Abstract:
An electrophotographic image forming device according to one example embodiment includes an optical emitter positioned to emit a light beam through a window into a reservoir holding toner toward a reflective surface in the reservoir as a paddle positioned within the reservoir rotates. An optical receiver is positioned to sense an amount of the light beam reflected by the reflective surface. At least one processor is configured to receive a signal related to the amount of light sensed by the optical receiver. The at least one processor includes computer executable program instructions including: instructions for calculating an average value for the signal for each of a plurality of sets of paddle revolutions, instructions for calculating a variation value for the signal for each of the plurality of sets of paddle revolutions, instructions for filtering each variation value to determine a plurality of short term variation values, instructions for monitoring whether at least one short term variation value exceeds a first threshold, and instructions for signaling that a toner level in the reservoir is low when the at least one short term variation value exceeds the first threshold.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This patent application is a continuation application of U.S. patent application Ser. No. 12/885,129, filed Sep. 17, 2010, entitled “Method for Determining Low Toner in an Electro-photographic Toner Cartridge.” 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to an electro-photographic toner cartridge, and more specifically to systems for detecting low toner in an electro-photographic toner cartridge using a light beam to detect the presence or absence of toner in the cartridge. 
         [0004]    2. Description of the Related Art 
         [0005]    Conventional electro-photographic printers comprise a toner cartridge having a chamber therein filled with toner. During the print process, toner is transferred from the chamber to print media thereby decreasing the amount of toner within the chamber over the life of the cartridge. When the toner level in the chamber approaches empty, the print quality may suffer. Ultimately, when the chamber is substantially empty, the printer will no longer be able to transfer images to print media. Accordingly, it is desirable to detect and signal to a user when the toner level within the toner cartridge chamber is low. 
         [0006]    If toner low notification occurs too late, print quality may already be suffering. Further, late notification may not provide the user with sufficient time to replace the toner. Conversely, if the notification is too early, ample toner may remain in the cartridge and the user may replace the cartridge prematurely. Accordingly, a method for detecting low toner before print quality suffers without indicating low toner prematurely is desirable. 
         [0007]    Given the foregoing, it will be appreciated that a method for detecting low toner in an electro-photographic toner cartridge that signals that the toner is low at an optimum time is preferable. 
       SUMMARY OF THE INVENTION 
       [0008]    An electrophotographic image forming device according to one example embodiment includes an optical emitter positioned to emit a light beam through a window into a reservoir holding toner toward a reflective surface in the reservoir as a paddle positioned within the reservoir rotates. An optical receiver is positioned to sense an amount of the light beam reflected by the reflective surface. At least one processor is configured to receive a signal related to the amount of light sensed by the optical receiver. The at least one processor includes computer executable program instructions including: instructions for calculating an average value for the signal for each of a plurality of sets of paddle revolutions, instructions for calculating a variation value for the signal for each of the plurality of sets of paddle revolutions, instructions for filtering each variation value to determine a plurality of short term variation values, instructions for monitoring whether at least one short term variation value exceeds a first threshold, and instructions for signaling that a toner level in the reservoir is low when the at least one short term variation value exceeds the first threshold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The above-mentioned and other features and advantages of the various embodiments of the invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a perspective view of a toner cartridge; 
           [0011]      FIG. 2  is a sectioned elevation view of the interior of a developer unit showing a toner chamber; 
           [0012]      FIG. 3  is a sectioned perspective view showing a toner chamber; 
           [0013]      FIG. 4  is a sectioned perspective view showing a toner chamber with the paddle and associated cross members removed; 
           [0014]      FIG. 5  is a sectioned perspective view showing a toner chamber with the paddle and associated cross members removed; 
           [0015]      FIG. 6  is a sectioned plan view of a toner chamber showing the optical path of an optical sensor; and 
           [0016]      FIG. 7  is a flow chart of a method for detecting low toner in an electro-photographic toner cartridge. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
         [0018]    In addition, it should be understood that embodiments of the invention include both hardware and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. 
