Patent Publication Number: US-2006002722-A1

Title: System and method for detecting a life time of a developer

Description:
FIELD OF THE INVENTION  
      The present invention relates to an image forming apparatus. More particularly, the present invention relates to a system and method for detecting a life time of a developer in an image forming apparatus.  
     BACKGROUND OF THE INVENTION  
      Image forming apparatuses, such as printers and photocopiers, typically use a developer to reproduce original images on a document. The developer includes a carrier and toner. The carrier is a charged particle that supports the toner and delivers the toner to a developing roller for application to a document on which the original image is being reproduced. As the hardcopy device operates over time, the supply of toner is used up, and a replacement of the toner, such as with a toner cartridge, is needed to continue operation.  
      Further, the fluidity of the carrier, which is a measure of the ability of the carrier to transport the toner, diminishes after repeated replacements of toner. Several factors cause this reduction in fluidity, including, for example, the stress applied to the carrier due to friction with rollers in the developer unit, the carrier losing its charge, and the actual carrying of toner particles by the carrier. Due to the reduction of the fluidity, the carrier itself must eventually be replaced. The time between carrier replacements can be referred to as the developer life.  
      One known method for determining when to replace the carrier is to use a toner density sensor, which measures toner density in the developer unit. In particular, the toner density is a measurement of the carrier divided by the sum of the carrier and the toner. The sensor is typically located in the developer unit downstream from the toner cartridge. In conventional systems, the end of the developer life is detected when the fluctuations of the toner density output exceed a threshold level.  
     SUMMARY OF THE INVENTION  
      Briefly, in one aspect of the invention, a system and method for detecting a life of a developer that is used in an image forming apparatus includes a sensor that detects a toner density of the developer and provides an output. The device also includes a control unit, coupled to the sensor, that is configured to determine a toner density recovery time, the toner density recovery time being a length of time from a first time that a. new toner source is added to the image forming apparatus to a second time that the sensor output reaches a predetermined value. The control unit determines whether the developer has reached a predetermined replacement point based on the toner density recovery time.  
      Further features, aspects and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows, when considered together with the accompanying figures of drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are herein incorporated and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain principles of the invention.  
       FIG. 1  is a block diagram of an image forming apparatus consistent with the present invention.  
       FIGS. 2A and 2B  are illustrations of a side view and a top view, respectively, of a developing device consistent with the present invention.  
       FIG. 3  is a block diagram of a developer life discrimination device consistent with the present invention.  
       FIG. 4  is a graphical illustration of exemplary changes in toner density after different toner cartridge replacements consistent with the present invention.  
       FIG. 5A  is a graphical illustration of exemplary changes in toner density after different toner cartridge replacements based on reaching a predetermined toner density consistent with the present invention.  
       FIG. 5B  is a graphical illustration of exemplary changes in toner density after different toner cartridge replacements based on reaching a predetermined time consistent with the present invention.  
       FIG. 6  is a graphical illustration of exemplary changes in toner density at a predetermined time after each toner cartridge replacement consistent with the present invention.  
       FIG. 7  is a graphical illustration of exemplary changes in toner density after each toner cartridge replacement accounting for operating conditions and predicting developer life consistent with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       FIG. 1  is a block diagram of an image forming apparatus consistent with the present invention. As shown in  FIG. 1 , an image forming apparatus  10  includes a user interface  12 , a scanner  14 , an image processing unit  16 , an image reproduction unit  18 , and a paper feeding unit  20 . The image forming apparatus  10  can be, for example, a copier, a multi-function peripheral or printer (MFP). In addition, the image forming apparatus can be a black and white (B/W) or a color device.  
      The user interface  12  is an interface through which a user can input information to the image forming apparatus  10 . The information input through the user interface  12  includes settings of a copy job, such as number of copies, paper size, enlargement/reproduction amount, etc. The user interface  12  can be implemented, for example, as a touch screen, an LCD display with corresponding buttons, or other configuration enabling a user to establish the settings of a copy job. The display of the user interface  12  can also provide information about the operations and status of the image forming apparatus  10 .  
