Patent Publication Number: US-7593653-B2

Title: Optical sensor system with a dynamic threshold for monitoring toner transfer in an image forming device

Description:
BACKGROUND 
   The present application is directed to methods and devices for monitoring toner transfer in an image forming device, and more particularly to optical reflectivity methods and devices for monitoring the toner transfer. 
   Image forming devices use toner to produce images on a media sheet. The toner may be housed within a toner cartridge that is refillable or removable from the image forming device. The toner cartridges are positioned within the image forming device at locations that provide convenient access to a user. Removal and installation of the toner cartridges may occur during initial start-up of the device, when the toner has been depleted from the cartridge, and miscellaneous other occurrences. 
   Toner cartridges may be replaceable or refillable to allow a user to input new toner into the image forming device after a first amount of toner originally within the device has been depleted. The image forming device should be designed to accurately monitor the amount of toner remaining in a toner cartridge to reduce operating costs, reduce toner waste, and to provide an accurate indicator of toner depletion. Further, the image forming device should be designed such that monitoring toner transfer does not greatly increase the manufacturing costs or size of the image forming device. 
   SUMMARY 
   The present application is directed to a device that monitors toner transfer within an image forming device. A reflectivity sensor senses movement of a toner transfer gear operatively connected to a toner transfer system. A threshold unit generates a dynamic threshold based on the output of the reflectivity sensor. In one embodiment, the threshold unit generates the dynamic threshold based on a time delayed average of the sensor output. An instantaneous sensor output is compared to the dynamic threshold. Based on the comparison, the device determines how much the toner transfer gear has rotated, and therefore, how much toner has been transferred from the toner cartridge. Based on this information, the device may determine how much toner remains in the toner cartridge. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic side view of an image forming device according to one embodiment. 
       FIG. 2  shows a schematic side view of a developer unit and a photoconductor unit according to one embodiment. 
       FIGS. 3A and 3C  show respective front and back perspective views of a toner cartridge according to one embodiment. 
       FIG. 3B  shows a perspective view of an interior of a toner cartridge including a plurality of shafts according to one embodiment. 
       FIG. 4  shows a rear perspective view of an imaging unit comprising four imaging stations according to one embodiment. 
       FIG. 5A  shows a block diagram of a reflectivity sensor according to one embodiment. 
       FIG. 5B  shows a block diagram of a reflectivity sensor according to one embodiment. 
       FIG. 6  shows one example of a reflectivity sensor output. 
       FIG. 7  shows potential differences between outputs for different reflectivity sensors. 
       FIG. 8A  shows a block diagram of a monitoring processor according to one embodiment. 
       FIG. 8B  shows a block diagram of a monitoring processor according to one embodiment. 
   

   DETAILED DESCRIPTION 
   Embodiments of the present application use a reflectivity sensor in conjunction with a dynamically generated threshold to determine how much toner has been transferred from a toner cartridge. In one embodiment, the dynamic threshold is generated based on a time delayed average of the reflectivity sensor output. By using a dynamic threshold, various embodiments minimize the impact of sensor tolerances on the manufacturing cost of the image forming device. Further, the dynamic threshold accommodates sensor degradation over the lifetime of the sensor, and therefore, reduces the affects of sensor degradation on the device performance. 
   To facilitate the description of various embodiments, the following first provides a general description of one exemplary image forming device. It will be appreciated, however, that the various embodiments are not limited to the described or illustrated image forming device.  FIG. 1  shows one embodiment of an image forming device  100 . Device  100  includes an input tray  102  sized to contain a stack of media sheets  104 . A pick mechanism  106  is positioned at the input tray  102  for moving a top-most sheet from the stack  104  and into a media path  108 . Alternatively, the media sheet may move into the media path  108  via a manual feed  109 . The media sheets move from the input tray  102  along the media path  108  to a second transfer area  142 . The media sheet receives one or more toner images at the second transfer area  142 . The media sheet with the toner images next moves through a fuser  118  to adhere the toner images to the media sheet. The media sheet is then either discharged into an output tray  120  or moved into a duplex path  122  for forming a toner image on a second side of the media sheet. Examples of the device  100  include Model Nos. C750 and C752, each available from Lexmark International, Inc. of Lexington, Ky., USA. 
