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

A method and device for monitoring toner transfer within an image forming device is described herein. 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 the how much the toner transfer gear has rotated, and therefore, how much toner has been transferred from the toner cartridge.

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.

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. 1shows one embodiment of an image forming device100. Device100includes an input tray102sized to contain a stack of media sheets104. A pick mechanism106is positioned at the input tray102for moving a top-most sheet from the stack104and into a media path108. Alternatively, the media sheet may move into the media path108via a manual feed109. The media sheets move from the input tray102along the media path108to a second transfer area142. The media sheet receives one or more toner images at the second transfer area142. The media sheet with the toner images next moves through a fuser118to adhere the toner images to the media sheet. The media sheet is then either discharged into an output tray120or moved into a duplex path122for forming a toner image on a second side of the media sheet. Examples of the device100include Model Nos. C750 and C752, each available from Lexmark International, Inc. of Lexington, Ky., USA.

An image formation area110forms the toner images and moves them to the second transfer area142. The area110includes an imaging unit112, a laser printhead114, and a transfer member116. Imaging unit112includes one or more imaging stations130that each comprise a developer unit132, a photoconductor unit134, and a toner cartridge136. In one embodiment, the toner cartridges136are independent of the imaging stations130and may be removed and replaced from the device100as necessary. In another embodiment, the toner cartridges136are integral with the imaging stations130. In one embodiment, each imaging station130is mounted such that photoconductive (PC) members138in the photoconductor units134are substantially parallel. For clarity, the units132,134, and cartridge136are labeled on only one of the imaging stations130inFIG. 1. In one embodiment, device100is a monochromatic image forming device comprising a single imaging station130for forming toner images in a single color. In another embodiment, the imaging unit112includes multiple separate imaging stations130, each being substantially the same except for the color of the toner. In one embodiment, the imaging unit112includes four imaging stations130each containing one of black, magenta, cyan, and yellow toner.

Laser printhead114includes a laser that discharges a surface of PC members138within each of the imaging stations130. Toner from a toner cartridge136in the imaging station130attracts to the surface area of the PC members138affected by the laser printhead114.

The transfer member116extends continuously around a series of rollers140. Transfer member116receives the toner images from each of the PC members138. In one embodiment, the toner images from each of the PC members138are placed onto transfer member116in an overlapping arrangement. In one embodiment, a multi-color toner image is formed during a single pass of the transfer member116. By way of example, the yellow toner may be placed first on the transfer member116, followed by cyan, magenta, and black. After receiving the toner images, transfer member116moves the images to the second transfer area142where the toner images are transferred to the media sheet. The second transfer area142includes a nip formed by a second transfer roller144and one of the rollers140. A media sheet moves along the media path108through the nip to receive the toner images from the transfer member116. The media sheet with the toner images next moves through the fuser118and discharges as discussed above.

FIG. 2shows a sectional view of a developer unit132and a photoconductor unit134. The developer unit132includes an inlet150that leads into a toner reservoir151. A paddle152is positioned within the reservoir151to agitate and move the toner. Paddle152is rotatably positioned within the reservoir151and includes a first arm153and a second arm154that each extend outward on opposite sides of a shaft155. A toner adder roll156is positioned to direct the toner towards the developer roll157. The photoconductor unit134includes a charge roll139and a PC member138positioned to receive the toner from the developer roll157. A blade158may be positioned against the PC member138to remove residual toner that is not transferred to the transfer member116. The residual toner falls into a housing and is moved by an auger159laterally through and out of the photoconductor unit134. In one embodiment, the developer unit132and the photoconductor unit134are separate members that are connected together as a single unit. One or more springs (not illustrated) may be positioned to maintain the developer roll157of the developer unit132in contact with the PC member138in the photoconductor unit134.

In one embodiment, toner is introduced through the inlet150of the developer unit132from a toner cartridge136.FIGS. 3A-3Cshow one exemplary toner cartridge136. Toner cartridge136includes an enclosed interior sized to hold a quantity of toner. The toner cartridge136includes an outlet160with a movable shutter161. The shutter161is 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 unit132. One or more toner transfer gears162are positioned on the exterior of the toner cartridge136to form a gear train. The gears162operatively connect to an auger163within the interior. Auger163includes a shaft164with an outwardly extending helical blade165. Rotation of the shaft164causes toner to be moved by the blade165and directed towards the outlet160. 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 unit112that includes one or more developer units132, photoconductor units134, and toner cartridges136may be positioned in a frame131within the body of the image forming device100, as illustrated inFIG. 4. When the toner cartridges136are attached to the frame131, the shutter161on the cartridges136moves from the closed orientation to the open orientation. When the transfer gear(s)162are activated, toner moves from the cartridges136and through the inlets150and into the reservoirs151of the developer units132. The toner cartridges136may be removably attached to the frame131such that they can be replaced when the toner is depleted. In one embodiment, toner cartridges136are inserted in a vertical direction Z, as illustrated inFIG. 4, and mount to the top of the frame131. The image forming device100may include a door along a top side to provide access for removal and insertion of the toner cartridges136.

The toner cartridge136periodically transfers toner to the developer unit132during the printing process. When the developer unit132needs more toner, the gears162of the toner transfer system engage with a drive mechanism in the body of the image forming device100, resulting in the rotation of the auger163, which transfers the toner out of the toner cartridge136and into the developer unit132.