      The scanner  14  scans original images from documents placed on a document table of the image forming apparatus  10 . The documents can be placed on the document table, which is typically a glass plate, with an automatic document feeder (ADF) or by hand. The scanner  14  includes a light source, such as a lamp, that scans light across the document. The light reflected by the document is directed to a light detecting sensor, which converts the detected light into digital image data. The light detecting sensor can be implemented as a charge-coupled device (CCD).  
      The image data generated by the light detecting sensor of the scanner  14  is processed by the image processing unit  16 . The image processing unit  16  can be configured to perform a variety of image processing functions. For example, the image processing unit  16  can perform image data conversion, gamma correction, compression, density adjustment, range compensation, halftone processing, dithering, error diffusion, smoothing, filtering, enlargement/reduction or other image processing functions.  
      The processed image data from the image processing unit  16  is used by the image reproduction unit  18  to reproduce the scanned original image from the document onto a copy paper. The image reproduction unit  18  can include an ink source, such as a developer or ink, an image generating unit for generating a latent image from the processed image data, an image transfer unit for transferring the latent image to the copy paper and a fusing unit for fusing the image to the copy paper. The ink source can include a developing device or unit, which includes developer for providing toner of a particular color. If the image forming apparatus  10  is a color device, there can be a separate developing device for each toner color, such as black, cyan, magenta, and yellow.  
      The copy paper is provided to the image reproduction unit  18  using a paper feeding unit  20 . The paper feeding unit  20  can include one or more cassettes holding one or more sizes of copy paper and transfer mechanisms for transferring the copy paper from the cassettes to the image reproduction unit  18 . The paper feeding unit  20  can also include a manual feed portion that enables a user to feed variably sized paper to the image reproduction unit  18 .  
       FIGS. 2A and 2B  are illustrations of a side view and a top view, respectively, of a developing device consistent with the present invention. The developing device can be a component of the image reproduction unit  18 . As shown in  FIG. 2A , the developing device includes a toner cartridge  50  holding toner  52 , a pair of screws  54  and  56 , a developing roller  58 , a regulating blade  60 , developer  62  and a toner density sensor  64 . The toner cartridge  50  can be a container or bottle made of any suitable material, such as plastic, for holding the toner  52 . The toner cartridge  50  supplies the toner  52  to the developer  62 .  
      The screws  54  and  56  generate a flow in the developer  62  and provide the developer  62  to the developing roller  58 . Instead of the screws  54  and  56 , the developing device can use alterative elements, such as mixers, that are capable of moving the developer  62  toward the developing roller  58 . The developing roller  58  provides the toner  52  in the developer  62  to a component of the image transfer unit of the image reproduction unit  18 , such as a photoelectric transfer drum or a transfer belt. The regulating blade  60  regulates an amount of developer on the surface of the developing roller  58 . For example, the regulating blade  60  may regulate the amount of developer so that an approximately uniform amount of developer is on the surface of the developing roller, as shown in  FIG. 2A .  
      As shown in  FIG. 2B , the toner cartridge  50  provides the toner  52  to the developer  62  at one end of the screw  54 . The rotation of the screw  54  leads the developer  62  to the other end of screw  54  at which the toner density sensor  64  is located. The toner density sensor  64  is preferably located away from the toner cartridge  50  to improve the accuracy of the toner density measurement. The toner density sensor  64  can be, for example, a permeability sensor. The output of the toner density sensor  64  is a value indicative of the toner density, and can be represented, for example, as a voltage value. The screw  56  generates a flow of the developer  62  in a direction opposite to the screw  54 . In total, the flow of the developer  62  is generally circular, flowing in one direction with the screw  54 , flowing in the opposite direction with the screw  56 , and back again. The developer  62  flowing with the screw  56  is also supplied to the developing roller  58 .  
