Patent Publication Number: US-2009232543-A1

Title: Developing device of image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from provisional U.S. Application 61/036,570 filed on Mar. 14, 2008, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a developing device for development using a dry developer used in an image forming apparatus such as a copier and printer. 
     BACKGROUND 
     As a developing device used in an image forming apparatus such as a copier and printer, there is a device for development using a dry developer. In the developing device using a dry developer, an air flow is generated through the developing operation in a direction in which air is taken into the developing device. When the pressure within the developing device increases due to the air flow, the air flow is ejected to the outside from a clearance gap of the developing device. The developer flies to the outside with the air flow ejected to the outside and contaminates surroundings of the developing device. 
     In order to prevent the increase in pressure within the developing device, a depressurizing hole is provided near the development position of a development container in some devices. The depressurizing hole allows the air taken from the clearance gap at the development position to escape to prevent the air to flow into the development container. A filter for collecting suspended toner is attached to the depressurizing hole to prevent the developer from flying to the outside. 
     When the depressurizing hole is provided near the opening of the development container, it is difficult to completely remove the air taken into the developing device from the depressurizing hole. Even if the depressurizing hole is provided, the developer may fly to the outside and contaminate the surroundings. 
     Development of a developing device that can prevent the developer from flying to the outside and prevent contamination due to the developer, even if the pressure within the developing device increases through the developing operation and the air flow is ejected from the clearance gap of the developing device to the outside, is desired. 
     SUMMARY 
     An aspect of the present invention is to prevent a developer from flying to the outside with developing operation and prevent contamination of surroundings of a developing device. 
     According to an embodiment, a developing device includes a development container having a carrying part that carries a developer and a supply part that supplies the developer to an image carrier, a developing roller that is located in the supply part and carries the developer to an opening part of the supply part, and a block part that is provided between the developing member and the development container at the downstream of the opening part in a rotational direction of the developing roller, and blocks an air flow from the supply part into the carrying part. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall configuration diagram showing an image forming apparatus of an embodiment; 
         FIG. 2  is a schematic configuration diagram showing a process cartridge of the embodiment; 
         FIG. 3  is a schematic configuration diagram showing a developing device of the embodiment; and 
         FIG. 4  is a diagram for explanation of lines of magnetic force of a magnet roller of the embodiment. 
     
    
    
     DETAILED DESCRIPTION  
     Hereinafter, an embodiment will be described. FIG.  1  is a schematic configuration diagram of a color printer  1  as an image forming apparatus of the embodiment. The color printer  1  is four tandem system. The color printer  1  has a paper discharge part  3  in the upper part. 
     The color printer  1  has four sets of image forming stations  11 Y,  11 M,  11 C and  11 K arranged in a line along the lower side of an intermediate transfer belt  10 . The image forming stations  11 Y,  11 M,  11 C and  11 K have photoconductive drums  12 Y,  12 M,  12 C and  12 K as image carriers, respectively. The respective image forming stations  11 Y,  11 M,  11 C and  11 K form toner images of yellow (Y), magenta (M), cyan (C), black (K) on the respective photoconductive drums  12 Y,  12 M,  12 C and  12 K. 
     The respective photoconductive drums  12 Y,  12 M,  12 C and  12 K rotate in a direction of an arrow m. Charging chargers  13 Y,  13 M,  13 C and  13 K, developing devices  14 Y,  14 M,  14 C and  14 K, photoconductor cleaners  16 Y,  16 M,  16 C and  16 K are provided around the respective photoconductive drums  12 Y,  12 M,  12 C and  12 K along the rotational direction, respectively. 
     As shown in  FIG. 2 , for each of the image forming stations  11 Y,  11 M,  11 C and  11 K, process cartridges  28 Y,  28 M,  28 C and  28 K are formed by integrating the respective photoconductive drums  12 Y,  12 M,  12 C and  12 K, charging chargers  13 Y,  13 M,  13 C and  13 K, developing devices  14 Y,  14 M,  14 C and  14 K, photoconductor cleaners  16 Y,  16 M,  16 C and  16 K. The respective process cartridges  28 Y,  28 M,  28 C and  28 K are independently and integrally attached to and detached from a main body of the color printer  1 , respectively. The configuration of the process cartridge is not limited to the above configuration as long as at least the photoconductor drum and the developing device are integrated. 
