Patent Publication Number: US-8538297-B2

Title: Charging apparatus using charging tube and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2010-0080358, filed on Aug. 19, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects relate to an image forming apparatus, and more particularly, to a charging apparatus using a charging tube. 
     2. Description of the Related Art 
     An image forming apparatus such as a printer, a facsimile machine, a copier, and a multifunction peripheral forms a predetermined image on a printing medium using electrophotography. Such an image forming apparatus generally carries out a charging process, a laser scanning process, a developing process, a transferring process, and a fusing process, in order to form an image. In the charging process, a charging apparatus electrically charges a photoconductive medium with a predetermined electric potential. In the laser scanning process, a laser scanning apparatus scans the photoconductive medium, which has been charged with the predetermined electric potential, with light, such that an electrostatic latent image corresponding printing data is formed on the photoconductive medium. In the developing process, a developing apparatus supplies toner to the photoconductive medium on which the electrostatic latent image is formed, thereby developing a toner image. In the transferring process, a transferring apparatus transfers the toner image formed on the photoconductive medium to a printing medium. In the fusing process, a fusing apparatus fuses the toner image onto the printing medium, thereby forming a predetermined image on the printing medium. After that, the printing medium is discharged out of the image forming apparatus and the image forming operation is completed. 
     In general, the charging apparatus is divided into an apparatus using a non-contact charging method and an apparatus using a contact charging method. The non-contact charging apparatus uses a corona discharge in general. The charging apparatus using the corona discharge has the advantage of charging a photoconductive medium uniformly, but has the disadvantage of generating a discharge product such as ozone. Therefore, an extra apparatus for processing the discharge product such as ozone is required and thus a size of the image forming apparatus increases and a manufacturing cost also increases. 
     The contact charging apparatus uses a charging roller which is in contact with a photoconductive medium and charges the photoconductive medium using a discharge occurring in a small gap between the charging roller and the photoconductive medium. The charging apparatus using the charging roller does not generate a discharge product such as ozone because it does not use a corona discharge, and makes it possible to achieve compactness of an image forming apparatus and reduce a manufacturing cost. However, there is a noise problem because the charging roller operates in contact with the photoconductive medium. Also, some of the low molecules forming the charging roller migrate to the photoconductive medium and thus there is a problem that the photoconductive medium is contaminated. 
     SUMMARY 
     Accordingly, it is an aspect to provide a charging apparatus using a charging tube and an image forming apparatus using the same. 
     Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
     The foregoing and/or other aspects are achieved by providing a charging apparatus including: a charging tube which has an outer surface contacting a photoconductive medium and electrically charges a surface of the photoconductive medium, a shaft which is disposed in the charging tube and to which a charging voltage is applied, and a conductive member which is connected to the shaft and contacts an inner surface of the charging tube. A friction coefficient between the conductive member and the inner surface of the charging tube may be less than a friction coefficient between the photoconductive medium and the outer surface of the charging tube, so that a slip phenomenon of the charging tube is prevented. 
     The charging apparatus may further include an elastic member which presses the charging tube against the photoconductive medium. 
     The shaft may include a recess to receive the elastic member. 
     The elastic member may be fixedly inserted into the recess. 
     The conductive member and the elastic member may be fixedly inserted into the recess. 
     The shaft may have a U-shaped cross section. 
     A plurality of dimples may be formed on at least one of a surface of the conductive member contacting the charging tube and the inner surface of the charging tube. 
     The charging tube may include: a first layer which contacts the photoconductive medium, and a second layer which contacts the conductive member. A material forming the second layer may be different from a material forming the first layer so that a friction coefficient between the second layer and the conductive member is less than a friction coefficient between the first layer and the photoconductive medium. 
     An electric resistance of the second layer may be less than an electric resistance of the first layer. 
     The electric resistance of the first layer may be less than or equal to 10 8 Ω and the electric resistance of the second layer may be less than or equal to 10 4 Ω. 
     The charging tube may be formed of nylon and a conductive additive. 
     The charging tube may be at least 0.1 mm thick. 
     The charging apparatus may further include a meandering prevention unit to prevent the charging tube from meandering in a lengthwise direction of the shaft. 
