Patent Publication Number: US-7711290-B2

Title: Developer agitator increasing electrification rate of developer, and developing apparatus and image forming device having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Application No. 2006-81259, filed Aug. 25, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Aspects of the present invention relate to an agitator, and more particularly, to an agitator that electrifies a developer with friction, a developing apparatus having the agitator, and an image forming device having the agitator. 
   2. Description of the Related Art 
   An image forming device, such as a printer, that uses an electrophotography process, is an apparatus, which forms an electrostatic latent image on a photoconductor using a light exposing unit, develops the electrostatic latent image with a developer by using a developing apparatus to form a developer image, and then transfers and fixes the developer image onto a printing medium. 
   The developer, which is used for developing the electrostatic latent image in the developing apparatus, is either a one-component system developer or a two-component system developer. In case of the one component system developer, toner particles are electrified by friction with themselves or friction with a charging member. The electrified toner particles are moved onto a developing roller and then attached to an electrostatic latent image region of the photoconductor to form a developer image. 
   A two-component system developer is a developer in which magnetic carrier particles are mixed with non-magnetic toner particles made of synthetic resins. The toner particles are electrified by friction with the carrier particles and with themselves. The electrified toner particles are moved onto the developing roller along with the carrier particles and then attached to an electrostatic latent image region of the photoconductor to form a developer image. 
   In general, a developing apparatus of an image forming device is provided with an agitator to electrify the toner particles of a developer by friction. A conventional agitator is shown in  FIGS. 1A and 1B . As shown in  FIG. 1A , the agitator  1  has a structure in which an agitating wing  3  is in the form of a helix on a rotary shaft  2 . The agitator  1  rotates in a developer-containing space of a developer casing (not shown). As the agitating wing  3  rotates, toner particles and, if it is a two-component system, carrier particles are mixed with one another, and the toner particles are electrified by friction. 
   The longer the contact time of the toner particles, and in a two-component system, to the carrier particles and the greater the number of the toner particles contacted, the smoother the electrification of the toner particles that is achieved. To carry out a printing operation at a high speed, it is required that the toner particles be charged in a short time. However, for a conventional agitator to lengthen the contact time of the toner particles to the carrier particles or to increase the number of the toner particles contacted, the agitating wing  3  should be quickly rotated or the diameter thereof enlarged. To quickly rotate the agitating wing  3 , a change to the design of the agitator driving system would be required, and to enlarge the diameter of the agitating wing  3  would require a layout change of the developing apparatus. Neither alternative is particularly desirable. 
   SUMMARY OF THE INVENTION 
   Several aspects and embodiments of the present invention provide an agitator with an increased contact area of an agitating wing to thereby increase the electrification rate of a developer, without the requirement to quickly rotate the agitating wing or to increase the diameter of the agitating wing. 
   Other aspects and embodiments of the present invention provide a developing apparatus and an image forming device having one or more agitators with the characteristics described above. 
   Additional aspects and/or advantages of the invention 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 invention. 
   In accordance with one aspect of an embodiment of the present invention, there is provided an agitator including a rotatable shaft, an agitating wing disposed on the circumferential surface of the shaft, and an uneven part formed on the surface of the agitating wing to increase a contact area with a substance to be agitated. 
   According to an aspect of the present invention, the uneven part may have a waved structure, a stepped structure, or a structure with both waved and stepped features. The uneven part may be constant along the agitator wing, or the waved and/or stepped features of the uneven part may vary along the length of the shaft. Also, the uneven part may be oriented in the longitudinal direction or the transverse direction of the agitating wing. 
   Preferably, but not necessarily, the agitating wing is disposed in the form of a helix along the shaft. 
   According to an aspect of the present invention, the substance to be agitated comprises a developer. 
   In accordance with another embodiment of the present invention, there is provided a developing apparatus including: a developing casing having a developer-containing space, a developing roller to rotate in the developing casing, a developer supplying roller to rotate in the developing casing to face the developing roller, so that the developer of the developer-containing space is supplied to the developing roller, and an agitator to electrify a developer contained in the developer-containing space by friction, as described above. 
