Patent Publication Number: US-11650522-B2

Title: Image forming apparatus capable of suppressing increase in size

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2020-066232 filed Apr. 1, 2020. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a drum unit which includes a conveying member configured to convey toner along with carrier, and an image forming apparatus which the drum unit can be attached to and detached from. 
     BACKGROUND 
     Conventionally, there has been known an image forming apparatus including a housing, a drum unit, and a toner cartridge as described in Japanese Patent Application Publication No. 2006-171105. The drum unit includes a developer container accommodating therein toner and carrier. In addition to the developer container, the image forming apparatus further includes a toner replenishing device between the toner cartridge and the developer container. The toner replenishing device is configured to temporarily store and agitate toner supplied from the toner cartridge in order to replenish the toner to the developer container. 
     SUMMARY 
     In the above-mentioned prior art, in order to replenish the toner in the toner cartridge to the developer container, the toner replenishing device is further required in addition to the toner cartridge, the developer container and the drum unit. However, providing the toner replenishing device in the image forming apparatus may lead to the increase in size of the drum unit and the image forming apparatus. 
     In view of the foregoing, it is an object of the present disclosure to provide an image forming apparatus and a drum unit capable of suppressing the increase in size of the image forming apparatus and the drum unit. 
     In order to attain the above and other objects, according to one aspect, the disclosure provides an image forming apparatus including a housing, a toner cartridge, and a drum unit. The housing is formed with an opening and having a front cover movable between an open position where the front cover opens the opening and a closed position where the front cover closes the opening. The toner cartridge is configured to accommodate therein toner. The toner cartridge is attachable to the drum unit. The drum unit is movable in a first direction relative to the housing in a state where the toner cartridge is attached to the drum unit. The drum unit is movable through the opening between an accommodated position where the drum unit is positioned in the housing and a pulled-out position where the drum unit is pulled out of the housing. The drum unit includes a photosensitive drum and a developing unit. The photosensitive drum is rotatable about a first axis extending in a second direction. The developing unit is positioned between the toner cartridge and the photosensitive drum. The developing unit includes a magnetic roller, a developer container, a first auger and a second auger. The magnetic roller is positioned between the toner cartridge and the photosensitive drum and rotatable about a second axis extending in the second direction. The magnetic roller faces a surface of the photosensitive drum. The developer container is configured to accommodate carrier. The developer container is formed with an inlet allowing the toner to be replenished from the toner cartridge. The first auger is positioned in the developer container and rotatable about a third axis extending in the second direction. The first auger is configured to circulate the toner and the carrier in the developer container. The second auger is positioned in the developer container and rotatable about a fourth axis extending in the second direction. The second auger is configured to convey the toner and the carrier to the magnetic roller. 
     According to another aspect, the disclosure provides a drum unit to which a toner cartridge is attachable. The toner cartridge is configured to accommodate therein toner. The drum unit is movable in a first direction relative to the housing in a state where the toner cartridge is attached to the drum unit. The drum unit is movable through the opening between an accommodated position where the drum unit is positioned in the housing and a pulled-out position where the drum unit is pulled out of the housing. The drum unit includes a photosensitive drum and a developing unit. The photosensitive drum is rotatable about a first axis extending in a second direction. The developing unit is positioned between the toner cartridge and the photosensitive drum. The developing unit includes a magnetic roller, a developer container, a first auger and a second auger. The magnetic roller is positioned between the toner cartridge and the photosensitive drum and rotatable about a second axis extending in the second direction. The magnetic roller faces a surface of the photosensitive drum. The developer container is configured to accommodate carrier. the developer container is formed with an inlet allowing the toner to be replenished from the toner cartridge. The first auger is positioned in the developer container and rotatable about a third axis extending in the second direction. The first auger is configured to circulate the toner and the carrier in the developer container. The second auger is positioned in the developer container and rotatable about a fourth axis extending in the second direction. The second auger is configured to convey the toner and the carrier to the magnetic roller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the disclosure will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG.  1    is a cross-sectional view of a color printer including a drum unit according to one embodiment of the present disclosure; 
