Patent Publication Number: US-6984084-B2

Title: Imaging media tray and method

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to loading imaging media in imaging systems such as printers. More particularly the present invention relates to an imaging media tray and a method of use thereof. 
   BACKGROUND OF THE INVENTION 
   An imaging system such as a printer typically includes an imaging media tray comprising a chassis and a cassette which holds the imaging media such as a stack of paper. To assist transmission of the media from the cassette to the printer, a rear wall of the cassette may be formed with a sloping rather than a straight or perpendicular surface. This allows a simplified transmission mechanism to be used comprising a single roller to push the media back against the sloping surface which then deflects the media up the wall and into the printer. Loading of the imaging media into the media tray is accomplished by removing the cassette from the chassis. After the imaging media is placed into the cassette, the cassette is slotted back into the chassis. When this action is performed rapidly there is a tendency to “slam” the cassette into the chassis. Due to the sloping rear surface and the inertia of the media especially when the cassette is inserted with too much force, there is a tendency for the media to ride up the sloping surface giving rise to jamming of the media during transmission thereof to the printer. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a blocking apparatus that prevents the media from moving up the slope even when a cassette is inserted above a certain force. 
   According to one aspect of the present invention there is provided an imaging media tray for an imaging system, said media tray including a media cassette having a sloping end wall, and a blocking means having a blocking mode adapted to prevent imaging media from moving up said sloping end wall at least when said media cassette is being inserted into said imaging system, and an inactive mode to facilitate transmission of said media to said imaging system, wherein said blocking means adopts said inactive mode after said media cassette is inserted into said imaging system. 
   According to a further aspect of the present invention there is provided in an imaging media tray including a media cassette having a sloping end wall, a method for preventing imaging media from moving up said sloping end wall at least when said media cassette is being inserted into an imaging system, said method including the steps of: 
   providing a blocking means having a blocking mode and an inactive mode; 
   setting said blocking means to said blocking mode at least when said media cassette is being inserted into said imaging system; and 
   setting said blocking means to said inactive mode after said media cassette is inserted into said imaging system to facilitate transmission of said media to said imaging system. 
   These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of a preferred embodiment as illustrated in the drawing figures. 

