Abstract:
A photosensitive drum unit includes a photosensitive drum, a shutter having a rotation axis shaft which opens and closes to selectively enable access to the photosensitive drum, and a coupler, wherein a linear motion thereof causes a rotational motion of the shutter about the rotation axis shaft. The coupler is coupled to a rotation axis shaft of the shutter and is capable of changing a straight line motion to a rotational motion in a narrow space. In an image forming apparatus equipped with the photosensitive drum unit of the invention, a pressing unit mounted at a support frame of the photosensitive drum unit is pressably engageable with the coupler.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2005-57924, filed Jun. 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Aspects of the present invention relate in general to an image forming apparatus, and more specifically, to a photosensitive drum with an improved shutter structure and an image forming apparatus having the same. 
   2. Description of the Related Art 
   In general, an image forming apparatus such as a laser printer, a copy machine, a scanner, a fax machine, etc., has a photosensitive drum unit for forming a latent image by laser beams on the surface thereof. The photosensitive drum, by its nature, is damaged when exposed to a light source for an extended period of time. Additionally, the photosensitive drum is protected by a shutter because it may easily be scratched when it is separated from an image forming apparatus. 
     FIG. 1  is a perspective view of a typical laser printer as one example of an image forming apparatus. Referring to  FIG. 1 , the laser printer includes a photosensitive drum unit  2 , which is detachably installed through a front door  5  of a printer main body  1 . The photosensitive drum unit  2  includes a photosensitive drum  2   a  where a latent image is formed by laser beam exposure, and a shutter  2   b  for covering the photosensitive drum  2   a . When the photosensitive drum unit  2  is installed into the printer main body  1 , the shutter  2   b  should be opened so that the transfer roller  4  and the photosensitive drum  2   a  can come in contact with each other, and also so that laser beams can be scanned onto the photosensitive drum  2   a . However, when the photosensitive drum unit  2  is separated from the main body  1 , the shutter  2   b  should be closed to protect the photosensitive drum  2   a  from external shock. Sometimes, a user opens a side door  3  of the printer to remove jammed paper from a paper cassette  6  or replace a component. In this case, it is important that the shutter  2   b  remains closed to protect the photosensitive drum  2   a  against light coming from the outside. Thus, in a related art image forming apparatus, the shutter  2   b  is built to be opened and closed interlockingly with the opening and closing of the side door  3  of the printer so that when the side door  3  is opened, the shutter  2   b  closes, and vice versa. 
   In effect, a number of techniques for opening and closing the shutter of the photosensitive drum unit interlockingly with the side door of the main body of the image forming apparatus have been suggested. For instance, according to a laser printer disclosed in Korean Patent No. 395522 and as depicted in  FIG. 2A , when a protrusion  3   a  on the side door  3  pushes a sliding member  11  to the right with the side door  3  closed, a pivotable bracket  2   c  of the photosensitive drum  2   a  is pushed in the direction indicated by the arrow “A” by a pivotable member  13  connected to a hinge, and the shutter  2   b  connected to the pivotable bracket  2   c  through a wire  2   d  is opened downwardly. In this state, the photosensitive drum  2   a  makes contact with a transfer roller  4 , and the print operation is performed normally. On the other hand, when the side door  3  is opened, for instance, because of a paper jam, as shown in  FIG. 2B , the transfer roller  4  and the photosensitive drum  2   a  are separated from each other, and the sliding member  11  is pressed by a spring  12 , causing the pivotable member  13  to move in the direction indicated by the arrow “B”. The pivotable bracket  2   c  of the photosensitive drum unit  2  is pulled by a tension spring  2   e , and the shutter  2   b  connected to the pivotable bracket  2   c  through the wire  2   d  is closed upwardly. In this sliding mechanism, a relatively large space is required for opening/closing the shutter because the shutter of the photosensitive drum unit is opened and closed according to the motion of the pivotable member  13  and the wire  2   d . A large space is also needed for the reciprocating motion of the sliding member  11 . 
