Patent Publication Number: US-7715758-B2

Title: Apparatus and method for cleaning residual toner from drums in an image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation of U.S. application Ser. No. 11/677,807, filed Feb. 22, 2007, which is a division of U.S. application Ser. No. 11/091,600, filed Mar. 29, 2005, the entire contents of all of which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to image forming apparatuses and, more particularly, to a system and method for cleaning residual toner from drums in an image forming apparatus. 
   BACKGROUND OF THE INVENTION 
   In a laser-type image forming apparatus, there are one or more photoelectric drums that are used in conjunction with the image formation process. If the image forming apparatus is a monochromatic or black and white (B/W) device, then there is typically only one drum used for black (K) image formation. If the image forming apparatus is color, however, there are typically four drums used, one each for black (K), cyan (C), magenta (M), and yellow (Y). During image formation, the photoelectric drum is exposed to a laser, which forms a latent image on the drum. The latent image on the surface of the drum passes by a toner source, such as a developing unit, which attracts toner to the surface of the drum to form a toner image. The toner image is then transferred to an image receiving medium, such as a paper sheet, and the transferred image is fused to the image receiving medium by a fusing unit. 
   To maintain proper image formation, the image forming apparatus employs a mechanism for cleaning the surface of the photoelectric drums.  FIG. 1  is a diagram of a conventional “cleaner-less” drum cleaning system in an image forming apparatus. In a cleaner-less system, there is no cleaning blade or other element contacting the drum  10  to remove toner from its surface. As shown in  FIG. 1 , the image forming apparatus includes a drum  10 , a developer  12 , a transfer roller  14 , a brush  16 , and a charger  18 . The drum  10  rotates in a clockwise direction, and the surface of the drum is charged by the charger  18 . The charged surface is exposed to a laser (not shown) to generate a latent image. The latent image passes by the developer  12 , which transforms the latent image into a toner image. The toner image is then transferred onto an image receiving medium by the transfer roller  14 . 
   As shown in  FIG. 1 , the vast majority of the toner on the surface of the drum  10  is negatively charged toner  20 , although there is some positively charged toner  22 . During image formation, the image area (area exposed by the laser) typically has a −60V charge, and the non-image area typically has a −400V charge. The developer  12  is typically biased at a voltage of −250V. As the latent image passes by the developer  12 , toner is transferred to the image areas. Any residual toner on the drum  10  in a non-image area is transferred to the developer  12 . 
   As also shown in  FIG. 1 , the brush  16  is positioned adjacent to the surface of the drum  10 . The brush  16  is given a positive voltage bias such as +600V. With the positive bias, the negative toner  20  is collected by the brush  16 . However, the brush  16  is not able to collect the positive toner  22 , although there are few positively charged toner particles  22 . During periods between image forming operations, the bias voltage of the brush  16  can be reversed, which discharges toner from the brush  16  to the drum  10 . The discharge to the drum  10  scatters the toner as a layer on the surface of the drum  10 , which is then collected by the developer  12 . In color image forming apparatuses, however, the toner filming is particularly severe on the color drums and cannot be effectively removed by the developer  12 . As a result, the filming often results in the whitening of printed image areas as the film blocks the surface of the drum  10  from being imaged effectively. 
   It would be desirable to have a design that effectively cleans toner from the drums. 
   SUMMARY OF THE INVENTION 
   According to an aspect of the invention, an image forming apparatus and method for cleaning a plurality of drums in an image forming apparatus includes applying a first bias to each of a plurality of disturbing members, each disturbing member associated with a corresponding drum of a plurality of drums. While performing an image forming operation wherein at least one of the plurality of drums is not use, the bias is changed of a disturbing member corresponding to at least one of the plurality of drums not used in performing the image forming operation from the first bias to a second bias different from the first bias. 
   Further features, aspects and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows, when considered together with the accompanying figures of drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a conventional cleaner-less drum cleaning system in a image forming apparatus. 
       FIG. 2  is a diagram of a drum cleaning system for an image forming apparatus consistent with the present invention. 
       FIG. 3  is a flow diagram of a drum cleaning process for the drum cleaning system of  FIG. 2  consistent with the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 2  is a diagram of a drum cleaning system for an image forming apparatus consistent with the present invention. The image forming apparatus can be, for example, a printer, a multi-function peripheral (MFP), a fax, a plotter, or any other device capable of generating a printout. As shown in  FIG. 2 , the image forming apparatus includes a black drum K  32 , a cyan drum C  34 , a magenta drum M  36 , and a yellow drum Y  38 . Each of the drums  32 - 38  is positioned adjacent to a respective transfer roller  40  with a transfer belt moving between the drums  32 - 38  and the transfer rollers  40 . Each of the drums  32 - 38  is also positioned adjacent to a corresponding toner disturbing member, charger, and developer. In particular, the K drum  32  is positioned adjacent to a disturbing member  52 , a developer  62 , and a charger  72 . The C drum  34  is positioned adjacent to a disturbing member  54 , a developer  64 , and a charger  74 . The M drum  36  is positioned adjacent to a disturbing member  56 , a developer  66 , and a charger  76 . The Y drum  38  is positioned adjacent to a disturbing member  58 , a developer  68 , and a charger  78 . 
