sheet of the media stack, sensing whether or not the pick roll is operating in a preselected manner in conjunction with the top most sheet, and moving the elevator vertically in a selected direction through a preset distance, in response to the pick roll not operating in the preselected manner in conjunction with the top most sheet, in order to overcome the occurrence of a media handling failure mode between the pick roll and the top most sheet. The elevator is lowered, in response to the pick roll rotating but the top most sheet not arriving at a sheet arrival sensor, to increase a normal force imposed on the top most sheet to overcome the occurrence of a ‘fails to feed’ failure mode. The elevator is raised, in response to the pick roll not rotating, to decrease the normal force imposed on the top most sheet to overcome the occurrence of a ‘pick roll stall’ failure mode. 
     In another aspect of the present invention, a media sheet feeding method for overcoming at least one media handling failure mode includes supporting a media stack on a generally vertically movable elevator, initiating operation of a pick roll by transmitting rotary motive power thereto and engaging the pick roll with a top most sheet of the media stack in order to pick and separate the top most sheet from the next sheet beneath the top most sheet and feed just the top most sheet from the stack, sensing whether or not the pick roll is rotating and whether or not the top most sheet has arrived at a sheet arrival sensor to determine whether or not a media handling failure mode has occurred, and moving the elevator in a predetermined direction through a preset distance, in response to the pick roll not rotating within a preset time and/or the top most sheet not arriving within a preset time after initiating operation of the pick roll, in order to sufficiently change a normal force imposed on the top most sheet by the pick roll so as to overcome the occurrence of a media handling failure mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale and in some instances portions may be exaggerated in order to emphasize features of the invention, and wherein: 
         FIG. 1  is a schematic representation of a media handling device embodying the sheet feeding system and method of the present invention, showing a stack elevator supporting a media stack with its top most sheet at an upper limit of pick positions relative to a restraint dam, and a pick mechanism at a near horizontal orientation with its pick roll rotating but experiencing a “fails to feed” failure mode relative to the top most sheet of the media stack. 
         FIG. 2  is a schematic representation of the media handling device similar to that of  FIG. 1  but now showing lowering the stack elevator through a short distance as the pick roll of the pick mechanism continuing to rotate overcomes the failure mode depicted in  FIG. 1  by successfully picking the top most sheet from the media stack and pushing it against the restraint dam where it is deflected in an upward direction to a media path. 
         FIG. 3  is a schematic representation of the media handling device similar to that of  FIG. 1  but now showing the stack elevator supporting a depleted media stack with its top most sheet at a lower limit of pick positions relative to the restraint dam, and the pick mechanism at a maximum downward sloped orientation with its pick roll not rotating but instead experiencing a ‘sheet feed stall’ failure mode. 
         FIG. 4  is a schematic representation of the media handling device similar to that of  FIG. 3  but now showing raising the stack elevator through a short distance as the pick roll of the pick mechanism resumes rotation and overcomes the failure mode depicted in  FIG. 3  by successfully picking the top most sheet from the media stack and pushing it against the restraint dam where it is deflected in the upward direction to the media path. 
         FIG. 5  is a flowchart depicting operational steps of the media sheet feeding method of the present invention for overcoming the media handling failure modes depicted in  FIGS. 1 and 3  in the manner depicted in  FIGS. 2 and 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the present invention are shown. Indeed, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numerals refer to like elements throughout the views. 
     Referring now to  FIG. 1 , there is illustrated a schematic representation of a high capacity media handing device, generally designated  10 , of an image forming machine (not shown) embodying the sheet feeding method of the present invention for overcoming multiple media handling failure modes during the feeding of media a sheet at a time from a stack  12  to a downstream media process, such as printing, copying and the like. The media handling device  10  includes a pick mechanism  14  operatively disposed above the media stack  12 , a buckler or restraint dam  16  disposed adjacent to and forwardly of the pick mechanism  14 , an elevator  18  disposed below the pick mechanism  14  and on which the stack  12  of media sheets is loaded and being operable for lifting and lowering the same toward and away from the pick mechanism  14 , and a pair of de-skew or feed-through rollers  20 ,  22  disposed above and aligned with an inclined surface  24  of the restraint dam  16 . The pick mechanism  14  has a pick roll  26  on an end  28 a of an arm  28  pivotally mounted so as to maintain the pick roll  26  on the top most sheet  30  of the stack  12  of media sheets. The top most sheet  30  of the stack  12  is pushed against the inclined surface  24  of the restraint dam  16  by the pick mechanism  14  and deflected in an upward direction to and between the rollers  20 ,  22  at an entry nip  32  to a media path  34  of the image forming machine. 