To make sure that the developer unit132has enough toner to prevent excessive wear on the PC member138and developer roll157, a minimum amount of toner is maintained in the developer unit132. Thus, the image forming device100should include means for reliably monitoring the amount of toner left in the toner cartridge136, and therefore, for reliably determining when the toner cartridge136needs to be refilled or replaced.

In one embodiment, the image forming device100uses an optical reflectivity sensor170coupled to a monitoring processor180to detect rotation of one or more of the gears162in the gear train. As shown inFIGS. 5A and 5B, one embodiment of a reflectivity sensor170comprises a light emitting element171, e.g., infrared light emitting diode (LED), and a light detection element172, e.g., a phototransistor or a photodiode. Generally, light emitted by the light emitting element171is periodically reflected when the gear162rotates. Light detection element172responds proportionally to the amount of reflected light in its field of view.

In one embodiment shown inFIG. 5A, the reflectivity sensor170detects the rotations of the gear162by detecting light reflected directly by the teeth166of the toner transfer gear162. In one embodiment shown inFIG. 5B, the reflectivity sensor170includes a reflective element174rotationally connected to the gear162, where the reflective element174has a contrasting pattern of reflective areas175and absorptive areas176. The reflective element174may be spaced from the gear162or may abut gear162. In either case, the reflective element174rotates with the gear162. In this embodiment, the reflective areas175reflect light emitted by the light emitting element171, while the absorptive areas176at least partially absorb the emitted light. In either case, the amount of emitted light that is reflected and detected by light detecting element172changes as gear162rotates, which provides a sensor output indicative of gear movement.

Monitoring processor180evaluates the output of the reflectivity sensor170to determine the amount of rotation of the gear162, and therefore, the amount of toner transfer.FIG. 6shows one exemplary output for the reflectivity sensor170. Processor180uses a threshold177to detect the peaks and valleys of the sensor output. With knowledge of the contrasting pattern on the reflective element174and/or the configuration of the gear162, processor180may determine how much the gear162has rotated based on the detected peaks and valleys. Based on the amount of gear rotation, processor180determines how much auger163has rotated. From that determination, the processor180may determine and monitor how much toner remains in the toner cartridge136.

The above-described threshold process works when the selected threshold177falls between the maximum and minimum sensor output. However, the manufacturing process may produce elements171,172having large performance variations, which makes pre-selecting a fixed threshold for all sensors difficult. For example, off-the-shelf light emitting elements171may have a 7:1 light output variation, and off-the-shelf light detection elements172may have a 3:1 light sensitivity variation from part to part, even within the same manufacturing batch. Further, many reflectivity sensors170are tuned for short detection distances, e.g., 1 mm. Thus, use of these sensors170for 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 element174and/or gear162.

FIG. 7illustrates the performance variation problem. The output of the sensor170changes as the reflectivity of the material in the sensor's field of view changes. InFIG. 7, sensor output178represents the sensor output for a sensor170having a bright light emitting element171when the reflective element174or gear162has areas of 90% reflectivity and areas of 18% reflectivity, and sensor output179represents the sensor output for a sensor170having a dim light emitting element171when the reflective element174or gear162has areas of 90% reflectivity and 18% reflectivity. The two represented sensors170have identical specifications and part numbers. However, the sensor outputs178,179inFIG. 7show that one threshold value will not suffice for both sensors170.

The above-described sensor variations make it difficult if not impossible to select one threshold for all sensors170. 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 sensors170to be rejected. In either case, past solutions generally increase product cost.

Embodiments used herein may provide a monitoring processor180that addresses this problem by using a dynamically adjusting threshold.FIG. 8Ashows one embodiment of a monitoring processor180comprising a threshold circuit181, a comparator182, and a position circuit183. Threshold circuit181generates a dynamic threshold184for the reflectivity sensor170based on the output of the sensor170. In one embodiment, threshold circuit181comprises an averaging circuit187and an optional buffer188. Averaging circuit187generates the dynamic threshold184by generating a time delayed average of the sensor output. Buffer188isolates the dynamic threshold184from the sensor to prevent feedback. In one embodiment, averaging circuit187comprises a Resistor-Capacitor (RC) filter that filters the sensor output over a predetermined period of time to generate the time delayed average. Comparator182generates a binary output186based on a comparison between the current instantaneous sensor output185and the dynamic threshold184. Position circuit183determines the amount of gear movement, and therefore the amount of toner transfer, based on multiple binary outputs186. By averaging the sensor output over time, the threshold circuit181generates a dynamic threshold that accommodates the sensor's particular maximum and minimum sensitivity values, even if those values change over time.

FIG. 8Bshows one embodiment that adds a hysteresis feedback filter190to the embodiment ofFIG. 8A. The hysteresis filter190may be implemented to reduce jitter in the binary output186that may be produced, for example, when the instantaneous sensor output185is noisy and/or when the instantaneous sensor output185and the dynamic threshold184have approximately the same value. To reduce the jitter, the hysteresis filter190filters the binary output186according to any known means. Combiner192combines the filter output191with the current instantaneous sensor output185to generate a modified instantaneous sensor output193having a reduced noise level.

While the above describes and illustrates the monitoring processor180as an independent processor, it will be appreciated that one or all of the monitoring processor180may be incorporated with a control processor (not shown) in the image forming device110. Further, it will be appreciated that one monitoring processor180may process the output of one reflectivity sensor170or multiple reflectivity sensors170associated with the same or different toner cartridges136.

The above-described embodiments monitor toner transfer from a toner cartridge136to a developer unit132. 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 device100.

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.