   According to still another aspect of an embodiment of the present invention, there is provided an image forming device including: a photoconductor on which an electrostatic latent image is formed, a developing apparatus to develop the electrostatic latent image of the photoconductor with a developer, a transferring apparatus to transfer the developer image formed on the photoconductor onto an printing medium, and a fusing apparatus to fix the developer image transferred onto an printing medium. The developing apparatus, as described above, includes an agitator constructed as described above in the developer-containing space to agitate the developer contained in the developer-containing space, thus electrifying the developer by friction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIGS. 1A and 1B  are a perspective view and a partially magnified cross-sectional view of a section of a conventional developer; 
       FIGS. 2A and 2B  are a perspective view and a partially magnified cross-sectional view of a section of a developer agitator according to an embodiment of the present invention; 
       FIGS. 2C and 2D  are partially magnified cross-sectional views of a developer agitator according to another embodiment of the present invention; 
       FIG. 3  is a perspective view exemplifying a section of a developer agitator according to another embodiment of the present invention; 
       FIG. 4  is a perspective view showing a developing apparatus to which the developer agitator according to an embodiment of the present invention has been applied; 
       FIG. 5  is a graph showing developer electrification by a developer agitator in an embodiment of the present invention and by the conventional developer agitator shown in  FIGS. 1A and 1B ; and 
       FIG. 6  is a cross-sectional view showing an example image forming device to which the developing apparatus of  FIG. 4  is applied. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Reference will now be made in detail to the present embodiments of the present invention, 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 invention by referring to the figures. 
   An embodiment of the present invention is illustrated in  FIGS. 2A and 2B : a developer agitator  40  includes a rotatable shaft  41 , an agitating wing  42  disposed in the form of a helix on the circumferential surface of the shaft  41 , and an uneven part  43  formed on a surface of the agitating wing  42 . 
   The agitator  40  constructed as described above can be used for electrifying a developer by friction in, for example, a developing apparatus  100  as illustrated in  FIG. 4 . In this case, the uneven part  43  formed on the surface of the agitating wing  42  increases the contact area for the developer, and thus improves the electrification rate of the developer. 
   That is, the conventional agitating wing  3  (see  FIGS. 1A and 1B ) has a smooth surface, but the agitating wing  42  of the developer agitator  40  according to the embodiment of the present invention has the uneven part  43  formed on the surface thereof, thereby allowing a surface area of the agitating wing  42  to be enlarged compared with the conventional agitating wing  3 . Accordingly, the contact area of the agitating wing  42  and the developer is increased, and thus without the requirement to quickly rotate the agitating wing  42  or increase the diameter thereof, the contact time between toner particles and, in a two component system developer, carrier particles of the developer, is lengthened and the number of particles contacted thereby is increased, increasing the electrification rate of the developer. 
   The uneven part  43  as described above can have a waved structure or a stepped structure, as illustrated by  53  and  63  in  FIGS. 2C and 2D , respectively. Besides the waved structure or the stepped structure, the uneven part  43  can be configured in any combination of both waved and stepped structures that is capable of increasing the surface area thereof, an embodiment being the uneven part  43  shown in  FIG. 2B . In one aspect of the present invention, the uneven part  43  has the same structure and cross-section along the entire length of the agitator  40 . In another aspect of the present invention, the uneven part  43  can vary along the length of the agitator  40 . 
     FIG. 3  is a perspective view exemplifying a section of a developer agitator  40 ′ according to another embodiment of the present invention. As illustrated in the drawing, the developer agitator  40 ′ has the same basic structure as that of the developer agitator  40  of the embodiment as described above and shown in  FIG. 2A , which includes a rotatable shaft  41 , an agitating wing  42  disposed in the formed of a helix on a circumferential surface of the shaft  41 , and an uneven part  43  formed on a surface of the agitating wing  42 . However, in the embodiment of the present invention shown in  FIG. 3 , the orientation of the uneven part  43 ′ is different from that of the uneven part  43  shown in  FIG. 2A . That is, in the embodiment shown in  FIG. 3 , the uneven part  43 ′ is oriented in the longitudinal direction of the agitating wing  42 ′, whereas in the previous embodiment shown in  FIG. 2A , the uneven part  43  is oriented in the transverse direction of the agitating wing  42 . 