     The pick arm  28  is free pivoted about a point  36  at least by gravity so as to maintain its pick roll  26  on the top most sheet  30  of the media stack  12 . The pick roll  26  rotates in a clockwise direction, as indicated by arrow  38  and depicted in  FIG. 1 , to move the top most sheet  30  off the stack  12  and into the restraint dam  16 . The pick mechanism  14  may include a drive train  40  operatively mounted on the pick arm  28  for transferring a driving force to the pick roll  26 . The drive train  40  includes a series of gears  42 , shown in dashed outline form in  FIG. 1 , that extend through the pick arm  28  and a plurality of pulleys and belts, as represented by line  44 , for transferring rotary power from a motor  46  to rotate the pick roll  26 . The motor  46  is operatively connected to a power supply  48  which, in turn, is operatively connected to a controller  50 . The motor  46  includes an encoder that is monitored by the controller  50  to control and regulate the speed of the motor  46 . The controller  50  receives data representing the drive current of the motor  46  and may send pick and timing commands to the motor  46  establishing the timing and speeds for picking the top most media sheet  30  from the stack  12 . 
     In operation, a pick command is sent by the controller  50  to the motor  46  causing it to drive rotation of the gears  42  of the drive train  40  within the pick arm  28  which, in turn, causes a downward torque, in a counterclockwise direction as indicated by arrow  52  and viewed in  FIG. 1 , to be applied to the pick arm  28  which is free to pivot about the point  36 . The rotation of the gears  42  further results in rotation of the pick roll  26  in the clockwise direction of arrow  38  as viewed in  FIG. 1 . The foregoing arrangement is typically designed for a ‘no slip’ condition to be produced between an outer tire surface  26   a  of the pick roll  26  and the top most sheet  30 , and the applied torque is intended to cause an increase in a normal force in a downward direction, as indicated by arrow  54  and viewed in  FIG. 1 , between the pick roll  26  and the top most sheet  30 . The top most sheet  30  is pressed with increasing force until the pick roll  26  begins to rotate. As the pick roll  26  rotates, the frictional adhesion between the tire surface of the pick roll  26  and the top media sheet  30  causes the top most sheet  30  to move or be pushed free of the next sheet  56  beneath it and towards the inclined surface  24  of the restraint dam  16 . The moved sheet  30  contacts the inclined surface  24  of the restraint dam  16  so as to temporarily restrain, restrict or hinder further movement of the sheet  30 . This hindrance causes the torque applied by the gears  42  to increase the normal force in the direction of arrow  54  between the pick roll  26  and the sheet  30 . The normal force will continue to build up causing the media sheet  30  to slightly buckle downward. As the buckle grows in size (not shown) the leading end of the sheet  30  then moves up the inclined surface  24  of the restraint dam  16 , concurrently unbuckling as it moves, into the entry nip  32  of the media path  34  between the rollers  20 ,  22 . The pick roll  26  then continues to rotate and feed the sheet  30  to the rollers  20 ,  22 . A sheet arrival sensor  58  connected to the controller  50  may be positioned adjacent to the rollers  20 ,  22  to detect the arrival of the leading edge of the sheet  30  and generate a signal that is received at the controller  50 . 