         [0019]    With reference to  FIG. 1 , an electro-photographic toner cartridge  10  is shown having a developer unit  12  therewith. With reference to  FIGS. 2 and 3 , a toner chamber  20  is disposed within the developer unit  12 . In operation, the toner chamber  20  contains toner. The toner chamber  20  includes a long dimension in which a toner paddle  22  is mounted. The paddle  22  extends across the long dimension generally perpendicular to a first end  24  and a second end  26  of the chamber  20 . In multiple embodiments, the long dimension of the cartridge  10  is at least the width of the paper or other media being imaged. In some embodiments, this is more than the 8½ inches width of paper widely used in the United States. 
         [0020]    The paddle  22  has a central, driven shaft  28  extending across the long dimension of the chamber  20 . In operation, the shaft  28  is rotated by a driving member from an imaging device (not shown). In some embodiments, the paddle  22  has stirring extensions  30   a ,  30   b , and  30   c , which extend to near the inner walls  20   a  of chamber  20  and which have cross members  30   aa ,  30   bb , and  30   cc  extending parallel to the shaft  28 . Embodiments include those wherein cross member  30   bb  is wider than cross members  30   aa  or  30   cc  so as to distribute the stirring action of paddle  22 . 
         [0021]    At the first end  24 , on the shaft  28 , is a flexible wiper blade  32 . In some embodiments, the wiper blade  32  is made of a solid urethane polymer. However, the wiper blade  32  may be made of any suitable material. Embodiments include those wherein the wiper blade  32  is mounted to the shaft  28  by a bolt fixed on an extension from the shaft  28 . However, the wiper blade  32  may be fixed to the shaft  28  by various alternatives such as, for example, being wrapped around the shaft  28  and held by adhesive or by a rivet. 
         [0022]    With reference to  FIGS. 4 and 5 , a transparent plate or window  36  is disposed at the first end  24  of the chamber  20  on a first extension  34  from the chamber  20 . The window  36  may be any material which is transparent to light and is sturdy enough to hold toner inside of the chamber  20 . Embodiments include those wherein the window  36  is made of polycarbonate. 
         [0023]    Opposite the window  36  is a reflective surface  38 . In some embodiments, the reflective surface  38  is spaced less than about b  40  millimeters from the window  36 . In one exemplary embodiment, the reflective surface  38  is about 10 millimeters away from the window  36 . The wiper blade  32  passes through the space between the window  36  and the reflective surface  38  once per paddle  22  revolution. As the wiper blade  32  passes through the space between the window  36  and the reflective surface  38 , opposite sides of the wiper blade  32  contact the window  36  and the reflective surface  38 , thereby cleaning the two surfaces to allow light to pass through the window  36  and be reflected by the reflective surface  38  back through the window  36 . 
         [0024]    Embodiments include those wherein the reflective surface  38  is an aluminized plastic sheet which is physically supported in the chamber  20  by a second extension  40  from the chamber  20 . As the paddle  22  rotates, it distributes toner so that toner remaining after use tends to settle evenly across the bottom of the chamber  20 , including the area of the bottom of the chamber  20  between the window  36  and the reflective surface  38 . 
         [0025]    With reference to  FIGS. 5 and 6 , an optical sensor  46  is spaced outside of the chamber  20  as part of the imaging device. The optical sensor  46  is positioned immediately outside the window  36 . The optical sensor  46  has an emitter  48  and a receiver  50 . In some embodiments, the emitter  48  and the receiver  50  are mounted together for structural convenience. Alternatives include those wherein a separate emitter  48  and separate receiver  50  are utilized. In some embodiments, the emitter  48  emits infrared light and the receiver  50  receives infrared light. Embodiments include those wherein the emitter  48  is an LED emitter. 
         [0026]    In operation, when printing occurs, toner is carried from the chamber  20  in small amounts by a developer roller (not shown) and a doctor blade (not shown). The paddle  22  rotates whenever printing takes place in order to keep the toner in the chamber  20  fluffed up and to push the toner towards the developer roller for removal from the chamber  20  for use in the printing process. As the paddle  22  rotates, at periodic intervals, the electronic controls of the imaging device having optical sensor  46 , cause light to be emitted from the emitter  48  and observe any sensing of that light on the receiver  50 . The emitter  48  emits light through the window  36  toward the reflective surface  38  continuously during each paddle  22  revolution. The receiver  50  senses the amount of light reflected through the window  36  by the reflective surface  38 . When no toner is present between the window  36  and the reflective surface  38 , the amount of light reflected is high. Conversely, when toner is present between the window  36  and the reflective surface  38 , the amount of light reflected is low because the toner blocks the optical path. For most of the life of the cartridge  10 , as soon as the wiper blade  32  exits the space between the window  36  and the reflective surface  38 , toner falls back into the space, blocking the optical path. There is often a brief period of time after the wiper blade  32  passes through the space between the window  36  and the reflective surface  38  where the optical path is unblocked. As the toner level within the chamber  20  approaches empty, the time period during each revolution of the paddle  22  in which the optical path is unblocked increases. Testing has shown that on a short time scale, the behavior of the toner and its blockage of the optical path is relatively random. 
