Patent Publication Number: US-7899378-B2

Title: Image forming apparatus having movable belt

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 from Korean Patent Application No. 2006-68735, filed on Jul. 21, 2006, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to an image forming apparatus in which a movable belt is movably installed to transfer an image formed on an image retainer to a printing medium. 
     2. Description of the Related Art 
     In general, an image forming apparatus, such as a laser color printer, includes an image retainer, such as a photoconductive drum, on which an image is developed, and a movable belt for transferring the image developed on the photoconductive drum to printing paper, namely, an intermediate transfer medium. Developing units for each color which sequentially develop Y, M, C and K color images on the photoconductive drum are installed around the photoconductive drum. 
     One example of the intermediate transfer medium is an intermediate transfer belt moving in contact with the photoconductive drum. Each color image is transferred from the photoconductive drum to the intermediate transfer belt in an overlapping type operation, so that the intermediate transfer belt can acquire a target color image. The final color image formed by overlapping is transmitted to a recording medium moving in contact with the intermediate transfer belt. 
     The intermediate transfer belt, supported by a plurality of supporting rollers including a driving roller and a tension roller, moves in one direction and transfers the overlap-transferred color image to the recording medium. The driving roller supplies power for moving the intermediate transfer belt, and the tension roller adjusts tension of the intermediate transfer belt. The length of the intermediate transfer belt eventually changes as a result of effects of the environment. Thus, the intermediate transfer belt can move under constant tension by adjusting the position of the tension roller. 
     On the other hand, while the intermediate transfer medium moves while supported by the driving roller and the tension roller, the intermediate transfer medium may shift to any one side due to mechanical errors of the supporting rollers. To solve the foregoing problem, guide rails are formed at both sides of the movable belt and both ends of the supporting rollers to support the movable belt. The guide rails formed at both sides of the movable belt prevent the movable belt from shifting to any one side along the axial directions of the supporting rollers, and guide the movable belt to move in a constant path. 
     However, when the guide rails are formed at both sides of the movable belt, a number of components increases to raise the unit cost of production. 
     To solve the above problem, there has been an attempt to reduce the number of the components and restrict shifting of the movable belt in side directions by forming the guide rail at one side of the movable belt.  FIG. 1  is a schematic structure diagram illustrating a conventional movable belt disclosed under U.S. Pat. No. 5,017,969. Referring to  FIG. 1 , a guide groove  11  is formed at one end of a supporting roller  10 , and the movable belt  20  supported by the supporting roller  10  includes a guide rib  21  corresponding to the guide groove  11 . The guide rib  21  is inserted into the guide groove  11  to prevent the movable belt  20  from shifting in a B 1  direction. 
     In the above structure, a number of components are reduced and shifting of the movable belt  20  in one direction B 1  is prevented by forming the guide rail  11  and guide rib  21  at one side of the movable belt  20 . However, it is difficult to restrict shifting of the movable belt  20  in another direction B 2 . That is, the movable belt  20  shifts in the B 2  direction due to a sum force F 3  of a tension F 1  applied to the movable belt  20  by the supporting roller  10  and a control force F 2  moving the movable belt  20  in the B 2  direction by the guide rail  11  and guide rib  21 . 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides an image forming apparatus having an improved structure which can apply a guide rail to one side of a movable belt and prevent shifting of the movable belt. 
     Additional aspects and advantages of the present general inventive concept 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 general inventive concept. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing an image forming apparatus, including: at least one supporting roller; a movable belt supported by the supporting roller; and a shifting restricting unit to prevent the movable belt from shifting to any one side along the axial direction of the supporting roller, wherein the shifting restricting unit includes: a guide rail formed between the movable belt and the supporting roller, to guide movement of one end of the movable belt; and a belt pressurizing member formed at the other end of the movable belt, to generate tension on the movable belt to compensate for a shifting force to the guide rail side by the guide rail. 
     The guide rail may include a guide groove formed on the outer circumference of one end of the supporting roller and a guide rib formed inside the movable belt to be inserted into the guide groove. 
     The guide rail may further include a flange protruding from one end of the supporting roller higher than the outer circumference of the supporting roller to support the end of the movable belt. 
     The belt pressurizing member may include a reinforcing film formed inside the other end of the movable belt at a predetermined width, to contact the outer circumference of the supporting roller and generating a step difference at the other end of the movable belt; and an adhesive formed between the reinforcing film and the movable belt at a predetermined thickness. 
     The reinforcing film may be thinner than the movable belt and thicker than the adhesive. 
