Patent Publication Number: US-8989611-B2

Title: Replaceable unit for an image forming device having a falling paddle for toner level sensing

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to image forming devices and more particularly to a replaceable unit for an image forming device having a falling paddle for toner level sensing. 
     2. Description of the Related Art 
     During the electrophotographic printing process, an electrically charged rotating photoconductive drum is selectively exposed to a laser beam. The areas of the photoconductive drum exposed to the laser beam are discharged creating an electrostatic latent image of a page to be printed on the photoconductive drum. Toner particles are then electrostatically picked up by the latent image on the photoconductive drum creating a toned image on the drum. The toned image is transferred to the print media (e.g., paper) either directly by the photoconductive drum or indirectly by an intermediate transfer member. The toner is then fused to the media using heat and pressure to complete the print. 
     The image forming device&#39;s toner supply is typically stored in one or more replaceable units installed in the image forming device. As these replaceable units run out of toner, the units must be replaced or refilled in order to continue printing. As a result, it is desired to measure the amount of toner remaining in these units in order to warn the user that one of the replaceable units is near an empty state or to prevent printing after one of the units is empty in order to prevent damage to the image forming device. Accordingly, a system for measuring the amount of toner remaining in a replaceable unit of an image forming device is desired. 
     SUMMARY 
     A replaceable unit for an electrophotographic image forming device according to one example embodiment includes a housing having an inner volume forming a reservoir for storing toner. A rotatable shaft is positioned within the reservoir. A paddle is mounted on the shaft and rotatable independent of the shaft. A driving member is rotatable with the shaft and positioned to push the paddle when the shaft rotates. The paddle is free to fall ahead of the driving member. The paddle includes a magnetic element rotatable with the paddle and detectable by a magnetic sensor when the replaceable unit is installed in the image forming device for detecting the motion of the paddle. 
     A replaceable unit for an electrophotographic image forming device according to a second example embodiment includes a housing having an inner volume forming a reservoir for storing toner. A rotatable shaft is positioned within the reservoir. The shaft has an agitator extending therefrom for agitating toner within the reservoir. A paddle is mounted on the shaft and free to rotate independent of the shaft. The agitator is positioned to push the paddle when the shaft rotates. The paddle is free to separate from the agitator. A magnetic element is connected to the paddle to rotate with the paddle and detectable by a magnetic sensor when the replaceable unit is installed in the image forming device for detecting the motion of the paddle. 
     A replaceable unit for an electrophotographic image forming device according to a third example embodiment includes a housing having an inner volume forming a reservoir for storing toner and an outlet port for exiting toner from the replaceable unit. The outlet port includes an opening into the reservoir for transferring toner out of the reservoir. A rotatable shaft is positioned within the reservoir. A paddle is mounted on the shaft and rotatable independent of the shaft. The paddle is positioned to rotate past the opening into the reservoir. A driving member is rotatable with the shaft and positioned to push the paddle when the shaft rotates. The paddle is free to fall ahead of the driving member. A magnetic sensor is mounted on an exterior portion of the housing. The paddle includes a magnetic element detectable by the magnetic sensor for detecting the motion of the paddle and the magnetic sensor is positioned to sense the magnetic element at a point where the paddle oscillates when the toner level in the reservoir is low when the replaceable unit is in an installed position in the image forming device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present disclosure, and together with the description serve to explain the principles of the present disclosure. 
         FIG. 1  is a block diagram depiction of an imaging system according to one example embodiment. 
         FIG. 2  is a schematic diagram of an image forming device according to a first example embodiment. 
         FIG. 3  is a schematic diagram of an image forming device according to a second example embodiment. 
         FIG. 4  is a perspective side view of a toner cartridge according to one example embodiment having a portion of a body of the toner cartridge removed to illustrate an internal toner reservoir. 
         FIG. 5  is a perspective end view of the toner cartridge shown in  FIG. 4 . 
         FIGS. 6A-C  are schematic diagrams of a side view of the toner cartridge illustrating the operation of a falling paddle at various toner levels. 
         FIG. 7A  is a front view of a paddle according to a first example embodiment. 
         FIG. 7B  is a front view of a paddle according to a second example embodiment. 
         FIG. 7C  is a front view of a paddle according to a third example embodiment. 
         FIG. 7D  is a front view of a paddle according to a fourth example embodiment. 
         FIG. 8  is a line graph of a time difference between the detection of a magnetic element of a falling paddle by a start sensor and the detection of the magnetic element by a stop sensor (in seconds) versus an amount of toner remaining in a reservoir (in grams) over the life of one example embodiment of a toner cartridge. 
         FIG. 9  is a bar graph of the number of passes of a falling paddle past a magnetic sensor per rotation of a shaft versus an amount of toner remaining in a reservoir (in grams) over the life of one example embodiment of a toner cartridge overlaid on the graph shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings where like numerals represent like elements. The embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the present disclosure. Examples merely typify possible variations. Portions and features of some embodiments may be included in or substituted for those of others. The following description, therefore, is not to be taken in a limiting sense and the scope of the present disclosure is defined only by the appended claims and their equivalents. 
     Referring now to the drawings and more particularly to  FIG. 1 , there is shown a block diagram depiction of an imaging system  20  according to one example embodiment. Imaging system  20  includes an image forming device  100  and a computer  30 . Image forming device  100  communicates with computer  30  via a communications link  40 . As used herein, the term “communications link” generally refers to any structure that facilitates electronic communication between multiple components and may operate using wired or wireless technology and may include communications over the Internet. 
     In the example embodiment shown in  FIG. 1 , image forming device  100  is a multifunction machine (sometimes referred to as an all-in-one (AIO) device) that includes a controller  102 , a print engine  110 , a laser scan unit (LSU)  112 , one or more toner bottles or cartridges  200 , one or more imaging units  300 , a fuser  120 , a user interface  104 , a media feed system  130  and media input tray  140  and a scanner system  150 . Image forming device  100  may communicate with computer  30  via a standard communication protocol, such as, for example, universal serial bus (USB), Ethernet or IEEE 802.xx. Image forming device  100  may be, for example, an electrophotographic printer/copier including an integrated scanner system  150  or a standalone electrophotographic printer. 
