Patent Publication Number: US-2005123311-A1

Title: Image forming apparatus and method for sensing remaining amount of developer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2003-88416, filed on Dec. 6, 2003 and No. 2004-11006, filed on Feb. 19, 2004, in the Korean Intellectual Property Office, the entire disclosures of each are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an image forming apparatus and method for sensing the amount of remaining developer. More particularly, the present invention relates to an image forming apparatus having a developer sensing device for sensing an amount of remnant developer in a development cartridge.  
      2. Description of the Related Art  
      In a general image forming apparatus, a toner, as a developer, is supplied to an electrostatic latent image formed on a surface of the photosensitive medium by an exposing unit to make the electrostatic latent image into a toner image. The toner image is transferred and fused to a printing medium such that a desired image is printed.  
      The developer is stored in a developer loading unit. A printing operation can be smoothly performed before the developer is exhausted by continuously supplying it to the developer loading unit. Therefore, a developer sensing device is required for checking the remaining amount of developer stored in the developer loading unit.  
       FIG. 1  is a view illustrating the construction of a developing device having a conventional remnant developer sensing device. Referring to  FIG. 1 , a photosensitive drum  16  for rotating at a constant speed is installed within a housing  11 . In order to charge the photosensitive drum  16  at a high voltage, a charging roller  17  is installed on one surface of the photosensitive drum  16 . An exposing unit  20  for exposing a constant image to the photosensitive drum  16  charged by the charging roller  17  is installed at one side of the photosensitive drum  16 . A developing roller  15  for supplying the toner to form the electrostatic latent image formed on a surface of the photosensitive drum  16  into the toner image is installed to be in contact with the surface of the photosensitive drum  16 .  
      A toner loading unit  12  for storing the toner (the developer) is installed within the housing  11 . An agitator  13  for agitating to prevent the toner from hardening is installed at a lower side of the toner loading unit  12 . A supplying roller  14  for supplying the toner stored in the toner loading unit  12  to the developing roller  15  is installed to be rotated in contact with the developing roller  15 .  
      A regulation blade  20  for regulating a thickness of the toner attached to a surface of the developing roller  15  is installed on one surface of the developing roller  15 . A cleaning blade  18  for cleaning the toner remaining after the toner image is transferred to a paper is installed on one surface of the photosensitive drum  16 . The toner cleaned by the cleaning blade  18  is temporarily housed in a waste-toner storing unit  19  and then is recovered by a recovery unit (not shown) for reuse.  
      As the remnant developer sensing device, a pressure sensor  30  is installed at a lower side of the toner loading unit  12 . The pressure sensor  30  senses a weight of the developer in the toner loading unit  12 , and provides a constant vibration and an electrical signal to recognize a difference between an input value and an output value and compares the input value with the output value to sense the remaining amount of the developer.  
      A photo sensor is used in another method for sensing the remaining amount of the developer by using a photo sensor. In this method, a light emitting unit and a light receiving unit are installed facing with each other at both sides of the toner loading unit, and how much light radiated from the light emitting unit is received by the light receiving unit is measured to sense the amount of the toner remaining in the toner loading unit. In other words, if the light radiated from the light emitting unit is not transmitted to the light receiving unit, it means that the toner is sufficient. However, if the light radiated from the light emitting unit is transmitted to the light receiving unit, it means that the toner is almost exhausted.  
      Further, a pixel counter or a dot counter is used in another method. In this method, a dot number of real printed data is calculated, thereby calculating an amount of used developer using a constant operational formula.  
      However, in a method for sensing the remaining amount of the developer by using a pressure sensor, there is a limit in the pressure sensors ability to exactly measure how much of the developer remains.  
      Further, in the method for sensing the remaining amount of developer using a photo sensor, the photo sensor is limited in exactly measuring the remaining amount of developer because the amount of developer can be erroneously sensed as being sufficient even when the light radiated from the light emitting unit is cut off and not received at the light receiving unit due to a concentration of the developer at a specific position in the toner loading unit.  