     When Young&#39;s module of the movable belt is 2000 Mpa and the thickness of the movable belt ranges from approximately 65 to approximately 85 μm, the thickness of the belt pressurizing member ranges from approximately 70 to approximately 110 μm. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a transfer assembly useable with an image forming apparatus, comprising: a transfer roller including a flange at one end thereof having a larger circumference than a circumference of the transfer roller and a guide groove formed therein adjacent to the flange; and a transfer belt in pressure contact with the transfer roller to rotate around the transfer roller, the transfer belt including a guide rail disposed at an inner surface at one side thereof to be guided within the guide groove and adjacent to the flange and a reinforcing film disposed at an inner surface of the other side thereof to be guided along the other end of the transfer roller. 
     The transfer assembly may further comprise another transfer roller disposed in parallel with the transfer roller including the flange and guide groove to rotatably support another end of the transfer belt, wherein one of the another transfer roller and the transfer roller including the flange and guide groove is a pressure roller to apply a pressure on the transfer belt in a direction away from the other transfer roller. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of preventing sliding movement of a transfer belt along axial directions of a pair of transfer rollers, comprising: applying a first force on one side of the transfer belt with a first belt pressurizing assembly; and applying a second force on another side of the transfer belt in a direction opposing the first force with a second belt pressurizing assembly. 
     The first force can be a sum force of a tension force applied on the transfer belt from one of the transfer rollers and the second force is a force applied on the transfer belt from the first belt pressurizing assembly and second force is a sum forced of a tension force applied on the transfer belt from the one of the transfer rollers and another tension force applied on the transfer belt from a step in the belt caused by the second belt pressurizing assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the present general inventive concept 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 structure diagram illustrating a conventional image forming apparatus; 
         FIG. 2  is a schematic structure diagram illustrating an image forming apparatus in accordance with an exemplary embodiment of the present general inventive concept; 
         FIG. 3  is a structure diagram illustrating a coupling state of an intermediate transfer belt and a supporting roller of  FIG. 2 ; 
         FIGS. 4 and 5  are structure diagrams illustrating major parts of  FIG. 3 , respectively; and 
         FIG. 6  is a structure diagram illustrating the intermediate transfer belt and the supporting roller seen from a C direction of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, 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 general inventive concept by referring to the figures. 
       FIG. 2  is a schematic structure diagram illustrating the image forming apparatus in accordance with the exemplary embodiment of the present general inventive concept. 
     As illustrated in  FIG. 2 , the image forming apparatus includes an image retainer  110 , a movable belt  120  (hereinafter, referred to as ‘intermediate transfer belt’) to which an image formed on the image retainer  110  is primarily transferred, a plurality of supporting rollers  131  and  132  to support the intermediate transfer belt  120  to be movable, a secondary transfer roller  140  connected or disconnected to/from the intermediate transfer belt  120 , to aid in the transfer of the image on the intermediate transfer belt  120  to a printing medium P, and a shifting restricting unit  200  to restrict shifting of the intermediate transfer belt  120 , namely, to prevent the intermediate transfer belt  120  from shifting to any one side along the axial directions of the supporting rollers  131  and  132 . 
     The image retainer  110  is rotated by a primary transfer roller  133  with a primary transfer nip from the intermediate transfer belt  120 . Developing units  111 ,  112 ,  113  and  114  for each color which sequentially develop Y, M, C and K color images on the image retainer  110  are installed in the rotating direction of the image retainer  110 . The developing units  111 ,  112 ,  113  and  114  form each color image on the image retainer  110 . The color images formed on the image retainer  110  are sequentially transferred to the intermediate transfer belt  120  in an overlapping type operation. 
     The intermediate transfer belt  120  moves in one direction, supported by the plurality of supporting rollers  131  and  132 . One of the supporting rollers  131  and  132  is a driving roller  131  that is rotated by a driving motor  151 , and the other supporting roller is a tension roller  132  that is outwardly pressurized by a pressurizing member  152 . The tension roller  132  pressurizes and supports the intermediate transfer belt  120  by the pressurizing member  152  to maintain a constant tension on the intermediate transfer belt  120 . The tension roller  132  is rotated by a friction force with the intermediate transfer belt  120 , which moves by a power of the driving roller  131 . 
     The full color image, which is overlap-transferred to the intermediate transfer belt  120  from the image retainer  110 , is transferred to the printing medium P that passes through a secondary transfer nip formed between the secondary transfer roller  140  and the intermediate transfer belt  120 . 
     The printing medium P is picked up from a paper feeding cassette  161  of the image forming apparatus, aligned by a register roller  162 , and supplied to the secondary transfer nip between the secondary transfer roller  140  and the intermediate transfer belt  120 . While the printing medium P passes through the secondary transfer nip, the image is transferred from the intermediate transfer belt  120  to the printing medium P. Thereafter, the printing medium P is transferred to a fixing unit  163 . While the printing medium P passes through the fixing unit  163 , it is fixed by a high temperature and a high pressure, and then externally discharged. 
