Patent Publication Number: US-9891554-B2

Title: Developing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-246149 filed Dec. 17, 2015. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a developing device and an image forming apparatus. 
     (ii) Related Art 
     In a known electrophotographic image forming apparatus, a latent image is formed on an image carrier, and a developing device develops the latent image with powdered coloring material, such as toner, to form an image. 
     SUMMARY 
     According to an aspect of the invention, there is provided a developing device including a container chamber that contains developer containing carrier and toner; a supply portion that is adjacent to the container chamber and to which supplying toner or supplying developer, which contains the supplying toner and supplying carrier, is supplied at a supplying position in the supply portion; a transporting member that transports the supplying toner or the supplying developer toward the container chamber in the supply portion; and a guide capable of guiding the developer to the supplying position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates the structure of an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a top view illustrating the interior of a developing device illustrated in  FIG. 1 ; 
         FIG. 3  illustrates the state in which toner has adhered to a rotating shaft of a transporting member; and 
         FIG. 4  illustrates a mechanism for removing the toner from the rotating shaft. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  illustrates the structure of an image forming apparatus  1  according to an exemplary embodiment of the present invention. 
     The image forming apparatus  1  illustrated in  FIG. 1  is a tandem-type color printer in which yellow (Y), magenta (M), cyan (C), and black (K) image engines  10 Y,  10 M,  10 C, and  10 K, which respectively form toner images of the respective colors in parallel, are arranged in tandem. The color printer is capable of printing monochrome images, and is also capable of printing full-color images by superposing the toner images of the four colors. 
     The image forming apparatus  1  includes toner cartridges  18 Y,  18 M,  18 C, and  18 K containing yellow (Y), magenta (M), cyan (C), and black (K) toners. These toners are examples of a coloring material according to the present invention. 
     The image forming apparatus  1  also includes an intermediate transfer belt  30 , a fixing device  60 , a sheet transporting unit  80 , a controller  41  that controls each component of the image forming apparatus  1 , and an environmental sensor  42  that detects the temperature and humidity in the image forming apparatus  1 . 
     The four image engines  10 Y,  10 M,  10 C, and  10 K have the same structure except for the developer used therein; therefore, the yellow image engine  10 Y will be explained as a representative example. The image engine  10 Y includes a photoconductor  11 Y, a charging device  12 Y, an exposure device  13 Y, a developing device  14 Y, a first transfer device  15 Y, and a photoconductor cleaner  16 Y. Among these components, the components other than the exposure device  13 Y and the first transfer device  15 Y are assembled into a process cartridge. The process cartridges have the same structure. 
     The photoconductor  11 Y includes a cylindrical body having a photosensitive material layer on the surface thereof, and rotates in the direction of arrow A, which is a direction around the axis of the cylindrical body, while carrying an image formed on the surface thereof. The charging device  12 Y, the exposure device  13 Y, the developing device  14 Y, the first transfer device  15 Y, and the photoconductor cleaner  16 Y are arranged in that order around the photoconductor  11 Y. The photoconductor  11 Y is an example of an image carrier according to the present invention. The combination of the charging device  12 Y and the exposure device  13 Y is an example of a latent-image forming unit according to the present invention. The developing device  14 Y is an example of a developing device according to the present invention. 
     The charging device  12 Y charges the surface of the photoconductor  11 Y by applying a bias voltage. The charging device  12 Y according to the present exemplary embodiment is a charging roller that is in contact with the surface of the photoconductor  11 Y. A voltage with the same polarity as the charging polarity of the toner in the developing device  14 Y is applied to the charging roller, so that the charging roller charges the surface of the photoconductor  11 Y that is in contact therewith. Instead of the charging roller, the charging device  12 Y may be, for example, a corona discharge device that is not in contact with the photoconductor  11 Y. 
     The exposure device  13 Y performs an exposure process on the surface of the photoconductor  11 Y by irradiating the photoconductor  11 Y with a laser beam in accordance with an image signal for the corresponding color (yellow in this case). The image signal is generated by the controller  41  on the basis of image data supplied from the outside of the image forming apparatus  1 . As a result of the exposure process performed by the exposure device  13 Y, an electrostatic latent image is formed on the surface of the photoconductor  11 Y. The exposure device  13 Y may be an LED array, in which plural LEDs are arranged in a scanning direction, instead of the system using the laser beam. 
     The developing device  14 Y forms a toner image by developing the electrostatic latent image on the surface of the photoconductor  11 Y by using a two-component developer containing toner and magnetic carrier. The developing device  14 Y receives the toner from the toner cartridge  18 Y. As described in detail below, the developing device  14 Y is a trickle-type developing device in which part of the developer contained in the developing device  14 Y is ejected little by little to refresh the magnetic carrier. A small amount of magnetic carrier is also supplied from the toner cartridge  18 Y together with the toner. The developing device  14 Y stirs the developer therein to charge the toner. An external additive may be added to the toner to improve the fluidity and chargeability of the toner. 