      Additionally, in the method for sensing the remaining amount of the developer using a pixel counter, it is a difficult to exactly calculate the exhaustion time of the developer since variables necessary in printing operation such as the printing environment, the printing resolution, the print density, and the like influence the operational formula.  
     SUMMARY OF THE INVENTION  
      The present invention provides an image forming apparatus having a remnant developer sensing device for exactly sensing the exhaustion time of a developer to allow a smooth image forming operation.  
      According to an aspect of the present invention, there is provided an image forming apparatus comprising a photosensitive medium being formed an electrostatic latent image thereon; a developing roller developing a developer to the photosensitive drum being formed an electrostatic latent image; and a remnant developer sensing device sensing an electrical value between the developing roller and the photosensitive medium and determining the remaining amount of the developer of the developing device. The remnant developer sensing device sensing also compares the sensed value with a reference value to determine a remaining amount of the developer.  
      According to another aspect of the present invention, there is provided an image forming apparatus comprising a photosensitive medium being formed a latent image thereon; a developing roller developing a developer to the photosensitive drum being formed an electrostatic latent image; a sensing unit measuring an electrical value between the developing roller and the photosensitive medium; and a remnant developer sensing device including a pixel counter measuring the number of pixels of an image formed on a paper and calculating an amount of toner used to form the image, to sense a remaining amount of toner in a toner loading unit.  
      According to another aspect of the present invention, there is provided a method for determining the amount of remaining toner in an image forming apparatus comprising the steps of being formed a latent image on a photosensitive medium; developing a developer on the photosensitive drum being formed an electrostatic latent image; measuring an electrical value between the developing roller and the photosensitive medium; and determining the remaining amount of the developer of the developing device. In addition, the method also comprises the step of comparing the measured electrical value with a reference value to inform a user whether or not developer remains.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a schematic view illustrating a construction of a developing device having a conventional remnant developer sensing device;  
       FIG. 2  is a view illustrating a schematic construction of an image forming apparatus having a remnant developer sensing device according to an embodiment of the present invention;  
       FIG. 3  is a view illustrating a construction of a remnant developer sensing device according to an embodiment of the present invention; and  
       FIG. 4  is a view illustrating an operation of a remnant developer sensing device in case where a developer is sufficiently developed between a photosensitive medium and a developing roller according to one embodiment of the present invention;  
       FIG. 5  is a view illustrating an operation of a remnant developer sensing device in case where a developer is not developed from a developing roller to a photosensitive medium according to an embodiment of the present invention;  
       FIG. 6  is a view illustrating an operation of a remnant developer sensing device in case where a developer is insufficiently developed from a developing roller to a photosensitive medium according to an embodiment of the present invention;  
       FIG. 7  is a view illustrating an operation of a remnant developer sensing device in case where a developing roller and a photosensitive medium are in contact with each other according to an embodiment of the present invention;  
       FIG. 8  is a view illustrating a construction of a remnant developer sensing device according to another embodiment of the present invention;  
       FIG. 9  is a view illustrating an operation of a remnant developer sensing device in case where a developer is sufficiently developed between a photosensitive medium and a developing roller according to another embodiment of the present invention;  
       FIG. 10  is a view illustrating an operation of a remnant developer sensing device in case where a developer is not transferred from a developing roller to a photosensitive medium according to another embodiment of the present invention;  
       FIG. 11  is a view illustrating an operation of a remnant developer sensing device in case where a developer is insufficiently developed from a developing roller to a photosensitive medium according to another embodiment of the present invention; and  
       FIG. 12  is a view illustrating an operation of a remnant developer sensing device in the case where a developing roller and a photosensitive medium are in contact with each other according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
       FIG. 2  is a schematic view illustrating a construction of an image forming apparatus having a remnant developer sensing device according to one embodiment of the present invention, and  FIG. 3  is a view illustrating a construction of the remnant developer sensing device according to one embodiment of the present invention.  