     On the other hand, in order to precisely transfer each color image from the image retainer  110  to the intermediate transfer belt  120  in an overlapping type operation, it is very important to control the intermediate transfer belt  120  to stably move without shifting to any one side. 
     The shifting restricting unit  200  restricts shifting of the intermediate transfer belt  120 . For example, the shifting restricting unit  200  prevents the intermediate transfer belt  120  from shifting along the axial directions of the rollers  131  and  132 . As illustrated in  FIG. 3 , the shifting restricting unit  200  includes a guide rail  210  formed at one end of the intermediate transfer belt  120 , and a belt pressurizing member  220  formed at the other end of the intermediate transfer belt  120 . 
     The guide rail  210  includes a guide groove  211  formed at one end of the support roller  131  or  132 , and a guide rib  213  formed on the inner surface of one side of the intermediate transfer belt  120  to be inserted into the guide groove  211 . The guide groove  211  is formed into the outer circumference of one end of the supporting roller  131  or  132  by a predetermined depth and width. The guide rib  213  is adhered to an inner surface of one side of the intermediate transfer belt  120  by an adhesive. The guide rib  213  can be made of polyurethane to be flexibly transformed like the intermediate transfer belt  120 . 
     The guide rail  210  can further include a flange  215  that protrudes from one end of the supporting roller  131  or  132  to a length that is higher than the outer circumference of the supporting roller  131  or  132  on which it protrudes. The flange  215  acts as the outer wall of the guide groove  211  and supports one side of the intermediate transfer belt  120 . 
     In the structure of the guide rail  210 , the guide rib  213  is thicker than the intermediate transfer belt  120 , and the guide groove  211  is formed deeper into the supporting roller  131  or  132  than the thickness of the guide rib  213 . Accordingly, the intermediate transfer belt  120  stably moves along the guide rail  210  without shifting in a B 2  direction as illustrated. 
     That is, as illustrated in  FIG. 4 , the intermediate transfer belt  120  receives a tension force F 1  in a perpendicular direction to the moving direction thereof by pressurization from the tension roller  132 . In addition, a control force F 2  is applied to the intermediate belt  120  in the axial direction of the roller  131  by the mechanical structure of the guide rail  210 , namely, by contact between the guide groove  211  and the guide rib  213 . The other side of the intermediate transfer belt  120  may shift in a B 1  direction due to a sum force F 3  of the tension force F 1  and the control force F 2 . 
     The belt pressurizing member  220  compensates for shifting of the intermediate transfer belt  120  generated by forming the guide rail  210  at one side thereof. As illustrated in  FIG. 5 , the belt pressurizing member  220  includes a reinforcing film  221  formed on an inner surface of the other side  122  of the intermediate transfer belt  120 , and an adhesive  223  positioned between the reinforcing film  221  and the intermediate transfer belt  120 . The reinforcing film  221  is adhered to the inner surface of the intermediate transfer belt  120  by the adhesive  223 , such as, for example, a double-sided tape. The reinforcing film  221  is formed to a predetermined width, which is thinner than the intermediate transfer belt  120 , and thicker than the adhesive  223 . When the reinforcing film  221  is adhered to the inner surface of the other side  122  of the intermediate transfer belt  120 , a step difference is generated at the other side  122  of the intermediate transfer belt  120 . A tension F 4  is generated in the B 2  direction at the other side  122  of the intermediate transfer belt  120  due to the step difference. A sum force F 5  of the tension F 4  and the tension F 1  applied to the intermediate transfer belt  120  is applied in an opposing direction to the direction of the sum force F 3  generated by the guide rail  210 , thereby preventing shifting of the intermediate transfer belt  120  toward the guide rail side  210 , namely, shifting of the intermediate transfer belt  120  in the direction B 1 . 
     The reinforcing film  221  can be a polyethylene terephthalate (PET) film, and the adhesive  230  can be a double-sided tape. In addition, the intermediate transfer belt  120  can be made of conductive polymide (PI). Young&#39;s module of the intermediate transfer belt  120  is 2000 Mpa, and the thickness thereof ranges from approximately 65 to approximately 85 μm. 
     The adhesive  230  can have a thickness of approximately 30 μm, which is maintained constant regardless of the thickness of the reinforcing film  221 . The thickness of the reinforcing film  221  ranges from approximately 40 μm to approximately 80 μm. That is, when the adhesive has a constant thickness of approximately 30 μm, the thickness of the belt pressurizing member  220  ranges from approximately 70 μm to approximately 110 μm, thereby generating sufficient tension to prevent shifting of the intermediate transfer belt  120 . Conversely, when the thickness of the reinforcing film  221  is below 40 μm, the tension is not sufficiently generated, and when the thickness of the reinforcing film  221  is over 80 μm, the intermediate transfer belt  120  may not stably move due to mechanical problems. 
     Table 1 shows experiment analysis results of generation or non-generation of shifting of the intermediate transfer belt  120  in movement by thickness variations of the reinforcing film  221 . 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Thickness of 
                 30 μm 
                 30 μm 
                 30 μm 
                 30 μm 
                 30 μm 
                 30 μm 
                  30 μm 
               
