Patent Publication Number: US-7717421-B2

Title: System and method for sensing a media stack from side of stack and delivery path to stack to detect given stack height

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to an image forming apparatus and, more particularly, to a system and method for sensing a media stack from a side of the stack and a side of a delivery path to the stack in order to detect a given stack height and thus when an output bin of the image forming apparatus is full. 
     2. Description of the Related Art 
     Traditional output bin sensing systems in image forming apparatus, such as electrophotographic printers, use a mechanical flag and sensor mechanism to sense when the height of a media stack reaches a predetermined level. When this happens, the system will generate output signals indicating the output bin is full and instruct the user to remove the media stack before proceeding with additional jobs. This system typically includes a mechanical flag type arm that acts on the top of the media stack in the output bin. An example of such a system is disclosed in U.S. Pat. No. 6,279,889 assigned to the assignee of the present invention. 
     Many printers are architected in a reverse “C” format where the media sheet exits in the back of the printer and away from the user. An example of such a printer is disclosed in U.S. Pat. No. 7,292,820 assigned to the assignee of the present invention. The traditional output bin full sensing system has a couple of drawbacks related to the human factors involved in using the output bin of these printers. First, the mechanical flag functions on the top of the media stack where it can impede the user in easily removing the stack from the output bin and pulling it towards the front of the printer. Second, if the media stack is replaced by the user into the output bin, the media stack can easily trap the mechanical flag in way that prevents the mechanical flag from functioning properly and thereby potentially leads to unintended media jams. These issues can lead to even worse human factors issues in an All-In-One (AIO) device where a scanner is positioned above the media stack. 
     Thus, there is a need for an innovation which will satisfactorily overcome the aforementioned drawbacks of the traditional output bin full sensing system without introducing any significant new drawbacks in place thereof. 
     SUMMARY OF THE INVENTION 
     The present invention meets this need by providing an innovation that resolves the above-mentioned drawbacks through sensing when a media stack has reached a given height, such as the height that fills the output bin of an image forming apparatus, by measuring the height of the media stack from a side of the stack, instead of the top of the stack, which side is also the same as a side edge position of a media sheet in the media delivery path to the stack. This approach, in particular, is thus useful in conjunction with a reference edge style media feed system. 
     Accordingly, in an aspect of the present invention, a system for sensing a media stack in order to detect a given height of the stack includes a media sheet stack site and a media contact member movably mounted adjacent to a side of the media sheet stack site in a predetermined state, such as a counterbalanced state, at a home position such that a contact element of the contact member extends into a path of delivery of repetitive media sheets to the stack site where the contact element is exposed to being struck by an edge of media sheets repetitively moving in the delivery path that causes the media contact member to repetitively movably deflect from the home position to a displaced position allowing each media sheet to repetitively pass the contact element of the media contact member and reach the stack site increasing the height of a stack of media sheets at the site, the predetermined state further causing the media contact member to repetitively movably return from the displaced position to the home position after each repetitive media sheet has passed the contact element of the media contact member until the given height of the media stack is reached at which the media contact member cannot return to the home position due to the contact element of the media contact member being unable to extend into the delivery path of the media sheet due to the presence of the media stack. The system further includes a sensor member disposed adjacent to the media contact member and operable to sense movement of the media contact member and in response thereto produce output that distinguishes between the media contact member at the home and displaced positions so as to provide an indication when the media stack is at the given height. 
     In another aspect of the present invention, a method for sensing a media stack in order to detect a given height of the stack includes movably mounting a media contact member adjacent to a side of a media sheet stack site in a predetermined state at a home position, placing a contact element of the media contact member into a path of delivery of a media sheet to the stack site where the contact element is exposed to being struck by an edge of media sheets repetitively moving in the delivery path, movably deflecting the media contact member repetitively from the home position to a displaced position in response to the edge of media sheets striking the contact element of the media contract member, allowing media sheets to repetitively pass the contact element of the media contact member and reach the stack site increasing the height of a stack of media sheets at the stack site, and movably returning the media contact member repetitively from the displaced position to the home position after each repetitive media sheet has passed the contact element of the media contact member until the given height of the media stack is reached at which the media contact member cannot return to the home position due to the contact element of the media contact member being unable to extend into the delivery path of the media sheet due to the presence of the media stack. The sensing method further includes sensing movement of the media contact member between the home and displaced positions, and in response thereto producing an output that distinguishes between the media contact member at the home and displaced positions so as to provide an indication when the media stack is at the given height. 
    
