Patent Publication Number: US-6663098-B2

Title: Compound kicker in media handling system

Description:
BACKGROUND 
     This invention relates generally to printing devices, and more particularly to techniques for handling media sheets during a pick process. 
     In a printing device, for example a printer partially shown in FIG. 1, a pick roller  101  picks a top sheet  111  atop a stack of media  109  accommodated in an input tray  107  of the printer. In addition, the pick roller  101  advances the top sheet  111  along a media path through a feed zone  113  in the printer for subsequently imprinting images on it. Due to the friction force between adjacent media sheets, several sheets next to the top sheet (hereinafter “next-to-top sheets,” not shown in FIG. 1) also leave the input tray  107  and follow the top sheet  111  into the feed zone  113 . To avoid such a multiple pick, where several sheets are picked and advanced through the feed zone, a separator  105  is mounted in the media path at the entrance  115  of the feed zone  113  approximately opposite the pick roller  101  for stopping further movement of at least part of the next-to-top sheets. Movements of the remaining part of the next-to-top sheets can be stopped by either the separator or printer structures located in the media path and before the separator in a media advancement direction. 
     To avoid affecting subsequent picks of sheets from the input tray during a printing operation, these next-to-top sheets that have moved out of the input tray  107  and stopped somewhere in the feed zone are supposed to be cleared from the feed zone before the next pick process starts. A conventional kicker  103 , which is mounted on the media path adjacent to an edge of the input tray and before the separator  105  in the media advancement direction, is commonly used to kick the next-to-top sheets back to the input tray  107 . Normally, such a conventional kicker  103  is made of rigid materials. 
     Additionally, the kicker is biased in a kicking position by a biasing spring (not shown) before a pick process starts. When the pick process starts, the kicker  103  is activated to move from the kicking position to an activated or feed position, in which the kicker  103  does not disturb the movements of the top sheet  111  or the next-to-top sheets. During the pick process, the kicker  103  will be kept in the feed position by the pick roller  101  or a kicker cam (not shown in FIG. 1) for a period until the leading edge of the top sheet has been fed into the feed zone  113  for a predetermined distance. Then the kicker  103  is released and moves back to the kicking position due to the biasing force to kick the next-to-top sheets back to the input tray  109 , which sheets have moved out of the input tray  109  and have stopped somewhere in the feed zone. 
     Note that in some designs as shown by FIG. 1, the conventional kicker  103  moves back to the kicking position when the trailing edge of the top sheet  111  has not yet passed the feed zone entrance  115  or the kicker  113 . The objective of this design is to try to kick the next-to-top sheets in the current pick process back to the input tray as soon as they are separated so as to avoid sheet-to-sheet dragging that could cause multiple pick. In that case, as shown in FIG. 1, the kicker  103  may interfere with the top sheet  111  being advanced through the feed zone  113  when the kicker  103  moves toward the kicking position. Such interference may increase the amount of stress on the top sheet  111  and therefore may degrade the printing performance. This is because the stress on the top sheet exists until the trailing edge leaves the kicker and may affect the linefeed of the top sheet and consequently the image quality of the top part of the printout. Additionally, the stress from the kicker is applied only at certain areas on the top sheet  111  where the interference occurs and is not uniformly distributed across the media width of the top sheet  111 . Thus, if the amount of stress is increased to a certain extent, the stress may cause the top sheet  111  to skew and affect its linefeed accuracy. As a result, the printing performance can be adversely affected. 
     There are ways of reducing the stress on the top sheet  111  caused by the interference between the kicker  103  and the top sheet  111 . For example, a kicker with a reduced length can be used to reduce the interference because normally a longer kicker will generate more interference. However, in most cases, the user may want the kicker to be as long as possible so as to cover a longer sweeping area. Reducing the length of the kicker may decrease its effectiveness. 
     Alternatively, the stress on the top sheet  111  can be reduced by reducing the biasing force applied to the kicker  103 , for example, by using a biasing spring with a lower stiffness, so as to reduce the kicking force exerted by the kicker  103 . However, reducing the kicking force may cause a less effective kick of the next-to-top sheets by the kicker  103 , especially if there is a heavy stack of next-to-top sheets. 
     Therefore, there is a need for an improved kicking mechanism in a printing device that effectively moves the next-to-top sheets back to the input tray with less interference between the kicking mechanism and the top sheet. 
