Abstract:
In one example a bend sensor is disclosed. The bend sensor extends into a media tray. The bend sensor has a tip where a deflection amount of the tip indicates a media parameter.

Description:
BACKGROUND 
       [0001]    Printers typically have at least one input tray and at least one output tray. The printer keeps track of the amount of media and the media size in the input and output trays using sensors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]      FIG. 1  is a block diagram of an example printer. 
           [0003]      FIG. 2A  is a schematic side view of the example printer from  FIG. 1 . 
           [0004]      FIG. 2B  is a schematic side view of the example printer from  FIG. 2A  with media  214  in the media tray. 
           [0005]      FIG. 3  is a schematic side view of another example printer. 
           [0006]      FIG. 4  is a top view of an example printer. 
           [0007]      FIG. 5  is a block diagram of an example printer. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Printers may use at least one sensor to detect the amount of media in an input or output tray. The sensors may be optical sensors that detect the amount of light reflected from the surface of the media. As the height of the media stack gets lower, the amount (or intensity) of light reflected becomes smaller. Therefore the printer can determine how much media is loaded in the media tray by reading the amount of light reflected from the surface of the media. Unfortunately the accuracy of this type of senor can be affected by the gloss level, brightness and/or the color of the media. 
         [0009]    Some printers use mechanical arms that rest on the top sheet of media in the stack. An encoder (or potentiometer) measures the position of the arm to determine the amount of media in the stack. These types of sensors have a number of moving parts and the accuracy may vary due to the mechanical tolerances of the parts. They may also be costly to produce. 
         [0010]    The printer may also have sensors that detect the length and width of the media in the tray. These sensors are typically coupled to the media guides in the tray. There may be a number of optical interrupt sensors to detect multiple widths or an analog encoder that can detect multiple positions of the guides. 
         [0011]    In one example, bend sensors will be used to detect the media properties of media in a media tray. A bend sensor is any sensor whose electrical resistance increases as the sensor is deflected or bent. One example bend sensor is a thin film, single layer, flexible sensor whose electrical resistance increases as the sensor is deflected. Bend sensors may also be known as flex sensors. An example bend sensor is the Flexpoint bend sensor  3000 - 000 . The Flexpoint bend sensor  3000 - 000  is 7.1 mm wide, 76.2 mm long and 0.2 mm thick (see www.flexpoint.com). 
         [0012]    At least one bend sensors may be used to detect different media properties of the media in a media tray. The different media properties may include the number of sheets in a stack of media, the width of the media and the length of the media. One bend sensor may detect the amount of media in the media tray by detecting the height of the stack of media in the media tray. Another bend sensor may be used to determine the width or length of the media in the media tray. 
         [0013]    When detecting the amount of media in the media tray, a bend sensor will be positioned such that one end of the bend sensor extends into the media tray of the printer. The end of the bend sensor will be deflected/bent by different amounts depending on the amount of media in the media tray. The bend sensor will have different resistance at the different deflected/bent positions. The printer can determine how many sheets of media are in the stack by measuring the resistance of the bend sensor. The printer may have a calibration table correlating the amount of electrical resistance with the number of sheets of media in the media tray. 
         [0014]    When detecting the width or length of media in the media tray, a bend sensor may be coupled to the media guides (or directly on the media) in the media tray. As the media guides are moved to accommodate different media widths/lengths, the bend sensor will be deflected by different amounts. The printer may have a calibration table correlating the amount of electrical resistance with the width or length of the media in the media tray. 
         [0015]      FIG. 1  is a block diagram of an example printer. The printer  102  comprises a media tray  104  and a bend sensor  106 . The media tray  104  may also be known as a media bin. The media tray  104  may be an input media tray that holds blank media or an output media tray that holds media after it has been printed on. Some example input media trays are removable and media is loaded into the tray once it has been removed from the printer. The loaded media tray is then re-inserted into the printer. Other example input media trays are fixed in place in the printer and the media is loaded directly into the media tray. In this example only one media tray  104  is shown. In other examples there may be multiple input media trays and/or multiple output media trays. 
         [0016]    The bend sensor  106  may be used to detect different media properties of media in the media tray. The different media properties may include the number of sheets of media in the media tray, the width of the media and/or the length of the media in the media tray. 