     FIG. 3  is a perspective view of another example of a related art photosensitive drum unit. In this case, the opening/closing of a shutter  220  according to the opening/closing of a side door  3  are done based on a totally different mechanism, i.e., a gear system. Unlike the photosensitive drum unit in  FIG. 2 , a photosensitive drum unit  200  in  FIG. 3  is built in a manner that the shutter  220  is mounted on a long circular-shaped rotation axis  221 , which is inserted into holes formed in a front and a rear supporter  203 ,  204 , respectively, of a housing  201 . A circular-shaped gear  211  is attached to one end of the rotation axis  221 , and the gear  211  is also in mesh with a sector-shaped gear  210 . The number of teeth of this sector-shaped gear  210  corresponds to the number of teeth required for the circular-shaped gear  211  to turn 360 degrees, or at least turned by a predetermined angle. Moreover, an arm  212  protrudes from one side of the sector-shaped gear  210 , and a twist spring  207  is installed at a hinge shaft  208 . One end of the twist spring  207  is connected to the sector-shaped gear  210 , and the other end of the twist spring  207  is connected to the rear supporter  204  of the housing  201 . According to the operational principle of this particular photosensitive drum unit  200 , when the side door  3  is closed and the arm  212  of the sector-shaped gear  210  is pushed by a protrusion  3   a  protruding from the side door  3 , the sector-shaped gear  210  rotates in the clockwise direction and causes the circular-shaped gear  211  to correspondingly rotate in the counterclockwise direction at the same time. As a result, the shutter  220  is opened upwardly. On the other hand, when the side door  3  is opened, the sector-shaped gear  210  returns to its original position by the twist spring  207 , and the circular-shaped gear  211  also returns to its original position while rotating in the clockwise direction. The shutter  220  then closes downward to protect the drum  202 . 
   In this gear system of  FIG. 3 , if the hinge shaft  208  of the side door  3  is mounted at a lower point of the side door  3 , the radius of rotation of the side door  3  is increased, and therefore the length of a protrusion mounted at the side door also needs to be increased. A large installation space is therefore required for the shutter as long as the opening and closing of the shutter corresponds to the opening and closing of the side door. This fact makes it more difficult to manufacture a small-sized image forming apparatus. 
   SUMMARY OF THE INVENTION 
   Aspects of the present invention, therefore, solve at least the above problems and/or disadvantages of the dependency of opening and closing of a shutter on the opening and closing of a side door in a related art image forming apparatus, and provide at least the advantages described hereinafter. 
   It is, therefore, one aspect of the present invention to provide a photosensitive drum unit with an improved coupling structure, which enables a shutter to be opened and closed interlockingly with the opening and closing of a side door even in a narrow space. Another aspect of the present invention is to provide an image forming apparatus equipped with the above-described photosensitive drum unit. 
   To achieve the above aspects and advantages, there is provided a photosensitive drum unit, including: a photosensitive drum, a shutter having a rotation axis shaft which opens and closes to selectively enable access to the photosensitive drum, and a coupler, wherein a linear motion thereof causes a rotational motion of the shutter about the rotation axis shaft. 
   Preferably, the shutter is detachably mounted at a rotation axis, and the rotation axis is supported to be rotatable against a front and a rear supporter. 
   Preferably, the coupler is coupled to the rotation axis on the side of the rear supporter. 
   Preferably, the coupler opens/closes the shutter by rotating the rotation axis while sliding along the outer circumference of the rotation axis. 
   In an exemplary embodiment, the coupler includes: a cylindrical-shaped main body with one end blocked and a rib formed on the outer surface, which slides along the outer circumference of the rotation axis and has a curved guide that is formed by cutting out a part of the main body in a curve so as to guide a guide protrusion formed at one end of the rotation axis; and an elastic body inserted into the main body and mounted at a protrusion extended from the rotation axis. 
   Preferably, a suspension means is formed at the cylindrical-shaped main body to prevent an easy escape of the coupler from a cover of the rear supporter. 
   In an exemplary embodiment, the suspension means comprises: a connecting member extended from one side of an opening that is formed by cutting out a part of the cylindrical-shaped main body; and a hook formed at one end of the connecting member. 
   Preferably, the photosensitive drum unit further includes: a spring mounted at the rotation axis close to the front supporter side, wherein one end of the spring is connected to the front supporter and the other end of the spring is connected to the shutter. 
   Another aspect of the present invention includes an image forming apparatus, including: a photosensitive drum; a shutter having a rotation axis shaft and which opens and closes to selectively enable access to the photosensitive drum; a coupler, wherein a linear motion thereof causes a rotational motion of the shutter about the rotation axis shaft; and a pressing unit mounted at a support frame of the photosensitive drum unit which is pressably engageable with the coupler. 
   In an exemplary embodiment, the pressing unit includes: a locking member attached to a support frame of the photosensitive drum unit; a hinge shaft detachably mounted at the locking member; and a hinge bar connected by the hinge shaft. 