   The drums  32 - 38  are preferably photoelectric drums that can form a latent image in response to exposure from a laser. The toner disturbing members  52 - 58  may be, for example, brushes, sponge rollers, or brush rollers that can be biased at one or more potentials, such as −600V and +600V. In addition, the disturbing members  52 - 58  can include or be coupled to a voltage source that allows for changes in the bias setting. The change in bias setting of the disturbing members  52 - 58  can be made instantaneously or at a specified rate of change, such as 100V/s. The change in bias setting can be controlled by a controller of the image forming apparatus. 
   The developers  62 - 68  preferably include a developer source (i.e., source of toner in combination with carriers) and a developer roller that provides toner to the surface of the respective drums  32 - 38  from the developer source. The developers  62 - 68  are preferably set to a predetermined bias, such as −250V. In addition, the developers  62 - 68  are capable of collecting toner from non-image areas of the surface of the drums  32 - 38 . An image area may have, for example, a bias of −60V, and a non-image area (i.e., area not exposed to laser light) may have, for example, a bias of −400V. 
   The chargers  72 - 78  charge the surface of the drums  32 - 38  to a particular bias, such as −400V. The chargers  72 - 78  are preferably positioned so that they are not in contact with the surface of the drums  32 - 38 . If a toner film is formed on the drums  32 - 38 , and the chargers  72 - 78  are in contact with the surface of the drums  32 - 38 , then a toner film may form on the chargers  72 - 78 , which can cause staining to the chargers  72 - 78 . If stained, the ability of the chargers  72 - 78  to charge the surface of the drums  32 - 38  diminishes. To charge the surface of the drums  32 - 38  effectively without contacting the surface, the chargers  72 - 78  can be implemented as corona chargers, which are separated from the surface of the drums  32 - 38 . 
   The disturbing members  52 - 58  are preferably positioned in contact with the photoconductor. Toner remaining on the drums  32 - 38  after transferring a toner image is collected by the disturbing members  52 - 58  to which is applied a predetermined bias voltage to attract the remaining toner. As the image forming process is repeated, the toner collected by the disturbing members  52 - 58  accumulates between the disturbing members  52 - 58  and the drums  32 - 38  if the bias voltage for the disturbing members  52 - 58  remains unchanged. In addition, the accumulated toner forms a toner film on the drums  32 - 38  because a predetermined mechanical pressure exists between the drums  32 - 38  and the disturbing members  52 - 58 . 
   To prevent the toner film from forming, the bias voltage for the disturbing members  52 - 58  is reversed, which discharges the accumulated toner from the disturbing members  52 - 58  onto the drums  32 - 38  by electrostatic force. The discharging of the accumulated toner from the disturbing members  52 - 58  reduces the amount of toner adhering to the surface of the disturbing members  52 - 58 , which substantially prevents the toner film formation. Toner filming is the phenomenon that occurs when the toner exists between the photoconductor and the disturbing member in too much or in too long time. 
     FIG. 3  is a flow diagram of a drum cleaning process for the drum cleaning system of  FIG. 2  consistent with the present invention. This process can be implemented by a controller in the image forming apparatus. The control unit may be implemented in hardware, software, or some combination thereof. For example, the control unit may include a CPU or microprocessor and a memory, such as a ROM or NVRAM, that stores instructions executed by the CPU or microprocessor to perform the process. 
   As shown in  FIG. 3 , the process first initiates an image forming operation (step  302 ). The image forming operation may be, for example, a copy job, a print job, a fax job, or any other function that generates a printout. The image forming operation can be initiated at the image forming apparatus, such as through a control panel on the image forming apparatus, or in response to a signal received by the image forming apparatus via a network or other communication line, such as a print request or a received fax. The image forming operation may be for a color print, a B/W print, or a print involving some combination of or individual ones of the drums  32 - 38 . In a color print, all of the drums  32 - 38  are typically used for image formation. In the B/W print, only the K drum  32  is used. In the other types of prints, such as a single color print (other than B/W), fewer than all of the drums  32 - 38  are used for the image formation. 