         [0027]    With reference to  FIG. 7 , a method for detecting low toner in an electro- photographic toner cartridge having an optical sensor using a light beam to detect the presence or absence of toner in the cartridge is provided. At step  101 , the optical sensor  46  transmits a signal related to the strength of the light beam sensed by the receiver  50  to a processor (not shown). In some embodiments, the optical sensor  46  transmits an analog output voltage related to the strength of each light beam sensed by the receiver  50  to an analog to digital (A/D) converter. A digital output voltage sample is then transmitted from the A/D converter to the processor. In one exemplary embodiment, a sample is taken every 16 milliseconds. This means multiple readings can occur for each paddle  22  revolution depending on the rotational speed of the paddle  22 . Embodiments include those wherein the signal transmitted to the processor is inversely related to the strength of the light beam sensed by the receiver  50 . In these embodiments, as the amount of light received increases, the signal strength decreases. Alternatives include those wherein the signal is directly related to the strength of the light beam sensed by the receiver  50  such that as the amount of light increases, the signal strength increases. 
         [0028]    In multiple embodiments, the processor counts the number of revolutions N of the paddle  22  over the life of the cartridge  10 . Each revolution of the paddle  22  has an associated value N such that for the first paddle  22  revolution, N=1, for the second revolution, N=2, and so on. 
         [0029]    At step  102 , the processor calculates an average value for the signal for each of a plurality of sets of paddle  22  revolutions. Embodiments include those wherein each set of paddle  22  revolutions consists of one paddle  22  revolution such that the processor calculates an average value for the signal for each revolution of the paddle  22 . Alternatives include those wherein each set of paddle  22  revolutions consists of multiple revolutions of the paddle  22 . The average value for the signal is the average strength of the signals transmitted to the processor during a set of paddle  22  revolutions. In some embodiments, the average value for the signal is an average paddle cycle voltage value V PCA,N , where N corresponds with a specific paddle  22  revolution such that the first paddle  22  revolution has an average paddle cycle voltage value V PCA,1 , the second paddle  22  revolution has an average paddle cycle voltage value V PCA,2  and so on. The average paddle cycle voltage value V PCA,N  is determined by calculating the average voltage transmitted to the processor during a paddle  22  revolution. For example, if during the fiftieth paddle  22  revolution five signals are transmitted to the processor, the signals measuring 2.5 V, 2.5 V, 2.5 V, 2.5 V and 0 V respectively, then V PCA,50 =2.0 V. In the embodiments where the signal is inversely related to the amount of light sensed, V PCA,N  decreases as the amount of toner in the chamber  20  decreases. 
         [0030]    Prior to the first use of the cartridge  10 , toner within the cartridge  10  may be concentrated at one end of the chamber  20 . Accordingly, in order to allow the toner to settle into a normal distribution, in some embodiments, prior to calculating an average value for the signal transmitted to the processor, the processor first counts a predetermined number of paddle  22  revolutions. This allows the processor to ignore data from the initial period of the cartridge  10  when the toner within the chamber  20  may be concentrated at one end. In some embodiments, the first  100  revolutions of the paddle  22  are counted before the processor begins to calculate an average value for the signal transmitted to the processor. 
