Patent Publication Number: US-6912368-B2

Title: Rotary body support structure and image forming apparatus using the same

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a rotary body support structure and an image forming apparatus using the same. More particularly, the present invention relates to a structure for positioning a photoconductive drum or image carrier or similar drum included in an image forming apparatus. 
   2. Description of the Background Art 
   Generally, a copier, printer, facsimile apparatus or similar image forming apparatus includes a plurality of drums for image formation, e.g., a photoconductive drum or image carrier and a drum included in an image transferring unit. A drum or similar rotary body is usually rotatably mounted on a shaft, i.e., freely rotatable relative to the shaft. Particularly, to facilitate machining and assembly, it is a common practice to prepare a shaft and a rotary body separate from each other and then insert the shaft into the rotary body to allow the latter to freely rotate on the former. 
   The shaft is, in many cases, mounted to the rotary body after its axis has been positioned, because the shaft determines the axis of the rotary body. Japanese Patent Laid-Open Publication No. 2001-208044, for example, discloses the following assembling procedure. One of end plates mounted on axially opposite ends of a photoconductive drum or rotary body is formed with slots, each being triangular as seen in a front view, at opposite sides of the center. A rotation transmitting member is formed with tapered surfaces capable of mating with the above slots on one of axially opposite sides and formed with a tapered, concave, conical surface on the other side. The rotation transmitting member is mounted to a rotary shaft, which is inserted in the drum, such that the tapered surfaces bite into the slots of the end plate. A knob member is mounted to the shaft with its boss mating with the tapered conical surface and is moved in the axial direction to position the drum in the axial direction. At the same time, the tapered portions mate with each other to match the axis of the drum and that of the rotation transmitting member. Further, when the knob member is mounted to a stationary portion included in an apparatus body, the drum is positioned inside the apparatus body because the knob member has been positioned relative to the axis of the drum. 
   While the procedure described above matches the axes of the members formed with tapered surfaces by causing the tapered surfaces to mate with each other, the procedure has the following problem left unsolved. 
   Today, there is an increasing demand for full-color or similar multicolor images as distinguished from single-color images. In this respect, accurately positioning a plurality of photoconductive drums relative to each other is essential for superposing images of different colors in accurate register. The drums, each being assigned to a particular color, each are sometimes mounted on a respective process cartridge or image forming unit together with various process units including a charger, a developing unit and a cleaning unit. In this case, a particular rotary shaft is inserted in each drum cartridge by cartridge. 
   Although a multicolor image forming apparatus tends to increase in size in accordance with the number of colors, size reduction is a prerequisite. For size reduction, the individual process cartridge and a space available in the apparatus are decreasing. To meet such a demand as to configuration, after the drum has been temporarily positioned, the rotary shaft is inserted into the drum. However, a space available for inserting the rotary shaft is extremely limited. Moreover, a space inside a small-size apparatus does not have a sufficient margin in the axial direction that is necessary for the drum of the document mentioned earlier, among the others, to be prevented from moving in the axial direction, i.e., in the direction of thrust. This is also true when maintenance or replacement must be performed by hand, resulting in extremely inefficient work. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a rotary body support structure capable of saving a space for assembly and simplifying assembly and an image forming apparatus using the same. 
   In accordance with the present invention, in a structure for rotatably supporting a rotary body including a rotary shaft, the rotary shaft is assembled integrally with or rigidly affixed to end plates, which are fitted in axially opposite ends of the rotary body, beforehand. The rotary body is therefore rotatable relative to or integrally with the rotary shaft. 
   An image forming apparatus using the above structure is also disclosed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which: 
       FIG. 1  shows an image forming apparatus to which the present invention is applied; 
       FIG. 2  demonstrates mounting and dismounting of a process cartridge from the apparatus of  FIG. 1 ; 
       FIG. 3  is a section showing a rotary body support structure embodying the present invention; and 
       FIG. 4  is a section showing an alternative embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1  of the drawings, an image forming apparatus to which the present invention is applied is shown. While the image forming apparatus to be described is implemented as a laser printer configured to write an image with a laser beam in accordance with image data, it may, of course, be implemented as, e.g., a copier, a facsimile apparatus or a printer. As shown, the laser printer, generally  1 , includes a photoconductive drum  2 , which is a specific form of an image carrier. Arranged around the drum  2  are a charger  3 , an optical writing unit  4 , a developing unit  5 , an image transferring unit  6 , and a cleaning unit  7 . 