         FIG.  2    is a cross-sectional view of the drum unit positioned at a pulled-out position; 
         FIG.  3    is a cross-sectional view of the drum unit to which toner cartridges are attached; 
         FIG.  4 A  is a perspective view of a developing unit; 
         FIG.  4 B  is another perspective view of the developing unit; 
         FIG.  5    is a cross-sectional view of the developing unit; 
         FIG.  6    is a perspective view of the drum unit according to the embodiment; 
         FIG.  7    is an exploded perspective view showing a structure of another side in the second direction of the drum unit; 
         FIG.  8    is an exploded perspective view showing a structure of one side in the second direction of the drum unit; 
         FIG.  9 A  is a diagram showing a method for assembling the drum unit; 
         FIG.  9 B  is another diagram showing the method for assembling the drum unit; and 
         FIG.  9 C  is still another diagram showing the method for assembling the drum unit. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a drum unit according to one embodiment of the present disclosure will be described with reference to the accompanying drawings. Firstly, an overall structure of a color printer  1  as an example of an image forming apparatus to which the drum unit is applied will be described with reference to  FIG.  1   . The color printer  1  includes a housing  10 , a sheet supply unit  20 , an image forming unit  30 , and a discharge unit  90 . 
     The housing  10  has an opening  10 A and includes a front cover  11 . The front cover  11  is movable between an open position where the front cover  11  opens the opening  10 A and a closed position where the front cover  11  closes the opening  10 A. Specifically, the front cover  11  is pivotally movable between the open position and the closed position. 
     The sheet supply unit  20  includes a supply tray  21 , and a sheet feed mechanism  22 . The supply tray  21  is configured to store a stack of sheets S. The sheet feed mechanism  22  is configured to convey the sheet S to the image forming unit  30  from the supply tray  21 . A heavy paper, a postcard, and a thin paper are available as the sheet S. 
     The image forming unit  30  includes a scanner unit  40 , a process unit U, a transfer unit  70 , and a fixing unit  50 . 
     The scanner unit  40  includes a laser emitting portion, a polygon mirror, lenses and reflection mirrors those not illustrated. 
     The process unit U includes a drum unit  50 , and four toner cartridges TC. 
     The toner cartridge TC is configured to accommodate therein toner which is non-magnetic material. As illustrated in  FIG.  3   , the four toner cartridges TC are attachable to and detachable from a frame of the drum unit  50 . Specifically, each toner cartridge TC is attachable to and detachable from the frame of the drum unit  50  in a direction perpendicular to the second direction (described later). The frame of the drum unit  50  will be described later with reference to  FIGS.  6  through  9   . 
     The drum unit  50  is movable in a first direction relative to the housing  10  through the opening  10 A. 
     Specifically, the drum unit  50  is movable in the first direction between an accommodated position where the drum unit  50  is accommodated in the housing  10  and a pulled-out position where the drum unit  50  is pulled out of the housing  10 . As illustrated in  FIG.  3   , the drum unit  50  includes four photosensitive drums  51 , four scorotron chargers  52 , four cleaning rollers  53 , four developing units  60 , and a sheet guide  54 . The above-described scanner unit  40  is configured to irradiate laser beam to the photosensitive drums  51 . 
     The photosensitive drum  51  is rotatable about a first axis X 1  extending in the second direction. The second direction crosses the first direction, and specifically, the second direction is perpendicular to the first direction. The four photosensitive drums  51  are arrayed one after another in the first direction. 
     The scorotron charger  52  is configured to charge the photosensitive drum  51 . Incidentally, a charge roller may be employed instead of the scorotron charger  52 . The cleaning roller  53  is configured to perform cleaning on the photosensitive drum  51 . Incidentally, a cleaning blade may be employed instead of the cleaning rollers  53 . 
     The four developing units  60  are arrayed one after another in the first direction. Each developing unit  60  is positioned between each toner cartridge TC and each photosensitive drum  51 . The developing unit  60  includes a magnetic roller  61 , a developer container  62 , a first auger  63 , a second auger  64 , and a layer thickness regulation blade  65 . 