     The meandering prevention unit may include an extension part extending from one end of the shaft to face one end of the charging tube. 
     The meandering prevention unit may include an extension part extending from a support frame supporting the shaft to face one end of the charging tube. 
     A clearance between the meandering prevention unit and the charging tube may be greater than or equal to 0.1% and less than or equal to 3% of an entire length of the charging tube. 
     The conductive member may be formed of an elastic metal sheet and the metal sheet may have a curved portion formed at a portion contacting the inner surface of the charging tube. 
     The foregoing and/or other aspects may also be achieved by providing a charging apparatus including: a charging tube which has an outer surface contacting a photoconductive medium and electrically charges a surface of the photoconductive medium, and a shaft which contacts an inner surface of the charging tube and to which a charging voltage is applied. The charging tube may include a first layer which contacts the photoconductive medium and a second layer which contacts the shaft. A material forming the second layer may be different from a material forming the first layer, so that a friction coefficient between the second layer and the shaft is less than a friction coefficient between the first layer and the photoconductive medium. 
     The foregoing and/or other aspects may also be achieved by providing a developing cartridge comprising the charging apparatus as described above. 
     The foregoing and/or other aspects may also be achieved by providing an image forming apparatus comprising the charging apparatus as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic view illustrating an image forming apparatus according to an exemplary embodiment; 
         FIG. 2  is a schematic view illustrating a charging apparatus of  FIG. 1 ; 
         FIG. 3  is an enlarged view of a part of the charging apparatus of  FIG. 2 ; 
         FIG. 4  is a graph illustrating change in a surface potential of a photoconductive medium according to change in a charging voltage; 
         FIG. 5  is a perspective view illustrating one end of the charging apparatus to show an example of a meandering prevention unit; 
         FIG. 6  is a perspective view illustrating one end of the charging apparatus to show another example of a meandering prevention unit; and 
         FIGS. 7 to 10  are schematic views illustrating a charging apparatus according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments, 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 embodiments by referring to the figures. It should be understood that various features are not drawn to scale and the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
       FIG. 1  is a schematic view illustrating an image forming apparatus  1  according to an exemplary embodiment. The image forming apparatus  1  may be diverse apparatuses for forming a predetermined image on a printing medium such as printers, facsimile machines, copiers, and multifunction peripherals.  FIG. 1  also illustrates an advancing path  2  of the printing medium. 
     A paper feeding apparatus  10  stores the printing medium such as paper therein. The printing medium is conveyed by a plurality of conveyance rollers  11  along the advancing path  2 . 
     A charging apparatus  100  electrically charges a surface of a photoconductive medium  20  using a contact charging method. The charging apparatus  100  will be explained later in detail. 
     A laser scanning apparatus  30  scans the surface of the photoconductive medium  20  with light, thereby forming an electrostatic latent image corresponding to printing data on the surface of the photoconductive medium  20 . 
     A developing apparatus  40  supplies toner to the surface of the photoconductive medium  20  on which the electrostatic latent image is formed, thereby developing a toner image. The developing apparatus  40  may include a toner container  41 , a toner supply roller  42 , a developing roller  43 , and a regulation blade  44 . 
     The toner container  41  contains toner therein. The toner supply roller  42  supplies the toner contained in the toner container  41  to the developing roller  42 , thereby forming a toner layer on the developing roller  43 . The regulation blade  44  makes the toner layer uniform. The toner layer formed on the developer roller  43  is moved to the electrostatic latent image formed on the surface of the photoconductive medium  20  due to a potential difference such that the toner image is developed. 
     A transferring apparatus  50  transfers the toner image formed on the surface of the photoconductive medium  20  to the printing medium. 
     A cleaning apparatus  60  removes toner remaining on the surface the photoconductive medium  20  after the transferring process. 
     A fusing apparatus  70  fuses the transferred toner image onto the printing medium. The printing medium onto which the toner image is fused is discharged to the outside of the image forming apparatus  1  through the plurality of conveyance rollers  11 . 