     Controller  102  includes a processor unit and associated memory  103  and may be formed as one or more Application Specific Integrated Circuits (ASICs). Memory  103  may be any volatile or non-volatile memory or combination thereof such as, for example, random access memory (RAM), read only memory (ROM), flash memory and/or non-volatile RAM (NVRAM). Alternatively, memory  103  may be in the form of a separate electronic memory (e.g., RAM, ROM, and/or NVRAM), a hard drive, a CD or DVD drive, or any memory device convenient for use with controller  102 . Controller  102  may be, for example, a combined printer and scanner controller. 
     In the example embodiment illustrated, controller  102  communicates with print engine  110  via a communications link  160 . Controller  102  communicates with imaging unit(s)  300  and processing circuitry  301  on each imaging unit  300  via communications link(s)  161 . Controller  102  communicates with toner cartridge(s)  200  and processing circuitry  201  on each toner cartridge  200  via communications link(s)  162 . Controller  102  communicates with fuser  120  and processing circuitry  121  thereon via a communications link  163 . Controller  102  communicates with media feed system  130  via a communications link  164 . Controller  102  communicates with scanner system  150  via a communications link  165 . User interface  104  is communicatively coupled to controller  102  via a communications link  166 . Processing circuitry  121 ,  201 ,  301  may include a processor and associated memory such as RAM, ROM, and/or NVRAM and may provide authentication functions, safety and operational interlocks, operating parameters and usage information related to fuser  120 , toner cartridge(s)  200  and imaging units  300 , respectively. Controller  102  processes print and scan data and operates print engine  110  during printing and scanner system  150  during scanning. 
     Computer  30 , which is optional, may be, for example, a personal computer, including memory  32 , such as RAM, ROM, and/or NVRAM, an input device  34 , such as a keyboard and/or a mouse, and a display monitor  36 . Computer  30  also includes a processor, input/output (I/O) interfaces, and may include at least one mass data storage device, such as a hard drive, a CD-ROM and/or a DVD unit (not shown). Computer  30  may also be a device capable of communicating with image forming device  100  other than a personal computer such as, for example, a tablet computer, a smartphone, or other electronic device. 
     In the example embodiment illustrated, computer  30  includes in its memory a software program including program instructions that function as an imaging driver  38 , e.g., printer/scanner driver software, for image forming device  100 . Imaging driver  38  is in communication with controller  102  of image forming device  100  via communications link  40 . Imaging driver  38  facilitates communication between image forming device  100  and computer  30 . One aspect of imaging driver  38  may be, for example, to provide formatted print data to image forming device  100 , and more particularly to print engine  110 , to print an image. Another aspect of imaging driver  38  may be, for example, to facilitate the collection of scanned data from scanner system  150 . 
     In some circumstances, it may be desirable to operate image forming device  100  in a standalone mode. In the standalone mode, image forming device  100  is capable of functioning without computer  30 . Accordingly, all or a portion of imaging driver  38 , or a similar driver, may be located in controller  102  of image forming device  100  so as to accommodate printing and/or scanning functionality when operating in the standalone mode. 
       FIG. 2  illustrates a schematic view of the interior of an example image forming device  100 . Image forming device  100  includes a housing  170  having a top  171 , bottom  172 , front  173  and rear  174 . Housing  170  includes one or more media input trays  140  positioned therein. Trays  140  are sized to contain a stack of media sheets. As used herein, the term media is meant to encompass not only paper but also labels, envelopes, fabrics, photographic paper or any other desired substrate. Trays  140  are preferably removable for refilling. User interface  104  is shown positioned on housing  170 . Using user interface  104 , a user is able to enter commands and generally control the operation of the image forming device  100 . For example, the user may enter commands to switch modes (e.g., color mode, monochrome mode), view the number of pages printed, etc. A media path  180  extends through image forming device  100  for moving the media sheets through the image transfer process. Media path  180  includes a simplex path  181  and may include a duplex path  182 . A media sheet is introduced into simplex path  181  from tray  140  by a pick mechanism  132 . In the example embodiment shown, pick mechanism  132  includes a roll  134  positioned at the end of a pivotable arm  136 . Roll  134  rotates to move the media sheet from tray  140  and into media path  180 . The media sheet is then moved along media path  180  by various transport rollers. Media sheets may also be introduced into media path  180  by a manual feed  138  having one or more rolls  139 . 
     In the example embodiment shown, image forming device  100  includes four toner cartridges  200  removably mounted in housing  170  in a mating relationship with four corresponding imaging units  300  also removably mounted in housing  170 . Each toner cartridge  200  includes a reservoir  202  for holding toner and an outlet port in communication with an inlet port of its corresponding imaging unit  300  for transferring toner from reservoir  202  to imaging unit  300 . Toner is transferred periodically from a respective toner cartridge  200  to its corresponding imaging unit  300  in order to replenish the imaging unit  300 . These periodic transfers are referred to as toner addition cycles and may occur during a print operation and/or between print operations. In the example embodiment illustrated, each toner cartridge  200  is substantially the same except for the color of toner contained therein. In one embodiment, the four toner cartridges  200  include black, cyan, yellow and magenta toner, respectively. Each imaging unit  300  includes a toner reservoir  302  and a toner adder roll  304  that moves toner from reservoir  302  to a developer roll  306 . Each imaging unit  300  also includes a charging roll  308  and a photoconductive (PC) drum  310 . PC drums  310  are mounted substantially parallel to each other when the imaging units  300  are installed in image forming device  100 . For purposes of clarity, the components of only one of the imaging units  300  are labeled in  FIG. 2 . In the example embodiment illustrated, each imaging unit  300  is substantially the same except for the color of toner contained therein. 
