Patent Publication Number: US-9405228-B2

Title: Developer discharging device for image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2014-0164345, filed on Nov. 24, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a developer discharging device for an image forming apparatus, and more particularly, to developer discharging device for an image forming apparatus, which is capable of preventing a developer from being sharply discharged, and thus constantly maintaining an amount of the developer. 
     2. Discussion of Related Art 
     An image forming apparatus, such as a copy machine, a printer and a multifunction printer, is divided into an ink-jet type, an electro-photographic type and a thermal printing type. Here, in the electro-photographic type image forming apparatus, an image is formed on a print medium through a series of charging, exposing, developing, transferring and fixing processes. 
     A conventional electro-photographic type image forming apparatus includes a cartridge assembly in which a drum unit having a photoconductive drum, a charging roller and a transfer roller, and a developing unit configured to accommodate a developer therein and having a developing roller and a supplying roller are integrally formed. 
     Here, the cartridge assembly accommodates the developer including toner and carrier, and the developer should be refilled or replaced due to a consumption of the toner according to a printing operation. 
     In a conventional refilling/replacing method of the developer, a waste developer, i.e., a waste toner and a waste carrier were collected and discharged at the same time, and then a new developer was refilled. However, in the conventional method, an amount of the developer sent to a dump was large, and a separate waste developer receiving part was required. 
     An image forming apparatus which collects and reuses toner in consideration of a conventional developer consumption is disclosed in Japanese Patent Publication No. 1993-66659 (related document 1). The related document 1 discloses a process cartridge in which a waste toner tank is integrally installed at the photoconductive drum, and a discharging mechanism for collecting the waste toner of the waste toner tank into the developing machine is installed. 
     Also, an image forming apparatus which collects and reuses the toner and controls a carrier supply is disclosed in Japanese Patent Publication No. 2001-194908 (related document 2). 
     Here, in the conventional image forming apparatus including the above-described documents, a method of discharging the developer of the developing unit to the waste toner tank may be classified into a reverse pitch screw method and a dam method. In the reverse pitch screw method, all of the developers passing through a reverse pitch screw are discharged to the waste toner tank, and in the dam method, when an amount or a load of the developer arrives a predetermined level, the developer is discharged. 
     However, in the case of the reverse pitch screw method, since all of the developers passing through the reverse pitch screw are discharged, the developer may be sharply discharged due to an increase in an internal pressure of the developing unit or an overage of a new developer, and thus a change amount of the developer in the developing unit may be increased. This has a bad influence on print quality. 
     Also, in the case of the dam method, all of the developers over the predetermined level are discharged. Here, even when the amount of the developer is the same, a volume thereof is changed according to a ratio between the carrier and the toner. When a ratio of the toner is relatively great, an entire volume thereof is increased, and the level of the developer is increased. Therefore, the developer may overflow and then may be discharged, and thus the amount of the developer is reduced. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a developer discharging device for an image forming apparatus, which is capable of preventing a developer from being sharply discharged, and thus constantly maintaining an amount of the developer. 
     Also, the present invention is directed to a developer discharging device for an image forming apparatus, which is capable of smoothly discharging the developer without an increase in a size of a developer collecting unit. 
     According to an aspect of the present invention, there is provided a developer discharging device for an image forming apparatus, which is installed in a developing unit configured to transfer and discharge a developer collected from a drum unit or a newly introduced developer, such that the developer is discharged to a developer collecting unit, including a first discharging part configured to extend from an end of a transferring screw installed in the developing unit, and a second discharging part disposed above the first discharging part in parallel with the first discharging part, wherein the developer discharged from the second discharging part falls into the developer collecting unit. 
     The first discharging part may include a reverse pitch screw having a pitch formed in an opposite direction to a pitch of the transferring screw, a normal pitch screw disposed at a downstream side of the reverse pitch screw to be adjacent to the reverse pitch screw and having a pitch formed in an opposite direction to the pitch of the reverse pitch screw, and a discharging port formed above the normal pitch screw. 
     The second discharging part may include a discharging screw configured to extend toward the developer collecting unit, an introducing port in communication with the discharging port, and a shutter installed at an end side of the discharging screw so that the developer falls into the developer collecting unit. 
     A pressing screw having a pitch formed in an opposite direction to the pitch of the reverse pitch screw and also having a plurality of pressing plates spaced in a circumferential direction may be installed at an upstream side of the reverse pitch screw. 