   The charger  3  uses a roller or contact type charging member. The developing unit  5  includes a sleeve  5 A facing the drum  2 . The image transferring device  6  is implemented as a rotatable roller facing the drum  2 . The cleaning unit  7  includes a non-rotatable cleaning blade  7 A capable of contacting the drum  2  and a discharging member. 
   In operation, the charger  3  uniformly charges the surface of the drum  2  being rotated. The writing unit  4  scans the surface of the drum  2  thus charged with a laser beam in accordance with image data to thereby form a latent image on the drum  2 . The developing unit  5  develops the latent image with a developer deposited on the sleeve  5 A for thereby forming a corresponding toner image. When a sheet or recording medium is conveyed from a sheet feeding device  8  to the image transferring unit  6 , the image transferring unit  6  transfers the toner image from the drum  2  to the sheet. More specifically, the sheet is paid out from a cassette  8 A by a pickup roller  8 B, stopped by a registration roller pair  8 C, and then driven by the registration roller pair  8 C toward a nip between the drum  2  and the image transferring unit  6  at preselected timing. 
   Subsequently, a fixing unit  9  fixes the toner image formed on the sheet with heat and pressure. The sheet or print coming out of the fixing unit  9  is driven out to a tray  11  by an outlet roller pair  10 . 
   After the image transfer, the cleaning unit  7  removes toner left on the drum  2  and then discharges the drum  2 , thereby preparing the drum  2  for the next image forming cycle. 
   In the laser printer  1 , the drum or rotary body  2 , charger  3 , developing unit  5  and cleaning unit  7 , including the non-rotatable cleaning blade  7 A, are mounted on a process cartridge PC together. 
   As shown in  FIG. 2 , part of the casing of the laser printer  1  is openable to admit the process cartridge PC into the casing. More specifically, when toner should be replenished to the developing unit  5  or when any one of the constituents of the process cartridge PC needs maintenance, the above part of the casing is opened to a position indicated by a solid line, and then the process cartridge PC is dismounted from the casing. 
     FIGS. 3 and 4  each show a particular structure for supporting the drum  2 , which is one of rotary bodies included in the process cartridge PC, embodying the present invention. In the illustrative embodiment shown in  FIG. 3 , the drum  2  is constructed integrally with a rotary shaft  12  beforehand. More specifically, end plates  2 A and  2 A′ are press-fitted or otherwise fixedly fitted in axially opposite ends of the drum  2 . Holes  2 A 1  and  2 A 1 ′ are formed throughout the centers of the end plates  2 A and  2 A′, respectively. 
   A gear portion  2 A 2  is formed on the outer periphery of the end plate  2 A and serves as drive transmitting portion. The end plate  2 A is fitted in the drum  2  before the other end plate  2 A′. More specifically, after the shaft  12  has been inserted in the drum  2 , the end plate  2 A′ is fitted in the drum  2 . Flanges  12 A and  12 A′ are formed on the shaft  12  inward of the end plates  2 A and  2 A′, respectively, in the axial direction of the shaft  12 . The flanges  12 A and  12 A′ prevent the drum  2  from moving on the shaft  12  in the direction of thrust. 
   In the illustrative embodiment, to position the drum  2  relative to the sleeve  5 A of the developing unit  5 A facing the drum  2 , the shaft  12  of the drum  2  and a rotary shaft  5 A 1 , supporting the sleeve  5 A, both are supported by positioning plates  13  at axially opposite ends thereof. Holes  13 A and  13 B are formed in each of the positioning plates  13  at preselected positions and assigned to the shafts  12  and  5 A 1 , respectively. The shafts  12  and  5 A 1  are respectively inserted in the holes  13 A and  13 B and positioned thereby. The positioning plates  13  are affixed to opposite end walls PC 1  of the process cartridge PC. 
   In assembly, after one end of the shaft  12  in the axial direction has been inserted in one end plate  2 A, the other end plate  2 A′ is fitted in the drum  2 . In this condition, the drum  2  is prevented from moving on the drum  2  in the direction of thrust by the flanges  12 A and  12 A′. Subsequently, the opposite ends of the shaft  12  are inserted in the holes  13 A of the positioning plates  13 , so that the drum assembly is mounted to the process cartridge PC. 
