Patent Publication Number: US-8116673-B2

Title: Printing medium supplying unit and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2007-0073030, filed on Jul. 20, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present disclosure relates to a printing medium supplying unit and an image forming apparatus having the same and, more particularly, to a printing medium supplying unit capable of adjusting the height of a printing medium loading component. 
     2. Description of Related Art 
     An image forming apparatus includes a printing medium supplying unit, an image forming unit, and a discharging unit. The printing medium supplying unit may be configured to supplying the printing medium to an image forming unit. This printing medium may include, for example, paper, transparent sheets, cardboard, or any other material on which an image may be formed. The image forming unit may be configured to forming an image on the printing medium. This image forming unit may include, for example, a photoreceptor. The photoreceptor may be in the form of a drum assembly made of photoconductive material on which a representation of an image can be formed by light. The image forming unit may form the image on the printing medium supplied from the printing medium supplying unit. The discharging unit may be configured to discharge the printing medium to an external unit once the image is formed on the printing medium. 
       FIGS. 1A and 1B  are perspective views illustrating an operation of a conventional printing medium supplying unit  10 . As shown therein, the conventional printing medium supplying unit  10  includes a feeding cassette  30 , a printing medium loading plate  31 , a pickup roller  20 , and a cam member  23 . The printing medium loading plate  31  moves up and down inside the feeding cassette  30  and allows a printing medium to be loaded thereon. The pickup roller  20  picks up the printing medium from the printing medium loading plate  31 . The cam member  23  is coaxially located with a rotation shaft  21  of the pickup roller  20 . The cam member  23  is configured to press or release the printing medium loading plate  31  so as to move the printing medium loading plate  31  down or up, respectively. 
     In  FIG. 1A , if a printing signal is not applied, the cam member  23  presses the printing medium loading plate  31  to separate the pickup roller  20  from the printing medium. On the other hand, as shown in  FIG. 1B , if the printing signal is applied, the rotation shaft  21  rotates and the pressure applied against the printing medium loading plate  31  is withdrawn. Accordingly, the printing medium loading plate  31  moves up toward the pickup roller  20 . The pickup roller  20  then picks up the printing medium and transfers the printing medium toward an image forming unit (not shown). Once the pickup roller  20  has picked up the printing medium, the cam member  23  once again presses the printing medium loading plate  31  to move the printing medium loading plate  31  down. 
     While the conventional printing medium supplying unit  10  may be used to provide a printing medium to an image forming unit, the unit  10  suffers from various shortcomings. For example, as shown in  FIG. 2 , in the conventional printing medium supplying unit  10 , a length l of a cam profile  23   a  is uniform along an axial line of the rotation shaft  21 . This uniform length l of the cam profile  23   a  causes the height at which the printing medium loading plate  31  is maintained to be uniform irrespective of the amount of the printing medium loaded on the printing medium loading plate  31 . Accordingly, if the amount of the printing medium loaded on the printing medium loading plate  31  is reduced, the speed of elevation of the printing medium loading plate  31  released from the pressing force increases. This increase in the elevation speed of the printing medium loading plate  31  may cause a loud noise upon impact when the printing medium loading plate  31  comes in contact with the pickup roller  20 . This impact noise is one of the noises most often heard when using an image forming apparatus that includes the conventional printing medium supplying unit  10 . 
     Furthermore, when the printing medium loading plate  31  is elevated at a high speed, the contact area  33  of the printing medium loading plate  31  that comes in contact with the cam member  23  may be damaged due to the impact. The present disclosure is directed towards overcoming one or more shortcomings of the conventional printing medium supplying unit  10 . 
     SUMMARY OF INVENTION 
     One aspect of the present disclosure includes a printing medium supplying unit. The unit comprises a printing medium loading plate configured to move up and down, and on which an amount of printing medium may be loaded and an elevation control unit configured to adjust an elevation height of the printing medium loading plate to vary a standby position of the printing medium loading plate based on the amount of the printing medium loaded on the printing medium loading plate, wherein the standby position of the printing medium loading plate is a position of the printing medium loading plate when the printing medium is not being supplied from the printing medium supplying unit. 