   In addition to initiating the image forming operation, the image forming apparatus sets the disturbing members  52 - 58  to a first bias (step  304 ). The first bias is a positively charged bias, such as +600V. The first bias is set to attract toner particles to the disturbing members  52 - 58 . The setting to the first bias can be in response to the initiation of the image forming operation or can be a default setting. 
   The image forming apparatus determines the type of image forming operation being performed (step  306 ). As described above, the image forming operation can be for a color print, a B/W print, or a print involving some combination of or individual ones of the drums  32 - 38 . Based on the determination, the image forming apparatus also determines which drums  32 - 38  are not involved in the image forming operation (step  308 ). For example, if it is a color print, then all of the drums  32 - 38  may be involved in the image forming operation. In contrast, the color drums  34 - 38  are not used for a B/W print, and some combination of drums  32 - 38  are not used for a single color print. 
   For any of the drums  32 - 38  not involved in the image forming operation, the image forming apparatus changes the bias of the corresponding disturbing member  52 - 58  to a second bias different from the first bias (step  310 ). The second bias is preferable a negatively charged bias, such as −600V. The second bias is set to cause toner particles collected at the disturbing members  52 - 58  to be ejected or emitted to the surface of the drums  32 - 38 . The changing of the bias from the first bias to the second bias can be done instantaneously. However, it is preferable for the change to be made more gradually. For example, the change can be made at 100V/s or less. The more gradual change in the bias helps to even out the spread of toner on the surface of the drums  32 - 38 , i.e., generate a more even distribution of toner on the surface of the drums  32 - 38 . As the drums  32 - 38  rotate during the image forming operation, the toner on the surface of the drums is substantially removed by the corresponding developers  62 - 68 . The removal of the toner is improved if the film is more evenly distributed on the surface of the drums  32 - 38 . 
   The change in bias is preferably made to each of the disturbing members associated with the drums  32 - 38  not involved in the image forming operation. For example, the color drums  34 ,  36 ,  38  have their associated disturbing member  54 ,  56 ,  58  changed if the operation is a B/W print. However, for any situation where more than one drum  32 - 38  is not involved in the image forming operation, it is also possible to change the bias of only one of them or some subset of the ones not involved in the image forming operation. In addition, when more than one drum  32 - 38  is not involved in the image forming operation, it is possible to rotate the bias change during the image forming operation, such as changing the bias of one disturbing member for the first half of the operation, and changing the bias of another disturbing member for the second half of the operation. These periods can be broken down into one-thirds in the case of color drums  34 - 38  having their respective disturbing members  54 - 58  changed in the case of a B/W print. 
   In addition to changing the bias of the disturbing members  52 - 58  associated with the drums  32 - 38  not involved in the image forming operation, it is also possible to change the rotation speed of the developers  62 - 68  (step  312 ). The developers  62 - 68  involved in the image forming operation are typically rotating at a predetermined speed to ensure that the toner images are transferred to the image receiving medium at a proper rate. For the developers  62 - 68  not involved in the image forming operation, the speed of rotation can be changed from this predetermined speed to improve the removal of the toner film from the surface of the drums  32 - 38  by the corresponding developers  62 - 68 . In particular, increasing the rotational speed enhances the ability of the developers  62 - 68  to collect unnecessary toner from the surface of the drums  32 - 38  because the collection of the remaining toner is performed by a mechanical and electrical force between the drums  32 - 38  and the developers  62 - 68 . 
   The image forming apparatus checks to determine if the image forming operation is complete (step  314 ). If not, the bias settings of the respective disturbing members  52 - 58  remains the same. If the image forming operation is complete, then the bias settings of the disturbing members  52 - 58  set to the second bias can be returned to the first bias (step  316 ). Instead of the returning the bias to the first bias, it is also possible to set the bias of the disturbing members  52 - 58  to some default bias, such as a positive bias at a lower voltage, that saves power. Steps  302 - 316  can be repeated for each subsequent image forming operation. 
   In accordance with the present invention, it is possible to improve the removal of toner from the surface of the drums  32 - 38  of the image forming apparatus. When a drum  32 - 38  is not involved in an image forming operation, the bias of its corresponding disturbing member  52 - 58  is reversed so that collected toner is emitted to form a film on the surface of the drum  32 - 38 . The bias change is preferably made so that the film is thin and substantially uniform. The speed of rotation of the developers  62 - 68  can be adjusted to help ensure the thinness of the toner film and to improve the removal of unwanted toner from the surface of the drums  32 - 38 . 
   The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light in the above teachings or may be acquired from practice of the invention. The embodiment was chosen and described in order to explain the principles of the invention and as practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.