               
                 Adhesive 
               
               
                 Thickness of 
                 20 μm 
                 40 μm 
                 50 μm 
                 60 μm 
                 70 μm 
                 80 μm 
                 100 μm 
               
               
                 reinforcing film 
               
               
                 Result 
                 NG 
                 OK 
                 OK 
                 OK 
                 OK 
                 OK 
                 NG 
               
               
                   
               
            
           
         
       
     
     The results of Table 1 are easily verified by calculating the tension generated by the step difference of the other side  122  of the intermediate transfer belt  120  from the thickness of the belt pressurizing member  220  and other mechanical conditions in consideration of the physical property of the intermediate transfer belt  120  by using following Formula 1.
 
 F (tension)= A×E /( I ×δ)  Formula 1
 
     Referring to  FIGS. 5 and 6 , in the above Formula 1, A represents the contact length L of the intermediate transfer belt  120  and the driving roller  132  in the rotating direction×the thickness T of the intermediate transfer belt  120 ; E represents Young&#39;s module (2000 Mpa) of the intermediate transfer belt  120 ; I represents the width of the intermediate transfer belt  120 ; δ represents the extended length of the intermediate transfer belt  120  (√{square root over (a 2 +b 2 )}−b, b=a/tan θ); θ represents the inclination angle by the step difference of the intermediate transfer belt  120 ; a represents the thickness of the belt pressurizing member  220 ; and b represents the step difference distance of the intermediate transfer belt  120 . 
     In Formula 1, it is presumed that the thickness T of the intermediate transfer belt  120  is approximately 0.065 mm, E is 2000 Mpa, A is 47.2 mm×0.065 mm, I is 240 mm, and θ is 6.52° regardless of the thickness of the reinforcing film  221 . 
     In the above conditions, when the thickness of the reinforcing film  221  is changed to 20, 40, 50, 60, 70 and 80 μm, the tension by the step difference generated on the intermediate transfer belt  120  is calculated by Formula 1. Table 2 illustrates the calculation results. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Thickness of Reinforcing film 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 20 μm 
                 40 μm 
                 50 μm 
                 60 μm 
                 70 μm 
                 80 μm 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 a 
                 0.05 
                 0.07 
                 0.08 
                 0.09 
                 0.1 
                 0.11 
               
               
                 (mm) 
               
               
                 b 
                 0.4375 
                 0.6125 
                 0.6999 
                 0.7875 
                 0.875 
                 0.9625 
               
               
                 (mm) 
               
               
                 δ 
                 0.00285 
                 0.003987 
                 0.004556 
                 0.005126 
                 0.0057 
                 0.006265 
               
               
                 (mm) 
               
               
                 F (N) 
                 0.073 
                 0.102 
                 0.1165 
                 0.131 
                 0.1456 
                 0.16 
               
               
                   
               
            
           
         
       
     
     As illustrated in Tables 1 and 2, in the above conditions, when the tension generated on the intermediate transfer belt  120  by the belt pressurizing member  220  is at least over 0.1 N, shifting of the intermediate transfer belt  120  is prevented. These conditions are efficient when the reinforcing film  221  has a thickness over 40 μm. In the case that the reinforcing film  221  has a thickness over 80 μm, a serious step difference is generated on the intermediate transfer belt  120 , which causes shifting or instable movement. 
     On the other hand, the above experiment results and formula are obtained with the presumption that θ is 6.52° regardless of variations of ‘a’. Therefore, a slight error may exist. However, it is recognized that such an error does not affect the effects of the present general inventive concept. 
     As discussed supra, in accordance with the image forming apparatus of the present general inventive concept, a guide rail is formed at one end of a movable belt such as an intermediate transfer belt, to prevent shifting of the belt in a sideways direction, and a belt pressurizing member to form a step difference by contacting an outer circumference of a supporting roller and outwardly pressurizing the movable belt is formed at the other end of the movable belt, to prevent shifting of the movable belt in the other sideways direction by the tension generated on the movable belt by the step difference. 
     That is, the shifting of the movable belt by a guide rail formed at one end of the movable belt is offset by a belt pressurizing member formed at the other end of the movable belt. As a result, shifting of the movable belt can be efficiently restricted with a simple structure and a small number of components. 
     Accordingly, reliability of the image forming apparatus can be improved by efficiently restricting shifting with a small number of components. 
     Although a few embodiments of the present general inventive concept 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 general inventive concept, the scope of which is defined in the appended claims and their equivalents.