Patent Publication Number: US-6711369-B2

Title: Photosensitive drum structure for image forming apparatus using photosensitive belt

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 2002-10261, filed Feb. 26, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photosensitive drum structure for an image forming apparatus using a photosensitive belt, and more particularly, to a photosensitive drum structure for an image forming apparatus used in an electrophotographic printer. 
     2. Description of the Related Art 
     In general, an electrophotographic printer such as a laser printer forms a latent electrostatic image on a photosensitive medium, develops the latent electrostatic image with a toner having a predetermined color, and transfers the developed toner image to a printing paper in order to obtain a desired image. The photosensitive medium is typically a photosensitive belt or a photosensitive drum. 
     FIG. 1 is a view of a portion of an image forming apparatus using a known photosensitive belt as a photosensitive medium. Referring to FIG. 1, the rotation path of a photosensitive belt  10  that travels a continuous path due to rollers  10   a ,  10   b , and  10   c  includes an eraser  12 , a charger  14 , a laser scanning unit (LSU)  16 , and a plurality of developing units  18   a ,  18   b ,  18   c , and  18   d . The eraser  12  erases charges on the photosensitive belt  10 . The charger  14  charges the photosensitive belt  10  with a predetermined electric potential. The LSU  16  radiates light onto the photosensitive belt  10  to form a latent electrostatic image. The plurality of developing units  18   a ,  18   b ,  18   c , and  18   d  are disposed in series along the travel direction of the photosensitive belt  10  and each develops the latent electrostatic image as a toner image with a different color. The developed toner image is transferred to a transfer belt  20  that circulates in contact with the photosensitive belt  10 . 
     However, in the above-described transfer method, the photosensitive belt  10  may move laterally outside of a transfer range of the image. Thus, a steering unit (not shown) is needed to adjust the photosensitive belt  10 . 
     FIG. 2 is a view of a portion of an image forming apparatus using a photosensitive drum as a photosensitive medium to solve the problems caused by the use of a photosensitive belt. Elements that are the same as those in FIG. 1 are described with the same numerals, and thus their detailed descriptions are omitted. 
     Referring to FIG. 2, instead of the photosensitive belt  10  of FIG. 1, a large-sized photosensitive drum  30  is used. A plurality of developing units  28  to develop a latent electrostatic image on the photosensitive drum  30  are disposed along the circumferential surface of the photosensitive drum  30 . Developer rollers  28   a ,  28   b ,  28   c , and  28   d  are positioned at the tip of each developing unit  28 . The developer rollers  28   a ,  28   b ,  28   c , and  28   d  contact the photosensitive drum  30  and develop the latent electrostatic image with a toner in the developing units  28  with a developing nip N, having a predetermined width. 
     However, a different problem occurs in the manufacture of the photosensitive drum  30 . That is, if a small-sized photosensitive drum  30  having a diameter of 25-32 mm is manufactured, a small-sized rotary drum having a diameter of 25-32 mm is dipped in a container containing a photosensitive solution to form a photosensitive layer on the surface of the rotary drum. In this case, a plurality of small-sized rotary drums are manufactured at the same time, and thus manufacturing costs are low. However, since the photosensitive drum  30  uses a large-sized rotary drum having a diameter of about 150 mm, it is difficult to dip multiple rotary drums in the container containing the photosensitive solution. Also, it is expensive to manufacture the photosensitive drum  30 . Further, since the photosensitive drum  30  is rigid, the developing N must be narrow, and the developing units  28  do not develop the image well. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a photosensitive drum structure for an image forming apparatus in which a gap to provide a cushion between a rotary drum and a photosensitive belt is formed by adhering the photosensitive belt on steps having a predetermined height that are formed at both ends of the circumferential surface of the rotary drum. 
     Additional objects and 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. 
     The foregoing and other objects of the present invention are achieved by providing a photosensitive drum for an image forming apparatus, the drum including a cylindrical rotary drum having steps at both ends of a circumferential surface thereof, and a photosensitive belt wound around the rotary drum and attached thereto with an adhesive adhered to the steps, wherein a gap is formed between the circumferential surface of the rotary drum and the photosensitive belt. 
     According to an aspect of the present invention, the gap is filled with air or an elastic member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a view of a portion of an image forming apparatus using a known photosensitive belt; 
     FIG. 2 is a view of a portion of an image forming apparatus using a known photosensitive drum; 
     FIG. 3 is a perspective view of a photosensitive drum structure according to a first embodiment of the present invention; 
     FIG. 4 is a cross-sectional view taken along line IV—IV of FIG. 3; 
     FIG. 5 is a schematic view of a printer using the photosensitive drum according to the first embodiment of the present invention; 
     FIG. 6 is an enlarged view of a portion of the schematic view shown in FIG. 5; 
     FIG. 7 is a perspective view of a photosensitive drum structure according to a second embodiment of the present invention; and 
     FIG. 8 is a cross-sectional view taken along line VIII—VIII of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In the drawings, the thicknesses of layers or regions are exaggerated for clarity. 