   Likewise, the opposite ends of the sleeve  5 A of the developing unit  5  are inserted in the holes  13 B of the positioning plates  13 . Consequently, the drum  2  and sleeve  5 A are positioned relative to each other while facing each other. This relative position is so set as to determine the height of a magnet brush, which the developer forms on the sleeve  5 A, and to insure accurate meshing of the gear portion  2 A 2  of the drum  2  and a gear  5 A 2  included in the sleeve  5 A. 
   In the configuration described above, the drum  2  is freely rotatable on the shaft  12  inserted in the end plates  2 A and  2 A′. Even in this configuration, the axis of the drum  2  is accurately positioned relative to the axis of the sleeve  5 A because the shaft  12  is positioned relative to the shaft  5 A 1  by the positioning plates  13 . 
   As for assembly, the drum  2  and shaft  12  are constructed integrally with each other beforehand and handled as a single body. Therefore, the shaft  12  can be mounted to the process cartridge PC only if the drum  2  is mounted to the process cartridge PC. This reduces or practically obviates the need for an extra space, compared to a case wherein the drum  2  is temporarily positioned in the process cartridge PC and then the shaft  12  is inserted. 
     FIG. 4  shows an alternative embodiment of the present invention. In  FIG. 4 , structural elements identical with those shown in  FIG. 3  are designated by identical reference numerals and will not be described specifically in order to avoid redundancy. This embodiment differs from the previous embodiment in that the drum  2  and end plates  2 A and  2 A′ are rigidly affixed to each other. 
   More specifically, in the illustrative embodiment, the holes  2 A 1  and  2 A 1 ′ formed in the end plates  2 A and  2 A′, respectively, are provided with an inside diameter that allows the shaft  12  to be push-fitted in the holes  2 A 1  and  2 A 1 ′. That is, the shaft  12  is press-fitted in the holes  2 A 1  and  2 A 1 ′. It is to be noted that legends  2 A 1  and  2 A 1 ′ are not shown in  FIG. 4  to clearly show the press-fitted condition. In this configuration, the drum  2  and shaft  12  are rigidly assembled together, so that the end plates  2 A and  2 A′ are rotatable together with the shaft  12 . In the illustrative embodiment, only one flange  12 A is formed on the shaft  12  because of the press-fitting of the end plates  2 A and  2 A′ and shaft  12 . 
   In each of the embodiments shown in  FIGS. 3 and 4 , the end plates  2 A and  2 A′ are respectively formed with large-diameter portions  2 A 10  and  2 A 10 ′ that allow the ends of the drum  2  to abut thereagainst. Particularly, in the end plate  2 A including the gear portion  2 A 2 , the side wall of the gear portion  2 A 2  constitutes the large-diameter portion  2 A 10 . 
   In the embodiment shown in  FIG. 4 , the end plates  2 A and  2 A′ and shaft  12  are affixed to each other by press-fitting without any gap existing therebetween. The axis of the drum  2  can therefore be positioned without any play otherwise brought about by the above gap. Further, irregular rotation ascribable to play, which would lower rotation accuracy, is obviated. 
   The process cartridge PC described above is applicable not only to a single-color image forming apparatus but also to a full-color or similar multicolor image forming apparatus. In the case of a multicolor image forming apparatus, a plurality of process cartridges each are provided with the respective support structure of the present invention, so that the drums  2  of the process cartridges can be positioned relative to each other and allow images of different colors to be brought into accurate register. 
   In summary, in accordance with the present invention, a rotary body and a shaft thereof are constructed integrally with each other beforehand. Therefore, it is not necessary to position the rotary body or the shaft and then insert the shaft or the rotary body later, obviating the need for an extra space for insertion. Particularly, the rotary body and shaft are rigidly affixed to each other without any play and can therefore be accurately positioned. Further, the rotary body and a non-rotatable body are mounted on a process cartridge together. Therefore, despite that a space available in the process cartridge is limited, the rotary body can be mounted or dismounted without resorting to any extra space. This facilitates assembly and replacement. 
   Various modifications will become possible for those skilled in the art after receiving the teachings of the present invention without departing from the scope thereof.