         [0031]    Generally, the sensitivity of each optical sensor  46  differs. Therefore, it is difficult to determine in advance a specific average signal value for a given optical sensor that will indicate that the toner is low. Accordingly, in some embodiments, each average value for the signal is normalized. Embodiments include those wherein the processor determines the maximum signal value and the minimum signal value transmitted to the processor. The maximum and minimum signal values are tracked over the life of the cartridge  10  and are stored in non-volatile memory. During each paddle  22  revolution, the processor compares each signal with the recorded maximum and minimum signal values to date. If a signal exceeds the maximum signal value, the processor updates the maximum with the new value. Similarly, if a signal falls below the minimum signal value, the processor updates the minimum with the new value. In some embodiments, the maximum and minimum signal values are used to determine a normalized average paddle cycle voltage value V NPCA,N  according to the following formula: V NPCA,N =(V PCA,N −V min )/(V max −V mm ). This formula produces a V NPCA,N  between zero and one. If approximately 100% of the light transmitted from the emitter  46  is received by the receiver  50  and the signal transmitted to the processor is inversely related to the amount of light sensed, then V NPCA,N  will be close to zero. Conversely, in this example, if the optical path is blocked approximately 100% of the time, then V NPCA,N  will be close to one. 
         [0032]    Testing has shown that the average value for the signal for each of the plurality of sets of paddle  22  revolutions has a substantial amount of short term randomness. Accordingly, in some embodiments, each average value for the signal is filtered to negate a portion of the short term variation in order to assist with detecting the long term trends of the signal. Embodiments include those wherein the average value for the signal is first normalized and then filtered and those wherein the average value for the signal is first filtered and then normalized. Further, embodiments include those wherein the average value for the signal is filtered but not normalized and those wherein the average value for the signal is normalized but not filtered. In some embodiments, a filtered average paddle cycle voltage value V FPCA,N  is determined by low-pass filtering each V NPCA,N  value. This low-pass filtering can be accomplished using the formula: V FPCA,N+1 =V FPCA,N +((V NPCA,N+1 −V FPCA,N )/X). In some embodiments, X is a constant. The constant X may be any suitable number, for example  100 . Alternatives include those wherein X depends on the number of paddle  22  revolutions N. The larger the value X, the slower the filtered value reacts to changes. Accordingly, a larger value X results in a longer delay in detecting long term signal shifts. 
         [0033]    A decrease in the average value for the signal generally indicates that the toner in the cartridge  10  is low. Testing has shown that the randomness of the average value for the signal increases just before the average value for the signal begins to fall. Accordingly, the variation of the average value for the signal can be analyzed to determine when the toner in the cartridge  10  is low. At step  103 , the processor calculates a variation value for the signal for each of the plurality of sets of paddle  22  revolutions. In some embodiments, a variation value Var N  for the signal is calculated for each paddle  22  revolution where N corresponds with a specific paddle  22  revolution such that the first paddle  22  revolution has a variation value Var 1 , the second paddle  22  revolution has a variation value Var 2  and so on. Embodiments include those wherein the variation value is determined by calculating the variance of the average value for signal or by calculating the standard deviation of the average value for signal. In some embodiments, the variation value is based on the difference between V FPCA,N  and V NPCA,N . For example, Var N =|V FPCA,N −V NPCA,N |. Alternatives include: Var N =(V FPCA,N −V NPCA,N ) 2 , Var N =the square root of (V FPCA,N −V NPCA,N ) 2 , and Var N =V FPCA,N −V NPCA,N . 
         [0034]    Embodiments include those wherein the processor calculates a long term average variation value for each of the plurality of sets of paddle  22  revolutions. In some embodiments a long term average variation value Var LA,N  is calculated for each paddle  22  revolution where N corresponds with a specific paddle  22  revolution such that the first paddle  22  revolution has a long term average variation value Var LA,1 , the second paddle  22  revolution has a long term average variation value Var LA,2  and so on. Embodiments include those wherein each Var LA,N  value is the lifetime average of the Var N  values to date. Alternatives include those wherein Var LA,N+1 =((Var LA,N *N)+Var N+1 )/(N+1). Additional alternatives include those wherein each Var LA,N  is determined by filtering each Var N  value. Embodiments include those wherein Var LA,N  is determined by low-pass filtering each Var N  value. This low-pass filtering can be accomplished using the formula: 
         [0000]        V ar LA,N+1   =V ar LA,N +(( V ar N+1   −V ar LA,N )/ Y ). 
         [0000]    In some embodiments, Y is a constant. Alternatives include those wherein Y depends on the number of paddle  22  revolutions N. The larger the value Y, the slower the long term average variation value reacts to changes in the variation value. 