     However, when the pick arm  28  is in the near horizontal orientation and thus extends near parallel with the top of the media stack  12  as shown in  FIG. 1 , the pick arm  28  is in a geometrical relationship with the top of the media stack  12  that is the least disposed to allow it to increase the normal force, in the direction of arrow  54 , imposed on the stack  12 , as compared to when it is in the downward inclined orientation relative to the top of the media stack  12  as in  FIG. 3  where the pick arm  28  is then in a geometrical relationship with the top of the media stack  12  that is most disposed to allow the pick arm  28  to increase the normal force imposed on the stack  12 . An increased normal force allows the pick arm  28  to move ‘difficult to move’ media sheets. The near horizontal orientation of the pick arm  28  in  FIG. 1 , in which it is constrained from increasing the normal force, occasionally results in the occurrence of a ‘fails to feed’ failure mode of the pick mechanism  14 . That is, the pick roll  26  rotates but, due to the aforementioned geometrical relationship, the normal force (as per arrow  54 ) the pick arm  28  imposes on the top most sheet  30  is too low to create frictional adhesion between the pick roll  26  and the top most sheet  30  sufficient to overcome both the friction between the top most sheet  30  and the sheet  56  directly beneath it and the force necessary to buckle the top most sheet  30  upward along the inclined surface  24  of the restraint dam  16 . 
     Referring now to  FIGS. 2 and 5 , there is illustrated in  FIG. 2  a first feature of the sheet feeding method of the present invention wherein the aforementioned geometrical relationship of the pick arm  28  with the top of the media stack  12  is changed in response to sensing the occurrence of the ‘fail to feed’ failure mode.  FIG. 5  sets forth a plurality of blocks  100 - 114  making up a flowchart of the sheet feeding method of the present invention which includes this first feature. Initially, as per block  100  of the flowchart, the controller  50  sends instructions to the motor  46 , initiating turn-on and thus operation of the motor  46  to drive the pick mechanism  14  and its pick roll  26  to impose a normal force on the stack  12  sufficient to pick and move the top most sheet  30  from the stack  12  toward and up the restraint dam  16 , pass the sheet arrival sensor  58  to the rollers  20 ,  22 . A pick sensor  60  supported onboard the pick motor  46  as well as the sheet arrival sensor  58 , both electrically connected to the controller  50 , will feed various signals to the controller  50  indicating the current status or state of operation of the media handling device  10 . The signal from the motor pick sensor  60  will indicate that the pick roll  26  is rotating. The signal from the sheet arrival sensor  58  will indicate arrival of the leading end of the top most sheet  30  and the trailing edge of sheet  30  or the trailing edge of sheet  56  if two sheets are fed at one time. This combination of these signals needs to be received by the controller  50  within preset times following the time of turn-on of the motor  46  to indicate to the controller  50  that the top most sheet  30  has successfully been fed into the media path entry nip  32  of rollers  20 ,  22 . In other words, the answers to both questions “Is pick roll rotating?” and “Did sheet arrive at sensor?”, as per respective blocks  102 ,  104 , must be YES to indicate that the top most sheet  30  was fed successfully to media path entry nip  32 , as per block  106 . 
     The occurrence of the ‘fail to feed’ failure mode, as per block  108 , is the result when an answer of NO to the question “Did sheet arrive at sensor?”, as per block  104 , is received at block  108 . Thus, the failure of the sheet arrival sensor  58  to sense the arrival of the top most sheet  30  within the allotted time and thus fail to send the appropriate signal to the controller  50 , in combination with the pick sensor  60  detecting rotation of the pick roll  26  and thus sending the appropriate signal to the controller  50  within the allotted time or, in other words, an answer of YES, as per block  102 , provides a combination of states at the controller  50  indicating the occurrence of the ‘fails to feed’ failure mode as per block  108 . This causes the controller  50  to then output a signal commanding a motor  62  operatively connected to the stack elevator  18  to turn-on and move the elevator  18  downward in the direction of arrow  64 , thereby lowering the elevator  18  and therewith the top of the stack  12  by a small distance, d 1 , as can be seen in  FIG. 2  and as per block  110  in  FIG. 5 . This readjustment of the elevation of the top of the stack  12  by lowering it changes the geometrical relationship of the pick arm  28  toward a more inclined orientation with the top of the media stack  12 . This readjustment is just enough to allow the pick arm  28  to generate a sufficient additional normal force, as per arrow  54 , on the top most sheet  30  to grip and advance it upward along the inclined surface  24  of the restraint dam  16  past the sheet arrival sensor  58  and to the media path entry nip  32  in the ordinary expected manner described earlier. The block  110  feeds back to block  104  and the answer or response to the question, “Did sheet arrive at sensor?”, now changes to YES and indicates, as per block  106 , that the sheet was fed successfully. 
