Patent Publication Number: US-6986509-B2

Title: Media stack tray status mechanism

Description:
FIELD OF INVENTION 
   The present invention relates to a mechanism for sensing the status of a media stack tray which dispenses media to a printing device. 
   BACKGROUND OF THE INVENTION 
   Modern office printing devices, such as printers, photocopiers and facsimile machines, and the like, typically incorporate a media stack tray which is used to store and dispense media (such as paper) from a media stack to a printing head of the device. The dispensing of the media is usually performed using a dispensing device, such as a pick arm or a roller mechanism of some kind, which selects and dispenses media from the media stack tray. 
   The media stack tray is usually installed within the printing device in such a way that the media stack is not readily visible to a user. Accordingly, the status of the media stack tray, in terms of whether it is empty or loaded with media, is not able to be determined by visual inspection without first removing the media stack tray from the equipment. 
   To overcome the problem described above, it is common for media stack trays to include a mechanism which provides a visual indication of the status of the media stack tray. 
   A mechanism for sensing the status of a media stack tray which dispenses media may be of the type disclosed in U.S. Pat. No. 5,700,003. Here, the mechanism includes an actuator, which itself includes a paper contacting unit and an elastic unit. The elastic unit supplies a force to the actuator so that the paper contacting unit contacts the topmost paper sheet of a stack of paper in the media stack tray and applies a downward force onto the same so that the actuator moves downwardly after the topmost sheet is dispensed. 
   The actuator is connected to a variable resistor so that as the actuator moves downwardly the resistance of the resistor effectively varies according to the height of the paper stack within the media stack tray. The resistance of the resistor is used to determine the status of the media stack tray. 
   Unfortunately, in mechanisms of the type disclosed in U.S. Pat. No. 5,700,003, the paper contacting unit contacts each sheet which is dispensed from the media stack tray. Such contact may interfere with, or indeed damage (for example, by scratching or marking), the paper which is being dispensed from the top of the paper stack. Where the contact is of a type which exerts a force onto the sheet which is being dispensed, the interference may cause the sheet to be skewed during a dispensing cycle. 
   U.S. Pat. No. 6,206,362 describes another media stack status indicator. That indicator also includes a paper contacting unit (in the form of a probe member) which rests on the top of a media stack in a media stack tray (such as a tray). Thus, this arrangement shares similar problems to those described in relation to the mechanism disclosed in U.S. Pat. No. 5,700,003. 
   Another type of mechanism for sensing the status of a media stack tray is disclosed in U.S. Pat. No. 5,236,348. Here, a pivotally mounted indicator is positioned within a housing of the media stack tray. The indicator includes a portion which contacts with a surface of a biased sheet stack platform which is itself movable according to the weight of the media stack on the stack platform. Unfortunately, arrangements of this type have difficulty differentiating between there being no sheets and a few sheets on the stack platform, particularly for media having a light weight. 
   SUMMARY OF THE INVENTION 
   In brief, the invention provides a mechanism for sensing the status of a media stack tray which dispenses media to a printing device, the media stack tray being associated with a dispensing device which dispenses media from the media stack tray. The mechanism includes a probe having at least two positions such that the probe is located in a first position when the media stack tray has an empty status and is located in a second position when the media stack tray has a loaded status. The probe is mounted relative to the media stack tray so that when the media stack tray has a loaded status the media is normally located between the probe and the dispensing device. The mechanism further includes a detector associated with the probe, the detector for detecting the position of the probe. 
   These and other objects of the invention will no doubt become obvious to those of ordinary skill in the art having read the following detailed description of the embodiment illustrated herein. 

   
     DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in relation to various embodiments illustrated in the accompanying drawings. However, it must be appreciated that the following description is not to limit the generality of the above description. 
     In the drawings: 
       FIG. 1  is a side sectional view of a mechanism according to an embodiment of the invention showing the arrangement of the mechanism when the media stack tray has a loaded status; 
       FIG. 2  is a side view of a sectional view of the mechanism according to the embodiment shown in  FIG. 1  showing the arrangement of the mechanism during a dispensing cycle; and 
       FIG. 3  is a side sectional view of a mechanism according to the embodiment shown in  FIG. 1  showing the arrangement of the mechanism when the media stack tray has an empty status. 