     SUMMARY 
     According to the present invention, a kicker in a printing device is mounted adjacent an entrance of a feed zone where a pick roller is located for picking a top sheet from an input tray in a pick process. A plurality of next-to-top sheets next to the top sheet move out of the input tray and stop approximately at the entrance of the feed zone during the pick process. The kicker includes a relatively rigid base part for kicking a first portion of the next-to-top sheets back to the input tray and a flexible top part attached to the base part for kicking a second portion of the next-to-top sheets back to the input tray. 
     According to a second aspect of the invention, a media handling system in a printing device includes a pick roller for picking a top sheet from an input tray toward a print zone during a pick process and a kicker mounted adjacent the pick roller. A plurality of next-to-top sheets next to the top sheet are drawn out of the input tray and stop approximately at an entrance of the print zone during the pick process. Furthermore, the kicker includes a relatively rigid base part for kicking a first portion of the next-to-top sheets back to the input tray and a flexible top part attached to the base part for kicking a second portion of the next-to-top sheets back to the input tray. 
     According to a further aspect of the invention, a method is provided for kicking a plurality of next-to-top sheets back to an input tray in a printing device. The next-to-top sheets move out of the input tray and stop approximately at an entrance of a feed zone during a pick process. The method includes the steps of: 
     providing a kicker having a relatively rigid base part and a flexible top part attached to the base part; 
     kicking a first portion of the next-to-top sheets back to the input tray by using the base part of the kicker; and 
     kicking a second portion of the next-to-top sheets back to the input tray by using the top part of the kicker. 
    
    
     Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrates by way of example the principles of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view illustrating that a conventional kicker in a prior art interferes with a top sheet being fed through a feed zone by a pick roller; 
     FIG. 2 is a perspective view of a media handling system in which an exemplary embodiment of the present invention can be used; 
     FIG. 3 is a perspective view of a compound kicker according to an exemplary embodiment of the invention; and 
     FIGS. 4A-4F are side views illustrating different stages of a pick process in which the kicker of FIG. 2 is used. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 illustrates an L-path media picking mechanism that is commonly used in inkjet printers. Although an exemplary embodiment of a compound kicker  203  of the present invention is herein described with reference to such a media picking mechanism, it is understood that the present invention is also applicable to other media picking mechanisms or other printing devices. 
     In FIGS. 2 and 4A, a pair of pick rollers  101  is mounted on a rotatable pick roller shaft  409  for picking a top sheet  111  atop a stack of media  109  accommodated in an input tray  107  of the printer. Furthermore, the pick roller  101  advances the top sheet  111  in a media advancement direction as shown by arrow A in FIGS. 2 and 4A along a media path through the feed zone  113  in the printer for subsequently imprinting images on it. Due to the friction force between adjacent media sheets, several sheets next to the top sheet  117 ,  119 ,  123 ,  125  (see FIGS. 4C,  4 E and  4 F, hereinafter “next-to-top sheets”) also leave the input tray  107  and follow the top sheet  111  into the feed zone  113 . To avoid a multiple pick, a separator  105  with a separating surface  106  is mounted in the media path at the entrance  115  of the feed zone  113  approximately opposite the pick roller  101  for stopping further movement of at least a first several next-to-top sheets  117 . Movements of the remaining part of the next-to-top sheets  119  are stopped by the printer structure  121  located in the media path and before the separator in the media advancement direction A. In addition, a motor (not shown) rotates the pick roller shaft  409  and consequently the pick rollers  101  through a gear train  403  mounted at an end of the pick roller shaft  409 . 
     The pick roller has a “D” profile that can be divided into two portions  403 ,  407  by an activating point  406  and a turning point  405  as shown in FIG.  4 A. Basically, the curved portion  403  that has an arc profile starts from the turning point  405  in a counterclockwise direction as shown by arrow B in FIG.  4 A and ends at the activating point  406 . The flat portion  407  that has a straight-line profile starts from the turning point  405  in the clockwise direction and ends at the activating point  406 . 
     The next-to-top sheets that have moved out of the input tray  107  and stopped somewhere in the feed zone are supposed to be cleared from the feed zone before the next pick process starts. For this purpose, a pair of compound kickers  203  according to an exemplary embodiment of the invention are provided for kicking the next-to-top sheets back to the input tray during a pick process. Each compound kicker  203  is mounted on a rotatable kicker shaft  415  opposite the pick roller  101  but displaced by a distance in a horizontal direction in which the kicker shaft extends. Furthermore, the kickers  203  are positioned in the media path adjacent to an edge of the input tray  107  and before the separator  105  in the media advancement direction such that the next-to-top sheets do not stay in contact with the separator after the kicking process. In addition, the kicker shaft  415  is biased by a spring (not shown) to keep the compound kickers in a kicking position, in which the kickers  203  project substantially perpendicular to the media advancement direction A. In FIG. 2, the kickers can be activated by a kicker cam  411  mounted on the pick roller shaft  409 , and the kicker cam  411  has a profile similar to the pick roller  101  but is oriented at a slightly different angle. In this way, as the pick process just starts but before the pick roller starts picking the top sheet, the kicker cam  411  pressed down a lever portion  417  mounted at an end of the kicker shaft  415  to activate the kickers  203 . 