   An image formation area  110  forms the toner images and moves them to the second transfer area  142 . The area  110  includes an imaging unit  112 , a laser printhead  114 , and a transfer member  116 . Imaging unit  112  includes one or more imaging stations  130  that each comprise a developer unit  132 , a photoconductor unit  134 , and a toner cartridge  136 . In one embodiment, the toner cartridges  136  are independent of the imaging stations  130  and may be removed and replaced from the device  100  as necessary. In another embodiment, the toner cartridges  136  are integral with the imaging stations  130 . In one embodiment, each imaging station  130  is mounted such that photoconductive (PC) members  138  in the photoconductor units  134  are substantially parallel. For clarity, the units  132 ,  134 , and cartridge  136  are labeled on only one of the imaging stations  130  in  FIG. 1 . In one embodiment, device  100  is a monochromatic image forming device comprising a single imaging station  130  for forming toner images in a single color. In another embodiment, the imaging unit  112  includes multiple separate imaging stations  130 , each being substantially the same except for the color of the toner. In one embodiment, the imaging unit  112  includes four imaging stations  130  each containing one of black, magenta, cyan, and yellow toner. 
   Laser printhead  114  includes a laser that discharges a surface of PC members  138  within each of the imaging stations  130 . Toner from a toner cartridge  136  in the imaging station  130  attracts to the surface area of the PC members  138  affected by the laser printhead  114 . 
   The transfer member  116  extends continuously around a series of rollers  140 . Transfer member  116  receives the toner images from each of the PC members  138 . In one embodiment, the toner images from each of the PC members  138  are placed onto transfer member  116  in an overlapping arrangement. In one embodiment, a multi-color toner image is formed during a single pass of the transfer member  116 . By way of example, the yellow toner may be placed first on the transfer member  116 , followed by cyan, magenta, and black. After receiving the toner images, transfer member  116  moves the images to the second transfer area  142  where the toner images are transferred to the media sheet. The second transfer area  142  includes a nip formed by a second transfer roller  144  and one of the rollers  140 . A media sheet moves along the media path  108  through the nip to receive the toner images from the transfer member  116 . The media sheet with the toner images next moves through the fuser  118  and discharges as discussed above. 
     FIG. 2  shows a sectional view of a developer unit  132  and a photoconductor unit  134 . The developer unit  132  includes an inlet  150  that leads into a toner reservoir  151 . A paddle  152  is positioned within the reservoir  151  to agitate and move the toner. Paddle  152  is rotatably positioned within the reservoir  151  and includes a first arm  153  and a second arm  154  that each extend outward on opposite sides of a shaft  155 . A toner adder roll  156  is positioned to direct the toner towards the developer roll  157 . The photoconductor unit  134  includes a charge roll  139  and a PC member  138  positioned to receive the toner from the developer roll  157 . A blade  158  may be positioned against the PC member  138  to remove residual toner that is not transferred to the transfer member  116 . The residual toner falls into a housing and is moved by an auger  159  laterally through and out of the photoconductor unit  134 . In one embodiment, the developer unit  132  and the photoconductor unit  134  are separate members that are connected together as a single unit. One or more springs (not illustrated) may be positioned to maintain the developer roll  157  of the developer unit  132  in contact with the PC member  138  in the photoconductor unit  134 . 
   In one embodiment, toner is introduced through the inlet  150  of the developer unit  132  from a toner cartridge  136 .  FIGS. 3A-3C  show one exemplary toner cartridge  136 . Toner cartridge  136  includes an enclosed interior sized to hold a quantity of toner. The toner cartridge  136  includes an outlet  160  with a movable shutter  161 . The shutter  161  is movable between a closed orientation to prevent toner from moving from the interior and an open orientation to allow the toner to move from the interior and into the developer unit  132 . One or more toner transfer gears  162  are positioned on the exterior of the toner cartridge  136  to form a gear train. The gears  162  operatively connect to an auger  163  within the interior. Auger  163  includes a shaft  164  with an outwardly extending helical blade  165 . Rotation of the shaft  164  causes toner to be moved by the blade  165  and directed towards the outlet  160 . One embodiment of a toner cartridge is disclosed in U.S. patent application Ser. No. 11/556,863 entitled “Shutter for a Toner Cartridge for Use with an Image Forming Device” that was filed on Nov. 6, 2006, which is herein incorporated by reference. 