     The magnetic roller  61  is configured to supply toner to the photosensitive drum  51 . The magnetic roller  61  includes a magnetic shaft  61 A and a magnetic sleeve  61 B. The magnetic shaft  61 A has alternating magnetic poles with a predetermined pattern in a circumferential direction thereof. The magnetic shaft  61 A is a solid cylindrical member in which a plurality of permanent magnets are embedded. The magnetic shaft  61 A is fixed to the developer container  62 . 
     The magnetic sleeve  61 B is a hollow cylindrical member made from non-magnetic metal as main component. The magnetic sleeve  61 B is rotatable about the magnetic shaft  61 A. The magnetic sleeve  61 B retains toner by magnetic force of the magnetic shaft  61 A. 
     The magnetic roller  61  is positioned between the toner cartridge TC and the photosensitive drum  51 . The magnetic sleeve  61 B is rotatable about a second axis X 2  extending in the second direction. The magnetic roller  61  faces the surface of the photosensitive drum  51 . The magnetic roller  61  is separated from the surface of the photosensitive drum  51 . 
     The developer container  62  is configured to accommodate carrier which is magnetic material. Iron powder is an example of the carrier. The developer container  62  has an inlet  62 A through which toner is replenished from the toner cartridge TC. The inlet  62 A is positioned opposite to the magnetic roller  61  with respect to the first auger  63  and the second auger  64 . The above described toner cartridge TC is attached to the developer container  62  in accordance with the attachment of the toner cartridge TC to the frame of the drum unit  50 . 
     The inlet  62 A is positioned above the first auger  63  and the second auger  64 . Specifically, the inlet  62 A is positioned vertically above the first auger  63 . The second axis X 2  is positioned below the first auger  63  and the second auger  64 . Specifically, the second axis X 2  is positioned vertically below the second auger  64 . 
     The first auger  63  is positioned in the developer container  62 . The first auger  63  is rotatable about a third axis X 3  extending in the second direction. The first auger  63  and the second auger  64  are arrayed with each other in the first direction. The first auger  63  is positioned closer to the inlet  62 A than the second auger  64  is to the inlet  62 A. The first auger  63  is configured to perform circulation of the toner and the carrier in the developer container  62 . The first auger  63  is configured to convey the toner replenished from the inlet  62 A to the second auger  64 . 
     The second auger  64  is positioned in the developer container  62 . The second auger  64  is rotatable about a fourth axis X 4  extending in the second direction. The second auger  64  is configured to convey the toner and the carrier in the developer container  62  toward the magnetic roller  61 . In other words, the second auger  64  is configured to supply toner to the magnetic roller  61 . The second auger  64  is configured to perform circulation of the toner and the carrier in the developer container  62 . 
     The layer thickness regulation blade  65  is configured to regulate a thickness of a toner layer formed on the magnetic roller  61 . The layer thickness regulation blade  65  is out of contact with the magnetic roller  61 . The layer thickness regulation blade  65  is positioned below the first auger  63  and the second auger  64 . Specifically, the layer thickness regulation blade  65  is positioned vertically below the first auger  63 . 
     The layer thickness regulation blade  65  is arrayed with the magnetic roller  61  in the first direction. The second axis X 2  is positioned between the layer thickness regulation blade  65  and the first axis X 1  in the first direction. 
     The sheet guide  54  is configured to guide the sheet S toward the photosensitive drums  51 . The sheet guide  54  is arrayed with the photosensitive drums  51  in the first direction. The sheet guide  54  is positioned at upstream side of the four photosensitive drums  51  in a conveying direction of the sheet S. 