   Thus, in the embodiment of the present invention shown in  FIG. 3 , the surface area of the agitating wing  42 ′ is also enlarged, so that the developer agitator  40 ′ can obtain the same results as that of the agitator  40  in the previous embodiment shown in  FIG. 2A . The formed orientation of the uneven part  43  is not limited to the examples illustrated in the drawings. For instance, the uneven part  43  can be formed in any other structure, for example, a slightly slanted structure that is capable increasing the surface area of the agitating wing  42 . 
     FIG. 4  is a perspective view schematically exemplifying a developing apparatus  100  to which the developer agitator  40 , according to the embodiment of the present invention as described above and shown in  FIG. 2A , is applied. As shown in  FIG. 4 , the developing apparatus  100  includes a developing casing  110  having a developer-containing space formed in a predetermined shape. The developing casing  110  is provided with a developer inlet and a developer outlet. A developer cartridge  120  is connected to the developer inlet, and a developing roller  130  and a developer supplying roller  140  are rotatably disposed at the developer outlet. 
   The developer agitator  40  includes a first developer agitator  410  and a second developer agitator  420 , which are rotatably disposed in the developer-containing space of the developing casing  110 . A developer contained in the developer-containing space is agitated by the first and second developer agitators  410  and  420 , so that the developer is electrified by friction. Because the agitating wings  42  of the developer agitators  410  and  420  have the contact areas for the developer enlarged by the uneven parts  43  formed on the surfaces thereof, the electrification rate of the developer is higher than if an agitator  1  with a smooth agitating wing  3  as shown in  FIG. 1A  was used. 
     FIG. 5  is a graph exemplifying the toner-electrification amount as compared to agitating time using the developer agitator according to an embodiment of the present invention. Referring to  FIG. 5 , by using the developer agitator according to an embodiment of the present invention, the toner-electrification amount was saturated in a shorter time compared to using a conventional developer agitator. In an image forming device, to form an acceptable developer image the toner-electrification amount should be at least 70% of a saturated state. In  FIG. 5 , a reference E indicates a suitable development image point. In the developer agitator of the embodiment of the present invention, the toner-electrification amount has reached the required value before the suitable development image point E, so that the developer agitator of the embodiment of the present invention can be used in high speed printing with a shorter development image point E. 
     FIG. 6  is a cross sectional view showing a section of an example image forming device to which the developing apparatus  100  of  FIG. 4  as described above is applied. Referring to the drawing, a photoconductor  200  is disposed to face the developing roller  130  of the developing apparatus  100 . A charging roller  210  is rotatably disposed in contact with the photoconductor  200  to charge the photoconductor  200 . A scanning unit  220 , using a light source such as a laser or light emitting diode (LED), scans a beam onto a surface of the photoconductor  200  electrified by the charging roller  210 , and thus forms a predetermined electrostatic latent image on the surface of the photoconductor  200 . 
   The electrostatic latent image of the photoconductor  200  is developed into a developer image by the developing apparatus  100 , and the developer image is transferred onto a printing medium P, such as paper, transparency, etc., which is conveyed between a transferring roller  230  and the photoconductor  200 . The developer image transferred onto the printing medium P is fixed on the printing medium P when it passes through a fusing apparatus  240 . 
   The image forming process as described above is the same as that of the conventional image forming device, except that by using the agitator  40  contained in the developer  100 , the electrification rate of the developer is increased by the developer agitator  40  as described above, thereby allowing the image forming device to be adapted to use in high speed printing. 
   As is apparent from the forgoing description, according to the embodiments of the present invention, the developer agitator, and the developing apparatus and the image forming device having the same can not only smoothly agitate the developer, but also increase the electrification rate of the developer. Accordingly, the developer agitator  40 , and the developing apparatus  100  and the image forming device having the same according to the embodiments of the present invention can obtain an electrification rate of the developer required for high speed printing, thereby allowing the image forming device to be operated at a high speed. 
   Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.