Patent Publication Number: US-6987935-B2

Title: Developer supply and recovery system used with wet electro-photographic image forming apparatus, and method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2003-90558, filed on Dec. 12, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present general inventive concept relates to a developer supply and recovery system used with a wet electro-photographic image forming apparatus, and more particularly, to a developer supply and recovery system used with a wet electro-photographic image forming apparatus, and a developer supply and recovery method using the same, in which whether a developer supply unit and a developer recovery unit are normally operated before printing is sensed, and a noise generated from the recovery unit is reduced during printing. 
   2. Description of the Related Art 
   In a wet electro-photographic image forming apparatus, a charge unit charges a surface of a photosensitive medium, and the charged surface of the photosensitive medium is exposed to light radiated from an exposure unit depending on a print signal to form an electrostatic latent image. An image is formed from the electrostatic latent image using a developer supplied from a development unit, and then a transfer belt transfers the formed image onto a print medium, thereby obtaining a desired image. 
   The wet electro-photographic image forming apparatus employs a contact charge way in which the charge unit is in contact with the photosensitive medium to form an electrical potential on the surface of the photosensitive medium. A difference in electrical potentials applied to the respective units is used to attach the developer to the electrostatic latent image formed on the photosensitive medium or to transfer the image from the photosensitive medium to the transfer belt or from the transfer belt to the print medium. 
   Further, the wet electro-photographic image forming apparatus includes a development roller to attach the developer to the electrostatic latent image formed on the photosensitive medium, and a developer supply and recovery system to supply the developer to a development roller and to recover a remaining developer. 
     FIG. 1  is a view illustrating a conventional developer supply and recovery system of a wet electro-photographic image forming apparatus. 
   Referring to  FIG. 1 , a developer supply and recovery system includes an ink cartridge  10  for storing a developer therein, a supply line  11  for connecting the ink cartridge  10  with a development bath  14 , a supply pump  12  installed on a supply line  11  to supply the developer from the ink cartridge  10  to the development bath  14 , a recovery line  17  for connecting the ink cartridge  10  with a developer container  13  for temporarily containing the developer overflowing from the development bath  14 , and a recovery pump  18  installed on the recovery line  17  to recover the developer contained in the developer container  13  to the ink cartridge  10 . 
   The development bath  14  includes a development roller  16  and a photosensitive drum  15  at an upper side thereof. The development roller  16  is installed to have one portion thereof dip into the developer of the development bath  14  such that the stored developer is supplied to the photosensitive drum  15  having an electrostatic latent image formed thereon. The photosensitive drum  15  is installed to rotate in contact with the development roller  16  while developing the electrostatic latent image with the supplied developer. 
   An operation of the above-constructed developer supply and recovery system will be described. 
   If the supply pump  12  is operated, the developer stored in the ink cartridge  10  flows into the development bath  14  through the supply line  11 , and the developer supplied to the development bath  14  is transferred to the photosensitive drum  15  by the development roller  16  to develop the electrostatic latent image formed on the photosensitive drum  15 . 
   In the meantime, the developer not supplied to the photosensitive drum  15  by the development roller  16  overflows from the development bath  14 , and is then contained in the developer container  13 . The developer contained in the developer container  13  is recovered by the recovery pump  18  to the ink cartridge  10  through the recovery line  17  provided at a bottom side of the developer container  13  to be re-supplied to the development bath  14  through the supply line  11 , thereby maintaining a print operation. 
   However, since the conventional developer supply and recovery system cannot exactly perceive states of the supply line  11 , the supply pump  12 , the recovery line  17  and the recovery pump  18 , it cannot perceive whether or not the developer normally flows from the development bath  14  to the ink cartridge  10 . 
   Accordingly, the conventional developer supply and recovery system has drawbacks in that if the supply line  11  and the supply pump  12  malfunction, the developer is not smoothly supplied to the development roller  16 , thereby causing the electrostatic latent image not to be developed, and if the recovery line  17  and the recovery pump  18  malfunction, the developer overflows from the development bath  14  such that the developer contained in the developer container  13  is not recovered but overflows from the developer container  13 , thereby polluting image forming apparatuses. 
   Further, the conventional developer supply and recovery system has drawbacks in that if the recovery pump  18  is not exactly controlled, the recovery pump  18  operates to recover the developer in a state where the developer does not exist at the developer container  13 . That is, in a state where an inlet of the supply line  17  is not completely dipped into the developer contained in the developer container  13 , air is introduced into the recovery line  17  together with the developer, thereby causing noise. The noise occurs because an amount of the developer contained in the developer container  13  is not appropriately controlled. 
   SUMMARY OF THE INVENTION 
   In order to solve the foregoing and/or other problems, it is an aspect of present general inventive concept to provide a developer supply and recovery system used with a wet electro-photographic image forming apparatus, and a developer supply and recovery method using the same, in which whether a developer supply pump and a developer recovery pump are normally operated before printing is sensed, thereby reducing a noise generated from the recovery unit during printing. 
   Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
   The foregoing and/or other aspects of the present general inventive concept, may be achieved by providing a developer supply and recovery system used with a wet electro-photographic image forming apparatus, the system including a recovery pump installed on a recovery line to recover a developer from a developer container to an ink cartridge, an overflow sensor installed at the developer container to sense the developer overflowing from a development bath, a control unit which controls operations of a supply pump and the recovery pump in response to a value sensed by the overflow sensor, wherein operation states of the supply pump and the recovery pump are sensed, and the developer is appropriately contained in the developer container such that air is not introduced together with the developer recovered by the recovery pump, thereby reducing a noise. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a view illustrating a conventional developer supply and recovery system of a wet electro-photographic image forming apparatus; 
       FIG. 2  is a view illustrating a wet electro-photographic image forming apparatus including a developer supply and recovery system according to an embodiment of the present general inventive concept; 
       FIG. 3  is a view illustrating the developer supply and recovery system of  FIG. 2 ; 
       FIGS. 4A and 4B  are flow charts illustrating a method of determining whether a developer is normally supplied and recovered according to another embodiment of the present general inventive concept; 
       FIG. 5  is a flow chart illustrating a developer recovery method of reducing noise according to another embodiment of the present general inventive concept; and 
       FIG. 6  is a timing diagram illustrating the method of determining whether a developer is normally supplied and recovered in the developer supply and recovery system, as shown in  FIGS. 2 through 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
     FIG. 2  is a view illustrating a wet electro-photographic image forming apparatus including a developer supply and recovery system according to an embodiment of the present general inventive concept, and  FIG. 3  is a view illustrating an a developer supply and recovery system according to another embodiment of the present general inventive concept. 
   Referring to  FIGS. 2 and 3 , the wet electro-photographic image forming apparatus may include a development unit  100 , a developer supply and recovery system  130 , a transfer unit  140  and a fixing unit  150 . 
   The development unit  100  may include a plurality of development units so as to form a color image, and can supply a developer T to each of electrostatic latent images formed on photosensitive drums  120  by exposure units  122  to develop the electrostatic latent images. The development unit  100  may include a development bath  111  to contain the developer T, and a developer container  110  to temporarily contain the developer overflowing from the development bath  110 . 
   A development roller  112  being in contact with the photosensitive drum  120  to supply the developer T to the photosensitive drum  120  can be installed in the development bath  111  such that a portion thereof is dipped into the developer T. Accordingly, the developer T contained in the development bath  111  can be supplied to the photosensitive drum  120  through the development roller  112  such that the electrostatic latent image formed on the photosensitive drum  120  is developed using the developer T, and the developer T not supplied to the photosensitive drum  120  by the development roller  112  may overflow from the development bath  111  to flow into the developer container  110 . 
   The developer supply and recovery system  130  may include a supply pump  133  installed on a supply line  132  to supply the developer T stored in an ink cartridge  131  to the development bath  111 , a recovery pump  136  installed on a recovery line  135  to recover the developer T contained in the developer container  110  to the ink cartridge  131 , and an overflow sensor  134  installed at the developer T container  110  to sense the developer overflowing from the development bath  111 . 
   Further, the developer supply and recovery system  130  may further include a control unit  137  connected to the overflow sensor  134 , the supply pump  133  and the recovery pump  136  to control their operations. 
   Referring to  FIG. 3 , the developer container  110  may have indications of H 0 , H 1 , and H 2  each representing height from a bottom of the developer container  110 . These indications are determined by predetermined heights depending on an amount of the developer T stored by the supply pump  133  in the developer container  110  and exhausted by the recovery pump  136  from the developer container  110 . 
   The transfer unit  140  can be supported by a driving roller  141 , a development backup roller  142  and a transfer backup roller  143  such that a closed curve configuration is formed. The transfer unit  140  may include a transfer belt  145  having the image developed by the developer T transferred from the photosensitive drum  120  and rotating together with the driving roller  141 , the transfer backup roller  143 , and the development backup roller  142 , and a transfer roller  144  to face the transfer backup roller  143  with respect to the transfer belt  145  such that the transfer belt  145  is interposed therebetween to transfer the image transferred to the transfer belt  145  to paper S. 
   The fixing unit  150  is installed on a paper eject path to apply heat and pressure to the image transferred to the paper S to fuse the image on the paper S. 
   A reference numeral  121  represents a cleaning blade installed to be in contact with the photosensitive drum  120  to clean the remaining developer that is not transferred from the photosensitive drum  120  to the transfer belt  145 . A reference numeral  122  represents a charger to charge the photosensitive drum  120 . 