     Each charging roll  308  forms a nip with the corresponding PC drum  310 . During a print operation, charging roll  308  charges the surface of PC drum  310  to a specified voltage such as, for example, −1000 volts. A laser beam from LSU  112  is then directed to the surface of PC drum  310  and selectively discharges those areas it contacts to form a latent image. In one embodiment, areas on PC drum  310  illuminated by the laser beam are discharged to approximately −300 volts. Developer roll  306 , which forms a nip with the corresponding PC drum  310 , then transfers toner to PC drum  310  to form a toner image on PC drum  310 . A metering device such as a doctor blade assembly can be used to meter toner onto developer roll  306  and apply a desired charge on the toner prior to its transfer to PC drum  310 . The toner is attracted to the areas of the surface of PC drum  310  discharged by the laser beam from LSU  112 . 
     An intermediate transfer mechanism (ITM)  190  is disposed adjacent to the PC drums  310 . In this embodiment, ITM  190  is formed as an endless belt trained about a drive roll  192 , a tension roll  194  and a back-up roll  196 . During image forming operations, ITM  190  moves past PC drums  310  in a clockwise direction as viewed in  FIG. 2 . One or more of PC drums  310  apply toner images in their respective colors to ITM  190  at a first transfer nip  197 . In one embodiment, a positive voltage field attracts the toner image from PC drums  310  to the surface of the moving ITM  190 . ITM  190  rotates and collects the one or more toner images from PC drums  310  and then conveys the toner images to a media sheet at a second transfer nip  198  formed between a transfer roll  199  and ITM  190 , which is supported by back-up roll  196 . 
     A media sheet advancing through simplex path  181  receives the toner image from ITM  190  as it moves through the second transfer nip  198 . The media sheet with the toner image is then moved along the media path  180  and into fuser  120 . Fuser  120  includes fusing rolls or belts  122  that form a nip  124  to adhere the toner image to the media sheet. The fused media sheet then passes through exit rolls  126  located downstream from fuser  120 . Exit rolls  126  may be rotated in either forward or reverse directions. In a forward direction, exit rolls  126  move the media sheet from simplex path  181  to an output area  128  on top  171  of image forming device  100 . In a reverse direction, exit rolls  126  move the media sheet into duplex path  182  for image formation on a second side of the media sheet. 
       FIG. 3  illustrates an example embodiment of an image forming device  100 ′ that utilizes what is commonly referred to as a dual component developer system. In this embodiment, image forming device  100 ′ includes four toner cartridges  200  removably mounted in housing  170  and mated with four corresponding imaging units  300 ′. Toner is periodically transferred from reservoirs  202  of each toner cartridge  200  to corresponding reservoirs  302 ′ of imaging units  300 ′. The toner in reservoirs  302 ′ is mixed with magnetic carrier beads. The magnetic carrier beads may be coated with a polymeric film to provide triboelectric properties to attract toner to the carrier beads as the toner and the magnetic carrier beads are mixed in reservoir  302 ′. In this embodiment, each imaging unit  300 ′ includes a magnetic roll  306 ′ that attracts the magnetic carrier beads having toner thereon to magnetic roll  306 ′ through the use of magnetic fields and transports the toner to the corresponding photoconductive drum  310 ′. Electrostatic forces from the latent image on the photoconductive drum  310 ′ strip the toner from the magnetic carrier beads to provide a toned image on the surface of the photoconductive drum  310 ′. The toned image is then transferred to ITM  190  at first transfer nip  197  as discussed above. 
     While the example image forming devices  100  and  100 ′ shown in  FIGS. 2 and 3  illustrate four toner cartridges  200  and four corresponding imaging units  300 ,  300 ′, it will be appreciated that a monocolor image forming device  100  or  100 ′ may include a single toner cartridge  200  and corresponding imaging unit  300  or  300 ′ as compared to a color image forming device  100  or  100 ′ that may include multiple toner cartridges  200  and imaging units  300 ,  300 ′. Further, although imaging forming devices  100  and  100 ′ utilize ITM  190  to transfer toner to the media, toner may be applied directly to the media by the one or more photoconductive drums  310 ,  310 ′ as is known in the art. 
     With reference to  FIGS. 4 and 5 , toner cartridge  200  is shown according to one example embodiment. Toner cartridge  200  includes a body  204  that includes walls forming toner reservoir  202 . In the example embodiment illustrated, body  204  includes a generally cylindrical wall  205  and a pair of end walls  206 ,  207 . In this embodiment, end caps  208 ,  209  are mounted on end walls  206 ,  207 , respectively such as by suitable fasteners (e.g., screws, rivets, etc.) or by a snap-fit engagement.  FIG. 4  shows toner cartridge  200  with a portion of body  204  removed to illustrate the internal components of toner cartridge  200 . A rotatable shaft  210  extends along the length of toner cartridge  200  within toner reservoir  202 . As desired, the ends of rotatable shaft  210  may be received in bushings or bearings  212  positioned on an inner surface of end walls  206 ,  207 . A drive element  214 , such as a gear or other form of drive coupler, is positioned on an outer surface of end wall  206 . When toner cartridge  200  is installed in the image forming device, drive element  214  receives rotational force from a corresponding drive component in the image forming device to rotate shaft  210 . Shaft  210  may be connected directly or by one or more intermediate gears to drive element  214 . One or more agitators  216  (e.g., paddle(s), auger(s), etc.) may be mounted on and rotate with shaft  210  to stir and move toner within reservoir  202  as desired. In one embodiment, a flexible strip  220  ( FIGS. 6A-6C ), for example a polyethylene terephthalate (PET) material such as MYLAR® available from DuPont Teijin Films, Chester, Va., USA, may be connected to a distal end of agitator(s)  216  to sweep toner from the interior surface of one or more of walls  205 ,  206 ,  207 . 
     An outlet port  218  is positioned on a bottom portion of body  204  such as near end wall  206 . In the example embodiment shown, toner exiting reservoir  202  is moved directly into outlet port  218  by agitator(s)  216 , which may be positioned to urge toner toward outlet port  218  in order to promote toner flow out of reservoir  202 . In another embodiment, exiting toner is moved axially with respect to shaft  210  by a rotatable auger from an opening into reservoir  202 , through a channel in wall  205  and out of outlet port  218 . The rotatable auger may be connected directly or by one or more intermediate gears to drive element  214  in order to receive rotational force. Alternatively, the rotatable auger may be driven separately from shaft  210  using a second drive element to receive rotational force from the image forming device independently from shaft  210 . As desired, outlet port  218  may include a shutter or a cover (not shown) that is movable between a closed position blocking outlet port  218  to prevent toner from flowing out of toner cartridge  200  and an open position permitting toner flow. Shaft  210  and the rotatable auger (if present) are rotated during each toner addition cycle to deliver toner from reservoir  202  through outlet port  218 . 