       FIG. 3  is a block diagram of a developer life discrimination device consistent with the present invention. As shown in  FIG. 3 , the developer life discrimination device includes the toner density sensor  64 , a memory  66 , a control unit  68 , environmental sensors  70  and control signals  72 . The control unit  68  can include, for example, a processor, such as a CPU or microprocessor, or any other or form of processing unit capable of processing data and outputting results indicative of the processing. The control unit  68  can also include a dedicated memory or cache comprising instructions executed by the processor.  
      The memory  66  is preferably configured to store data output from the toner density sensor  64 , the control unit  68 , and the environmental sensors  70 . The memory  66  can also store the instructions executed by the processor of the control unit  68 . The memory  66  can be implemented, for example, as a RAM, NVRAM or EPROM. The environmental sensors  70  includes sensors capable of detecting one or more environmental conditions in which the image forming apparatus  10  and/or the developing device is operating, such as temperature, pressure, and humidity.  
      In operation, the outputs of the toner density sensor  64  and the environmental sensors  70  are received by the control unit  68 . Their outputs can also be stored in the memory  66 . Based on these sensor outputs, the control unit  68  is configured to determine or discriminate the life of the developer  62 . To determine the life of the developer, the control unit  68  is configured to use the sensor outputs at various different points including, for example, as follows: the time at which the toner cartridge  50  is replaced, the time when the developing device in the image forming apparatus  10  begins operating after installing a new toner cartridge  50 , a predetermined time after the replacement of the toner cartridge  50  or commencement of operation of the developing device, the time the toner density reaches a predetermined level, and the time the toner density reaches a normal operating level.  
      The control unit  68  uses one or more of these detected toner density levels and the times that they are detected to determine the life of the developer  62 . The control unit  68  also stores the detected toner density levels and the times at which they are detected in the memory  66 . In addition, based on the time and toner density data, the control unit  68  generates the control signals  72 . The control signals  72  utilize the results of the analysis by the control unit  68  and indicate, for example, whether or not the developer  62  needs to be replaced, a prediction of how much life the developer  62  has left, the toner density output from the toner density, the amount of time it took the toner density to reach a certain level, and any other relevant information that can be derived from the toner density sensor  64  and the environmental sensors  70 . The indications provided by the control signals  72  can be displayed by the image forming apparatus  10 , such as on the LCD display of the user interface  12 . It is also possible for the control signals  72  to be provided to a maintenance person or network administrator, such as by an e-mail message.  
       FIG. 4  is a graphical illustration of exemplary changes in toner density after a number of toner cartridge replacements consistent with the present invention. As shown in  FIG. 4 , the graph illustrates the changes in toner density when the toner is empty, when the toner is replaced after the first replacement, and after the twelfth replacement. When the toner is empty, the toner density value output from the toner density sensor  64  is at a relatively constant level. In normal operation, one typical value when the toner is empty is about 3.0 volts.  
      After the first replacement of the toner cartridge  50 , the toner density drops to a reference value. This reference value corresponds to a normal operating toner density value, and can be, for example, approximately 2.5 volts. The time T 1 , which can be referred to as a toner density recovery time, corresponds to the time it takes for the toner density output to reach the reference value after the first replacement of the toner cartridge  50 . Alternatively, instead of starting the time measurement from the time that the toner cartridge  50  is replaced, the time T 1  may correspond to the time it takes for the toner density output to reach the reference value after the developing device begins operation with the new toner cartridge  50 . For reasons of simplicity, the following description will generally refer to the time measurement beginning from the time of replacement of the toner cartridge  50 . It should be understood, however, that the beginning of the time measurement can also be from the time the developing device begins operation after the replacement without departing from the present embodiment.  
      As further shown in  FIG. 4 , the toner density also drops to a reference value after the twelfth replacement of the toner cartridge  50 . The time T 12  corresponds to the time it takes for the toner density output to reach the reference value after the twelfth replacement of the toner cartridge  50 . The time T 12  is greater than the time T 1 , meaning that it took longer to reach the reference value, i.e., the normal operating toner density value, after the twelfth replacement as compared with the first replacement. This increase in time between the first and twelfth replacements reflects the weakening of the carrier and a reduction of the fluidity of the developer  62 .  