      Referring to  FIGS. 2 and 3 , a paper cassette  110  for storing a paper (P) is detachably installed at a lower portion of a body  100 , and a multi-purpose paper feeding tray  123  for loading the paper (P) is installed at a side portion of the body  100 . Pickup rollers  121  and  124  for picking up the loaded paper (P) sheet by sheet are respectively installed at upper sides of the cassette  110  and the multi-purpose paper feeding tray  123 .  
      A developing unit  130  for developing an image and a transferring unit  140  for transferring the image developed by the developing unit  130  to the paper (P) are installed along a transport path through which the paper picked-up by the pickup rollers  121  and  124  is transported by a transport roller  122 .  
      The developing unit  130  is surrounded by a housing  130   a . A photosensitive medium  131  on the surface of which an electrostatic latent image is formed by an exposing unit  150  is installed within the housing  130   a  to be faced with the transferring unit  140  with the transported paper being interposed therebetween.  
      The developing unit  130  comprises a developer loading unit  132  for storing a toner (developer); an agitator  133  installed at a lower portion of the developer loading unit  132  to agitate the toner to prevent the developer housed in the developer loading unit  132  from being hardened; a developing roller  135  installed to be at a distance from the photosensitive medium  131  to supply the developer to the electrostatic latent image formed on the surface of the photosensitive medium  131 ; and a supplying roller  134  installed to be rotated in contact with the developing roller  135  to supply the developer loaded on the developer loading unit  132  to the developing roller  135 .  
      Further, the developing unit  130  includes a regulation blade  136  for regulating the thickness of the developer attached to the surface of the developing roller  135  by the supplying roller  134 ; and a cleaning blade  138  for cleaning the remaining toner not transferred from the photosensitive medium  131  to the paper (P). Waste-toner cleaned by the cleaning blade  138  is stored in a waste-toner storing unit  139  and then is recovered by a recovery unit (not shown).  
      The transferring unit  140  is installed to face and to be in contact with the photosensitive medium  131  to apply pressure on the paper (P) toward the photosensitive medium  131  such that a toner image formed on the photosensitive drum  131  is transferred to the paper (P).  
      The toner image transferred to the paper (P) by the transferring unit  140  is heated and pressurized through a fixing unit  160  installed at a paper path to be fused to the paper (P), and then the paper (P) is discharged to the exterior of the body  100  by discharging rollers  171  and  172  on a paper discharge tray  180 .  
      The image forming apparatus includes the remnant developer sensing device  190  to sense an amount of the developer stored in the developer loading unit  132 .  
      The remnant developer sensing device  190  comprises a sensing unit  191  installed to be electrically connected to the photosensitive medium  131  to measure an electrical value between the developing roller  135  and the photosensitive medium  131 ; and a controlling unit  192  for comparing the measured value of the sensing unit  191  and a predetermined reference value with each other to check whether the measured value between the developing roller  135  and the photosensitive medium  131  is less or more than the reference value such that the remaining amount of the developer housed in the developer loading unit  132  is sensed. The measured value of the sensing unit  191  and the predetermined reference value are stored in a memory unit (not shown).  
      The remnant developer sensing device  190  measures an electrical value between the developing roller  135  and the photosensitive medium  131  to sense the remaining amount of the developer housed in the developer loading unit  132 .  
      The developer from the developing roller  135  is developed onto the photosensitive medium  131  by using a voltage difference between the developing roller  135  and the photosensitive medium  131 . Therefore, in order to generate the voltage difference, the developing roller  135  is connected with a power source  193  to have a constant electric potential, and the photosensitive medium  131  is charged to a high potential by a charge roller  137  and a portion of the photosensitive medium  131  exposed using the exposing unit  150  has a varied potential to generate an electric potential difference with the developing roller  135 . A direct current power source (DC), an alternating current power source or a combination of the direct current power source and the alternating current power source can be used as a power source  193  connected to the developing roller  135 .  