   An operation of the above-constructed wet electro-photographic image forming apparatus is described with reference to  FIGS. 2 and 3 . 
   The developer stored in the ink cartridge  131  can be supplied to the development bath  111  through the supply line  132 . The developer supplied to the development bath  111  can be supplied to the photosensitive drum  120  by the development roller  112  to develop the electrostatic latent image formed on the photosensitive drum  120 . 
   The images respectively formed on the photosensitive drums  120  by the developing unit  100  having the plurality of development units through the above operation can be sequentially transferred to the transfer belt  145  to overlap one another so that a desired image is formed. 
   The image formed on the transfer belt  145  can be transferred to the paper S passing between the transfer roller  143  and the transfer backup roller  144 , and the transferred image can be fixed on the paper S when the paper S passes through the fixing unit  150 . 
   Meanwhile, the developer T which Is not supplied to the photosensitive drum  120  or overflows from the development bath  111 , can be stored in the developer container  110  and then, can be recovered using the recovery pump  136  to the ink cartridge  131 . The overflow sensor  134  can sense an amount or a height of the developer T overflowing from the development bath  111  to the developer container  110 . The control unit  137  connected to the overflow sensor  134  can control operations of the supply pump  133  and the recovery pump  136  to allow an appropriate amount of the developer T to be contained in the developer container  110  or to determine whether the supply pump  133  and the recovery pump  136  are operated in an orderly fashion. 
     FIGS. 4A and 4B  are flow charts illustrating a method of determining whether a developer is normally supplied and recovered according to another embodiment of the present general inventive concept, and  FIG. 6  is a timing diagram illustrating the method of determining whether the developer is normally supplied and recovered in the wet electro-photographic image forming apparatus shown in  FIGS. 2 through 5 . 
   Referring to  FIGS. 2 through 6 , before the wet electro-photographic image forming apparatus performs a print operation, a speed of the developer flowing through the supply pump  133  and the recovery pump  136  is measured and determined so as to determine whether the developer smoothly flows through the supply line  133  and the recovery line  135  being not clogged or whether the supply pump  133  and the recovery pump  136  are normally operated. 
   The supply pump  133  can be operated to supply the developer stored in the ink cartridge  131  to the development bath  111  (operation  210 ). The control unit  137  can control to measure a time interval t 1  counted (calculated) from an operation time of the supply pump  133 , and to determine whether the time interval t 1  lapses. Here, the time interval t 1  represents a predetermined time taken for the developer to be supplied by an operation of the supply pump  133  such that the developer overflowing from the development bath  111  is housed up to the height H 2  of the developer container  110 . The time interval t 1  can be determined depending on the supply pump  133  and the supply line  132 . 
   If it is determined that the time interval t 1  lapses, the control unit  137  can control to determine whether the overflow sensor  134  senses the developer (operation  222 ). If it is determined that the time interval t 1  does not lapse, it is again determined whether the time interval t 1  lapses. 
   If the overflow sensor  134  does not sense the developer, it is determined that the developer does not flow from the development bath  111  to the developer container  110  even though the time interval t 1  counted from the operation time of the supply pump  133  lapses. Since it indicates that the supply line  132  is clogged or the supply pump  133  is not smoothly operated, a message of “supply-pump operation error” can be displayed on a display of the image forming apparatus or can be notified to a user (operation  225 ). 
   When the overflow sensor  134  senses the developer, a supply speed of the developer supplied to the development bath  111  through the supply line  132  can be calculated (operation  223 ). Since the time interval t 1  taken to supply the developer, and the amount of the developer supplied to the development bath  111  can be appreciated, the supply speed of the developer can be calculated. 
   The control unit  137  can measure the calculated supply speed of the developer to compare the measured supply speed with a previous stored supply speed. When it is determined that they are identical to each other, it is determined that the supply line  132  and the supply pump  133  are normally operated. When they are not identical to each other, it is determined that the supply line  132  is clogged or the supply pump  133  is not normally operated, thereby displaying the message of “supply-pump operation error” to notify the user. 
   In the determining operation  221  through the displaying operation  225 , it is determined whether the developer is normally supplied through the supply line  132  and the supply pump  133  in operation  220 . 
   The control unit  137  can stop the supply pump  133  after a time interval t 2  lapses (operation  230 ). Here, the time interval t 2  represents an interval from a time when the overflow sensor  134  senses the developer, until a time when the developer reaches the height H 2 . 
   The control unit  137  can control the recovery pump  136  to operate to recover the developer contained in the developer container  110  to the ink cartridge  131  (operation  240 ). The control unit  137  can measure a time interval t 3  from an operation time of the recovery pump  136 , and can determine whether the time interval t 3  lapses (operation  251 ). Here, the time t 3  represents a predetermined time taken for the developer to be reduced from the height H 2  to the height H 1  of the developer container  110  when the developer is recovered by an operation of the recovery pump  136  from the developer container  110  to the ink cartridge  131 . The time t 3  can be determined depending on the recovery pump  136  and the recovery line  135 . 