     The magnetic roller  61  positioned at most upstream side in the sheet conveying direction among the four magnetic rollers  61  is positioned between the sheet guide  54  and the second auger  64 . Further, each of the four magnetic rollers  61  is positioned between the sheet guide  54  and the first and second augers  63 ,  64  in a third direction perpendicular to the first and second directions. The layer thickness regulation blade  65  positioned at most upstream side in the sheet conveying direction among the four layer thickness regulation blades  65  is positioned between the sheet guide  54  and the first auger  63 . Further, each of the four layer thickness regulation blades  65  is positioned between the sheet guide  54  and the first and second augers  63 ,  64  in the third direction. 
     As illustrated in  FIG.  1   , the transfer unit  70  is configured to transfer toner images on the photosensitive drums  51  to the sheet S. The transfer unit  70  is positioned between the sheet supply unit  20  and the drum unit  50 . The transfer unit  70  includes a drive roller  71 , a follower roller  72 , a conveyer belt  73 , and transfer rollers  74 . 
     The drive roller  71  and the follower roller  72  are spaced away from each other in the first direction. The conveyer belt  73  is an endless belt looped over the drive roller  71  and the follower roller  72 . The transfer rollers  74  are positioned in a space encircled by the conveyer belt  73 . The conveyer belt  73  is nipped between the photosensitive drums  51  and the transfer rollers  74 . The conveyer belt  73  is an example of a transfer member. 
     The fixing unit  80  includes a heat roller  81  and a pressure roller  82 . The sheet S is nipped between the heat roller  81  and the pressure roller  82 . The discharge unit  90  includes a plurality of discharge rollers  91 . 
     In the image forming unit  30 , the scorotron charger  52  charges the surfaces of the photosensitive drum  51 , and thereafter, the scanner unit  40  irradiates laser beam to the surface of the photosensitive drum  51 , whereupon an electrostatic latent image is formed on the surface of the photosensitive drum  51 . 
     The toner cartridge TC replenishes toner to the interior of the developer container  62 . The first auger  63  conveys toner and carrier in the developer container  62  to the second auger  64 . The second auger  64  supplies toner to the magnetic roller  61 . The magnetic roller  61  supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum  51 . Hence, toner image is formed on the photosensitive drum  51 . 
     The conveyer belt  73  conveys the sheet S, so that the sheet S moves through a portion between the photosensitive drums  51  and the transfer rollers  74 . At this time, each toner image formed on each photosensitive drum  51  is successively transferred onto the sheet S. Then, the sheet S passes through a portion between the heat roller  81  and the pressure roller  82 . At this time, toner image on the sheet S is thermally fixed to the sheet S. Then, the conveyer rollers  91  conveys the sheet S to a position outside the housing  10 . 
     As shown in  FIG.  4 A , the developing unit  60  has one end portion in the second direction including a boss  60 A and a pair of protrusions  60 B. The boss  60 A extends in the second direction. The boss  60 A has an outer peripheral surface centered on the second axis X 2 . 
     The pair of protrusions  60 B protrude from the outer peripheral surface of the boss  60 A in the direction perpendicular to the second direction. The second axis X 2  is positioned between the pair of protrusions  60 B. The boss  60 A extends in a direction away from the developer container  62  farther than the pair of protrusions  60 B. 
     As shown in  FIG.  4 B , the developing unit  60  has another end portion in the second direction including a shaft  60 C. The shaft  60 C extends in the second direction. The shaft  60 C has an outer peripheral surface centered on the second axis X 2 . An outer diameter of the shaft  60 C is smaller than an outer diameter of the boss  60 A. The inlet  62 A is positioned at another end portion in the second direction of the developer container  62 . 
     As shown in  FIG.  5   , the developer container  62  includes a first accommodation chamber  62 B, a second accommodation chamber  62 C, and a partition wall  62 D, and is formed with a supply opening  62 E, and a recovery opening  62 F. The first accommodation chamber  62 B defines an internal space in which the first auger  63  is accommodated. The second accommodation chamber  62 C defines an internal space in which the second auger  64  is accommodated. Toner and carrier are accommodated in the first accommodation chamber  62 B and the second accommodation chamber  62 C. 