      The time between the replacement of the toner cartridge  50  and reaching the reference value can be used to determine whether or not the developer  62  needs to be replaced. If the time is greater than a predetermined threshold, then the life of the developer  62  is determined to be over. In other words, when the time is greater than a predetermined threshold, the developer should be replaced and has reached a predetermined replacement point. The predetermined threshold generally depends upon the type of developer  62  being used and may be adjusted through the user interface  12  to a different setting. In general, the predetermined threshold can be set to some time between about 100 and 150 seconds, and more preferably to about 100 seconds. In other words, when it takes at least 100 seconds to reach the reference value from the point of replacing the toner cartridge, the developer is deemed to have reached the end of its useful life.  
      With reference to  FIG. 4 , the time T 1  may be  30  seconds, and the time T 12  may be 105 seconds. If the predetermined threshold is  100  seconds, then the control unit  68  would determine that the life of the developer  62  is over after the twelfth replacement of the toner cartridge  50 . To indicate the need to replace the developer  62 , the control unit  68  generates a control signal  72  that provides an indication on the display of the image forming apparatus  10  or creates an e-mail to indicate the need for the replacement (or other form of notification such as display on a central website). The indication may be generated, for example, at the time the determination is made or after the toner cartridge  50  becomes empty.  
       FIG. 5A  is a graphical illustration of exemplary changes in toner density after different toner cartridge replacements based on reaching a predetermined toner density consistent with the present invention.  FIG. 5A  is similar to  FIG. 4 , with the exception that  FIG. 5A  further includes an early reference value. The early reference value corresponds to a toner density value between the reference value of  FIG. 4 , which relates to the normal operating toner density of the developer  62 , and the toner density value when the toner is empty. The early reference value can be, for example, about 2.7 volts or 2.8 volts.  
      The times T 1  and T 12  in  FIG. 5A  correspond to the time between the first and twelfth replacement, respectively, of the toner cartridge  50  and the output of the toner density sensor reaching the early reference value. Like the times for reaching the reference value of  FIG. 4 , the time T 12  for reaching the early reference value is greater than the time T 1 . Further, the time between the replacement of the toner cartridge  50  and reaching the early reference value can also be used to determine whether or not the developer  62  needs to be replaced. If the time for reaching the early reference value is greater than a predetermined threshold, then the life of the developer  62  is determined to be over and the developer  62  should be replaced. Since the early reference value is reached before the reference value of  FIG. 4 , the predetermined threshold for reaching the early reference value is preferably set to be a shorter time, such as between about 30 and 60 seconds, and more preferably to about 30 seconds.  
      With reference to  FIG. 5A , the time T 1  may be 10 seconds, and the time T 12  may be 35 seconds. If the predetermined threshold for reaching the early reference value is 30 seconds, then the control unit  68  would determine that the life of the developer  62  is over after the twelfth replacement of the toner cartridge  50  based on the early reference value. To indicate the need to change the developer  62 , the control unit  68  generates a control signal  72  that provides an indication on the display of the image forming apparatus  10  or creates an e-mail to indicate the need for the change (or other form of notification such as a central website). The indication can be generated at the time the determination is made or after the toner cartridge  50  becomes empty.  
       FIG. 5B  is a graphical illustration of exemplary changes in toner density after different toner cartridge replacements based on reaching a predetermined time consistent with the present invention. The graphical illustration of  FIG. 5B  is also similar to that of  FIGS. 4 and 5 A. However, instead of having a reference value corresponding to a particular value of the toner density sensor  64 , the graphical illustration of  FIG. 5B  includes a reference time. The reference time corresponds to a particular time after the replacement of the toner cartridge  50  (or after the developing device begins to operate after replacement). The reference time can be, for example, between about 10 to 30 seconds, and more preferably about 10 seconds. At the reference time, the value of the toner density sensor  64  is detected by the control unit  68 .  