   If it is determined that the time interval t 3  lapses in operation  251 , the control unit  137  can determine whether the overflow sensor  134  senses the developer (operation  252 ). If it is determined that the time interval t 3  does not lapse, the determining operation  29  can repeat to determine whether the time interval t 3  lapses. 
   If the overflow sensor  134  senses the developer, it indicates that the developer is not normally recovered, thereby not being reduced from the height H 2  to the height H 1  of the developer container  110  even though the time interval t 3  lapses from the operation time of the recovery pump  136 . Since it indicates that the recovery line  135  is clogged or the recovery pump  136  is not smoothly operated, a message of “recovery-pump operation error” can be displayed on the display of the image forming apparatus or can be notified to the user (operation  255 ). 
   When the overflow sensor  134  senses the developer, the supply speed of the developer recovered from the developer container  110  to the ink cartridge  131  through the recovery line  135  can be calculated (operation  253 ). Since the time interval t 3  taken to recover the developer, and the amount of the developer supplied to the ink cartridge  131  can be appreciated, the recovery speed of the developer can be calculated. 
   The control unit  137  can measure the calculated recovery speed of the developer to compare the measured recovery speed with the previously stored recovery speed. When it is determined that they are identical to each other, it can be determined that the recovery line  135  and the recovery pump  136  are normally operated. When it is determined that they are not identical, it can be determined that the recovery line  135  is clogged or the recovery pump  136  is not normally operated, thereby displaying the message of “recovery-pump operation error” to notify the user. 
   In the determining operation  251  through the displaying operation  255 , it is determined whether or not the developer is normally supplied through the recovery line  135  and the recovery pump  136  in operation  250 . 
   The control unit  137  can stop the recovery pump  136  after a time interval t 4  lapses (operation  260 ). Here, the time interval t 4  represents an interval from a time when the overflow sensor  134  senses the recovered developer, until a time when the developer reaches the height H 0 . 
     FIG. 5  is a flow chart illustrating a developer recovery method of reducing noise according to another embodiment of the present general inventive concept. 
   Referring to  FIGS. 3 and 5 , while the print operation is performed, the noise can be prevented from being generated due to the air introduced together with the developer into the recovery line  135  in a procedure of recovering when the developer is recovered from the developer container  110  to the ink cartridge  131 . 
   The noise may occur when the developer is recovered to the ink cartridge  131  through the recovery pump in a state where the developer is not housed up to an appropriate height of the developer container  110 . The amount of the developer and the operation of the recovery pump  136  are appropriately controlled such that the noise can be prevented from being generated while the developer is recovered together with the air from the development container  110 . 
   The supply pump  133  can be operated to supply the developer stored in the ink cartridge  131  to the development bath  111  (operation  350 ). The developer overflowing from the development bath  111  can be housed while gradually filling in the developer container  110 . The overflow sensor  134  can determine whether to sense the developer (operation  320 ). The overflow sensor  134  can sense the developer from the time when the developer fills up to the height H 1 . When the overflow sensor  134  does not sense the developer, the determining operation  320  can repeat to determine whether the overflow sensor  134  senses the developer. 
   If the overflow sensor  134  senses the developer, the recovery pump  136  can be operated after the time interval t 2  lapses (operation  330 ). In this case, both of the supply pump  133  and the recovery pump  136  can operate, and the developer contained in the developer container  110  reaches at least the height H 1 . 
   Next, it is determined whether the overflow sensor  134  senses the developer ( 340 ). It is also determined whether the developer contained in the developer container  110  is gradually reduced and reached to the height H 1  while the developer contained in the developer container  110  is recovered by the recovery pump  136 . 
   If the overflow sensor  134  senses the developer, it indicates that the developer is not yet reduced down to the height H 1 . If it does not sense the developer, it indicates that the developer is reduced down to the height H 1  while being recovered. 
   If the overflow sensor  134  does not sense the developer, the recovery pump  136  can be stopped after the time interval t 4  lapses (operation  360 ). The recovery pump  136  stops to prevent the noise from being generated while the developer is recovered to the recovery line  135  together with the air if the developer is reduced down to the height H 0 . 
   It is determined whether the print operation is performed (operation  360 ) in the above state. If it is determined that the image forming apparatus is in a print state, the determining operation  320  can repeat the above operation, and if it is determined that the image forming apparatus is not in the print state, the procedure is ended. 
   As described above, the developer supply and recovery system of the wet electro-photographic image forming apparatus may have advantages in that the overflow sensor is installed to exactly sense the amount of the developer contained in the developer container, and it can be determined whether the supply pump and the recovery pump are normally operated, thereby securing reliability. 
   Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.