     The partition wall  62 D partitions the developer container  62  into the first accommodation chamber  62 B and the second accommodation chamber  62 C. The supply opening  62 E is positioned at one end of the partition wall  62 D in the second direction. The supply opening  62 E allows the first accommodation chamber  62 B and the second accommodation chamber  62 C to communicate with each other. The supply opening  62 E permits the toner and the carrier to move from the first accommodation chamber  62 B to the second accommodation chamber  62 C. 
     The recovery opening  62 F is positioned at another end of the partition wall  62 D in the second direction. The recovery opening  62 F allows the first accommodation chamber  62 B and the second accommodation chamber  62 C to communicate with each other. The supply opening  62 E permits the toner and the carrier to move from the second accommodation chamber  62 C to the first accommodation chamber  62 B. 
     The inlet  62 A is open to the first accommodation chamber  62 B. A distance from the inlet  62 A to the supply opening  62 E is greater than a distance from the inlet  62 A to the recovery opening  62 F. 
     The first auger  63  is configured to convey the toner replenished into the first accommodation chamber  62 B through the inlet  62 A to the supply opening  62 E along with the carrier. The second auger  64  is configured to convey the toner supplied into the second accommodation chamber  62 C through the supply opening  62 E toward another end of the developer container  62  in the second direction. Toner conveyed in the second direction by the second auger  64  is attracted to the surface of the magnetic roller  61  because of the magnetic force thereof. The toner and the carrier conveyed to the other end of the developer container  62  in the second direction is moved to the first accommodation chamber  62 B through the recovery opening  62 F. 
     As illustrated in  FIGS.  6  through  9   , the frame of the drum unit  50  supporting the photosensitive drums  51  and the developing units  60  includes a first side wall W 1 , a second side wall W 2 , a third side wall W 3 , a fourth side wall W 4 , a front wall W 5 , and a rear wall W 6 . The frame is configured to support the photosensitive drum  51  and the developing unit  60 . These walls W 3 , W 4 , W 5 , W 6  are made from resin. 
     Each developing unit  60  is positioned between the third side wall W 3  and the fourth side wall W 4  in the second direction. The front wall W 5  spans between one end portion in the first direction of the third side wall W 3  and one end portion in the first direction of the fourth side wall W 4 . The rear wall W 6  spans between another end portion in the first direction of the third side wall W 3  and another end portion in the first direction of the fourth side wall W 4 . 
     The third side wall W 3  includes a cartridge support portion W 31 . The cartridge support portion W 31  is configured to support an outer peripheral surface of the toner cartridge TC. The fourth side wall W 4  includes a cartridge support portion similar to the cartridge support portion W 31 . 
     As shown in  FIGS.  7  and  8   , the first side wall W 1  and the second side wall W 2  are plates supporting each end portions of the photosensitive drum  51  and the developing unit  60  in the second direction. The first side wall W 1  and the second side wall W 2  are made from metal, for example. 
     The first side wall W 1  is formed with four first holes W 11 . The first hole W 11  allows the boss  60 A positioned at the one end portion of the developing unit  60  in the second direction to extends through the first hole W 11 . That is, the boss  60 A is inserted in the first hole W 11 . Hence, the boss  60 A is supported by the first side plate W 1 . The second side wall W 2  faces the first side wall W 1  in the second direction. The second side wall W 2  is formed with four second holes W 21 . The pair of protrusions  60 B positioned on the outer peripheral surface of the boss  60 A is in contact with a surface W 12  of the first side wall W 1  facing the second side wall W 2  to fix a position of the developing unit  60  in the second direction (see  FIGS.  9 B and  9 C ). The fourth side wall W 4  is positioned opposite to the second side wall W 2  with respect to the first side wall W 1 . 
     As shown in  FIG.  7   , the drum unit  50  includes four cylindrical members P. Each of four cylindrical members P includes a cylinder P 1  and flange P 2 . 
     The cylinder P 1  has a cylindrical shape. The cylinder P 1  is inserted into the second hole W 21 . The cylinder P 1  has an outer peripheral surface P 11  and an opening P 12 . The shaft  60 C (illustrated in  FIG.  4 B ) positioned at the other end portion of the developing unit  60  in the second direction is inserted into the opening P 12 . 