     FIG. 3 is a perspective view of a photosensitive drum structure  130  according to a first embodiment of the present invention, and FIG. 4 is a cross-sectional view taken along line IV—IV of FIG.  3 . Referring to FIGS. 3 and 4, steps S having a predetermined height are formed at both ends of the circumferential surface of a cylindrical rotary drum  132  made of aluminium or an aluminium alloy. Double-sided tapes (not shown) are adhered on the steps S, on which a photosensitive belt  134  is wound one turn, covering the circumferential surface of the rotary drum  132 . The steps S form an air gap g between the circumferential surface of the rotary drum  132  and the photosensitive belt  134 . The photosensitive belt  134  is formed of a sequential stack of a base layer, a conductive layer, and a photosensitive layer. When a laser is radiated onto the surface of the photosensitive belt  134 , electrons of the photosensitive layer pass through the conductive layer to the outside, thereby forming a latent electrostatic image. The thickness of the photosensitive belt  134  is generally 20-1000 μm. 
     A height of the steps S, which defines the length of the air gap g, may be 100 μm or more. The maximum height of the steps S is generally 2 mm or less. A width of the steps S may be at least 2 mm or more. 
     The operation of the drum  130  having the above-described structure will be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic view of a printer using the photosensitive drum  130  according to the first embodiment of the present invention, and FIG. 6 is an enlarged view of a portion of the schematic view shown in FIG.  5 . 
     Referring to FIGS. 5 and 6, the printer includes the photosensitive drum  130 , an eraser  112 , a charger  114 , a laser scanning unit (LSU)  116 , developing units  128 , a transfer belt  140 , a first transfer roller  142 , a second transfer roller  144 , and a fixing unit  160 . The photosensitive drum  130  is a photosensitive body. The eraser  112  erases an electric potential on the photosensitive drum  130 . The charger  114  charges the photosensitive drum  130  with the electric potential. The LSU  116  radiates light onto the photosensitive drum  130  to form a predetermined latent electrostatic image. The developing units  128  develop the latent electrostatic image with toners, each having one of four colors, i.e., yellow Y, magenta M, cyan C, and black K. The first transfer roller  142  transfers the image that is developed on the photosensitive drum  130  to the transfer belt  140 . The second transfer roller  144  transfers the image having four colors that are developed on the transfer belt  140  to a paper. The fixing unit  160  hot-presses the paper to permanently fix the transferred image on the paper. The developing units  128  include four developer units  128 -Y,  128 -M,  128 -C, and  128 -K, which are spaced apart from each other from the photosensitive drum  130 , sequentially move toward the photosensitive drum  130  by a contact unit (not shown), and contact developer rollers  128   a ,  128   b ,  128   c , and  128   d  at the tips of the developer units  128 -Y,  128 -M,  128 -C, and  128 -K with the photosensitive drum  130 . Reference numerals  150  and  170  represent a paper cassette and a transfer path to hold and discharge the papers, respectively. 
     A process of forming an image in the printer shown in FIG. 5 will now be described. The charger  114  charges the photosensitive drum  130  with a predetermined potential. The LSU  116  radiates light onto the photosensitive drum  130  to form a latent electrostatic image that will be developed with a first color in a predetermined area of the photosensitive drum  130 . For example, if the first color is yellow, the yellow developer unit  128 -Y contacts the photosensitive drum  130  with a contact unit. Thus, the toner that is attached to the circumferential surface of the developer roller  128   a  is transferred to the latent electrostatic image of the photosensitive drum  130  that contacts the circumferential surface of the developer roller  128   a . Here, the developer roller  128   a  contacts the photosensitive drum  130  so as to press the air gap g formed between the rotary drum  132  and the photosensitive belt  134  with a predetermined pressure. Then, the photosensitive belt  134  is pushed toward the rotary drum  132  and forms a nip N having a predetermined width. The yellow image is well developed by the developing nip N. The developed image is transferred to the transfer belt  140  through a first transfer nip N 1 . A latent electrostatic image for magenta is formed by charging the photosensitive drum  130  with a predetermined potential and exposing the photosensitive drum  130  to light. The developing unit  128  develops the magenta image and transfers the developed magenta image to the transfer belt  140  through the first transfer nip N 1 . Cyan and black images are developed and transferred by this method, and then a desired color image is finally formed on the transfer belt  140 . The color image on the transfer belt  140  is transferred to a paper that is supplied to a second transfer nip N 2  between the transfer belt  140  and the second transfer roller  144 . The completed color image is hot-pressed when passing through the fixing unit  160  and permanently fixed on the paper. 
     FIG. 7 is a perspective view of a photosensitive drum  230  according to a second embodiment of the present invention, and FIG. 8 is a cross-sectional view taken along line VIII-VIII of FIG.  7 . The detailed description of the same elements as those in the first embodiment is omitted. 
     Referring to FIGS. 7 and 8, an elastic member  250 , which is formed of a silicon sponge, a polyester sponge, or an elastic rubber, is inserted into the gap between a photosensitive belt  234  and a rotary drum  232 . 
     The elastic member  250  according to the second embodiment performs a cushion operation similar to the air gap g, and thus a detailed description thereof is omitted. 
     As described above, in a photosensitive drum structure for an image forming apparatus according to the present invention, an inexpensive photosensitive belt is wound around a rotary drum. Thus, manufacturing costs are reduced. Also, a cushion operation is performed on the photosensitive drum so that there is contact with the developer roller, in order to obtain good development of the image. 
     Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.