     A paddle  230  is mounted on shaft  210  and is free to rotate on shaft  210 . In other words, paddle  230  is rotatable independent of shaft  210 . Paddle  230  is axially positioned next to end wall  206  but may be positioned elsewhere in reservoir  202  so long as a magnetic element  240  of paddle  230  is detectable by a magnetic sensor as discussed below. Paddle  230  is spaced from the interior surfaces of walls  205 ,  206 ,  207  so that walls  205 ,  206 ,  207  do not impede the motion of paddle  230 . In the example embodiment illustrated, paddle  230  is axially positioned above the opening from outlet port  218  into reservoir  202  such that the rotational path of paddle  230  passes above the opening from outlet port  218  into reservoir  202 . However, if the toner level for a particular design of reservoir  202  is substantially uniform, paddle  230  may be positioned elsewhere along shaft  210 . Paddle  230  includes a pair of radial mounts  232 ,  234  each having an opening that receives shaft  210 . Alternatively, paddle  230  may include one or more than two mounts. In the embodiment illustrated, stops  236 ,  238  are positioned on opposite axial sides of one or more of radial supports  232 ,  234  to limit the axial movement of paddle  230  along shaft  210 . 
     Paddle  230  includes a magnetic element  240  that rotates with paddle  230  and is detectable by a magnetic sensor for determining an amount of toner remaining in reservoir  202  as discussed in greater detail below. In one embodiment, magnetic element  240  is positioned at an axially outermost portion of paddle  230  near end wall  206  in order to permit detection by a magnetic sensor on end wall  206  (either mounted directly on end wall  206  or indirectly on end wall  206 , such as on end cap  208 ) or on a portion of the image forming device adjacent to end wall  206  when toner cartridge  200  is installed in the image forming device. In one embodiment, paddle  230  is composed of a non-magnetic material and magnetic element  240  is held by a friction fit in a cavity  242  in paddle  230 . For example, paddle  230  may be formed of plastic overmolded around magnetic element  240 . Magnetic element  240  may also be attached to paddle  230  using an adhesive or fastener(s) so long as magnetic element  240  will not dislodge from paddle  230  during operation of toner cartridge  200 . Magnetic element  240  may be any suitable size and shape so as to be detectable by a magnetic sensor. For example, magnetic element  240  may be a cube, a rectangular, octagonal or other form of prism, a sphere or cylinder, a thin sheet or an amorphous object. In another embodiment, paddle  230  is composed of a magnetic material such that the body of paddle  230  forms the magnetic element  240 . Magnetic element  240  may be composed of any suitable magnetic material such as steel, iron, nickel, etc. In one embodiment, body  204  and agitator  216  are composed of a non-magnetic material, such as plastic, in order to permit detection of the position of magnetic element  240  by a magnetic sensor. 
     Paddle  230  is axially aligned on shaft  210  with a driving member  217  mounted on shaft  210  such that paddle  230  is in the rotational path of driving member  217 . In this manner, driving member  217  is able to push paddle  230  when shaft  210  rotates. In the example embodiment illustrated, an agitator  216  serves as driving member  217 ; however, a paddle or other form of extension from shaft  210  may serve as the driving member  217 . In one embodiment, shaft  210  and driving member  217  rotate at a substantially constant rotational speed when driven by drive element  214 . Driving member  217  pushes a rear surface  230 A of paddle  230 . Paddle  230  may include ribs or other predefined contact points on its rear surface  230 A for engagement with driving member  217 . 
       FIGS. 6A-6C  schematically depict the relationship between paddle  230  and driving member  217 .  FIGS. 6A-6C  depict a clock face in dashed lines along the rotational path of paddle  230  in order to aid in the description of the operation of paddle  230 . When toner reservoir  202  is relatively full as depicted in  FIG. 6A , toner  203  present in reservoir  202  prevents paddle  230  from rotating freely about shaft  210 . Instead, paddle  230  is pushed through its rotational path by driving member  217  when shaft  210  rotates. As a result, when toner reservoir  202  is relatively full as shaft  210  rotates, the rotational motion of paddle  230  follows the rotational motion of driving member  217 . Toner  203  prevents paddle  230  from advancing quicker than driving member  217 . 
     As the toner level in reservoir  202  decreases as depicted in  FIG. 6B , as paddle  230  is pushed through the upper vertical position of rotation (the “12 o&#39;clock” position) by driving member  217 , paddle  230  tends to separate from driving member  217  and fall faster (toward the “3 o&#39;clock” position) than driving member  217  is being driven due to the weight of paddle  230 . As a result, paddle  230  may be referred to as a falling paddle. Paddle  230  falls forward under its own weight until a front face  230 B of paddle  230  contacts toner  203 , which stops the rotational advance of paddle  230 . In this manner, paddle  230  remains substantially stationary on top of (or slightly below the surface of) toner  203  until driving member  217  catches up with paddle  230 . When driving member  217  advances and re-engages with rear surface  230 A of paddle  230 , driving member  217  resumes pushing paddle  230  through its rotational path. 
     When the toner level in reservoir  202  gets low as depicted in  FIG. 6C , paddle  230  tends to fall forward away from driving member  217  as paddle passes the “12 o&#39;clock” position and tends to swing all the way down to the lower vertical position of its rotational path (the “6 o&#39;clock” position). Depending on how much toner  203  remains, paddle  230  may tend to oscillate back and forth in a pendulum manner about the “6 o&#39;clock” position until driving member  217  catches up to resume pushing paddle  230 . As a result, it will be appreciated that the rotational motion of paddle  230  relates to the amount of toner  203  remaining in reservoir  202 .  FIGS. 6A-6C  show shaft  210  rotating in a clockwise direction when viewed from end wall  206 ; however, the direction of rotation may be reversed as desired. 