   Additional aspects and/or 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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention 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 perspective view of a related art laser printer; 
       FIG. 2A  illustrates a state where a shutter of a photosensitive drum is closed, and  FIG. 2B  illustrates a state where a shutter of a photosensitive drum is opened; 
       FIG. 3  is a perspective view of another related art photosensitive drum unit; 
       FIG. 4  is a front view of a photosensitive drum unit according to an embodiment of the present invention; 
       FIG. 5  is an exploded perspective view of  FIG. 4 ; 
       FIG. 6  is a detailed view of a rear supporter in  FIG. 4 ; 
       FIG. 7A  is a front view of a coupler in  FIG. 6 , and  FIG. 7B  is a plan view of the coupler in  FIG. 6 ; 
       FIG. 8  is a detailed view of a front supporter in  FIG. 4 ; 
       FIG. 9  is a perspective view of a coupler pressing unit according to an embodiment of the present invention; 
       FIG. 10  illustrates an operational state of a side door and a coupler in an image forming apparatus according to an embodiment of the present invention; and 
       FIG. 11A  illustrates an operational state of a shutter and a coupler when the shutter is closed,  FIG. 11B  illustrates an operational state of a shutter and a coupler when the shutter is partially open, and  FIG. 11C  illustrates an operational state of a shutter and a coupler when the shutter is open. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Reference will now be made in detail to the present embodiments of the present invention, 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 invention by referring to the figures. 
     FIG. 4  is a front view of a photosensitive drum unit according to an embodiment of the present invention, and  FIG. 5  is an exploded perspective view of  FIG. 4 . As shown in  FIGS. 4 and 5 , the photosensitive drum unit includes a shutter  120  opened and closed by a coupler  110  which changes a straight line motion to a rotational motion, and a photosensitive drum  102  covered by the shutter  120  for protection. 
   In addition, a front and a rear supporter  103 ,  105 , respectively, are formed on both ends of a housing  101 , and the photosensitive drum  102  is disposed between these supporters  103 ,  105 . Here, the drum  102  is rotatably linked to the front and rear supporters  103 ,  105 , respectively. 
   The supporters  103 ,  105  are covered by front and rear covers  104 ,  106 , respectively, and the photosensitive drum  102  is covered by the shutter  120  for protection. 
   The shutter  120  can be drawn into or out of a rotation axis  121  that is rotatably joined with the supporters  103 ,  105 . In other words, the rotation axis  121  and the coupler  110  are coupled. Detailed views of a rear supporter  105  and a coupler  110  are shown in  FIGS. 6 ,  7 A and  7 B, respectively. 
     FIG. 6  is a detailed view of a rear supporter of the photosensitive drum unit.  FIG. 7A  is a front view of the coupler  110  and  FIG. 7B  is a plan view of the coupler  110 . Referring to the drawings, the coupler  110  includes a main body  112  and an elastic member  114 . 
   The main body  112  is a hollow cylinder, and one end thereof is blocked to push the elastic member  114 . The main body has a curved guide  116  having a portion cut in a curve, and a guide protrusion  122  formed at one end of the rotation axis along the curved guide  116 . The curved guide  116  has a spiral shape, and a space  116   a  for the guide protrusion  122  to rest is formed at the end portion. Therefore, when the coupler  110  performs a straight line motion, the guide protrusion  122  is guided along the curved guide  116  and the rotation axis  121  rotates. Furthermore, a rib  113  is formed on the outer surface of the main body  112 . The rib  113  is inserted into an opening groove  106   b  of the rear cover  106 . As such, although the rotation axis  121  of the shutter may rotate, the coupler  110  does not rotate but simply slides in a direction of the rotation axis  121 . 
   The elastic member  114  is inserted into the main body  112 . In detail, the elastic member  114  is oriented around an outer circumference of a protrusion  123  extended from the rotation axis  121 . Preferably, a compression spring is used as the elastic member  114 . 
   When the coupler  110  is driven by an external force it moves in a straight line motion inwardly (in a right direction of  FIGS.6 ,  7 A and  7 B) along the rotation axis. As a result, the rotation axis  121  rotates, and the shutter  120  is rotated to an open position. When the external force is removed, the coupler  110  returns to its original position by the restoring force of the elastic member  114 . In order to prevent the coupler  110  from escaping from the rear cover  106 , a suspension unit  111  is preferably formed on the main body  112 . The suspension unit  111  comprises a connecting member  111   b  extended from one side of an opening  111   c  that is formed by cutting out a part of the main body, and a hook  111   a  formed at one end of the connecting member  111   b . To make the coupler  110  easily insertable into but not easily drawn out of the rear cover  106 , one side of the hook  111   a  is preferably rounded and the other side of the hook  111   a  has a hook shape. 
   In short, because of the suspension unit  111 , the coupler  110  can be easily inserted into a hole  106   a  of the cover  106  for the rear supporter  105 , and does not easily get drawn out of the hole  106   a . Although it is preferable to have the suspension unit with one side having a round shape and the other side having a hook shape, the sides of the suspension unit can be designed in any number of shapes. 