     The first transfer device  15 Y faces the photoconductor  11 Y with the intermediate transfer belt  30  interposed therebetween. A voltage with a polarity opposite to the charging polarity of the toner is applied to the first transfer device  15 Y, so that the toner image on the photoconductor  11 Y is electrostatically attracted to the intermediate transfer belt  30 . 
     The photoconductor cleaner  16 Y cleans the surface of the photoconductor  11 Y after the transfer process by scraping off the residual toner, external additive, paper dust, etc., from the surface of the photoconductor  11 Y with a cleaning blade that is in contact with the surface of the photoconductor  11 Y. 
     The intermediate transfer belt  30  is an endless belt provided around the belt support rollers  31  to  35 , and is rotated in the direction of arrow B via the image engines  10 Y,  10 M,  10 C, and  10 K and a second transfer device  50 . The toner images of the respective colors formed by the image engines  10 Y,  10 M,  10 C, and  10 K are transferred onto the intermediate transfer belt  30  in a superposed manner, so that a color toner image is formed. The intermediate transfer belt  30  rotates in the direction of arrow B while carrying the toner image, and transports the toner image to the second transfer device  50 . 
     In the sheet transporting unit  80 , a sheet P contained in a sheet container T is picked up by a pick-up roller  81  and transported in the direction of arrow C to the second transfer device  50  along a sheet transport path R by transport rollers  82 . 
     The second transfer device  50  is a roller that rotates while the intermediate transfer belt  30  and the sheet are sandwiched between the roller and a backup roller  34 , which is one of the belt support rollers  31  to  35 . A voltage with a polarity opposite to the charging polarity of the toner is applied to the second transfer device  50 , so that the toner image on the intermediate transfer belt  30  is electrostatically attracted to the sheet and an unfixed toner image is formed on the sheet. 
     A belt cleaner  70  brings a blade into contact with the intermediate transfer belt  30  that has passed through the second transfer device  50 , thereby scraping off the toner, external additive, paper dust, etc., from the intermediate transfer belt  30 . 
     The fixing device  60  fixes the unfixed toner image to the sheet by applying heat and pressure. 
     The sheet with the toner image fixed thereto is ejected to the outside of the apparatus by an output roller  86 , which is a component of the sheet transporting unit  80 . 
     The developing device will be further described. In the following description, the characters representing the colors, that is, ‘Y’, ‘M’, ‘C’, and ‘K’, attached to the reference numerals are omitted. 
       FIG. 2  is a top view illustrating the interior of a developing device illustrated in  FIG. 1 . 
     The developing device  14  includes a developer containing chamber  201  that contains the developer therein, a toner supplying portion  202  disposed adjacent to the developer containing chamber  201 , two transporting members  203  and  204  that extend parallel to each other, and a developing roller  205  that extends parallel to the transporting members  203  and  204  and rotates in a direction perpendicular to the transporting members  203  and  204 . The developer containing chamber  201  is an example of a container chamber according to the present invention, and the toner supplying portion  202  is an example of a supply portion according to the present invention. 
     The developing roller  205  includes a magnet disposed therein, and rotates while attracting the developer to the surface thereof with a magnetic force, thereby carrying the developer from the developer containing chamber  201  to a developing position at which the developing roller  205  faces the photoconductor  11 . The latent image is developed at the developing position. After the developing process, the developer is returned to the developer containing chamber  201  by the rotation of the developing roller  205 . 
     A separation wall  206  is disposed between the two transporting members  203  and  204  in the developer containing chamber  201 , so that the developer containing chamber  201  is divided into two sections  207  and  208 . The separation wall  206  has openings  209  and  210  at both ends thereof in the longitudinal direction. 
     The two transporting members  203  and  204  include circular rod-shaped rotating shafts  211  and  212 , and helical blades  213  and  214  that extend helically around the rotating shafts  211  and  212  in the direction in which the rotating shafts  211  and  212  extend. The transporting members  203  and  204  are rotated such that the first transporting member  203  transports the developer in the first section  207  in the direction of arrow X while stirring the developer, and such that the second transporting member  204  transports the developer in the second section  208  in the direction of arrow Y while stirring the developer. The developer transported in the direction of arrow X passes through the first opening  209  and enters the second section  208 , and the developer transported in the direction of arrow Y passes through the second opening  210  and enters the first section  207 . Thus, the developer in the developer containing chamber  201  is circulated while being stirred by the two transporting members  203  and  204 . As described above, the toner contained in the developer is charged when the developer is stirred. 
     The transporting members  203  and  204  extend into the toner supplying portion  202  that is adjacent to the developer containing chamber  201 . However, normally, the developer circulates without passing through the toner supplying portion  202 . 