     Paddle  230  has minimal rotational friction other than its interaction with toner  203  in reservoir  202 . As a result, shaft  210  provides radial support for paddle  230  but does not impede the rotational movement of paddle  230 . Paddle  230  may be weighted as desired in order to alter its rotational movement. Paddle  230  may take many shapes and sizes as desired. For example,  FIG. 7A  illustrates the paddle  230  shown in  FIGS. 4 and 5 . In this embodiment, front face  230 B of paddle  230  is substantially planar and normal to the direction of motion of paddle  230  (parallel to shaft  210 ) to allow front face  230 B of paddle  230  to strike toner  203  as paddle  230  falls. In an alternative embodiment, front face  230 B of paddle  230  is angled with respect to the direction of motion of paddle  230  (angled with respect to shaft  210 ). As shown in  FIG. 7A , paddle  230  may include one or more weights  231  mounted on paddle  230  and positioned relative to an axis of rotation  239  of paddle  230  as desired to control the rotational movement of paddle  230 .  FIG. 7B  illustrates a V-shaped paddle  1230  having a front face  1230 B forming a concave portion of the V-shaped profile for directing toner  203  away from end wall  206  and into outlet port  218 .  FIG. 7C  illustrates a paddle  2230  having a comb portion  2230 C for decreasing the friction between paddle  2230  and toner  203 .  FIG. 7D  illustrates a paddle  3230  having a front face  3230 B having a smaller surface area as compared with front face  230 B of paddle  230  in order to reduce the drag through toner  203 . 
     One or more magnetic sensors  250  positioned on end wall  206  of toner cartridge  200  or positioned on a portion of the image forming device adjacent to end wall  206  when toner cartridge  200  is installed in the image forming device may be used to determine the amount of toner  203  remaining in reservoir  202  by sensing the motion of paddle  230  as shaft  210  rotates. Magnetic sensor(s)  250  may be any suitable device capable of detecting the presence or absence of a magnetic field. For example, magnetic sensor(s)  250  may be a hall-effect sensor, which is a transducer that varies its electrical output in response to a magnetic field. Two magnetic sensors  250 A,  250 B are depicted in  FIGS. 6A-6C . A first magnetic sensor  250 A is positioned between about the “5 o&#39;clock” position and about the “7 o&#39;clock” position, such as at about the “6 o&#39;clock” position as shown. An optional second magnetic sensor  250 B is positioned between about the “2 o&#39;clock” position and about the “4 o&#39;clock” position. In the example embodiment illustrated, magnetic sensor  250 B is positioned at about the “3 o&#39;clock” position. 
       FIG. 5  shows magnetic sensor  250 A positioned on an outer surface of end wall  206 . In this embodiment, magnetic sensor  250 A is in electronic communication with processing circuitry  201  of toner cartridge  200 , which may also be mounted on end wall  206  (either directly on the outer surface of end wall  206  or indirectly on end wall  206 , such as on end cap  208 ). Processing circuitry  201  and/or magnetic sensor  250 A contains one or more electrical contacts  201 A that contact corresponding electrical contact(s) in the image forming device when toner cartridge  200  is installed in the image forming device to facilitate communication with controller  102 . Magnetic sensor(s)  250  and processing circuitry  201  may be positioned on other portions of body  204  as desired so long as magnetic sensor(s)  250  are able to detect the presence of magnetic element  240  of paddle  230  at a point in the rotational path of paddle  230 . For example, in another embodiment, magnetic element  240  is positioned along the outer radial edge of paddle  230  and magnetic sensor  250 A is positioned along the bottom of the outer surface of wall  205 . 
     In one embodiment, two magnetic sensors  250 A and  250 B are used to determine an amount of toner  203  remaining in reservoir  202 . Magnetic sensor  250 B is positioned to sense the presence of magnetic element  240  as paddle  230  begins to move away from driving member  217  once the toner level in reservoir  202  is low enough to allow paddle  230  to advance ahead of driving member  217 . Magnetic sensor  250 A is aligned at or near the lowest center of gravity of paddle  230  to sense the presence of magnetic element  240  near the lowest center of gravity of paddle  230  where paddle  230  oscillates when the toner level in reservoir  202  is low. In this embodiment, magnetic sensors  250 A and  250 B provide time stamp data used by controller  102  or a processor in communication with controller  102 , such as a processor of processing circuitry  201 , to determine how long it takes paddle  230  to pass from magnetic sensor  250 B to magnetic sensor  250 A during rotation of shaft  210 . In this manner, magnetic sensor  250 B may be referred to as the start sensor and magnetic sensor  250 A may be referred to as the stop sensor. 
       FIG. 8  shows a graph of the time difference ΔT between the detection of magnetic element  240  of paddle  230  by the start sensor and the detection of magnetic element  240  by the stop sensor (in seconds) during rotation of shaft  210  versus the amount of toner  203  remaining in reservoir  202  (in grams) over the life of one example embodiment of toner cartridge  200 . The graph is divided into three “Zones” to help illustrate the operation of paddle  230 . In Zone 1, reservoir  202  is relatively full of toner  203  such as depicted in  FIG. 6A . In Zone 1, paddle  230  moves at the same speed as driving member  217  due to the resistance provided by toner  203 . As a result, the time difference ΔT values in Zone 1 reflect the rotational speed of shaft  210  and driving member  217 . In the example embodiment illustrated in  FIG. 8 , shaft  210  was rotated at 100 RPM (0.6 seconds per revolution) and magnetic sensors  250 A and  250 B were separated by 90 degrees resulting in a ΔT of about 0.15 seconds in Zone 1. 