     Another aspect of the present disclosure includes an image forming apparatus. The apparatus comprises a printing medium supplying unit. The printing medium supplying unit comprises a printing medium loading plate configured to move up and down, and on which an amount of printing medium may be loaded and an elevation control unit configured to adjust an elevation height of the printing medium loading plate to vary a standby position of the printing medium loading plate based on the amount of the printing medium loaded on the printing medium loading plate, wherein the standby position of the printing medium loading plate is a position of the printing medium loading plate when the printing medium to an image forming unit. The apparatus also comprises an image forming unit configured to form an image on a printing medium supplied from the printing medium supplying unit and a printing medium discharging unit configured to discharge the printing medium on which the image is formed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and/or other features of the present disclosure will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1A and 1B  are perspective views illustrating an operating process of a conventional printing medium supplying unit; 
         FIG. 2  is a perspective view illustrating a cam configuration of the conventional printing medium supplying unit; 
         FIGS. 3A and 3B  are perspective views illustrating a configuration of a printing medium supplying unit according to an exemplary disclosed embodiment; 
         FIG. 4  is a perspective view illustrating a configuration of an external force receiving unit according to an exemplary disclosed embodiment; 
         FIG. 5  is a perspective view illustrating a configuration of an elevation control unit according to an exemplary disclosed embodiment; 
         FIGS. 6A and 6B  exemplarily illustrate an elevation process of the printing medium supplying unit if a large number of printing mediums are loaded; 
         FIGS. 7A and 7B  exemplarily illustrate an elevation process of the printing medium supplying unit if a small number of printing mediums are loaded; 
         FIGS. 8A and 8B  illustrate an external force applying unit according to an alternative exemplary disclosed embodiment; and 
         FIG. 9  is a schematic view illustrating a configuration of an image forming apparatus employing the printing medium supplying unit according to an exemplary disclosed embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF INVENTION 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIGS. 3A and 3B  are perspective views illustrating a configuration of a printing medium supplying unit  200  according to an exemplary disclosed embodiment. As shown therein, the printing medium supplying unit  200  includes a cassette unit  210 , a pickup unit  220 , and an elevation control unit  230 . The cassette unit  210  accommodates a printing medium loading plate  215  in which a printing medium is loaded. The pickup unit  220  picks up the printing medium loaded in the printing medium loading plate  215  and provides the picked up printing medium to an image forming unit. The elevation control unit  230  adjusts an elevation height of the printing medium loading plate  215 . This elevation height may be adjusted depending on the amount of printing medium loaded in the printing medium loading plate  215 . Furthermore, the elevation height is adjusted so that the pickup unit  220  can pick up the printing medium. 
     The cassette unit  210  includes a cassette main body  211 . The main body  211  accommodates the printing medium that is loaded on the printing medium loading plate  215 . The printing medium loading plate  215  is configured to move up and down between a standby position and a supply position inside the cassette main body  211 . The printing medium loading plate  215  includes an upper surface on which the printing medium is loaded. The cassette unit  210  also includes an elevation adjusting elastic member (not shown) provided between the printing medium loading plate  215  and the cassette main body  211 . The elevation adjusting elastic member may be configured to supply an elastic force to raise the printing medium loading plate  215  to a supply position to supply the printing medium to the pickup unit  220 . 
     The printing medium loading plate  215  is provided to move up and down between a standby position and a supply position. As shown in  FIG. 3A , the standby position is one in which the printing medium loading plate  215  is distanced from a pickup roller  223 . As shown in  FIG. 3B , the supply position is one in which the printing medium loading plate  215  moves up to the pickup roller  223  so that the printing medium can come in contact with the pickup roller  223 . In addition, a side of the printing medium loading plate  215  is provided with a contact member  213  that protrudes from a bottom surface. The contact member  213  may be configured to come in contact with and be separated from an external force receiving unit  233  (as shown in  FIG. 4 ). The contact member  213  may beneficially include an idle roller driven by rotation of the external force receiving unit  233 . 
     As shown in  FIGS. 3A and 6A , in the standby position, the printing medium loading plate  215  moves down toward the cassette main body  211  so that the printing medium loaded in the printing medium loading plate  215  is not in contact with the pickup roller  223 . On the other hand, as shown in  FIGS. 3B and 6B , in the supply position, the printing medium loading plate  215  moves up so that the printing medium loaded in the printing medium loading plate  215  can be in contact with the pickup roller  223 . The height by which the printing medium loading plate  215  moves up and down is the difference between the height of a printing medium positioned in the top in the standby position, and the height which the top-positioned printing medium has in the supply position. 
     As shown in  FIGS. 6A and 6B , the elevation adjusting elastic member  217  is provided between the cassette main body  211  and the printing medium loading plate  215 . In an exemplary embodiment, the elevation adjusting elastic member  217  may be configured to apply an elastic force such that the printing medium loading plate  215  moves up. On the other hand, the elevation adjusting elastic member  217  is forced down by the weight of the printing medium loaded in the printing medium loading plate  215 . By being forced down, and together with the operation of the elevation control unit  230  as will be further described, the elevation adjusting elastic member  217  maintains the printing medium loading plate  215  in the standby position. In an exemplary embodiment, the elevating adjusting elastic member  217  may be provided as a coil spring (as shown), a leaf spring, or the like. 
     The pickup unit  220  may be configured to pick up the printing medium from the printing medium loading plate  215  when the printing medium loading plate  215  moves up to the supply position. In an exemplary embodiment, the pickup unit  220  may include a rotation shaft  221  and a pickup roller  223 . The rotation shaft  221  may rotate based on an input of a control signal. Specifically, a pickup gear (not shown) may drive the rotation shaft. Additionally, the pickup roller  223  may be coupled to the rotation shaft  221  to pick up the printing medium. 
     The rotation shaft  221  may be provided to be coaxial with the pickup gear to rotate together with the pickup gear when a driving force is transmitted to the pickup gear. Beneficially, the pickup roller is in contact with a solenoid (not shown), and receives a signal from the solenoid to rotate according to a printing signal applied from a control unit (not shown). 