     A subsidiary reverse pitch screw having a pitch formed in an opposite direction to the pitch of the normal pitch screw may be installed at a downstream side of the normal pitch screw. 
     The second discharging part may have a conical case of which a diameter is gradually reduced in a discharging direction of the developer, and the discharging screw may be accommodated in the case so as to have a pitch of which a diameter is gradually reduced in the discharging direction of the developer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view illustrating a cartridge assembly of an image forming apparatus equipped with a developer discharging device in accordance with the present invention; 
         FIG. 2  is a perspective view illustrating a state in which an upper portion of a developing unit for the image forming apparatus in accordance with the present invention is cut away; 
         FIG. 3  is a side view schematically illustrating the developing unit and a developer collecting unit of  FIG. 2 ; 
         FIG. 4  is a plane view schematically illustrating the developing unit and the developer collecting unit of  FIG. 2 ; 
         FIG. 5  is a front view schematically illustrating the developing unit and the developer collecting unit of  FIG. 2 ; and 
         FIG. 6  is a side view illustrating the developer discharging device for the image forming apparatus in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring to  FIGS. 1 and 2 , a cartridge assembly equipped with a developer discharging device for an image forming apparatus in accordance with the present invention includes a drum unit  100  and a developing unit  200  which are installed in the image forming apparatus to form an image. A developer collecting unit  300  which collects a developer located in the developing unit  200  is installed at one side of the drum unit  100 . 
     The drum unit  100  includes various components for forming a latent image, such as a photoconductive drum, charging roller and a transfer roller. Also, a water toner transferring route (not shown) is formed in the drum unit  100  to transfer waste toner collected from a surface of the photoconductive drum  110  to one side of the drum unit  100 . 
     The developing unit  200  is provided with a developing roller  210  which supplies the developer to the latent image formed on the photoconductive drum  110 , and also coupled with the drum unit  100  so that the developing roller  210  is in contact with the photoconductive drum  110  of the drum unit  100 . 
     Also, the developing unit  200  is configured to receive the developer collected from the drum unit  100  or a newly introduced developer into the developing unit  200 . To this end, a first transferring screw  220  and a second transferring screw  230  which extends in parallel with each other in a lengthwise direction thereof are installed in the developing unit  200 . A partition  240  is provided between the first transferring screw  220  and the second transferring screw  230 , and the developer is moved along the first transferring screw  220  and the second transferring screw  230 . Further, the developing unit  200  is provided with a developer discharging device  400  which discharges the developer located therein to the developer collecting unit  300 . The developer discharging device  400  will be described later. 
     The developer collecting unit  300  is provided at one side of the drum unit  100 , i.e., one side of the drum unit  100  in a direction that the waste toner is collected to be integrally formed with the drum unit  100 . The developer collecting unit  300  serves to collect the developer discharged by the developer discharging device  400  of the developing unit  200 . 
     Referring to  FIGS. 2 to 6 , the developer discharging device  400  for the image forming apparatus in accordance with the present invention includes a first discharging part  410  and a second discharging part  420  which are installed in the developing unit  200  and also disposed up and down in parallel with each other so as to discharge the developer to the developer collecting unit  300 . 
     The first discharging part  410  extends to an end of the second transferring screw  230 , i.e., a downstream side of the second transferring screw  230 . And the second discharging part  420  is disposed above the first discharging part  410  in parallel with the first discharging part  410  so that the developer falls into the developer collecting unit  300 . Due to a stacking structure of the first and second discharging parts  410  and  420 , the developer transferred toward the first discharging part  410  is moved up to the second discharging part  420 , and then falls into the developer collecting unit  300  through the second discharging part  420 . 
     Here, the terms “downstream side” and “upstream side” are based on a developer discharging direction designated by arrows of  FIG. 3 . 
     The first discharging part  410  includes a reverse pitch screw  411 , a normal pitch screw  412  and a discharging port (not shown). The reverse pitch screw  411  has a pitch (which means a direction and a shape of the screw) formed in an opposite direction to a pitch of the second transferring screw  230 , and is disposed at a downstream side of the second transferring screw  230 . The normal pitch screw  412  is disposed at a downstream side of the reverse pitch screw  411  to be adjacent to the reverse pitch screw  411  and to have a pitch formed in an opposite direction to a pitch of the reverse pitch screw  411 . And the discharging port is formed above the normal pitch screw  412  so that the developer is transferred to the second discharging part  420 . 