     In Zone 2, the toner level in reservoir  202  is low enough that paddle  230  falls forward ahead of driving member  217  after paddle  230  passes the “12 o&#39;clock” position such as depicted in  FIG. 6B . In Zone 2, paddle  230  falls forward away from driving member  217  and reaches the start sensor ahead of driving member  217 . Paddle  230  then rests on toner  203  in reservoir  202  between the start sensor and the stop sensor until driving member  217  catches up with paddle  230  and resumes pushing paddle  230 . As a result, the time difference ΔT values in Zone 2 increase with respect to the ΔT values in Zone 1 due to the arrival of paddle  230  at the start sensor ahead of driving member  217 . 
     In Zone 3, the toner level in reservoir  202  is low such as depicted in  FIG. 6C . In Zone 3, paddle  230  falls forward away from driving member  217  and passes both the start sensor and the stop sensor as a result of its own inertia without needing to be pushed by driving member  217 . As a result, the time difference ΔT values in Zone 3 reflect the rotational speed of paddle  230  as it falls ahead of driving member  217 . The time difference ΔT values in Zone 3 are less than the ΔT values in Zones 1 and 2. The ΔT values in Zone 3 continue to decrease as the toner level in reservoir  202  decreases due to decreased resistance to paddle  230  as paddle  230  falls. 
     The amount of toner  203  remaining in reservoir  202  at the transitions from Zone 1 to Zone 2 and from Zone 2 to Zone 3 may be determined empirically for a particular toner cartridge design. As a result, the detection of these transitions may be used to determine the amount of toner  203  remaining in reservoir  202 . Further, the nearly linear decrease in ΔT values in Zone 3 can be converted to an amount of toner  203  remaining in reservoir  202  providing a measurement of the toner  203  remaining when reservoir  202  is near empty. When the toner level is in Zones 1 and 2 between the transitions from Zone 1 to Zone 2 and from Zone 2 to Zone 3, the toner level in reservoir  202  can be approximated based on an empirically derived feed rate of toner  203  from toner reservoir  202  into the corresponding imaging unit. For example, in one embodiment, it has been observed that the feed rate of toner  203  from reservoir  202  decreases linearly as the toner level in reservoir  202  decreases. The feed rate of toner  203  from reservoir  202  may be measured as the mass of toner delivered from reservoir  202  per each toner addition cycle. The amount of rotation of and geometry of agitator(s)  216  and the rotatable auger (if present) determine how much toner  203  is fed per toner addition cycle. It will be appreciated by those skilled in the art that the use of a rotatable auger to exit toner  203  from reservoir  202  helps control the precision of the feed rate of toner  203  exiting toner cartridge  200 . The linear decrease in the feed rate of toner  203  from reservoir  202  is due to the decrease in density of the toner  203  in reservoir  202  as the height of toner  203  decreases. As a result, the toner level in reservoir  202  in Zone 1 can be approximated by starting with the initial amount of toner  203  supplied in reservoir  202  and reducing the amount of toner  203  in reservoir  202  per each toner addition cycle based on the empirically determined feed rate. The estimated amount of toner remaining may be reset when the transition from Zone 1 to Zone 2 is detected based on the empirically determined amount of toner remaining when this transition occurs. The toner level in reservoir  202  in Zone 2 can then be approximated based on the empirically determined feed rate. The estimated amount of toner remaining may be reset again when the transition from Zone 2 to Zone 3 is detected based on the empirically determined amount of toner remaining when this transition occurs. The ΔT values detected in Zone 3 may then be converted to an amount of toner  203  to provide an estimate of the amount of toner  203  remaining in reservoir  202  until toner cartridge  200  is empty. In one embodiment, reservoir  202  is deemed empty or near empty and a message indicating that reservoir  202  is empty or near empty is displayed on user interface  104  and/or display monitor  36  when the ΔT values detected fall below a predetermined value. 
     The transitions from Zone 1 to Zone 2 and from Zone 2 to Zone 3 depend on such factors as the geometry of paddle  230 , the friction between paddle  230  and shaft  210 , the weight of paddle  230  and the rotational speed of shaft  210 . For example, increasing the weight of paddle  230  tends to make the transitions from Zone 1 to Zone 2 and from Zone 2 to Zone 3 occur at greater toner amounts (i.e., the transition points shown in  FIG. 8  would move to the right). Decreasing the weight of paddle  230  tends to have the opposite effect. Further, if shaft  210  is rotated too fast (e.g., at speeds above about 200-300 RPM), paddle  230  may not fall away from driving member  217  thereby inhibiting the ability to use the time difference ΔT values to determine the amount of toner remaining in reservoir  202 . 
     As mentioned above, when the toner level in reservoir  202  is very low, paddle  230  may tend to oscillate back and forth about the “6 o&#39;clock” position until driving member  217  catches up to resume pushing paddle  230 . As a result, the stop sensor may sense magnetic element  240  multiple times as paddle  230  oscillates before the start sensor once again senses magnetic element  240 . The extra passes of magnetic element  240  of paddle  230  past the stop sensor may be ignored by software executed by controller  102  (or another processor processing the data from magnetic sensors  250 A and  250 B). 
     It will be appreciated that shaft  210  may start and stop its rotation at random times and at random points along the rotational path of shaft  210 . As a result, in Zones 1 and 2, paddle  230  may be positioned between the start sensor and the stop sensor when shaft  210  stops rotating potentially producing an extremely large ΔT value since paddle  230  won&#39;t reach the stop sensor until shaft  210  rotates again. In Zone 3, on the other hand, paddle  230  tends to fall through both the start sensor and the stop sensor. In one embodiment, shaft  210  is rotated at least about 1.5 revolutions (540 degrees) each time it rotates in order to ensure that paddle  230  passes both the start sensor and the stop sensor at least once per toner addition cycle. 
     In one embodiment, one magnetic sensor  250 A is used to determine an amount of toner  203  remaining in reservoir  202  (without magnetic sensor  250 B). Magnetic sensor  250 A is aligned at or near the lowest center of gravity of paddle  230  to sense the presence of magnetic element  240  near where paddle  230  oscillates when the toner level in reservoir  202  is low. The number of passes of paddle  230  past magnetic sensor  250 A per each revolution of shaft  210  may be correlated to the amount of toner  203  in reservoir  202  when the toner level is low. 