     On the other hand, if the pick arm  28  is in the maximum inclined orientation as depicted in  FIG. 3 , the most common failure mode is the ‘sheet feed stall’ failure mode, as mentioned earlier. This occurs when the controller  50  supplies sufficient current to turn on the motor  46  and power the pick roll  26  of the pick mechanism  14  to rotate but there is no rotation of the pick roll  26  sensed by the motor pick sensor  60  of the pick arm  28 . In this case no signal is received from the pick sensor  60  in the preset time so the answer to the question, as per block  102 , “Is pick roll rotating?” is NO. The method then branches from block  102  to block  112 , which indicates that a ‘pick roll stall’ failure mode has occurred. 
     Referring to  FIG. 4 , there is illustrated a second feature of the sheet feeding method of the present invention wherein the aforementioned geometrical relationship of the pick arm  28  to the top of the media stack  12  is changed in response to the occurrence of the ‘sheet feed stall’ failure mode. Again, the occurrence of this failure mode is recognized by the controller  50  when it does not receive the appropriate signal in the allotted time from the onboard pick sensor  60 . Upon recognizing this occurrence as per block  112 , the controller  50  outputs a signal commanding turn-on of the motor  62 , operatively connected to the stack elevator  18 , to move the elevator  18  upward in the direction of arrow  64 , as per block  114 , thereby raising the elevator  18  and therewith the top of the stack  12  by a small distance, d 2 , as can be seen in  FIG. 4 . This readjustment of the elevation of the top of the stack  12  by raising it changes the geometrical relationship of the pick arm  28  with the top of the media stack  12  toward a less inclined orientation. This readjustment is just enough to allow the pick arm  28  to be less aggressive and generate a reduced normal force, as per arrow  54 , on the top most sheet  30  and hence reduced frictional adhesion between the top sheet  30  and the sheet  56  immediately beneath it, thereby allowing only the top sheet  30  to advance upward along the inclined surface  24  of the restraint dam  16  toward the media path entry nip  32 . Additionally the movement of the elevator  18  up without the pick motor  46  being energized will move the top most sheet  30  toward the restraint dam  24  by the rotation of the pick arm  28  up and slightly toward the restraint dam  24 . The block  114  feeds back to the input side of block  102  where the answer to the question “Is pick roll rotating?” now changes to YES as does also the answer to the question of block  104 , “Did sheet arrive at sensor?”, such that the method now branches from block  104  to block  106  indicating a successful feed of the sheet. 
     Another failure mode is the ‘multiple sheet feed’. This occurs when more than one sheet is fed at the same time. Sometimes a set of multiple sheets, usually two, travels through the image forming machine without ever being detected. Other times the sheet may appear to be too long and cause a paper jam. If this is detected and previous sheets from the same input source were not detected as too long the machine may assume the failure mode to be a ‘multiple sheet feed’. Multiple sheet feeds are caused partially by a high normal force  54  increasing the frictional force between sheet  30  and sheet  56  causing sheet  56  to move with sheet  30 . When this happens sheet  56  is typically 1 in. to 1.5 in. later than sheet  30 . This is sensed as a longer than anticipated sheet at the sheet arrival sensor  58 . The trailing edge of sheet  56  is sensed about 0.15 in. plus paper length after the leading edge of sheet  30  is sensed. As mentioned the increase in normal force may cause this and to resolve it the elevator  18  should be raised to lower the normal force. 
     The advantages of the sheet feeding method of the present invention for overcoming media handling failure modes are the following: (1) media that occasionally experience a ‘fails to feed’ failure mode due to the pick arm  28  being at the nearly horizontal orientation can now be fed; and (2) media that occasionally experience a ‘sheet feed stall’ failure mode of the pick mechanism  14  when the pick arm  28  is at the maximum inclined orientation can now be fed; and (3) media that occasionally experience a ‘multiple sheet feed’ failure mode can now be fed. One potential disadvantage, however, is that the algorithm employed by the controller  50  for controlling the operation of the pick mechanism  14  is now somewhat more complex. Nonetheless, implementation the method of the present invention would appear to be a net positive in terms of improved operating efficiency when these multiple advantages are compared with the one disadvantage. 
     The foregoing description of several embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.