     Due to the reverse pitch screw  411 , the developer transferred to the downstream side by the second transferring screw  230  is introduced into the first discharging part  410  along the reverse pitch screw  411 , only when a predetermined load, i.e., a predetermined amount of the developer exceeds a pressure of the reverse pitch screw  411  by the reverse pitch screw  411  of the first discharging part  410 . Also, due to the normal pitch screw  412 , the developer introduced into the first discharging part  410  along the reverse pitch screw  411  is further smoothly introduced and moved up toward the discharging port. 
     The second discharging part  420  includes a discharging screw  421 , an introducing port (not shown) and a shutter  422 . The discharging screw  421  is disposed above the first discharging part  410  to extend toward the developer collecting unit  300  in parallel with the first discharging part  410 , such that the developer is transferred to the developer collecting unit  300 . The introducing port is formed to face the discharging port of the first discharging part  410 , and the first and second discharging parts  410  and  420  are in communication with each other through the discharging port and the introducing part. A portion of  FIG. 6  designated by an arrow S is a communication portion between the discharging port and the introducing port. The shutter  422  is installed at a downstream end of the discharging screw  421 , and has an opening which is selectively opened and closed, and thus the developer may falls into the developer collecting unit  300 . The shutter  422  is rotatably provided at an end of the second discharging part  420 . When the cartridge assembly is installed at the image forming apparatus, the shutter  422  is rotated, and thus the opening is located downward, and a discharging route of the developer is opened. When the cartridge assembly is separated from the image forming apparatus, the shutter  422  is rotated to its original position, and thus the opening is located toward a side surface, and the discharging route of the developer is closed. 
     Due to the first and second discharging parts  410  and  420 , the developer passing through the reverse pitch screw  411  of the first discharging part  410  is moved up to the second discharging part  420 , and then discharged through the shutter  422  of the second discharging part  420 , and thus the developer is prevented from being sharply discharged. Therefore, a change (a ratio change between the toner and the carrier) in the amount of the developer in the developing unit  200  may be constantly maintained. 
     Also, the developer moved up to the second discharging part  420  through the first discharging part  410  falls to a lower side through the discharging screw  421  and the shutter  422 . Therefore, the developer collecting unit  300  is not needed to extend to a lower side of the first discharging part  410 , and thus a size of the developer collecting unit  300  may be reduced. 
     Preferably, a pressing screw  414  is installed at an upstream side of the reverse pitch screw  411 . The pressing screw  414  is installed between the reverse pitch screw  411  and the second transferring screw  230 , and has a pitch formed in an opposite direction to the pitch of the reverse pitch screw  411 . A plurality of pressing plates  414   a  are provided on an outer circumferential surface of the pressing screw  414  to be spaced in a circumferential direction thereof. The pressing screw  414  applies a predetermined pressure in a reverse pitch direction using the pressing plates  414   a . Therefore, the developer transferred by the second transferring screw  230  may be transferred toward the reverse pitch screw  411  with a predetermined pressure (load) generated by the pressing screw  414 . 
     Further, a subsidiary reverse pitch screw  415  is installed at a downstream side of the normal pitch screw  412 . The subsidiary reverse pitch screw  415  has a pitch formed in an opposite direction to a pitch of the normal pitch screw  412  so as to apply a predetermined pressure toward the reverser pitch screw  411 . Therefore, the pressure is applied at both sides of the reverse pitch screw  411  in opposite directions to each other, and the developer on the reverse pitch screw  411  is moved upward. Thus, the developer of the first discharging part  410  may be smoothly introduced into the second discharging part  420 . 
     Meanwhile, the second discharging part  420  includes a conical case  423  of which a diameter is gradually reduced in a discharging direction of the developer. Also, the discharging screw  421  accommodated in the case  423  has a pitch corresponding to a shape of the case  423 , of which a diameter is gradually reduced in the discharging direction of the developer. Due to the shapes of the case  423  and the discharging screw  421 , the developer discharged from the second discharging part  420  to the developer collecting unit  300  is prevented from being sharply discharged. 
     According to the present invention, it is possible to prevent the developer from being sharply discharged, and thus to constantly maintain a change in the amount of the developer (a ratio change between the toner and the carrier). 
     Also, the developer collecting unit is not needed to extend to the lower side of the first discharging part, and thus the size of the developer collecting unit can be reduced. 
     It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers all such modifications provided they come within the scope of the appended claims and their equivalents.