       FIG. 9  shows a graph of the number of passes of paddle  230  past magnetic sensor  250 A per rotation of shaft  210  versus the amount of toner  203  remaining in reservoir  202  (in grams) over the life of one example embodiment of toner cartridge  200  overlaid on the graph shown in  FIG. 8 . Before the toner level in reservoir  202  is low such as depicted in  FIGS. 6A and 6B , paddle  230  passes magnetic sensor  250 A once per revolution of shaft  210 . Specifically, the resistance provided by toner  203  in reservoir  202  prevents paddle  230  from reaching magnetic sensor  250 A ahead of driving member  217 . Once the toner level in reservoir  202  is low, however, as depicted in  FIG. 6C  paddle  230  begins to oscillate or swing in a pendulum manner past magnetic sensor  250 A more than one time per revolution of shaft  210 . As the toner level decreases, the number of passes of paddle  230  past magnetic sensor  250 A per revolution of shaft  210  increases as a result of the decreased resistance from toner  203 . The number of passes of paddle  230  past magnetic sensor  250 A per revolution of shaft  210  may reach twelve or more when the toner level in reservoir  202  is very low depending on the speed of shaft  210  and the swing period of paddle  230 . In one embodiment, reservoir  202  is deemed empty or near empty and a message indicating that reservoir  202  is empty or near empty is displayed on user interface  104  and/or display monitor  36  when the number of passes of paddle  230  past magnetic sensor  250 A per revolution of shaft  210  exceeds a predetermined value (e.g., four passes per revolution, twelve passes per revolution, etc.). 
     It will be appreciated from  FIG. 9  that counting or monitoring the number of passes of paddle  230  past magnetic sensor  250 A provides an indication of the amount of toner  203  remaining in reservoir  202  when the toner level is low (i.e., when paddle  230  passes magnetic sensor  250 A more than once per revolution of shaft  210 ). Before the toner level is low (i.e., when paddle  230  passes magnetic sensor  250 A once per revolution of shaft  210 ), the toner level in reservoir  202  can be approximated based on the empirically determined feed rate of toner  203  from toner reservoir  202  into the corresponding imaging unit as discussed above. As a result, the toner level in reservoir  202  can be approximated by starting with the initial amount of toner  203  supplied in reservoir  202  and reducing the amount of toner  203  in reservoir  202  per each toner addition cycle based on the empirically determined feed rate. This estimation of the toner level in reservoir  202  may be used until magnetic sensor  250 A detects paddle  230  passing more than once during a revolution of shaft  210 . Once paddle  230  begins passing magnetic sensor  250 A more than once per revolution of shaft  210 , the number of pulses detected by magnetic sensor  250 A per revolution of shaft  210  may be used to determine the amount of toner  203  remaining in reservoir  202 . 
     Where a single magnetic sensor  250 A is used, in one embodiment, shaft  210  is driven at a relatively low speed such as, for example, from less than 10 RPM to about 80 RPM including all increments and values therebetween such as about 40 RPM or less in order to allow paddle  230  to oscillate past magnetic sensor  250 A more than once per revolution of shaft  210  when reservoir  202  has little toner remaining before driving member  217  resumes pushing paddle  230 . The slower shaft  210  rotates, the more paddle  230  may oscillate before driving member  217  catches up to paddle  230 . 
     If shaft  210  rotates at a relatively high speed such as, for example, greater than about 80 RPM, paddle  230  may not have time to oscillate past magnetic sensor  250 A before driving member  217  catches up or paddle  230  may not fall away from driving member  217 . However, regardless of the speed of shaft  210 , the number of oscillations of paddle  230  past magnetic sensor  250 A may be measured when shaft  210  is stopped. As a result, in another embodiment, shaft  210  is rotated at a speed of at least about 40 RPM and stopped periodically in order to collect oscillation data. It will be appreciated that in this embodiment if driving member  217  is positioned near the “6 o&#39;clock” position when shaft  210  stops, driving member  217  may interfere with the oscillation data of paddle  230 . Accordingly, where shaft  210  is driven at speed above about 40 RPM and stopped periodically to collect oscillation data, it is preferred to avoid rotating shaft  210  a full 360 degree rotation or a multiple thereof each time shaft  210  rotates (i.e., 360 degrees, 720 degrees, 1080 degrees, etc.), otherwise driving member  217  may tend to be positioned near the “6 o&#39;clock” position every time shaft  210  stops thereby interfering with the oscillation data of paddle  230 . Similarly, if shaft  210  is rotated in half rotation increments each time shaft  210  rotates (i.e., 180 degrees, 540 degrees, 900 degrees, etc.), driving member  217  may tend to be positioned near the “6 o&#39;clock” position every other time shaft  210  stops. Accordingly, in one embodiment where shaft  210  is driven at speed above about 40 RPM and stopped periodically to collect oscillation data, shaft  210  is rotated at least about 10 degrees more or less than any full or half rotation (e.g., between about 190 degrees and about 350 degrees, between about 370 degrees and about 530 degrees, between about 550 degrees and about 710 degrees, between about 730 degrees and about 890 degrees, etc.) each time shaft  210  rotates in order to prevent driving member  217  from repeatedly stopping near the “6 o&#39;clock” position and interfering with the oscillation data of paddle  230 . For example, in the example embodiment illustrated in  FIGS. 8 and 9 , shaft  210  was rotated 550 degrees at 100 RPM and paused for about 3 seconds between each 550 degree rotation in order to allow paddle  230  to swing. 
     In addition to the rotational speed of shaft  210 , the point at which the transition from Zone 2 to Zone 3 occurs (the sensing range when one magnetic sensor  250 A is used) and the swing period of paddle  230  depend on the weight of paddle  230  and the radius of gyration of paddle  230 . As discussed above, paddle  230  may be weighted using one or more optional weights  231  in order to provide a desired weight distribution to define the weight and radius of gyration of paddle  230 . Specifically, control of the sensing range by the weight of paddle  230  and the center of gravity of paddle  230  is governed by the initial energy state at the onset of the fall of paddle  230  for a given weight and radius of gyration of paddle  230 . As paddle  230  encounters toner  203  in reservoir  202  with each oscillation, this energy is diminished by an amount that is a function of the mass of toner  203  encountered by paddle  230  during that oscillation. This decrease in energy occurs until paddle  230  stops swinging (either through encounters with toner  203  or through other frictions or resistance such as the energy lost in the frictional interface between paddle  230  and shaft  210 ). In addition to the sensing range, the number of oscillations of paddle  230  that occur when reservoir  202  is empty (the sensing resolution when one magnetic sensor  250 A is used) also depends on the weight distribution of paddle  230 . 