      Under this approach, the toner density V 1  corresponds to the toner density value of the toner density sensor at the reference time after the first replacement of the toner cartridge  50 , and toner density V 12  corresponds to the toner density value of the toner density sensor at the reference time after the twelfth replacement of the toner cartridge  50 . Alternatively, as shown in  FIG. 5B , the toner densities V 1  and V 12  may be the difference between the toner density value when the toner is empty and the toner density at the reference time after the first and twelfth replacements, respectively.  
      The density values V 1  and V 12  are compared to a threshold to determine if the life of the developer  62  is over. If the magnitude of the toner density value at the reference time is used for the density values V 1  and V 12 , then the threshold can be, for example, between about 2.85 and 2.95 volts, and more preferably about 2.9 volts. If the density value is greater than the threshold, then the developer  62  needs to be replaced. For example, if the reference value is 2.9 volts, and V 12  is 2.92 volts, then the developer  62  needs to be replaced after the twelfth replacement.  
      Alternatively, if the density values correspond to the difference between the values when the toner is empty and at the reference time is used, then the threshold can be, for example, between about 0.05 and 0.15 volts, and more preferably about 0.1 volts. In this case, if the density value is less than the reference value, then the developer  62  needs to be replaced. For example, if the reference value is 0.1 volts, and V 12  is 0.08 volts, then the developer needs to be replaced after the twelfth replacement.  
       FIG. 6  is a graphical illustration of exemplary changes in toner density at a predetermined time after each toner cartridge replacement consistent with the present invention. The graphical illustration of  FIG. 6  is derivative of the graphical illustration of  FIG. 5B . In particular, the graph of  FIG. 6  illustrates the density value of the toner density sensor  64  at a reference time after each toner cartridge replacement. The graph shows that the density value generally rises after each toner cartridge replacement. The life level, as shown in  FIG. 6 , corresponds to the reference value of  FIG. 5B , and can be, for example, about 2.9 volts. In addition, in this example, a reference time of 10 seconds is employed, as in the example of  FIG. 5B .  
      As described above with respect to  FIG. 5B , the control unit  68  can determine that the developer  62  needs to be replaced when the toner density value after the replacement of a toner cartridge  50  exceeds the life level. As shown in  FIG. 6 , at the twelfth replacement, the toner density value, which has been detected by the control unit  68  at the reference time after the replacement of the toner cartridge  50 , reaches/exceeds the life level. As such, the developer  62  needs to be replaced at this time.  
      In each of the prior examples described above with respect to  FIGS. 4-6 , a time or toner density value is compared to some threshold after the replacement of a toner cartridge  50  with a new toner cartridge to determine whether the developer  62  needs to be replaced. It is also possible to use the data collected after the replacements to make predictions about which replacement of the toner cartridge  50  will require the developer  62  to be replaced. In addition, the collected data can be adjusted to take into account environmental factors that may affect the values of the collected data.  
       FIG. 7  is a graphical illustration of exemplary changes in toner density after each toner cartridge replacement, further accounting for operating conditions and predicting developer life, consistent with the present invention. The format of the graphical illustration of  FIG. 7  is similar to that of  FIG. 6 , showing the output of the toner density sensor  64  at a predetermined or fixed time after each replacement of a toner cartridge  50 . In this case, however, the values from each replacement are used as a basis for predicting when the toner density detected at some predetermined time will surpass the life level, which enables the control unit  68  to identify after which replacement of the toner cartridge  50  that the developer  62  will need to be changed in advance.  
      As described above, after each replacement of a toner cartridge  50 , the control unit  68  can store the detected toner density in the memory  66  (such as at a predetermined time). The control unit  68  can reference these stored toner densities to make a prediction as to after which replacement of the toner cartridge  50  that the developer  62  will need to be changed. To make this prediction, the control unit  68  can perform a regression analysis based on the stored data to identify when the detected toner density will exceed the life level. It is also possible to calculate a slope derived from the most recently detected toner densities, and to use the slope to identify when the detected toner density will exceed the life level. For example, if the detected toner density for the fourth replacement is 2.77 volts and the detected toner density for the third replacement is 2.75 volts, then the slope would be 0.02 volts per replacement. Using that slope and assuming a life level of 2.9 volts, the control unit would predict the need to replace the developer  62  after the eleventh replacement as that replacement would have a detected toner density of 2.91 volts based on the determined slope. It should be understood that prediction of when the replacement of the developer  62  is needed can also be determined based on the times for reaching a reference level, such as described with reference to  FIGS. 4 and 5 A, and not just based on the toner density detected at a predetermined time.  