     A developing cartridge  80  may integrally include the elements such as the charging apparatus  100 , the photoconductive medium  20 , and the developing apparatus  40 . After the image forming apparatus  10  is used for a predetermined time, a user may remove the developing cartridge  80  and re-mount a new developing cartridge in the image forming apparatus  1 . In this embodiment, the developing cartridge  80  includes the toner container  41  therein, but, in another exemplary embodiment, the developing cartridge  80  may not include the toner container  41  therein. In other words, there may be an extra toner cartridge for containing toner and such an extra toner cartridge may be combined with the developing cartridge  80 . In this case, the user may replace the toner cartridge and the developing cartridge  80  separately. 
     Hereinafter, the charging apparatus  100  according to a first exemplary embodiment will be explained in detail with reference to  FIGS. 2 and 3 .  FIG. 2  is a schematic view illustrating the charging apparatus  100  of  FIG. 1 , and  FIG. 3  is an enlarged view of a part of the charging apparatus  100  of  FIG. 2 . 
     A charging tube  110  has a hollow shape having an empty space therein. An outer surface of the charging tube  110  contacts the photoconductive medium  20  and the charging tube  110  electrically charges the surface of the photoconductive medium  20  in a contact charging method. The charging tube  110  may be formed of nylon and a conductive additive, for example. The conductive additive may be carbon black, an ion conductor, etc. As the photoconductive medium  20  is rotated, the charging tube  110  is also rotated due to a friction between the charging tube  110  and the photoconductive medium  20 . 
     A shaft  120  is disposed in the charging tube  110 . The shaft  120  may be formed of a metal material having conductivity, for example. A charging voltage for charging the surface of the photoconductive medium  20  is supplied to the shaft  120  from an external power source (not shown). 
     A conductive member  130  is connected to the shaft  120  and contacts an inner surface of the charging tube  110 . The conductive member  130  may be formed in a thin film. The conductive member  130  may be formed of a material having flexibility and conductivity. The charging voltage applied to the shaft  120  may be transmitted to the charging tube  110  through the conductive member  130 . 
     An elastic member  140  presses the charging tube  110  and the conductive member  130  against the photoconductive medium  20 . The elastic member  140  may be formed of a sponge. The elastic member  140  makes the charging tube  110  stably in contact with the photoconductive medium  20 . 
     The materials and the shapes of the charging tube  110 , the shaft  120 , the conductive member  130 , and the elastic member  140  are merely examples and it should be understood that they can be modified variously. 
     The charging voltage applied to the shaft  120  is transmitted to the charging tube  110  through the conductive member  130  and accordingly a discharge occurs in a small gap of a wedge shape between the outer surface of the charging tube  110  and the photoconductive medium  20 . Although the photoconductive medium  20  is a nonconductor of electricity, a surface potential is generated on the surface of the photoconductive medium  20  due to such a discharge phenomenon. The charging voltage applied to the shaft  120  may be an AC voltage, a DC voltage, or a mixture of the AC voltage and the DC voltage. Since the charging voltage could be easily understood by an ordinary skilled person in the related art, a detailed description thereof is omitted. 
       FIG. 4  is a graph illustrating change in the surface potential of the photoconductive medium  20  according to change in the charging voltage. It can be seen from  FIG. 4  that the surface potential is linearly changed according to the change in the charging voltage applied to the shaft  120 . As described above, it can also be seen that the charging performance of the charging apparatus  100  is suitable for the image forming apparatus  1 . 
     The charging apparatus  100  using the above-described discharge phenomenon may cause a noise. In particular, in the case that the charging voltage is the AC voltage, the noise becomes a serious problem. In order to reduce the noise, the charging apparatus  100  according to an exemplary embodiment uses the charging tube  110  of the hollow shape instead of a charging roller. Since the charging tube  110  is more flexible than the charging roller, the noise caused during the discharge can be reduced. 
     Also, the charging apparatus using the charging roller may contaminate the photoconductive medium since some of low molecules of the charging roller are migrated to the photoconductive medium. If the photoconductive medium is contaminated, image quality deteriorates. Such a migration phenomenon is more serious as a contact force between the charging roller and the photoconductive medium increases. Since the charging apparatus  100  according to an exemplary embodiment uses the charging tube  110  of the hollow shape instead of the charging roller, a mass of the charging tube  110  is noticeably less than that of the charging roller. Therefore, the contact force between the photoconductive medium  20  and the charging tube  110  is greatly reduced so that the migration phenomenon can be prevented. 