     The flange P 2  protrudes radially outward from the outer peripheral surface P 11  of the cylinder P 11 . The flange P 2  is positioned opposite to the first side wall W 1  with respect to the second side wall W 2 . The third side wall W 3  is positioned opposite to the first side wall W 1  with respect to the second side wall W 2 . 
     As shown in  FIG.  9 C , the flange P 2  is positioned between the second side wall W 2  and the third side wall W 3  in the second direction. The first side wall W 1  and the second side wall W 2  are positioned between the third side wall W 3  and the fourth side wall W 4  in the second direction. 
     Next, a method of assembling the drum unit  50  will be described. As shown in  FIG.  9 A , each of the photosensitive drums  51  is attached to the first side wall W 1  and the second side wall W 2 . Although illustration is omitted, a unit including the scorotron charger  52  and the cleaning roller  53  is also attached to the first side wall W 1  and the second side wall W 2 . 
     Then, as shown in  FIGS.  9 A and  9 B , the shaft  60 C of the developing unit  60  is inserted into the second hole W 21  of the second side wall W 2 . Then, the boss  60 A of the developing unit  60  is inserted into the first hole W 11  in a direction from the second side wall W 2  to the first side wall W 1 . As a result, the pair of protrusions  60 B come into contact with the surface W 12  of the first side wall W 1 , the surface W 12  facing the second side wall W 2 . 
     After the pair of protrusions  60 B contact the surface W 12  of the first side wall W 1  facing the second side wall W 2 , the cylindrical member P is inserted into the second hole W 21  in the direction from the second side wall W 2  to the first side wall W 1  and is attached to the shaft  60 C of the developing unit  60 . Hence, the flange P 2  is positioned opposite to the first side wall W 1  with respect to the second side wall W 2 . 
     Then, as shown in  FIG.  9 C , the third side wall W 3  is attached to the surface of the second side wall W 2 , the surface being opposite to the surface of the second side wall W 2  facing the first side wall W 1 . Further, the fourth side wall W 4  is attached to the surface of the first side wall W 1 , the surface being opposite to the surface W 12 . 
     The following effects can be obtained in the present embodiment. The toner cartridge TC is attachable to the drum unit  50 , and the toner is directly replenished from the toner cartridge TC attached to the drum unit  50  to the developing container  62 . Therefore, conventional toner replenishing device can be omitted, and hence, an increase in size of the drum unit  50  and the color printer  1  can be suppressed. 
     Since the flange P 2  is positioned opposite to the first side wall W 1  with respect to the second side wall W 2 , a release of the cylindrical member P from the second side wall W 2  can be restrained. 
     Since the flange P 2  is sandwiched between the second side wall W 2  and the third side wall W 3 , the release of the cylindrical member P from the second side wall W 2  can further be restrained. 
     Since the first side wall W 1  and the second side wall W 2  are positioned between the third side wall W 3  and the fourth side wall W 4 , the first side wall W 1  and the second side wall W 2  can be protected by the third side wall W 3  and the fourth side wall W 4 . 
     Various modifications may be conceivable. For example, the first direction is perpendicular to the second direction. However, the first direction may be directed in parallel to the second direction. 
     In the above-described embodiment, the scorotron charger  52  is exemplified as the charger. However, charging rollers may be available as the charger. 
     The drum unit according to the above-described embodiment is applied to the color printer  1 . However, the drum unit may be applied to an image recording apparatus other than the color printer  1 , such as a monochromatic printer, a copying machine, and a multifunction peripheral. 
     In the above-described embodiment, the heavy paper, the postcard, and the thin paper are available as the sheet S. However, an OHP sheet is also available as the sheet S. 
     In the above-described disclosure, the conveyer belt  73  is exemplified as the transfer member. However, transfer rollers contacting the photosensitive drums  51  may be available as the transfer member. 
     While the description has been made in detail with reference to the specific embodiment and modifications, it would be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope and spirit of the disclosure.