     Accordingly, an amount of toner remaining in a reservoir may be determined by sensing the rotational motion of a falling paddle, such as paddle  230 , mounted on a rotatable shaft and rotatable independent of the shaft within the reservoir. Because the motion of paddle  230  is detectable by a sensor outside of reservoir  202 , paddle  230  may be provided without an electrical or mechanical connection to the outside of body  204  (other than shaft  210 ). This avoids the need to seal an additional connection into reservoir  202 , which could be susceptible to leakage. Because no sealing of paddle  230  is required, no sealing friction exists that could alter the motion of paddle  230 . Further, positioning the magnetic sensor(s) outside of reservoir  202  reduces the risk of toner contamination, which could damage the sensor(s). The magnetic sensor(s) may also be used to detect the installation of toner cartridge  200  in the image forming device and to confirm that shaft  210  is rotating properly thereby eliminating the need for additional sensors to perform these functions. 
     While the example embodiments illustrated show magnetic element  240  positioned on the body of paddle  230  in line with front face  230 B of paddle  230  and the center of gravity of paddle  230 , it will be appreciated that magnetic element  240  may be offset angularly from paddle  230  as desired. For example, magnetic element  240  may be positioned on an arm or other form of extension that is angled with respect to paddle  230  and connected to paddle  230  to rotate with paddle  230 . For example, where two magnetic sensors  250 A,  250 B are used to collect time difference ΔT values, if magnetic element  240  is offset 90 degrees ahead of paddle  230 , magnetic sensor  250 A is positioned between about the “8 o&#39;clock” position and about the “10 o&#39;clock” position, such as at about the “9 o&#39;clock” position, to detect when paddle  230  is at or near its lowest center of gravity where paddle  230  oscillates and magnetic sensor  250 B is positioned between about the “5 o&#39;clock” position and about the “7 o&#39;clock” position, such as at about the “6 o&#39;clock” position, to detect when paddle  230  begins to fall away from driving member  217 . Similarly, where one magnetic sensor  250 B is used to collect oscillation data, if magnetic element  240  is offset 180 degrees from paddle  230 , magnetic sensor  250 A is positioned between about the “11 o&#39;clock” position and about the “1 o&#39;clock” position, such as at about the “12 o&#39;clock” position, to detect when paddle  230  is at or near its lowest center of gravity where paddle  230  oscillates. Further, while the examples discussed above sensing time difference ΔT values to determine the amount of toner  203  remaining in reservoir  202  use two magnetic sensors  250 A,  250 B to detect the motion of one magnetic element  240 , it will be appreciated that time difference ΔT values may also be determined using a single magnetic sensor  250  to detect the motion of a pair of angularly offset magnetic elements  240 . In this embodiment, one or both of the magnetic elements  240  may be positioned on an arm or extension connected to paddle  230  to rotate with paddle  230 . 
     The shape, architecture and configuration of toner cartridge  200  shown in  FIGS. 4 and 5  are meant to serve as examples and are not intended to be limiting. For instance, although the example image forming device discussed above includes a pair of mating replaceable units in the form of toner cartridge  200  and imaging unit  300 , it will be appreciated that the replaceable unit(s) of the image forming device may employ any suitable configuration as desired. For example, in one embodiment, the main toner supply for the image forming device, toner adder roll  304 , developer roll  306  and photoconductive drum  310  are housed in one replaceable unit. In another embodiment, the main toner supply for the image forming device, toner adder roll  304  and developer roll  306  are provided in a first replaceable unit and photoconductive drum  310  is provided in a second replaceable unit. 
     Although the example embodiments discussed above utilize a falling paddle in the reservoir of the toner cartridge, it will be appreciated that a falling paddle, such as paddle  230 , having a magnetic element may be used to determine the toner level in any reservoir or sump storing toner in the image forming device such as, for example, a reservoir of the imaging unit or a storage area for waste toner. Further, although the example embodiments discussed above discuss a system for determining a toner level, it will be appreciated that this system and the methods discussed herein may be used to determine the level of a particulate material other than toner such as, for example, grain, seed, flour, sugar, salt, etc. 
     Although the examples above discuss the use of one or two magnetic sensors, it will be appreciated that more than two magnetic sensors may be used as desired in order to obtain more information regarding the movement of the falling paddle having the magnetic element. Further, while the examples discuss sensing a magnetic element using a magnetic sensor, in another embodiment, an inductive sensor, such as an eddy current sensor, or a capacitive sensor is used instead of a magnetic sensor. In this embodiment, the falling paddle includes an electrically conductive element detectable by the inductive or capacitive sensor. As discussed above with respect to magnetic element  240 , the metallic element may be attached to the falling paddle by a friction fit, adhesive, fastener(s), etc. or the falling paddle may be composed of a metallic material or the metallic element may be positioned on an arm or extension that is rotatable with the falling paddle. In another alternative, the falling paddle includes a shaft that extends to an outer portion of body  204 , such as through wall  206  or  207 . An encoder wheel or other form of encoded device is attached or formed on the portion of the shaft of the falling paddle that is outside reservoir  202 . A code reader, such as an infrared sensor, is positioned to sense the motion of the encoded device (and therefore the motion of the falling paddle) and in communication with controller  102  or another processor that analyzes the motion of the falling paddle in order to determine the amount of toner remaining in reservoir  202 . 
     The foregoing description illustrates various aspects of the present disclosure. It is not intended to be exhaustive. Rather, it is chosen to illustrate the principles of the present disclosure and its practical application to enable one of ordinary skill in the art to utilize the present disclosure, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the present disclosure as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.