         [0017]    When detecting the amount of media in the media tray  104 , the bend sensor  106  will be positioned such that the tip of the bend sensor  106  extends into the media tray  104 . The tip of the bend sensor  106  will be deflected/bent by different amounts depending on the amount of media in the media tray  104 . The bend sensor  106  will have a different resistance at the different deflect/bent positions. The printer  102  can determine how many sheets of media are in the stack by measuring the resistance of the bend sensor  106 . 
         [0018]      FIG. 2A  is a schematic side view of the example printer from  FIG. 1 . Printer  102  comprises a printer body  220 , a bend sensor  206  and a media tray  204 . In this example the media tray  204  has a bottom surface  212  that forms a plane to support a stack of media. The media tray  204  also has a front wall, a back wall and two side walls (the two side walls are not shown for clarity). The bend sensor  206  has a base  210  and a tip  208 . The base  210  is attached to the printer body  220  and the bend sensor  206  extends into the media tray  204  at an angle α with respect to the bottom surface  212  of the media tray  208 . In some examples angle α is between 0 and 90 degrees, for example, 45 degrees. 
         [0019]    In this example, the tip  208  of the bend sensor  206  contacts the bottom surface  212  of the media tray  204  when the media tray  204  is empty (as shown). Because the tip  208  of the bend sensor  206  contacts the bottom surface  212  of the media tray  204 , the bend sensor  206  will be slightly bent/deflected even when the media tray  204  is empty. Even when only one sheet of media is loaded into the media tray  204 , the tip  208  of the bend sensor  206  will be deflected more than when the media tray  204  is empty. This allows for the detection of a single sheet of media loaded in the media tray  204 . 
         [0020]      FIG. 2B  is a schematic side view of the example printer from  FIG. 2A  with media  214  in the media tray. The tip  208  of the bend sensor  206  has been displaced upward by distance d. In some examples an input media tray may hold up to 500 sheets of media. Depending on the weight of the media, 500 sheets may be between 45 to 60 mm thick, for example 50 mm thick. Other Input media trays may hold up to 1,000 sheets of media. Therefore the defection of the tip  208  of the bend sensor from when the input media tray  204  is full to when it is empty (i.e. distance d) be between 45 mm to 120 mm. Output media trays typically hold fewer sheets than input media trays, for example 350 sheets. Therefore the defection of the tip  208  of the bend sensor from when an output media tray  204  is full to when it is empty (i.e. distance d) may be between 0 mm to 40 mm. 
         [0021]      FIG. 3  is a schematic side view of another example printer. Printer  302  includes a printer body  320 , a bend sensor  306  and a media tray  304 . The media tray  304  has a front wall, a back wall and two side walls (the two side walls are not shown for clarity). In this example the media tray  304  has a bottom surface  312  and a number of parallel ribs  322  (only one is shown). The parallel ribs extend along the length of the media tray  304  and the top surface of the ribs form a plane that is above the bottom surface of the media tray  304  such that the ribs support media in the media tray  304 . 
         [0022]    The bend sensor  306  has a base  310  and a tip  308 . The base is attached to the printer base  320 . When the media tray is empty (as shown), the tip  308  of the bend sensor  306  extends below the plane defined by the top surface of the ribs  322  but does not contact the bottom surface  312  of the media tray  304 . Therefore the bend sensor  306  is un-deflected or not bent when the media tray  304  is empty. When media is positioned into the media tray  304  the tip  308  of the bend sensor  306  will be defected/bent to a position above the level of the plane defined by the ribs  322  top surface. In other examples the media tray  304  may not have ribs but the bottom surface of the media tray  304  may have a recess or depression where the tip of the bend sensor  306  can extend into such that the tip of the bend sensor  306  is not deflected when the media tray  304  is empty. 
         [0023]      FIG. 4  is a top view of an example printer. Printer  402  includes a printer body  420 , a bend sensor  406  and a media tray  404 . In this example the media tray  404  has a media guide movable along channel  442  between a number of different positions in the direction shown by arrow  444 . The media guide is shown in two different positions ( 440 A and  440 B). In the first position  440 A a media of a first width will fit in the media tray  404  and in the second position  440 B media of a different, smaller, width will fit in the media tray  404 . 