     FIG. 8  is a detailed view of the front supporter side  103  in the photosensitive drum unit  100 . Referring to the drawing, a spring  107  is mounted at the rotation axis  121  on the front supporter side  103 . That is, one end  107   a  of the spring is connected to the front supporter  103 , whereas the other end  107   b  of the spring is connected to the shutter  120 . This spring  107 , located on the front supporter side  103  of the photosensitive drum unit  100 , balances the force caused by the elastic member  114  located on the rear supporter side  105  of the photosensitive drum unit  105 . Although a spring is preferable, anything capable of applying force on the shutter  120  may be used to balance the force of the elastic member  114 . 
   An image forming apparatus according to another aspect of the present invention includes the photosensitive drum unit  100  described above. Besides the photosensitive drum unit  100 , the image forming apparatus of the invention includes a pressing unit  130  mounted at a support frame  108  of the photosensitive drum for pressing the coupler  110 , and a side door  30  with a protrusion  134  that comes in contact with the pressing unit  130  when the side door  30  is closed. 
   The pressing unit is installed in a narrow space between the photosensitive drum unit  100  and a printer main body  1 . The pressing unit may take any shape or pattern as long as it is able to press one side of the coupler. 
     FIG. 9  shows an embodiment of the pressing unit for the coupler, according to an aspect of the present invention. As depicted in  FIG. 9 , the pressing unit  130  comprises a locking member  132  attached to a support frame  108  of the photosensitive drum unit  100 , a hinge shaft  131  detachably mounted at the locking member  132 , and a hinge bar  133  connected to the support frame  108  by the hinge shaft  131 . 
   When the side door  30  is closed, a protrusion  134  of the side door  30  comes in contact with the hinge bar  133  of the pressing unit  130 , and the hinge bar  133  pivots around the hinge shaft  131  and presses the coupler  110 . Preferably, the front side  134   a  of the protrusion  134  of the side door  30  makes contact with the front side  133   a  of the hinge bar  133 . 
   With reference to drawings, the following description explains the operation of the image forming apparatus according to the preferred embodiment of this aspect of the present invention, and more specifically, the operation of the pressing unit  130 . 
     FIG. 10  illustrates an operational state of the side door and the coupler in the image forming apparatus according to an embodiment of the present invention, and  FIGS. 11A through 11C  illustrate operational states of the shutter and the coupler. As shown in  FIG. 10 , when the side door  30  is closed, the protrusion  134  of the side door  30  pushes the hinge bar  133  of the pressing unit  130 , and the hinge bar  133  pivots around the hinge shaft  131 , thereby pressing the coupler  110 . 
   As a result of the hinge shaft  131  pressing the coupler  110 , the coupler  110  slides along the outer circumference of the rotation axis  121  in the “A” direction, as shown in  FIGS. 11A to 11C . In the course of sliding, the rib  113  of the coupler  110  remains inserted into the opening groove  106   b  (shown in  FIG. 6 ) of the rear cover  106  (shown in  FIG. 6 ), so the coupler  110  does not rotate while the guide protrusion  122  of the rotation axis  121  moves along the curved guide  116  of the coupler  110 . As a result, the rotation axis  121  rotates in the “B” direction and the shutter  120  is opened. While the shutter  120  is opened, the normal operation of the image forming apparatus can be performed, e.g., scanning laser beams onto the photosensitive drum unit. 
   On the other hand, when the side door  30  is opened, the protrusion  134  of the side door  30  is separated from the hinge bar  133  of the pressing unit  130 , and the coupler  110  is pushed back to its original position (as shown in  FIG. 11A ) by the elastic member  114 . At this point, the rotation axis  121  is guided along the curved guide  116  by means of the guide protrusion  122  and as a result, the shutter  120  closes. 
   Since the shutter  120  is closed not only by force of the elastic member  114  but also by the force of the spring  107  mounted at the rotation axis  121  on the side of the front supporter  103 , the forces acting on both sides of the shutter  120  can be balanced, stabilizing the opening and closing motion of the shutter. 
   Above all, the present invention is advantageous in that the coupling structure for opening and closing the shutter interlockingly with the side door is very simple and can be installed in a very narrow space. As aforementioned, in a related art, if the radius of rotation is large because the rotation hinge point of the side door is positioned at a lower point, the length of the protrusion of the side door had to be correspondingly increased. This corresponding increase was troublesome for securing a sufficient installation space for the coupling structure. However, the problem can be solved through the simple coupling structure suggested by the present invention. 
   In conclusion, by making the coupler control the opening and closing of the shutter, the photosensitive drum unit according to aspects of the present invention has a very simple structure, and therefore can easily be installed in a narrow space. 
   Moreover, the image forming apparatus according to the present invention features a smooth opening and closing motion of the shutter, and additionally may have a small size which requires a reduced installation space. 
   Although a few embodiments of the present invention 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.