      The control unit  68  can also make predictions as to when the developer  62  needs to be replaced based on characteristics of the image forming apparatus. Such a prediction can be made at the time of the first toner cartridge replacement. For example, a time factor Ft and a voltage factor F v  for a particular image forming apparatus can be determined by experiment and stored in the memory  66 . After the first toner cartridge replacement, the time factor F t  can be multiplied by the time T 1  (shown in  FIG. 4 ) to determine a threshold value for time. In a subsequent toner cartridge replacement, if it takes longer than the threshold value for time to reach the toner density reference value from the point of replacing the toner cartridge, the developer  62  is deemed to have reached the end of its useful life. In an exemplary embodiment, the time factor F t  is in the range of approximately 2 to 3. Similarly, the voltage factor F v  can be multiplied by the density value V 1  (shown in  FIG. 5B ) to determine a threshold value for voltage. In a subsequent toner cartridge replacement, if the difference between the toner empty value and the toner density sensor value at the reference time is less than the threshold value for voltage, the developer  62  is deemed to have reached the end of its useful life. In an exemplary embodiment, the voltage factor F v  is in the range of approximately ¼ to ⅓. The life judgment value, for predicting life of toner, can be done in one replacement.  
      In addition to making predictions as to when the developer  62  needs to be replaced, the control unit  68  can also take into account environmental conditions. As described above, the environmental sensors  70  can detect various environmental conditions, such as temperature, pressure, and humidity. The environmental conditions  70  can affect both the operation of the toner density sensor  64  and the ability of the carrier to hold the toner  52 . For example, higher temperatures may cause the toner density sensor  64  to output higher toner density values than under normal operating conditions. Further, an increase in humidity may diminish the ability of the carrier to hold the toner  52 , thus causing the toner density values output by the toner density detector  64  to be higher than normal.  
      Understanding the effects of the environmental conditions on the toner density sensor  64  and the developer  62  allows the control unit  68  to normalize the detected toner density values. To be able to normalize the detected toner density values, the control unit  68  can refer to tables that identify how the detected toner density value should be adjusted taking into account the environmental conditions detected by the environmental sensors  70 . The tables can be developed, for example, by performing testing at varying environmental settings and recording how the changes in environmental settings affect the detected toner density values. The tables can be stored in a dedicated memory within the control unit  68  or stored in a separate storage area, such as the memory  66 . After normalizing the detected toner density values, the control unit  68  can store the normalized values in the memory  66 . By normalizing the detected toner density values, the control unit  68  is capable of more accurately determining when the developer  62  should be replaced.  
      As shown in  FIG. 7 , two data examples are shown as Operating Condition  1  and Operating Condition  2 . Operating Condition  1  corresponds to the raw data output by the toner density sensor  64  that has not been normalized by the control unit  68 . Operating Condition  2  corresponds to the normalization of the raw data output by the toner density sensor  64  based on the environmental conditions detected by the environmental sensors  70 . For example, if the temperature and humidity detected by the environmental sensors  70  are high in comparison to normal operating conditions for Operating Condition  1 , then it may be expected that the toner density values output by the toner density sensor  64  would be higher as well. Taking this into account, the normalized values would result in a data example resembling Operating Condition  2 .  
      As described above, it is possible to determine the life of the developer  62  based on the toner densities detected at predetermined times and based on the times it takes to reach a predetermined toner density. It is also possible, based on this data, to predict when the developer  62  will need to be replaced, as well as to account for the environmental conditions that may affect the time and toner density data.  
      The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. Of course, the various steps of detecting text, background, graphical and picture regions can be done in any order. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light in the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical application to enable one skilled in the art to utilize the invention in various other embodiments and with various modifications are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.