     As shown in  FIG. 2 , the shaft  120  includes a recess  121  to receive the elastic member  140  and has a U-shaped cross section. The conductive member  130  and the elastic member  140  are fixedly inserted into the recess  121  of the shaft  120 . To achieve this, the recess  121  is formed to have a width a little less than an entire width of the conductive member  130  and the elastic member  140 . In this case, a conductive adhesive for fixing the conductive member  130  and the elastic member  140  is not required so that a manufacturing process can be simplified and a cost of production can be reduced. Also, an electric resistance can be prevented from being increased due to the presence of the conductive adhesive, 
     A slip phenomenon of the charging tube  110  may occur according to a working condition of the charging apparatus  100 . In other words, even if the photoconductive medium  20  is well rotated, the charging tube  110  may not be rotated. In this case, the photoconductive medium  20  is not uniformly charged, causing unevenness in an image formed on the printing medium. As the charging tube  110  of the hollow shape is used, the mass or the moment of inertia of the charging tube  110  is reduced such that the charging tube  110  sensitively responds to a friction exerted to the inner surface (a surface contacting the conductive member  130 ) and the outer surface (a surface contacting the photoconductive medium  20 ). Therefore, the slip phenomenon occurs more easily in the case of the charging tube  110  than in the case of using the charging roller. 
     According to various working conditions, such as temperature, a contact force and material composition, the friction exerted to the inner surface and the outer surface of the charging tube  110  is changed. In order to prevent the slip phenomenon of the charging tube  110 , it is necessary to significantly reduce a friction coefficient between the conductive member  130  and the inner surface of the charging tube  110  less than a friction coefficient between the photoconductive medium  20  and the outer surface of the charging tube  110  in the various working conditions. As shown in  FIG. 3 , a plurality of dimples  131  are formed on one surface of the conductive member  130  contacting the charging tube  110 . The inventors found out that the friction coefficient between the conductive member  130  and the inner surface of the charging tube  110  is greatly reduced because of the plurality of dimples  131  formed on the one surface of the conductive member  10 . Accordingly, the charging apparatus  100  according to an exemplary embodiment can prevent the slip phenomenon of the charging tube  110  and deterioration of the image quality. According to another exemplary embodiment, a plurality of dimples may be formed on the inner surface of the charging tube  110  rather than the conductive member  130  or a plurality of dimples may be formed on both the conductive member  130  and the inner surface of the charging tube  110 . 
       FIG. 5  is a perspective view illustrating one end of the charging apparatus  100  to show an example of a meandering prevention unit  150 . 
     The charging tube  110  is rotated in contact with the photoconductive medium  20 , but an ununiform contact force may be generated along a lengthwise direction of the shaft  120 . The ununiform contact force may cause the charging tube  110  to meander in the lengthwise direction of the shaft  120 . 
     The meandering prevention unit  150  is able to prevent the charging tube  110  from meandering along the lengthwise direction of the shaft  120 . As shown in  FIG. 5 , the meandering prevention unit  150  may include an extension part  151  extending from one end of the shaft  120 . The extension part  151  is formed to face one end of the charging tube  110 . If the charging tube  110  meanders further than a predetermined distance, the extension part  151  prevents the charging tube  110  from meandering. Albeit not shown, a part similar to the extension part  151  of  FIG. 5  may be formed on the shaft  120  at the other end of the charging apparatus  100 . Since the extension part  151  is integrally formed with the shaft  120 , an extra element for preventing the charging tube  110  from meandering is not required so that the manufacturing process can be simplified and the manufacturing cost can be reduced. 
     A clearance ‘c’ between the meandering prevention unit  150  and the charging tube  110  is designed in consideration of a coefficient of thermal expansion of the charging tube  110  and an image forming area. The clearance ‘c’ may be greater than or equal to 0.1% and less than or equal to 3% of the entire length of the charging tube  110 . If the clearance ‘c’ is less than 0.1% of the entire length of the charging tube  110 , the meandering prevention unit  140  may press the charging tube  110  when the charging tube  110  thermally expands and thus the charging tube  110  may be deformed regardless of whether the meandering of the charging tube  110  occurs or not. On the other hand, if the clearance ‘c’ is greater than 3% of the entire length of the charging tube  110 , the charging tube  110  suffers from great meandering before the meandering prevention unit  150  prevents the meandering of the charging tube  110  and thus is likely to be deviated from the image forming area (in other words, a width of a printing medium). 