       FIG. 4  is a view illustrating the operation of a remnant developer sensing device in the case where a developer is sufficiently developed between a photosensitive medium and a developing roller according to an embodiment of the present invention.  FIG. 5  is a view illustrating an operation of a remnant developer sensing device in the case where a developer is not developed from a developing roller to a photosensitive medium according to one embodiment of the present invention.  FIG. 6  is a view illustrating an operation of a remnant developer sensing device in the case where a developer is insufficiently developed from a developing roller to a photosensitive medium according to an embodiment of the present invention.  FIG. 7  is a view illustrating an operation of a remnant developer sensing device in the case where a developing roller and a photosensitive medium are in contact with each other according to an embodiment of the present invention.  
      Referring to  FIG. 4 , while the developer is developed from the developing roller  135  to the photosensitive medium  131 , the developing roller  135  and the photosensitive medium  131  are connected to each other by the toner (T). At this time, since the toner (T) is a conductive material, the photosensitive medium  131  is electrically connected with the developing roller  135 . Since the developing roller  135  and the photosensitive medium  131  are grounded, a closed circuit is wholly constituted.  
      Accordingly, the sensing unit  191  can measure the electrical value between the developing roller  135  and the photosensitive medium  131 . The electrical value measured by the sensing unit  191  between the developing roller  135  and the photosensitive medium  131  can be any one of a current value (I), a voltage value (V) or an electrostatic capacitance (C).  
      In the case where the sensing unit  191  is used to measure the current value (I) flowing between the developing roller  135  and the photosensitive medium  131 , a current meter is installed to measure the current value (I) flowing between the developing roller  135  and the photosensitive medium  131 . The current value flowing when the developer is normally developed from the developing roller  135  to the photosensitive medium  131  is previously measured and compared with the stored reference value. If it is identical with the reference value, it means that the developer loading unit  132  is filled with the developer.  
      As shown in  FIG. 5 , if due to an insufficient developer, the developer is attached only to the surface of the developing roller  135  and is not developed to the photosensitive medium  131 , the developer is insufficiently loaded on the developer loading unit  132 . At this time, the current does not flow between the developing roller  135  and the photosensitive medium  131 , thereby causing the current value (I) measured by the sensing unit  191  to be approximately zero. Since this value is less than the reference value, it means that the developer loading unit  132  does not have a sufficient amount of the developer remaining to form a quality reproduction.  
      Further, even in the case where the developer partially connects the developing roller  135  with the photosensitive medium  131  as shown in  FIG. 6 , the current value (I) measured by the sensing unit  191  is less than in the case where the developer connects the developing roller  135  with the photosensitive medium  131  as shown in  FIG. 4 . Since the current value is less than the reference value, it means that the developer loading unit  132  does not have a sufficient of developer.  
      A reason for why the electrical value is measured between the developing roller  135  and the photosensitive medium  131  is to measure the remaining amount of developer loaded in the developer loading unit  132  as described above is as follows. The conventional remnant developer sensing devices quantitatively measure how much developer is loaded on the developer loading unit  132 . Actually, an insufficient amount of developer is supplied, even though the developer loading unit  132  is filled with developer, to the developing roller  135 . Therefore, the developer is not supplied with its normal amount of developer from the developing roller  135  to the photosensitive medium  131 . Therefore, the toner image is not formed on the photosensitive medium  131 .  
      Therefore, when the developer is normally supplied from the developing roller  135  to the photosensitive medium  131 , the developer is sufficiently loaded on the developer loading unit  132 . When the developer is abnormally supplied from the developing roller  135  to the photosensitive medium  131 , the developer is insufficient or exhausted from the developer loading unit  132 .  
      Referring to  FIG. 7 , a basic construction of the remnant developer sensing device  190  is the same as that of  FIG. 3 , but the toner is transferred from the developing roller  135  to the photosensitive medium  131  when the developing roller  135  is in contact with the photosensitive medium  131 .  