     Respective exposure lights by a laser exposure device  17  is applied to parts from the charging chargers  13 Y,  13 M,  13 C and  13 K to the developing devices  14 Y,  14 M,  14 C and  14 K around the photoconductive drums  12 Y,  12 M,  12 C and  12 K, respectively. The laser exposure device  17  has a polygon mirror  17   a,  an imaging lens system  17   b,  a reflecting mirror  17   c,  etc. The laser exposure device  17  scans a laser beam output from a semiconductor laser device in an axis direction of the photoconductive drums  12 Y,  12 M,  12 C and  12 K. Electrostatic latent images are formed on the respective photoconductive drums  12 Y,  12 M,  12 C and  12 K by the application of the exposure light from the laser exposure device  17 . The respective charging chargers  13 Y,  13 M,  13 C and  13 K and the laser exposure device  17  form a latent image forming part. 
     The respective developing devices  14 Y,  14 M,  14 C and  14 K develop the electrostatic latent images on the photoconductive drums  12 Y,  12 M,  12 C and  12 K. The respective developing devices  14 Y,  14 M,  14 C and  14 K perform development using two-component developers having the respective toner of yellow (Y), magenta (M), cyan (C), black (K) and carrier. 
     The intermediate transfer belt  10  is hung around a backup roller  21 , a driven roller  20  and first to third tension rollers  22 - 24  and rotated in a direction of an arrow s. The intermediate transfer belt  10  faces in contact with the photoconductive drums  12 Y,  12 M,  12 C and  12 K. Primary transfer rollers  18 Y,  18 M,  18 C and  18 K are provided in positions of the intermediate transfer belt  10  facing the photoconductive drums  12 Y,  12 M,  12 C and  12 K. The respective primary transfer rollers  18 Y,  18 M,  18 C and  18 K primarily transfer the toner images formed on the photoconductive drums  12 Y,  12 M,  12 C and  12 K onto the intermediate transfer belt  10 . The respective photoconductor cleaners  16 Y,  16 M,  16 C and  16 K remove and collect the residual toner on the respective photoconductive drums  12 Y,  12 M,  12 C and  12 K after primary transfer. 
     A secondary transfer roller  27  is allowed to face a secondary transfer part of the intermediate transfer belt  10  supported by the backup roller  21 . At the secondary transfer part, a predetermined secondary transfer bias is applied to the backup roller  21 . After a sheet P passes between the intermediate transfer belt  10  and the secondary transfer roller  27 , the toner images on the intermediate transfer belt  10  are secondarily transferred onto the sheet P. The sheet P is fed from paper feed cassettes  4   a,    4   b  or a manual feed mechanism  31 . After the secondary transfer has been finished, the intermediate transfer belt  10  is cleaned by a belt cleaner  10   a.    
     Pickup rollers  2   a,    2   b,  separating rollers  5   a,    5   b , transport rollers  6   a,    6   b  and a pair of resist rollers  36  are provided in a part from the paper feed cassettes  4   a ,  4   b  to the secondary transfer roller  27 . A manual feed pickup roller  31   b  and a manual feed separating roller  31   c  are provided in a part from a manual feed tray  31   a  of the manual feed mechanism  31  to the pair of resist rollers  36 . Along a longitudinal transport path  34 , a fixing device  30  is provided at the downstream of the secondary transfer part. The fixing device  30  fixes the toner images transferred onto the sheet P in the secondary transfer part on the sheet P. At the downstream of the fixing device  30 , a gate  33  that distributes the sheet P in a direction toward a paper discharge roller  41  or a direction toward a retransport unit  32  is provided. The sheet P guided to the paper discharge roller  41  is discharged to the paper discharge part  3 . The sheet P guided to the retransport unit  32  is guided toward the secondary transfer roller  27  again. 
     Next, the developing devices  14 Y,  14 M,  14 C and  14 K will be described in detail. Since the developing devices  14 Y,  14 M,  14 C and  14 K have the same structure, they will be described using common reference numerals and signs. As shown in  FIG. 3 , each of the developing devices  14 Y,  14 M,  14 C and  14 K has a case  50  as a development container made of a resin or the like for containing a developer  51 , a stirring mixer  56  and a carrying mixer  57 , a developing roller  58  as a developing member, and a toner concentration sensor  64 . 
     The developing roller  58  has a cylindrical developing sleeve  67  made of a non-magnetic material such as aluminum, stainless, or conductive resin. The developing sleeve  67  rotates in a direction of an arrow r. The developing roller  58  has a magnet roller  68  fixed inside the developing sleeve  67 . The magnet roller  68  has a developing magnetic pole N 1  of a North pole and a collecting magnetic pole S 1  of a South pole. The magnet roller  68  has a first separating magnetic pole N 2  of the North pole as a first magnetic pole, a second separating magnetic pole N 3  of the North pole as a second magnetic pole and a supply magnetic pole S 2  of the South pole. The magnet roller  68  forms lines of magnetic force  71  shown in  FIG. 4  by the developing magnetic pole N 1 , the collecting magnetic pole S 1 , the first separating magnetic pole N 2 , the second separating magnetic pole N 3  and the supply magnetic pole S 2 . 