     FIG. 3 shows the compound kicker  203  according to an exemplary embodiment of the invention that can be used in the media picking mechanism of FIG. 2 as well as other media picking mechanisms or other printing devices. In the exemplary embodiment, the compound kicker  203  basically has a thin, flexible top part  205  in a flat plate shape and a rigid base part  207  in a shape similar to the conventional kicker  103  but with a reduced length. Both parts extend in the same direction perpendicular to the kicker shaft  415  in the exemplary embodiment. Furthermore, a plane surface  208  of the base portion  207  allows the top part  205  to be attached thereon. A pair of projections  211  made of the same material as the base part  207  and mounted to the base part  207  restrict the top part  205  to be in contact with the base part. Alternatively, adhesive materials can be applied between the top part  205  and the base part  207  for fastening them together. In addition, in the exemplary embodiment, the base part  207  is molded together with the kicker shaft  415  so that the kicker  203  can also rotate in the printer. 
     As shown in FIG. 3, in the current application, the length of the base part L 1  is defined as a distance between a center of the kicker shaft and an end  217  of the base part, while the length of the top part L 2  is defined as a distance between the center of the kicker shaft and an end  219  of the top part. 
     In the exemplary embodiment, the length of the base part  207  is designed to be approximately the same as the distance between the kicker shaft  415  and the mid point of the separator  105  in the media advancement direction. The length of the base part  207  is designed to not interfere with the top sheet  111  being fed through the print zone  113  during the kicking process. Furthermore, the length of the base part  207  is designed so that it can catch a main stack  215  of the next-to-top sheets as shown in FIG.  4 D. The main stack  215  of the next-to-top sheets basically includes the next-to-top sheets  119  stopped by the printer structure  121 . The main stack  215  can also include some next-to-top sheets stopped by the separator  105 . 
     On the other hand, the length of the top part  205  is designed to be long enough to catch the next-to-top sheets that are stopped by the separator but not caught by the base part  207  in the kicking process. In the exemplary embodiment, the length of the top part  205  is designed to be approximately the same as a distance between the kicker shaft  415  and the end of the separator away from the kicker shaft  415  in the media advancement direction A. Note all the next-to-top sheets are supposed to stop before a contact point of the picker roller with the separating surface, and the contact point is roughly at the middle of the separating surface. Thus, the length of the top part  205  covers a further distance than any next-to-top sheets are expected to travel during a pick process. Given the length of the base part and the top part, it is noted that the top part of the compound kicker has a first portion  215  protruding outside the base part. 
     It is mentioned that the top part is flexible while the base part is relatively rigid. In the exemplary embodiment, the base part  207  has a relatively high bending rigidity, while the top part has a relatively low bending rigidity. Therefore, the base part can hardly be deformed, while the top part can relatively easily bend over even if only a relatively small amount of force is applied to its end. As a result, the base part provides a relatively large kicking force, while the top part provides a relatively small kicking force. In particular, in the exemplary embodiment, the top part is a polyester film for example the Mylar polyester film available from DuPont Company and is approximately as flexible as transparency materials, while the base part  207  is a molded polycarbonate block that is relatively rigid. 
     FIG. 4A illustrates the compound kicker  203  biased in the kicking position before the pick process starts and the pick roller  101  in a home position  102 . When the pick roller is in its home position, its flat portion  407  is approximately parallel to the separating surface  106  of the separator  105 . It is also noted that the compound kicker  203  does not interfere with the pick roller  101  due to the horizontal offset. 
     In FIG. 4B, as the pick process starts, the pick roller as well as the kicker cam rotates in the counterclockwise direction B in which the pick roller rotates toward the media stack  109  for picking and advancing the top sheet  111 . Before the activating point  406  of the pick roller has reached the top sheet  11 , the compound kicker  203  is activated by the kicker cam  411  and rotates toward a feed position, in which the kicker  203  extends in a direction substantially parallel to the separating surface of the separator. When the activating point  406  contacts the top sheet  111 , the pick roller starts picking the top sheet and advancing the top sheet  111  forward in the media advancement direction. In addition, the friction forces between adjacent sheets start drawing several next-to-top sheets out of the input tray  107 . 