    
     
       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 wherein: 
         FIG. 1  is a schematic perspective view of an output bin of an image forming apparatus in which a sensing system and method of the present invention are employed for media stack side sensing of when the media stack reaches a given height to detect when the output bin is full. 
         FIG. 2  is a schematic side elevational view of a flag and sensor of the system and used by method of the present invention, showing the flag and sensor at a stack side home position when the output bin is not yet full. 
         FIG. 3  is a schematic side elevational view similar to that of  FIG. 2  but now showing the flag and sensor at a stack side deflected position to which the flag is pivotally displaced from its original home position by the force of impact of an individual media sheet on the flag while in the media sheet delivery path to the media stack, the flag being prevented from returning to its original home position as a result of the media stack reaching the given height at which output bin is full. 
         FIG. 4  is a schematic side elevational view similar to that of  FIG. 2  but now showing the media stack being lifted and moved in a removal direction relative to the flag and sensor. 
     
    
    
     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 invention are shown. Indeed, the 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  FIGS. 1-3 , there is illustrated a media output bin, generally designated  10 , of an image forming apparatus, such as an electrophotographic printer. A stack side sensing system, generally designated  12 , of the present invention, operating in accordance with a stack side sensing method of the present invention, is employed at a media sheet stack site  14  in the output bin  10  for sensing when a media stack  16  (see  FIG. 3 ) reaches a given height in order to detect when the output bin  10  is full. A media sheet  18  (see  FIG. 2 ) is discharged by exit rollers  20  of the printer into a media sheet delivery path  22 , as represented by dashed lines in  FIG. 1 , such that the media sheet  18  falls onto the site  14  in the output bin  10 , landing on the media stack  16  and increasing its height. 
     The stack side sensing system  12  located in the output bin  10  includes the media sheet stack site  14  and a media contact member, such as in the form of a mechanical flag  24 , pivotally mounted at  26  located adjacent to a side  14 A of the site  14  in a predetermined, such as a counterbalanced, orientation or state by a predetermined load  28 , such as a weighted portion  24 A of the flag  24  or an external spring or other suitable means. In the counterbalanced state, the flag  24  is normally disposed in an upright home position, as seen in  FIG. 1  and in the solid line form in  FIG. 2 . 
     The flag  24  has an elongated stem element  30  and a contact element  32 . The stem element  30  is pivotally mounted to the side  14 A of the media sheet stack site  14  at the location  26  adjacent to one end  30 A of the stem element  30  such that the stem element  30  normally extends along a reference line  34  which corresponds to an upright side edge  16 A of the stack  16  of media sheets  18  and the edge  18 A of the media sheet  18  as it is delivered along the path to the stack site  14 . The stack  16  is increased in height at the site  14  by repetitive delivery of media sheets  18  along the path  22  to the site  14 . The contact element  32  of the flag  24  has an exposed tip surface portion  32 A which extends or protrudes beyond the reference line  34  and thus into the path  22  of the repetitive delivery of the media sheets  18  to the site  14  when the mechanical flag  24  is at the upright home position. 
     The contact element  32  is exposed to being struck by the edge  18 A of the media sheets  18  repetitively moving in the delivery path  22 . Such repetitive striking of the contact element  32  by the sheet edge  18 A causes the flag  24  to movably or pivotally deflect from the home position, as shown in solid line form in  FIG. 2 , to a displaced position, as shown in dashed line form in  FIG. 2 , allowing each media sheet  18  to repetitively pass the contact element  32  and reach the stack site  14 , increasing the height of the stack  16  of media sheets  18  at the stack site  14 . The predetermined or counterbalanced state of the flag  24  further causes it to movably or pivotally return from the displaced position to the home position after each repetitive media sheet  18  has passed the contact element  32  of the flag  24  until the given height of the media stack  16  is reached at which point the flag  24  cannot return to the home position due to the contact element  32  of the flag  24  being unable to extend or protrude into the delivery path  22  of the media sheet  18  due to the presence of the media stack  16 . 