   

   DETAILED DESCRIPTION OF AN EMBODIMENT 
     FIGS. 1 ,  2  and  3  illustrate a mechanism  10  for sensing the status of a media stack tray  12 . The media stack tray  12  dispenses media  14  (refer to  FIG. 2  and  FIG. 3 ) from a media stack  16  to a printing device (such as a printer, a copier, a facsimile machine or the like). To aid in the description of an embodiment of the invention the media  14  will be referred to as a “sheet(s)”, such as a sheet of paper. However, it will be appreciated that the media  14  may include a wide range of media from plain paper to special media such as cardboard, print film or the like. 
   As is shown, the media stack tray  12  is associated with a dispensing device  18  (shown here in dashed lines) which dispenses sheets from the media stack tray  12  during a dispensing cycle. In the embodiment illustrated, the dispensing device  18  is a pick arm  20  which is able to select the topmost sheet  22  of the media stack  16  and dispense the selected sheet from the media stack tray  12  during a dispensing cycle. 
   As is shown in  FIGS. 1 and 3 , the mechanism  10  includes a probe  24  and a detector  26  which is associated with the probe  24 . The probe  24  shown here has two positions such that the probe  24  is located in a first position  28  (ref.  FIG. 3 ) when the media stack tray  12  has an empty status, and is located in a second position  30  (refer  FIG. 1 ) when the media stack tray  12  has a loaded status. 
   In an embodiment, the detector  26  is arranged relative to the probe  24  so as to detect the position of the probe  24  in the first position  28 . However, it is envisaged that other arrangements will be possible in which the detector  26  may be arranged so as to detect the probe  24  in the second position  30 , or both the second position  30  and the first position  28 . Of course, in the case where the probe  24  has two positions, although the detector  26  may be arranged so as to detect the position of the probe  24  in the first position  28 , it will be appreciated that when the detector  26  does not detect that the probe  24  is in the first position  28 , then the probe  24  must be in the second position  30 . 
   The probe  24  shown in  FIGS. 1 to 3  includes a shaft  32  which is pivotably mounted to the media stack tray  12  using a pivot  34  (ref.  FIG. 3 ). The illustrated probe  24  also includes a media contacting part  36  which is shown here as a convex surface arranged towards an end of the shaft  32 . 
   As is illustrated in  FIGS. 1 and 2 , the probe  24  is arranged relative to the media stack tray  12  so that when the media stack tray  12  has a loaded status the media stack  16  is normally located between the probe  24  and the dispensing device  18 . As will be described in more detail later, this arrangement results in the lowermost sheet  38  of the media stack  16  bearing against the media contacting part  36  of the probe  24  so as to locate the probe  24  in the second position  30 . Accordingly, when there are plural sheets on the media stack tray  12 , the media contacting part  36  of the probe  24  does not contact the sheet (generally the topmost sheet) which is being dispensed by the dispensing device  18 . Indeed, in the illustrated embodiment, when the media stack tray  12  has a loaded status (and thus the probe  24  is located in the second position  30 ) the probe  24  is flush with the top surface of the media stack tray  12 . 
   As is shown in  FIG. 3 , the illustrated arrangement of the pivotable mounting of the shaft  32  allows the probe  24  to freely rotate from the first position  28  to the second position  30  once the lowermost sheet  38  no longer bears against the media contacting part  36  of the probe  24 . In the illustrated embodiment, the shaft  32  is mounted to the media stack tray  12  so that the probe  24  is situated in a slot  40  in the media stack tray  12  so as to allow the probe  24  to freely rotate therein. 
     FIG. 1  and  FIG. 2  show the mechanism  10  with a loaded media stack tray  12 . More specifically, in  FIG. 1  there is shown a media stack tray  12  having a full media stack  16 , whereas in  FIG. 2  there is shown a media stack tray  12  having a media stack  16  from which one or more sheets have been dispensed. Nevertheless, in both  FIG. 1  and  FIG. 2  the media stack tray  12  has a loaded status. Thus, throughout this specification reference to the term “loaded” is to be understood to be reference to the media stack tray as containing at least one sheet. 