   
     DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings wherein: 
       FIG. 1  shows a perspective view of a media tray including a chassis and cassette; 
       FIG. 2  shows a prior art tray body with the chassis removed; 
       FIG. 3  shows the tray body of  FIG. 2  with the chassis inserted; 
       FIG. 4  shows a perspective view of a blocking mechanism according to the present invention; 
       FIGS. 5A and 5B  show side and rear perspective views respectively of the blocking mechanism in an unloaded position; 
       FIGS. 6A and 6B  show side and rear perspective views respectively of the blocking mechanism in a loaded blocking position; 
       FIGS. 7A and 7B  show side and rear perspective views respectively of the blocking mechanism in a loaded inactive position; 
       FIG. 8  shows a chassis incorporating a blocking mechanism according to the present invention in a position corresponding to  FIGS. 5A and 5B ; 
       FIG. 9  shows a chassis incorporating a blocking mechanism according to the present invention in a position corresponding to  FIGS. 6A and 6B ; and 
       FIG. 10  shows a chassis incorporating a blocking mechanism according to the present invention in a position corresponding to  FIGS. 7A and 7B . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a media tray  10  for an imaging system such as an inkjet printer, including a tray body  11 , a cassette  12  and a chassis  13 . Cassette  12  is adapted to hold imaging media such as a stack of paper. The media (paper) is transferred from cassette  12  to the associated printer via a transmission mechanism associated with chassis  13 . The transmission mechanism typically includes means for lifting the media above the rear wall of the cassette  12  to facilitate transfer of the media from the cassette  12  to the printer. The lifting means is required to lift the media above the straight perpendicular rear wall that would otherwise obstruct the paper path. 
   To simplify the transmission mechanism and avoid using a lifting means, the cassette  12  includes a backwardly sloping rear wall  80  (refer  FIG. 8 ). A sloping rear wall allows a relatively simple transmission mechanism to be used wherein the mechanism includes a single roller, to push the media back against the sloping rear wall  80  which subsequently deflects the media up the rear wall  80  and into the printer. When cassette  12  is inserted into chassis  13  above a certain force there is a tendency due to inertia, for the media to move up the sloping rear wall  80 . This can cause the media to jam during transmission thereof to the associated printer. 
   In an embodiment a blocking mechanism may be fitted to tray body  11  for increasing the probability of correct transmission of imaging media.  FIG. 4  shows a perspective view of the blocking mechanism  40 . The blocking mechanism  40  includes a blocking door  41  pivotably mounted on a base  42 . A pair of blocking elements  43 ,  44  is formed with or mounted on door  41 . Blocking elements  43 ,  44  include blocking faces  45 ,  46  respectively. Door  41  pivots between a blocking position in which blocking faces  45 ,  46  project beyond the sloping rear wall  80  such that they are substantially normal to the floor  81  of cassette  12 , and an inactive position in which blocking faces  45 ,  46  are substantially parallel, flush or recessed with respect to the sloping rear wall  80  of cassette  12 . 
   The blocking mechanism  40  contains a trigger device including a retainer element  47  that is adapted to translate back and forth along a direction in which cassette  12  is inserted into chassis  13 . Retainer element  47  includes a rib  48  at one end and a riser  49  at the other. When cassette  12  is inserted into chassis  13 , it makes contact with rib  48  causing retainer element  47  to translate rearwardly relative to base  42 . One end of a resilient element such as spring  50  is fixed to riser  49 . The other end of spring  50  is fixed to a projection  51  on blocking door  41 . 
   Blocking door  41  is mounted on base  42  such that it is biased to the blocking position at least when cassette  12  is being inserted into chassis  13 . This is done by locating pivot axis  52  relative to the centre of mass of door  41  including blocking elements  43 ,  44 , such that the weight of door  41  causes a rotating torque (anticlockwise in  FIGS. 5A ,  6 A) that biases the door  41  to the blocking position. The pivot axis  52  is also positioned such that a force applied to blocking face  45 ,  46  substantially normally, such as by the media stack moving under inertia when cassette  12  is inserted into chassis  13 , does not give rise to any appreciable rotating torque (clockwise in  FIGS. 5A ,  6 A) that would dislodge it from the blocking position. 
   After a user places media into cassette  12  and slots it into chassis  13 , a leading edge of cassette  12  contacts rib  48  and pushes it back along the media path. Even if cassette  12  is inserted above a certain force the media stack contacts the projecting perpendicular surfaces of blocking faces  45 ,  46  and is prevented from moving beyond blocking faces  45 ,  46 . In this way the stack of media is effectively prevented from riding up sloping rear wall  80 . 
   Meanwhile movement of rib  48  from the start position shown in  FIG. 5A  to the end of travel position shown in  FIG. 6A  causes retainer element  47  to be pushed to the end as well. This causes riser  49  to move to the position shown in  FIGS. 6A and 6B  and spring  50  to be elongated. Elongation of spring  50  exerts a pulling force on the blocking door  41  via projection  51  that overcomes frictional forces and its weight bias, and causes blocking door  41  to rotate to the inactive position shown in  FIGS. 7A and 7B . The frictional forces and elongation of spring  50  act as a delay mechanism that delays rotation of the blocking door to the inactive position. This is exactly what is required to perform the blocking function and then a falling behind the sloping rear wall  80  of cassette  12  to clear a path for the media to move up into the associated printer. 
   Following loading of cassette  12  into chassis  13 , the degree of delay prior to rotation of blocking door  41  to the inactive position may be adjusted by changing spring  50  to one having a heavier or lighter modulus of elasticity, and/or by applying dampening grease (Nye PG-44A Extra Heavy) to moving parts of the blocking mechanism to damp the falling action of blocking door  41  to the inactive position. If the steps triggering the falling action of blocking door  41  are allowed to happen too fast, the blocking faces  45 ,  46  may actually move to the recessed position before they have a chance to block the media. 
   Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.