   An imaging unit  112  that includes one or more developer units  132 , photoconductor units  134 , and toner cartridges  136  may be positioned in a frame  131  within the body of the image forming device  100 , as illustrated in  FIG. 4 . When the toner cartridges  136  are attached to the frame  131 , the shutter  161  on the cartridges  136  moves from the closed orientation to the open orientation. When the transfer gear(s)  162  are activated, toner moves from the cartridges  136  and through the inlets  150  and into the reservoirs  151  of the developer units  132 . The toner cartridges  136  may be removably attached to the frame  131  such that they can be replaced when the toner is depleted. In one embodiment, toner cartridges  136  are inserted in a vertical direction Z, as illustrated in  FIG. 4 , and mount to the top of the frame  131 . The image forming device  100  may include a door along a top side to provide access for removal and insertion of the toner cartridges  136 . 
   The toner cartridge  136  periodically transfers toner to the developer unit  132  during the printing process. When the developer unit  132  needs more toner, the gears  162  of the toner transfer system engage with a drive mechanism in the body of the image forming device  100 , resulting in the rotation of the auger  163 , which transfers the toner out of the toner cartridge  136  and into the developer unit  132 . 
   To make sure that the developer unit  132  has enough toner to prevent excessive wear on the PC member  138  and developer roll  157 , a minimum amount of toner is maintained in the developer unit  132 . Thus, the image forming device  100  should include means for reliably monitoring the amount of toner left in the toner cartridge  136 , and therefore, for reliably determining when the toner cartridge  136  needs to be refilled or replaced. 
   In one embodiment, the image forming device  100  uses an optical reflectivity sensor  170  coupled to a monitoring processor  180  to detect rotation of one or more of the gears  162  in the gear train. As shown in  FIGS. 5A and 5B , one embodiment of a reflectivity sensor  170  comprises a light emitting element  171 , e.g., infrared light emitting diode (LED), and a light detection element  172 , e.g., a phototransistor or a photodiode. Generally, light emitted by the light emitting element  171  is periodically reflected when the gear  162  rotates. Light detection element  172  responds proportionally to the amount of reflected light in its field of view. 
   In one embodiment shown in  FIG. 5A , the reflectivity sensor  170  detects the rotations of the gear  162  by detecting light reflected directly by the teeth  166  of the toner transfer gear  162 . In one embodiment shown in  FIG. 5B , the reflectivity sensor  170  includes a reflective element  174  rotationally connected to the gear  162 , where the reflective element  174  has a contrasting pattern of reflective areas  175  and absorptive areas  176 . The reflective element  174  may be spaced from the gear  162  or may abut gear  162 . In either case, the reflective element  174  rotates with the gear  162 . In this embodiment, the reflective areas  175  reflect light emitted by the light emitting element  171 , while the absorptive areas  176  at least partially absorb the emitted light. In either case, the amount of emitted light that is reflected and detected by light detecting element  172  changes as gear  162  rotates, which provides a sensor output indicative of gear movement. 
   Monitoring processor  180  evaluates the output of the reflectivity sensor  170  to determine the amount of rotation of the gear  162 , and therefore, the amount of toner transfer.  FIG. 6  shows one exemplary output for the reflectivity sensor  170 . Processor  180  uses a threshold  177  to detect the peaks and valleys of the sensor output. With knowledge of the contrasting pattern on the reflective element  174  and/or the configuration of the gear  162 , processor  180  may determine how much the gear  162  has rotated based on the detected peaks and valleys. Based on the amount of gear rotation, processor  180  determines how much auger  163  has rotated. From that determination, the processor  180  may determine and monitor how much toner remains in the toner cartridge  136 . 