     The case  50  has a carrying part  50   a  that supports the stirring mixer  56  and the transport mixer  57  and a supply part  50   b  that supports the developing roller  58 . In the carrying part  50   a,  the stirring mixer  56  and the transport mixer  57  are partitioned by a partitioning plate  60 . The stirring mixer  56  and the transport mixer  57  circulate and carry the developer  51  within the carrying part  50   a.    
     At the bottom of the carrying part  50   a,  the toner concentration sensor  64  is provided. As the toner concentration sensor  64 , for example, a magnetic permeability sensor is used. When the reduction in toner concentration of the developer  51  within the case  50  is detected from the detection result of the toner concentration sensor  64 , toner is supplied to the case  50  from the toner cartridge, for example, according to the detection result. Thereby, the toner concentration of the developer  51  within the case  50  is maintained constant. 
     New carrier is supplied to the carrying part  50   a  from a carrier cartridge, for example. In supply of the new carrier, only carrier may be supplied. Alternatively, the new carrier may be supplied by supplying a two-component developer having toner and carrier. By supplying a predetermined amount of new carrier during the developing operation, the deteriorated old carrier is gradually replaced by the new carrier. Thereby, the toner charge performance of the developer  51  within the case  50  is maintained uniformly. 
     On the side of the carrying part  50   a,  a discharge opening  53  as a developer discharge part is formed. The excessive developer  51  corresponding to the increased amount of the developer  51  within the case  50  due to supply of new carrier is discharged from the discharge opening  53  and collected. Within the case  50 , the amount of developer  51  is maintained constant. Concurrently, within the case  50 , the deteriorated old carrier of the developer  51  is gradually replaced by new carrier. 
     The supply part  50   b  has a supply portion  61  as an opening part for toner supply in a position facing each of the photoconductive drums  12 Y,  12 M,  12 C and  12 K. At the supply portion  61 , a doctor blade  50   c  is provided. An air hole feature  62  as a depressurizing part is provided at the downstream of the supply portion  61  in the rotational direction of the developing sleeve  67 . At the air hole feature  62 , an air filter  63  that collects suspended toner is provided. The air filter  63  is replaceably provided. 
     In a position facing between the first separating magnetic pole N 2  and the second separating magnetic pole N 3  at the downstream of the air hole feature  62  in the rotational direction of the developing sleeve  67 , a rubber-like magnet  72  is provided on the outer wall of the supply part  50   b.  The magnetic property of the magnet  72  is 31.0 mT (measured at the center of N-pole surface with thickness magnetization by EMIC), the size of the magnet  72  is, for example, 310 mm in length in the axis direction of the developing roller  58 , 5 mm in width, and 1.3 mm in thickness (the thickness including a double-faced tape). The magnet  72  is bonded to the outer wall of the supply part  50   b  by the double-faced tape. 
     The developing roller  58  is partially exposed from the supply portion  61 . Regarding the developing roller  58 , when the developing sleeve  67  rotates in the r direction, the developer  51  forms a magnetic brush  68   a  around the developing sleeve  67  due to the lines of magnetic force  71  of the magnet roller  68 . The supply part  50   b  supports the developing roller  58  so as to provide a space that does not obstruct the carrying of the magnetic brush  68   a  between the inner circumference of the supply part  50   b  and the developing sleeve  67 . 
     The developing sleeve  67  raises the magnetic brush  68   a  by attracting the developer from the carrying part  50   a  using the second separating magnetic pole N 3  and the supply magnetic pole S 2 . The height of the magnetic brush  68   a  is controlled by the doctor blade  50   c  provided at the supply portion  61 . The magnetic brush  68   a  with the controlled height reaches the developing magnetic pole N 1  facing each of the photoconductive drums  12 Y,  12 M,  12 C and  12 K. The magnetic brush  68   a  supplies the developer to each of the photoconductive drums  12 Y,  12 M,  12 C and  12 K by the developing magnetic pole N 1  and develops the electrostatic latent image for visualization. 