     In FIG. 4C, as the pick roller  101  further rotates in the counterclockwise direction B, the top sheet  111  is advanced into the feed zone  113 , followed by the next-to-top sheets. As the next-to-top sheets further move on in the pick process, first several next-to-top sheets  117  just underneath the top sheet are stopped by the separator  105 . Another portion of the next-to-top sheets  119 , which lies under the first several next-to-top sheets  117 , is stopped by part of the printer structure  121  located in the media path before the separator  105  in the media advancement direction. The compound kicker  203  is further pressed down to its feed position by the kicker cam  411  (see FIG. 2) until it is fully depressed in the media path as shown in FIG.  4 C. 
     In FIGS. 2 and 4D, the turning point  405  has just passed the compound kicker  203 . The kicker cam  411 , which has a profile similar to the pick roller  101 , releases the lever  417  on the kick shaft  415 , and the kicker  203  starts rotating back to its kicking position due to the biasing force provided by the spring (not shown). Furthermore, rotation of the kicker back to the kicking position will kick the next-to-top sheets back to the input tray  107  as further discussed with reference to FIGS. 4E and 4F. 
     It is understood that typically at this stage, the top sheet  111  has reached another feed roller (not shown) in the printer. This feed roller further advances the top sheet to a print zone (not shown) for imprinting images on it. 
     In FIG. 4E, the turning point  405  has passed the compound kicker  203 , and the flat portion  407  of the pick roller now approximately faces the kicker  203 . The flat portion  407  of the pick roller  101  now leaves a space between the compound kicker  203  and the pick roller as well as the top sheet  111 . Without the limitation applied by the curved potion  403  of the pick roller  101 , the compound kicker  203  is free to rotate back to its kicking position. 
     As discussed before, the length of base part  207  is designed to not interfere with the top sheet  111 , which is being fed through the feed zone  113  when the compound kicker  203  is rotating back to the kicking position. However, the top part  205 , specifically the first portion  215  that protrudes outside the base part, is designed long enough to meet the top sheet  111 . Since the top part  205  is made of flexible material, the first portion  215  is bent by the top sheet  111  from the time when it comes into contact with the top sheet  111  and provides a relatively small kicking force. In this way, the interference between the top sheet  111  and the compound kicker  203  and consequently the stress on the top sheet applied by the kicker are reduced as compared to the conventional kicker  103  of FIG.  1 . 
     Furthermore, as shown in FIG. 4E, the rigid base part  207  of the compound kicker  203  kicks the main stack  125  of the next-to-top sheets through a portion of the top part thereabove. It is understood that the main stack of the next-to-top sheets can be relatively thick and thus requires a relatively large kicking force. The rigidity of the base part  207  accordingly allows the compound kicker  203  to provide the necessary kicking force for kicking the heavy main stack back to the input tray  107 . In this way, the effectiveness of the kicking operation is maintained. 
     FIG. 4E also shows the first portion  215  of the top part  205  of the compound kicker  203  in contact with several next-to-top sheets  123  between the top sheet  111  and the main stack  125 . These several next-to-top sheets  123  are to be kicked back to the input tray  107  by the first portion  215  of the top part  205 . 
     In FIG. 4F, the compound kicker  203  has reached its kicking position, with the main stack  215  kicked back to the input tray  107 . Note that the several next-to-top sheets  123  kicked by the first portion of the top part during the kicking process may still cling to the top part  205 . This is because that the top part of the kicker is still bent over by the top sheet  111  that is now being fed by the feed roller (not shown) into the print zone (not shown). When the top sheet  111  has fully passed through the feed zone, the top part  205  bounces back to its kicking position due to its own resilient force and then kicks the several next-to-top sheets  123  back to the input tray (not shown). In addition, since only a small amount of kicking force is needed for kicking back merely one or two sheets, kicking the several next-to-top sheets  123  can be easily done by the flexible top part of the compound kicker. 
     Furthermore, when the pick roller  101  reaches its home position as shown in FIG. 4A, the pick roller stops rotating, and the top sheet  111  is further advanced by the feed roller instead. The pick roller  101  stays in its home position until next pick process starts. 
     Alternatives can be made to the preceding embodiment. For example, instead of overlying atop the base part, the top part can be simply a portion that protrudes outside the base part, just like the first portion  215  alone. Adhesive materials or other mechanism are needed to fasten the top part and the base part together.