   As described previously, when the media stack tray  12  has a loaded status the media stack  16 , via the lowermost sheer  38 , bears against the media contacting part  36  of the probe  24  so as to locate the probe  24  in the second position  30 . 
   In the illustrated embodiment, the media stack tray  12  is a biased platform  42  which moves upwardly  44  in response to the topmost sheet  22  of the media stack  16  being dispensed from the media stack tray  12 . As a result of the movement of the platform  42 , as the sheets are dispensed from the platform  42  a substantial constant positional relationship is maintained between the topmost sheet  22  of the media stack  16  and the pick arm  20 . Moreover, after the lowermost sheet  38  has been dispensed from the media stack tray  12 , the platform  12  is located at a predetermined position relative to the pick arm  20 , and thus the detector  26 . 
   As described briefly above, in the illustrated embodiment the probe  24  is pivotably mounted to the biased media platform  42 . This is a particularly advantageous arrangement since after the lowermost sheet  38  of the media stack  16  has been dispensed from the media stack tray  12  the platform  42  is located in a predetermined position with respect to the dispensing device  18 . Consequently, the position of the probe  24  relative to the detector  26  will also be predetermined. As a result, the probe  24  is able to be preconfigured so as to render the operation of the mechanism  10  independent of the height of the media stack  16 . Accordingly, in this embodiment of the invention the mechanism  10  is able to accommodate a range of second media stack heights without requiring the geometry (for example, the length) of the probe  24  to be adjusted. 
   The probe  24  is gravitationally biased such that when the media stack tray  12  has an empty status the probe  24  rotates to the first position  28  (refer to  FIG. 3 ). Thus, the probe  24  only rotates from the second position  30  to the first position  28  after the last sheet (in the present case, the lowermost sheet  38 ) no longer bears against the media contacting part  36  of the probe. On the other hand, when a sheet(s) is present in the media stack tray  12 , the lowermost sheet  38  bears against media contacting part  36  so as to prevent the probe  24  from rotating to the first position  28 . Thus, when a sheet(s) is located in the media stack tray the shaft is not located the first position  28 , rather, it is located in second position  30  (refer to  FIGS. 1 and 3 ). 
   In the illustrated embodiment, movement of the probe  24  from the second position  30  to the first position  28  occurs after the trailing edge of the lowermost sheet  38  moves so as to no longer bear against the media contacting part  36  of the probe  24 . In this respect, in the illustrated embodiment once the trailing edge of the lowermost sheet  38  has so moved, the biasing of probe  24  caused the probe  24  to move in a clockwise direction to the first position  28 . 
   According to the embodiment illustrated, when the media stack tray  12  is empty, the probe  24  does not need to be manipulated by a user for the purposes of reloading the media stack tray  12 . Thus, the illustrated probe  24  does not need additional mechanisms for deactivating the probe to allow the media stack tray  12  to be removed from the printing device. 
   Having described the probe  24 , the description will now turn to the detector  26 . In an embodiment, the detector  26  is an opto-sensor, including, for example, a light emitting device (not shown) and a photodetector (not shown), which are arranged so that when the probe  24  is located in the first position  28  a portion of the probe  24  is located between the light emitting device and the photodetector to thereby interrupt a path therebetween. Thus, the location of the probe  24  in the first position  28  is sensed by detector  26  which then causes a signal to be generated which is indicative of the media stack tray  16  having an empty status. 
   In an embodiment of the invention, the detector  26  is connected to a monitoring circuit (not shown) which generates an alarm signal in response to the interruption of the path. The signal may be used to activate a response on a display, or audible device to thereby alert a user to the empty status of the media stack tray  12 . 
   In  FIGS. 1 to 3 , the detector  26  is shown mounted to the pick arm  20 . It is not essential that the detector  26  be mounted to the pick arm  20 . Indeed, any suitable mounting may be used provided that the detector  26  is able to detect the probe  24  being located in the first position  28 . 
   Finally, it will be understood that there may be other variations and modifications to the configurations described herein that are also within the scope of the present invention.