         [0035]    At step  104 , the processor filters each variation value to determine a plurality of short term variation values. In some embodiments, a short term variation value Var S,N  is calculated for each paddle  22  revolution where N corresponds with a specific paddle  22  revolution such that the first paddle  22  revolution has a short term variation value Var S,1 , the second paddle  22  revolution has a short term variation value Var S,2  and so on. Embodiments include those wherein Var S,N  is determined by low-pass filtering each Var N  value. This low-pass filtering can be accomplished using the formula: 
         [0000]        V ar S,N+1   =V ar S,N +(( V ar N+1   −V ar S,N )/ Z ). 
         [0000]    In some embodiments, Z is a constant. The constant Z may be any suitable number, for example  50 . Alternatives include those wherein Z depends on the number of paddle  22  revolutions N. In embodiments where Var LA,N  is determined by low-pass filtering, Y should be greater than Z so that Var LA,N  reacts to changes in Var N  slower than Var S,N . In some embodiments, over a predetermined number of paddle  22  revolutions at the beginning of the life of the cartridge  10 , the short term variation is initialized by replacing the short term variation value calculated with the corresponding long term average variation value. For example, for N≦50, Var S,N =Var LA,N . 
         [0036]    At step  105 , the processor monitors whether at least one short term variation value exceeds a first threshold. The term “exceeds” as used herein is meant to encompass either monitoring whether a variable is greater than or equal to (≧) a threshold or monitoring whether a variable is greater than (&gt;) a threshold. The first threshold should be large enough to ensure that the increased signal variation is due to low toner but small enough to provide a timely notification that the toner is low. Embodiments include those wherein the first threshold is a function of the long term average variation value. In some embodiments, the first threshold is equal to Var LA,N  multiplied by a constant, such as, for example, two. In this exemplary embodiment, the processor monitors whether Var S,N &gt;Var LA,N *2. In some embodiments, the first threshold has a minimum value to make certain that the first threshold is large enough to ensure that the increased signal variation is due to low toner. For example, where the first threshold is a function of Var LA,N , the minimum first threshold may be 0.02. 
         [0037]    In some embodiments, testing has shown that if the cartridge  10  is removed from the imaging device and the toner is redistributed within the chamber  20  toward the second end  26  of the chamber  20 , in some cases, it may take a few paddle  22  revolutions for the toner to redistribute normally across the chamber  20 . During this redistribution, it is possible that Var S,N  will exceed the first threshold, falsely indicating that the toner is low. In some embodiments, in order to ensure that the satisfaction of the first threshold is due to low toner and not a redistribution of toner within the chamber  20 , the processor monitors whether at least one Var N  value exceeds a second threshold. Embodiments include those wherein the second threshold is a function of Var LA,N . In some embodiments, the second threshold is equal to Var LA,N  multiplied by a constant, such as, for example, 10. In this exemplary embodiment, the processor monitors whether Var N &gt;Var LA,N *10. Testing has shown that under normal operation, Var N  will be less than Var LA,N *10; accordingly, satisfaction of the second threshold indicates that the toner has been redistributed. Embodiments include those wherein when Var N  exceeds the second threshold, the Var N  value is deemed unreliable and replaced with Var LA,N . For example, if the one-hundredth variation value Var S,N  exceeds the second threshold, Var 100  is replaced with Var LA,100 . Alternatives include those wherein when Var N  exceeds the second threshold, the processor stops monitoring whether Var S,N  exceeds the first threshold for a predetermined number of paddle  22  revolutions; after the predetermined number of paddle  22  revolutions, the processor resumes monitoring whether Var S,N  exceeds the first threshold. This alternative essentially ignores the data recorded after a large redistribution of toner in order to prevent a false determination that the toner level is low. 
         [0038]    At step  106 , when the at least one short term variation value exceeds the first threshold, the processor signals that the toner level is low. The signaling may include any conventional means for signaling or alerting a user such as, for example, activating an indicator (not shown), such as, for example, an LED, disposed on the imaging device or activating a display on a display device (not shown), such as, for example, an LCD screen, disposed on the imaging device. 
         [0039]    The foregoing description of several methods and an embodiment of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.