     As shown in  FIGS. 2-4 , the system  12  also includes a sensor member  36  disposed adjacent to the mechanical flag  24 . The sensor member  36  is operable to sense movement of the flag  24  and produce an output that distinguishes between the flag  24  being at the upright home position and the inclined displaced position. In such manner, the output of the sensor member  36  provides an indication when the stack  16  of media sheets  18  has increased to the given height and that the output bin  10  is full. The sensor member  36  can be of any suitable well-known type, such as in the form of photo-interrupters or other electro-mechanical switches. The flag  24  may be the type that has a shutter mounted thereon that will move with it and block light passage between portions of the sensor member  36  at certain angular positions of the flag  24  but not at other angular positions, with the blocking or non-blocking of light passage causing the sensor member  36  to produce different outputs, which may be of analog or digital form. 
       FIG. 2  shows the sensing flag  24  when the stack  16  has not reached the given height and thus the output bin  10  is not full.  FIG. 3  shows the sensing flag  24  when the stack  16  and thus the output bin  10  are full. Dimension L shown in  FIG. 2  is the amount of interference between the known reference edge line  34  of the media sheet  18  and the media stack  16 . It is preferred that this dimension is sufficient enough to generate a displacement of the flag  24  at the sensor member  36  to cause the photo beam to break reliably. This ideally is in the range of 1-20 mm. Dimension H is the distance from the pivot  26  of the flag  24  to where the sheet  18  strikes the contact element  32  of the flag  24 . It is desired that this distance be large so that a small force on the contact element  32  of the flag  24  creates a large moment at the pivot  26  of the flag  24  to activate the sensor member  36 . This large dimension also makes the design more insensitive to the weight and stiffness of the media. 
     Regarding the forces F x  and F y  shown in  FIG. 2 , as the trailing edge of a media sheet  18  falls from the paper exit rollers  20  onto the sensing flag  24 , the edge  18 A of the sheet  18  strikes the contact element  32  of the flag  24  creating a force on the top thereof. The F x  component of this force causes the moment about the pivot  26  that rotates or pivots the flag  24  and allows the sheet to pass and drop into the stack  16  at the site  14 . The angled surface portion  32 A on the top side of the tip or contact element  32  of the flag  24  allows the trailing edge of the sheet  18  to create the F x  component of the force that actuates the flag  24 . It is desirable that this angle be 45° or less from vertical to ensure proper operation of the system  12 . As the flag  24  rotates or pivots to relieve the interference with the sheet reference edge  34 , the sheet falls into the output bin  10  and the flag  24  returns to its home position either under the influence of gravity due to its inherent counterbalanced load or weight or under a spring load. 
     When the media stack height is achieves the full position, as seen in  FIG. 3 , the flag  24  can no longer rotate or pivot back into the output bin site or its home position. At this point, the beam of the sensor member  36  is made for a long length of time and the printer engine firmware detects that the output bin  10  is full and prompts a user to remove the media stack  16 . The sensing system  12  that detects output bin full by sensing from the side of the stack  16  allows for easy removal and replacement of the stack  16 , as shown in  FIG. 4 . When the user pulls the stack  16  from the output bin  10 , the top of the stack  16  creases a force on the flag  24  having a F x  component that causes a moment about the pivot  26  that rotates or pivots the flag  24  and allows the stack  16  to be removed from the output bin  10 . The other angled surface portion  32 B on the bottom of the contact element  32  allows the top of the stack  16  to create this component of the force that actuates the flag  24 . It is desired that this angle be 135° or more from vertical to ensure proper orientation of the system  12 . As the flag  24  rotates or pivots to relieve the interference with the top of the stack  16 , the user can easily remove the stack  16  from the output bin  10  and the flag  24  returns to its home position either under the influence of gravity or under a spring load. 
     The benefits and advantages of the present invention may be summarized as follows: (1) provides a means of sensing when the output bin is full based upon detecting the height of the stack by sensing from the side of the stack (as opposed to the traditional approach of sensing stack full on the top of the stack); (2) by sensing bin full on the side of the stack, the human factors of removing the stack from and putting the stack back into the output bin can be improved since the user does not have to work the top of the stack out from under a bin full sensing flag; (3) the system is scalable to the desired output capacity of the bin; (4) allows for improved human factors where the paper path is of a reverse “C” architecture; (5) allows for improved human factors where the device is an AIO with a scanner positioned on the top of the printer and impedes the user from removing the stack from the output bin; and (6) geometry allows for flag to easily pivot out of the way under small applied load of falling sheets from the exit rollers or when the stack is removed from the bin. 
     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.