      The electrical value measured by the sensing unit  191  between the developing roller  135  and the photosensitive medium  131  is a sum of an electrical value caused by a contact thereof and an electrical value caused by the developer while the developer passes between the developing roller  135  and the photosensitive medium  131 .  
      Accordingly, if the amount of the developer passing between the developing roller  135  and the photosensitive medium  131  varies, the electrical value sensed by the sensing unit  191  is varied. This is used to sense the remaining amount of the developer.  
      The controlling unit  192  is connected with a displaying unit  194  to compare the measured value sensed by the sensing unit  191  with the reference value and display the comparative result such that a user can easily recognize the remaining amount of the developer loaded on the developer loading unit  132 .  
       FIG. 8  is a view illustrating a construction of a remnant developer sensing device according to another embodiment of the present invention. The same reference numerals as those of  FIG. 3  denote the same elements performing the same functions.  
      Referring to  FIG. 8 , the remnant developer sensing device  290  includes a sensing unit  291 , which is an electrical sensor, for sensing an electrical value between a developing roller  135  and a photosensitive medium  131  and comparing the sensed value with a reference value to determine a remaining amount of toner; a pixel counter  296  for measuring the number of pixels of an image formed on a paper (P) and calculating a used amount of toner, to sense the remaining amount of toner in the toner loading unit  132 ; a memory unit  295  for storing the sensed value of the sensing unit  291  and the reference value, and storing a value of the sensed remaining amount of toner of the pixel counter  296  and a value of a fully loaded amount of the toner of the toner loading unit  132 ; a displaying unit  294  for informing the user of information on whether or not the toner remains; and a controlling unit  292  for performing general controls of the sensing unit  291 , the pixel counter  296 , the memory unit  295  and the displaying unit  294 .  
       FIG. 9  is a view illustrating an operation of the remnant developer sensing device in the case where the developer is sufficiently developed between the photosensitive medium and the developing roller according to another embodiment of the present invention.  
      Referring to  FIG. 9 , while the toner is developed from the developing roller  135  to the photosensitive medium  131 , the developing roller  135  and the photosensitive medium  131  are connected to each other by the toner (T). At this time, since the toner (T) is a conductive material, the photosensitive medium  131  is electrically connected with the developing roller  135 . Since the developing roller  135  and the photosensitive medium  131  are grounded, a closed circuit is wholly constituted.  
      Accordingly, the sensing unit  291  can measure the electrical value between the developing roller  135  and the photosensitive medium  131 . The electrical value measured by the sensing unit  191  between the developing roller  135  and the photosensitive medium  131  can be any one of a current value (I), a voltage value (V) or an electrostatic capacitance (C).  
      In the case where the sensing unit  191  is used to measure the current value (I) flowing between the developing roller  135  and the photosensitive medium  131 , a current meter is installed to measure the current value (I) flowing between the developing roller  135  and the photosensitive medium  131 . The current value, which flows when the developer is normally developed from the developing roller  135  to the photosensitive medium  131 , is previously measured to compare the reference value stored in the memory unit  295  with the measured value measured in the sensing unit  291 . If this measured value is identical with the reference value, it means that the toner is normally supplied to the developing roller  135 . Therefore, the toner loading unit  132  is filled with the toner.  
       FIG. 10  is a view illustrating an operation of the remnant developer sensing device in the case where the developer is not developed from the developing roller to the photosensitive medium according to another embodiment of the present invention.  
      As shown in  FIG. 10 , if the toner is attached only to a surface of the developing roller  135  and is not developed onto the photosensitive medium  131  due to the insufficiency of the toner, the toner is insufficiently loaded on the toner loading unit  132 . At this time, the current does not flow since the developing roller  135  is spaced apart from the photosensitive medium  131 . Accordingly, the current value (I) measured by the sensing unit  291  is approximately zero. Since this value is less than the reference value, it means that the developer loading unit  132  does not have the remaining amount of the developer.  