     If a hardness of the charging tube  110  is weak, one end of the charging tube  110  contacting the meandering prevention unit  150  may wear out easily or may be damaged when the meandering prevention unit  150  prevents the meandering of the charging tube  110 . Therefore, the charging tube  110  needs to have a hardness greater than a predetermined level. To achieve this, it is preferable that the charging tube  110  is at least 0.1 mm thick and it is more preferable that the charging tube  110  is 0.15 mm thick. 
       FIG. 6  is a perspective view illustrating one end of the charging apparatus  100  to show another example of the meandering prevention unit  150 . 
     A support frame  85  rotatably supports the photoconductive medium  20  and also supports the shaft  120  of the charging apparatus  100 . The support frame  85  may be a lateral frame of the developing cartridge  80 . As shown in  FIG. 6 , the meandering prevention unit  150  may include an extension part  152  extending from the support frame  85 . The extension part  152  is formed to face one end of the charging tube  110 . If the charging tube  110  meanders further than a predetermined distance, the extension part  152  prevents the charging tube  110  from meandering. Albeit not shown, a part similar to the extension part  152  of  FIG. 6  may be formed on the other end of the charging apparatus  100 . Since the extension part  152  is integrally formed with the support frame  85 , an extra element for preventing the meandering of the charging tube  110  is not required so that the manufacturing process can be simplified and the manufacturing cost can be reduced. 
       FIG. 7  is a schematic view illustrating a charging apparatus  100   a  according to a second exemplary embodiment. The elements performing the same functions as those of the aforementioned embodiment are given the same reference numerals and a detailed description thereof is omitted. 
     In the first exemplary embodiment shown in  FIG. 2 , the plurality of dimples are formed on the conductive member  130  in order to prevent the slip phenomenon of the charging tube  110 , whereas in the second exemplary embodiment shown in  FIG. 7 , the charging tube  110  includes a first layer  111  and a second layer  112  instead of having the plurality of dimples formed on the conductive member  130 . The first layer  111  contacts the photoconductive medium  20  and the second layer  112  contacts the conductive member  130 . The second layer  112  is formed of a material different from that of the first layer  111  so that a friction coefficient between the second layer  112  and the conductive member  130  is greatly lower than a friction coefficient between the first layer  111  and the photoconductive medium  20 . Accordingly, the slip phenomenon of the charging tube  110  can be prevented. 
     In the second exemplary embodiment of  FIG. 7 , in order to further reduce the friction coefficient between the second layer  112  and the conductive member  130 , a plurality of dimples may be formed on the conductive member  130  as in the first exemplary embodiment. Alternatively, the plurality of dimples may be formed on the second layer  112  of the charging tube  110  or may be formed on both the second layer  112  of the charging tube  110  and the conductive member  130 . 
     An electric resistance of the charging tube  110  should be more than a predetermined level in order to prevent a discharge generated in a small gap of a wedge shape between the outer surface of the charging tube  110  and the photoconductive medium  20  from becoming a spark discharge. However, if the electric resistance of the charging tube  110  is excessive, the photoconductive medium  20  may not be charged uniformly. In order to prevent ununiform charging, the materials forming the first and the second layers  111  and  112  are adjusted so that an electric resistance of the second layer  112  is less than an electric resistance of the first layer  111 . As the electric resistance of the second layer  112  which is formed on the inner surface of the charging tube  110  is lowered, electric conduction can be improved and ununiform charging can be prevented. It is preferable that the electric resistance of the first layer  111  is less than or equal to 10 8 Ω and the electric resistance of the second layer  112  is less than or equal to 10 4 Ω. 