     An inlet  215  for the toner supplied from the toner cartridge  18  is formed in the top surface of the toner supplying portion  202  at a location separated from the developer containing chamber  201 . The toner injected into the developing device  14  through the inlet  215  is transported by the transporting members  203  and  204  to the first section  207  of the developer containing chamber  201 , and is mixed with the developer. Portions of the transporting members  203  and  204  that extend into the toner supplying portion  202  are an example of a transporting member according to the present invention. The transporting member according to the present invention may be a component other than the stirring member that stirs the developer in the developer containing chamber  201 . However, as in the present exemplary embodiment, the transporting members  203  and  204  may be used to simplify the structure. 
     An outlet  216  is formed at the bottom of the toner supplying portion  202  at a location between the inlet  215  and the developer containing chamber  201 . A partition is provided between the developer containing chamber  201  and the toner supplying portion  202 . Therefore, most of the developer transported in the direction of arrow Y through the second section  208  of the developer containing chamber  201  is guided to the second opening  210  by the partition between the developer containing chamber  201  and the toner supplying portion  202  and enters the first section  207 . However, some of the developer overflows and moves over the partition to enter the toner supplying portion  202 . The developer that has entered the toner supplying portion  202  is discharged from the developing device  14  through the outlet  216 . The outlet  216  may be opened and closed by a shutter under the instructions of the controller  41  illustrated in  FIG. 1 . 
     The developing device  14  includes a TC sensor  217  that measures a toner-to-carrier (TC) ratio in the developer that circulates in the developer containing chamber  201 . Based on the measurement value obtained by the TC sensor  217 , the controller  41  issues an instruction for supplying the toner from the toner cartridge  18  so that the TC ratio of the developer is maintained constant. 
     Since the toner density in the toner supplying portion  202  is high, when the temperature or humidity is high or when formation of high-density images is continuously performed, there is a risk that the toner will adhere to the transporting members  203  and  204 . 
       FIG. 3  illustrates the state in which the toner has adhered to the rotating shaft  211  of the transporting member  203 . 
     When the temperature or humidity is high or when formation of high-density images is continuously performed, there is a risk that toner  220  will adhere to the rotating shaft  211  of the transporting member  203  and remain at the rotating shaft  211 . The adhesion of the toner  220  leads to a reduction in the transporting force of the transporting member  203 . As a result, the following toner may be blocked in the transport path and clogging of the path may occur. 
     Although  FIG. 3  illustrates the first transporting member  203  among the two transporting members, the second transporting member  204  also has a similar risk. 
     To suppress the adhesion of the toner  220 , the developing device  14  according to the present exemplary embodiment closes the outlet  216  when a change in conditions that may increase the adhesion of the toner  220  has occurred. In the present exemplary embodiment, such a change in conditions includes a change in temperature or humidity beyond a certain criterion and an increase in the density of the image to be formed beyond a certain criterion. The changes in temperature and humidity are detected by the environmental sensor  42  illustrated in  FIG. 1 , and the change in the image density is detected by the controller  41  illustrated in  FIG. 1 . 
     When the outlet  216  is closed, the toner  220  is easily removed from the rotating shaft  211 , as described below. 
       FIG. 4  illustrates a mechanism for removing the toner  220  from the rotating shaft  211 . 
     When the outlet  216  is closed by a shutter  218  as shown by the shaded area in  FIG. 4 , the developer that has overflowed the developer containing chamber  201  and entered the toner supplying portion  202  is transported by the transporting members  203  and  204  in the toner supplying portion  202  and guided to a region below the inlet  215 . The shutter  218  is an example of a guide according to the present invention. The guided developer is further transported by the transporting members  203  and  204  in the toner supplying portion  202  toward the developer containing chamber  201 . When the developer is being transported, the developer comes into contact with the aggregate of toner  220  that has adhered to the rotating shafts  211  and  212 . Since the developer contains the magnetic carrier, the aggregate of toner  220  is disintegrated when the developer comes into contact therewith, and the toner  220  is easily removed from the rotating shaft  211 . As a result, the adhesion of the toner to the transporting members  203  and  204  is suppressed, and the transporting force of the transporting members  203  and  204  is maintained. 
     In the present exemplary embodiment, the shutter that guides the developer that has overflowed the developer containing chamber  201  to the region below the inlet  215  is described as an example of the guide according to the present invention. However, the guide according to the present invention may instead be configured to forcibly guide the developer out of the developer containing chamber  201 . 
     Furthermore, although a tandem-type image forming apparatus including plural image carriers is described above as an example of an image forming apparatus, the image forming apparatus according to the present invention may instead be a revolver-type image forming apparatus in which toner images of respective colors are formed on a single image carrier. 
     Furthermore, although a printer is described above as an example of an image forming apparatus, the image forming apparatus according to the present invention may instead be a facsimile machine, a copy machine, or a multifunction machine. 
     Furthermore, although an indirect-transferring image forming apparatus including an intermediate transfer belt is described above as an example of an image forming apparatus, the image forming apparatus according to the present invention may instead be a direct transferring image forming apparatus in which the toner images are directly transferred onto a sheet of paper from an imager carrier. 
     The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.