       FIG. 11  is a view illustrating an operation of a remnant developer sensing device in the case where a developer is insufficiently developed from a developing roller to a photosensitive medium according to another embodiment of the present invention.  
      Further, even in the case where the developer partially connects the developing roller  135  with the photosensitive medium  131  as shown in  FIG. 11 , the current value (I) measured by the sensing unit  291  is less than in the case where the developer connects the developing roller  135  with the photosensitive medium  131  as shown in  FIG. 4 . Since the current value is less than the reference value, it means that the developer loading unit  132  does not have a sufficient amount of developer remaining to provide a quality reproduction.  
       FIG. 12  is a view illustrating an operation of the remnant developer sensing device in the case where the developing roller and the photosensitive medium are in contact with each other according to another embodiment of the present invention.  
      Referring to  FIG. 12 , the toner is transferred from the developing roller  135  to the photosensitive medium  131  when the developing roller  135  is in contact with the photosensitive medium  131 .  
      The electrical value measured by the sensing unit  291  between the developing roller  135  and the photosensitive medium  131  is a sum of an electrical value between the photosensitive medium  131  and the developing roller  135 , which is caused by a contact therebetween, and an electrical value caused by the toner when the toner passes between the developing roller  135  and the photosensitive medium  131 .  
      Accordingly, if the amount of the toner passing between the developing roller  135  and the photosensitive medium  131  varies, the electrical value sensed by the sensing unit  291  is varied. This is used to sense the remaining amount of the toner.  
      The controlling unit  292  is connected with a displaying unit  294  to compare the measured value sensed by the sensing unit  291  with the reference value stored in the memory unit  295  and inform the user with a message of “toner low or “toner empty” or other similar message. Accordingly, the user can easily recognize the remaining amount of the toner loaded on the developer loading unit  132 .  
      Alternatively, the pixel counter  296  calculates the number of pixels or the number of dots printed on the paper by using a pixel counter or a dot counter to calculate an amount of the used toner by using a predetermined operation formula and store the calculate amount in the memory unit  295 . Additionally, the controlling unit  292  compares the measured amount measured in the pixel counter  296  with an amount of an initial toner of the toner loading unit  231  to quantitively sense a remaining amount of toner.  
      The remaining amount of toner can-be displayed using a character or a specific symbol through a display panel, or indicated to the user through a lamp on a panel. Further, at a specific time point, usage information or information related to an amount of remaining developer can be output. Additional information can be provided by outputting corresponding information when the user presses a predetermined key.  
      The electrical sensing unit  291  and the pixel counting unit  296  are operated at the same time when a print signal is transmitted to the image forming apparatus, and they continuously measure the remaining amount of toner during the printing.  
      The below is an explanation of why the electrical value is measured between the photosensitive medium  131  and the developing roller  135  to measure the remaining amount of toner loaded on the toner loading unit  132  as described above.  
      Sometimes, the toner is not supplied in sufficient amounts even though the toner loading unit  132  is filled with toner because the toner is not supplied from the developing roller  135  to the photosensitive medium  131  in its normal fashion. Therefore, the toner image is not formed on the photosensitive medium  131 .  
      Accordingly, when the toner is normally supplied from the developing roller  135  to the photosensitive medium  131 , the toner is sufficiently loaded on the toner loading unit  132 . When the toner is abnormally supplied from the developing roller  135  to the photosensitive medium  131 , the toner is insufficient in the toner loading unit  132 .  
      Further, it is required to quantitively measure how much of the toner remains in the toner loading unit  132 . This can be realized using the pixel counting method.  
      As described above, the image forming apparatus according to the present invention has an effect in that an exhaustion time for the developer can be exactly recognized by measuring a variation of the electrical value depending on the toner amount provided between the developing roller and the photosensitive medium to detect the remaining amount of developer and at the same time, quantitively measuring the remaining amount of toner in the toner loading unit by using a pixel counter.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.