     In the charging tube  110  according to the second exemplary embodiment of  FIG. 7 , the second layer  112  may be coated over an inner surface of the first layer  111  by a coating process. Alternatively, the first layer  111  may be coated over an outer surface of the second layer  112  by a coating process. By this coating process, the first layer  111  and the second layer  112  may be formed of different materials. To this end, the electric resistances and the friction coefficients of the first and the second layers  111  and  112  become different. Herein, the coating process is used for forming the first and the second layer  111  and  112  with different material. However, this is merely an example and the charging tube  110  may be manufactured by various methods besides the coating process. For example, the first layer  111  and the second layer  112  may be manufactured separately and then bonded to each other. 
     Although the charging tube  110  includes the first layer  111  and the second layer  112  in the second exemplary embodiment of  FIG. 7 , the charging tube  110  may further include another layer between the first and the second layers  111  and  112 . 
       FIG. 8  is a schematic view illustrating a charging apparatus  100   b  according to a third exemplary embodiment. The elements performing the same functions as those of the aforementioned embodiments are given the same reference numerals and a detailed description thereof is omitted. 
     Unlike in the aforementioned embodiments, in the third exemplary embodiment of  FIG. 8 , the conductive member  130  and the elastic member  140  are not used. Instead, the shaft  120  contacts the inner surface of the charging tube  110 , more specifically, the second layer  112  of the charging tube  110 . Therefore, the charging voltage applied to the shaft  120  is transmitted directly to the charging tube  110  without passing the conductive member  130 . Since the conductive member  130  and the elastic member  140  are omitted, the manufacturing process can be simplified and the manufacturing cost can be reduced. 
     By forming the first layer  111  and the second layer  112  with different materials, the friction coefficient between the first layer  112  and the shaft  120  is made less than the friction coefficient between the first layer  111  and the photoconductive medium  20  and the electric resistance of the second layer  112  is made less than the electric resistance of the first layer  111 . To this end, the slip phenomenon of the charging tube  110  and the ununiform charging can be prevented. Also, in order to further reduce the friction coefficient between the second layer  112  and the shaft  120 , the plurality of dimples may be formed on a part of the shaft  120  contacting the first layer  111  and/or the second layer  112 . 
       FIG. 9  is a schematic view illustrating a charging apparatus  100   c  according to a fourth exemplary embodiment. The elements performing the same functions as those of the aforementioned embodiment are given the same reference numerals and a detailed description thereof is omitted. 
     In the fourth exemplary embodiment, the elastic member  140  is omitted and an elastic metal sheet  135  is formed for the conductive member  130 . The metal sheet  135  may be a stainless steel plate (SUS). Since the metal sheet  135  has elasticity, the metal sheet  135  is able to generate a sufficient contact force between the metal sheet  135  and the photoconductive medium  20  even if no elastic member  140  exists. 
     If the contact force between the metal sheet  135  and the photoconductive medium  20  excessively increases, the surface of the photoconductive medium  20  may be damaged and the charging tube  110  may be deformed. Accordingly, as shown in  FIG. 9 , the metal sheet  135  may be bent at least two times. 
     The metal sheet  135  has a curved portion  135   a  at a portion contacting the inner surface of the charging tube  110 . A radius of curvature of the curved portion  135   a  is equal to that of the charging tube  110 . Since a friction coefficient between the metal sheet  135  and the inner surface of the charging tube  110  is reduced due to the curved portion  135   a , the charging tube  110  is smoothly rotated without any slip phenomenon. 
       FIG. 10  is a schematic view illustrating a charging apparatus  100   d  according to a fifth exemplary embodiment. The elements performing the same functions as those of the aforementioned embodiments are given the same reference numerals and a detailed description thereof is omitted. 
     The fifth exemplary embodiment of  FIG. 10  is similar to the first embodiment of  FIG. 2 , except for the position of the conductive member  130 . Only the elastic member  140  is inserted into the recess  121  of the shaft  120 . In the fifth embodiment of  FIG. 10 , the conductive member  130  is bonded to a side surface of the shaft  120  rather than being fixedly inserted into the recess  121  of the shaft  120  so that the conductive member  130  can be fixed more stably. Therefore, the conductive member  130  is prevented from being separated from the shaft  120  during the operation of the charging apparatus  100   d.    
     Although a few embodiments 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.