   The above-described threshold process works when the selected threshold  177  falls between the maximum and minimum sensor output. However, the manufacturing process may produce elements  171 ,  172  having large performance variations, which makes pre-selecting a fixed threshold for all sensors difficult. For example, off-the-shelf light emitting elements  171  may have a 7:1 light output variation, and off-the-shelf light detection elements  172  may have a 3:1 light sensitivity variation from part to part, even within the same manufacturing batch. Further, many reflectivity sensors  170  are tuned for short detection distances, e.g., 1 mm. Thus, use of these sensors  170  for detection distances beyond the stated range may result in even larger part to part variations. It will be appreciated that other issues may cause additional performance variations, e.g., the age of the sensor components, variations in operating temperature, mechanical placement tolerances, and contamination along the optical path, including contamination of the reflective element  174  and/or gear  162 . 
     FIG. 7  illustrates the performance variation problem. The output of the sensor  170  changes as the reflectivity of the material in the sensor&#39;s field of view changes. In  FIG. 7 , sensor output  178  represents the sensor output for a sensor  170  having a bright light emitting element  171  when the reflective element  174  or gear  162  has areas of 90% reflectivity and areas of 18% reflectivity, and sensor output  179  represents the sensor output for a sensor  170  having a dim light emitting element  171  when the reflective element  174  or gear  162  has areas of 90% reflectivity and 18% reflectivity. The two represented sensors  170  have identical specifications and part numbers. However, the sensor outputs  178 ,  179  in  FIG. 7  show that one threshold value will not suffice for both sensors  170 . 
   The above-described sensor variations make it difficult if not impossible to select one threshold for all sensors  170 . Past methods for addressing this problem include sensor characterization during the manufacturing process, sensor calibration during the manufacturing process, hand tuning the sensor and/or threshold to achieve the desired response, etc. All of these techniques are labor intensive. Further, these techniques may cause an undesirably large number of sensors  170  to be rejected. In either case, past solutions generally increase product cost. 
   Embodiments used herein may provide a monitoring processor  180  that addresses this problem by using a dynamically adjusting threshold.  FIG. 8A  shows one embodiment of a monitoring processor  180  comprising a threshold circuit  181 , a comparator  182 , and a position circuit  183 . Threshold circuit  181  generates a dynamic threshold  184  for the reflectivity sensor  170  based on the output of the sensor  170 . In one embodiment, threshold circuit  181  comprises an averaging circuit  187  and an optional buffer  188 . Averaging circuit  187  generates the dynamic threshold  184  by generating a time delayed average of the sensor output. Buffer  188  isolates the dynamic threshold  184  from the sensor to prevent feedback. In one embodiment, averaging circuit  187  comprises a Resistor-Capacitor (RC) filter that filters the sensor output over a predetermined period of time to generate the time delayed average. Comparator  182  generates a binary output  186  based on a comparison between the current instantaneous sensor output  185  and the dynamic threshold  184 . Position circuit  183  determines the amount of gear movement, and therefore the amount of toner transfer, based on multiple binary outputs  186 . By averaging the sensor output over time, the threshold circuit  181  generates a dynamic threshold that accommodates the sensor&#39;s particular maximum and minimum sensitivity values, even if those values change over time. 
     FIG. 8B  shows one embodiment that adds a hysteresis feedback filter  190  to the embodiment of  FIG. 8A . The hysteresis filter  190  may be implemented to reduce jitter in the binary output  186  that may be produced, for example, when the instantaneous sensor output  185  is noisy and/or when the instantaneous sensor output  185  and the dynamic threshold  184  have approximately the same value. To reduce the jitter, the hysteresis filter  190  filters the binary output  186  according to any known means. Combiner  192  combines the filter output  191  with the current instantaneous sensor output  185  to generate a modified instantaneous sensor output  193  having a reduced noise level. 
   While the above describes and illustrates the monitoring processor  180  as an independent processor, it will be appreciated that one or all of the monitoring processor  180  may be incorporated with a control processor (not shown) in the image forming device  110 . Further, it will be appreciated that one monitoring processor  180  may process the output of one reflectivity sensor  170  or multiple reflectivity sensors  170  associated with the same or different toner cartridges  136 . 
   The above-described embodiments monitor toner transfer from a toner cartridge  136  to a developer unit  132 . However, it will be appreciated that the various embodiments described herein are not so limited and may be used to monitor toner transfer in other areas of the image forming device  100 . 
   The various embodiments described herein may, of course, be carried out in other ways than those specifically set forth herein without departing from the essential characteristics. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.