         [0024]    A bend sensor  406  is attached to the printer body  420  and the tip  408  extends into the media tray  404  and contacts the media guide. As the media guide is moved to different positions in the direction shown by arrow  444 , the tip  408  of the bend sensor  406  is defected to a greater or lesser amount. The printer  402  can determine the location of the media guide and, therefore, the width of the media by measuring the resistance of the bend sensor  406 . In other examples, the bend sensor base may be attached to the media tray  404  instead of the printer body  420 . 
         [0025]    In this example, the media tray  404  has a single media guide. In other examples, there may be two media guides that move in opposite directions to keep the media centered in the media tray  404 . In this example, the tip of the bend sensor  406  moves in a one-to-one relationship with the media guide. In other examples, the tip of the bend sensor  406  may be coupled to the media guide through a reduction linkage such that a given movement of the media guide will produce a proportional but smaller movement of the tip of the bend sensor  406 . 
         [0026]      FIG. 5  is a block diagram of an example printer. Printer  502  includes an input media tray  504 , a first bend sensor  506 A, a pick wheel  552 , a pair of pinch rollers  554 , a pair of feed rollers  556 , a print engine  558 , a controller  560 , a pair of output rollers  562 , an output media tray  505  and a second bend sensor  506 B. A paper path in defined as the path media takes as it travels through the printer from the input tray to the output tray. In this example, the paper path starts at the input media tray  504  where the pick wheel feeds the top sheet of media  515 , from the stack of media  514 , into the pair of pinch rollers  554 . The paper path continues between the pair of feed rollers  556 , underneath the print engine  558 , between the pair of output rollers  562  and into the output media tray  505 . The paper path shown is a simplex paper path, but other paper paths may also be present, for example a duplex paper path. 
         [0027]    As the media passes underneath the print engine, printing fluid is deposited onto the media from the print engine  558 . In this example, the print engine  558  is depicted as an inkjet print engine, but any type of print engine could be used, for example a LaserJet engine or the like. In this example, the printer  502  uses sheets of media as the blank media. In other examples, the printer  502  may use a continuous roll or web of media as the blank media. The web of media may be cut into sheets after the print engine  558  has deposited printing fluid onto the surface of the media. The cut sheets of media are then stacked into an output media tray. In this example, a single input media tray and one output is shown. In other examples, there may be multiple input media trays and/or multiple output media trays. 
         [0028]    The first bend sensor  506 A extends into the input media tray  504 . The tip of the first bend sensor is deflected by different amounts depending on the amount of media  514  loaded into the input media tray  504 . The controller  560  is coupled to the first bend sensor and can determine the resistance of the bend sensor. The controller may contain memory that has a calibration table that correlates the resistance of the bend sensor to the number of media sheets in the stack of media  514 . The controller can determine the amount of media in the stack using the resistance of the bend sensor and the calibration table. 
         [0029]    In one example, there may be only one calibration table for media of a default weight. In other examples there may be multiple calibration tables for media of different weights. In yet another example there may be only one calibration table that has a formula to adjust the number of sheets in the stack of media dependent on the weight of media in the stack. 
         [0030]    The controller may also use the bend sensor to determine when/if the trailing edge of the top sheet of media passes underneath the bend sensor. Once the pick wheel has been activated to feed the top sheet  515  of media into the pair of pinch rollers  554 , the controller can detect when the resistance of the bond sensor deceases when the trailing edge of the top sheet  515  of media goes past the first bend sensor. When the resistance of the first bend sensor  506 A has not decrease after a threshold amount of time, the controller may indicate that the media has jammed or that a miss pick has occurred. 
         [0031]    The second bend sensor  506 B extends into the output media tray  505 . The tip of the second bend sensor is deflected by different amounts depending on the amount of media  514  loaded into the output media tray  505 . The controller  560  is coupled to the second bend sensor and can determine the resistance of the bend sensor. The controller  560  may contain memory that has a calibration table that correlates the resistance of the bend sensor to the number of media sheets in the stack of media  514 . The controller  560  can determine the amount of media in the stack using the resistance of the bend sensor and the calibration table. 
         [0032]    The controller may also use the bend sensor to determine when/if the leading edge of the sheet of media enters the output media tray  505 . As the pair of output rollers  562  move media  566  towards the output media tray  505 , the controller can detect when the resistance of the bend sensor increase when the leading edge of the media  566  goes past the second bend sensor  506 B. When the resistance of the bend sensor has not increased after a threshold amount of time, the controller may indicate that the media has jammed.