     After the electrostatic latent image is developed, the magnetic brush  68   a  is collected into the development container  50  using the collecting magnetic pole S 1 . The magnetic brush  68   a  reaches the first separating magnetic pole N 2 . The magnetic brush  68   a  forms a blocking brush  73  as a block part between the first separating magnetic pole N 2  and the second separating magnetic pole N 3 . 
     Between the first separating magnetic pole N 2  and the second separating magnetic pole N 3 , the lines of magnetic force  71  of the magnetic roller  68  reach from the first separating magnetic pole N 2  to the magnet  72 . The lines of magnetic force  71  are from the magnet  72  toward the developing sleeve  67 . The lines of magnetic force  71  reach the second separating magnetic pole N 3  along the developing sleeve  67 . 
     By the lines of magnetic force  71  from the magnet  72  toward the developing sleeve  67 , the magnetic brush  68   a  forms the blocking brush  73  between an inner wall of the supply part  50   b  and the developing sleeve  67 . After forming the blocking brush  73 , the magnetic brush  68   a  separates from the developing sleeve  67  while reaching the second separating magnetic pole N 3 , and is collected in the carrying part  50   a.    
     At the time of image formation, when each of the photoconductive drums  12 Y,  12 M,  12 C and  12 K rotates in the direction of the arrow m and the developing sleeve  67  rotates the direction of the arrow r, an air flow α shown by a solid line in  FIG. 3  is generated within the case  50 . A part α 1  of the air flow α directly moves to the air hole feature  62  and is discharged to the outside. The excessive air flow β that is not directly discharged from the air hole feature  62  moves toward inside the supply part  50   b . The blocking brush  73  is formed within the supply part  50   b . The excessive air flow β collides with the blocking brush  73 . The excessive air flow β colliding with the blocking brush  73  does not enter the carrying part  50   a  but is returned toward the air hole feature  62  and discharged from the air hole feature  62  to the outside. The suspended toner contained in the air flow α 1  and air flow β is caught by the air filter  63 . 
     All of the air flow α entering from the supply portion  61  of the case  50  due to rotations of each of the photoconductive drums  12 Y,  12 M,  12 C and  12 K and the developing sleeve  67  is discharged from the air hole feature  62  to the outside. The blocking brush  73  blocks the air flow entering the carrying part  50   a  of the case  50 . The internal pressure of the carrying part  50   a  is not increased and no air flow is ejected from the gap due to the internal pressure of the carrying part  50   a.  The air flow ejected to the outside and the suspended toner flying to the outside are prevented. 
     The air filter  63  that catches the suspended toner contained in the air flow α 1  and air flow β flowing out from the air hole feature  62  is replaced at maintenance according to how dirty it is, or the number of rotations of the developing roller  58  or the like. At the maintenance of replacement of the air filter  63  or the like, one of the process cartridges  28 Y,  28 M,  28 C and  28 K that needs maintenance is detached from the main body of the color printer  1  and the maintenance is done, or one of the process cartridges  28 Y,  28 M,  28 C and  28 K is replaced. 
     In the embodiment, the magnet  72  is provided facing between the first separating magnetic pole N 2  and the second separating magnetic pole N 3  on the outer wall of the supply part  50   b  of the case  50 . By the rotation of the developing sleeve  67 , the first separating magnetic pole N 2  and the second separating magnetic pole N 3  form the blocking brush  73  between the supply part  50   b  and the developing sleeve  67  due to the magnetic force of the magnet  72 . The blocking brush  73  prevents the excessive air flow β entering from the supply portion  61  and passing through the air hole feature  62  from entering into the carrying part  50   a.  The air flow β blocked by the blocking brush  73  returns toward the air hole feature  62  and is discharged from the air hole feature  62  to the outside. No air flow is ejected from the clearance due to increase in the internal pressure of the carrying part  50   a,  the suspended toner is prevented from flying to the outside, and contamination of the surroundings by the suspended toner is prevented. 
     The invention is not limited to the above embodiment, but various changes can be made within the scope of the invention. For example, the developing device may be used for a monochrome image forming apparatus in which a toner image formed on an image carrier is directly transferred onto a sheet. The image forming apparatus is not limited to a printer, but may be a copier, facsimile, or the like. The number of magnetic poles or the arrangement of magnetic poles of the magnetic roller is not limited as long as the blocking brush can be formed between the developing roller and the development container. For example, a magnetic pole for forming the blocking brush between the developing roller and the development container may separately be provided. If the blocking brush can be formed between the developing roller and the development container, the shape or attachment method of the magnet is not limited. The unit forming the process cartridge is not limited as long as at least the image carrier and the developing device can integrally be attached to or detached from the apparatus main body.