     The pickup roller  223  rotates in contact with the top-positioned printing medium loaded in the printing medium loading plate  215 . By rotating in contact with the top-positioned printing medium, a frictional force is generated between the pickup roller  223  and the top-positioned printing medium. This frictional force may be used to transfer the top-positioned printing medium from the printing medium loading plate  215  to the pickup roller  223 . In an exemplary embodiment, the pickup roller  223  includes an elastic layer  223   a  formed of a material such as, for example, rubber, having a big friction force. 
     The elevation control unit  230  adjusts the height of the standby position of the printing medium loading plate  215  based on the amount of printing medium loaded on the printing medium loading plate  215 . To this end, the elevation control unit  230  includes an external force receiving unit  233 , a pressing elastic member  235 , and an external force applying unit  231 . The external force receiving unit  233  is slidably provided to the rotation shaft  221  of the pickup roller  223 . Furthermore, the pressing elastic member  235  elastically presses the external force receiving unit  233  and the external force applying unit  231  coupled to the printing medium loading plate  215 . This pressure applied by the pressing elastic member  235  forces the external force receiving unit  233  in a resisting direction against an elastic force of the pressing elastic member  235 . 
     As shown in  FIG. 4 , the external force receiving unit  233  includes an external force receiving main body  233   a  in contact with the external force applying unit  231 , a shaft coupling member  233   c  extending from the external force receiving main body  233   a  to be coupled to the rotation shaft  221 , and an elastic member coupling unit  233   d  to which the pressing elastic member  235  is coupled. 
     The external force receiving main body  233   a  includes an elevation profile  233   b . This elevation profile  233   b  is provided to the rotation shaft  221  and has a varying maximum diameter R that is in contact with the contact member  213 . That is, a contact radius of the external force receiving main body  233   a  varies according to the direction of the rotation shaft  221 , and the diameter of the rotation shaft  221 . 
     In an exemplary embodiment, the radius R of the elevating profile  233   b  may decrease continuously from an outer side of the rotation shaft  221  to an inner side. Alternatively, the radius R of the elevating profile  233   b  may decrease discontinuously. For example, the radius R may decrease in steps instead of decreasing continuously. 
     In an exemplary embodiment, the radius R of the external force receiving main body  233   a  may determine the standby position of the printing medium loading plate  215 . The standby position of the printing medium loading plate  215  is determined depending on a contact position of the elevation profile  233   b  with the contact member  213 . Accordingly, the elevation height of the printing medium loading plate  215  is determined based on the contact position of the elevation profile  233   b  with the contact member  213 . That is, as shown in  FIG. 6A , if the radius R of the elevating profile  233   b  is maximum, the standby position of the printing medium loading plate  215  is provided to a position adjacent to the cassette main body  211 . On the other hand, as shown in  FIG. 7A , if the radius R of the elevating profile  233   b  decreases, the standby position of the printing medium loading plate  215  moves up further towards the pickup roller  223  as compared with the case shown in  FIG. 6A . Thus, as there is movement from the outer side of the elevating profile  233   b  to the inner side thereof along the rotation shaft  221 , the height of the standby position of the printing medium loading plate  215  gradually increases. 
     The external force receiving main body  233   a  is provided to slide on the rotation shaft  221 . Furthermore, a rotation shaft accommodating hole  233   e  is formed through the external force receiving main body  233   a . The rotation shaft accommodating hole  233   a  has an inner diameter bigger than a diameter of the rotation shaft  221 . As shown in  FIG. 5 , the external force receiving main body  233   a  moves horizontally along the rotation shaft  221  based on the interplay between the external force applying unit  231  and the pressing elastic member  235 . 
     The pressing elastic member  235  applies an elastic force to the external force receiving unit  233  so that an increasing area of the external force receiving main body  233   a  can come in contact with the contact member  213 . That is, as shown in  FIG. 5 , the pressing elastic member  235  applies an elastic force so that the external force receiving unit  233  can move toward the external force applying unit  231 . 
     As discussed above, the external force applying unit  231  is pressed by the external force receiving unit. Consequently, the external force applying unit  231  applies a reactionary external force to the external force receiving unit  233 . Upon receiving such a force from the external force applying unit  231 , the external force receiving unit  233  presses the printing medium loading plate  215 . In an exemplary embodiment, the external force applying unit  231  may be provided as an adjusting cam that presses in contact with the external force receiving unit  233 . Alternatively, the external force applying unit  231  may be a solenoid that adjusts the position of the external force receiving unit  233  based on receipt of a control signal. 
     As disclosed in  FIG. 5 , the external force applying unit  231  according to an exemplary disclosed embodiment may be an adjusting cam. In addition, the external force applying unit  231  includes an adjusting profile  231   a . As shown in  FIG. 5 , the adjusting profile  231   a  is shaped such that the distance between the line RL and the external force receiving unit  233  varies along the length of line RL. Also, the external force applying unit  231  is fixedly coupled to the printing medium loading plate  215  to move up and down together with the printing medium loading plate  215 , which moves up and down between the standby position and the supply position. 
     As shown in  FIG. 5 , the distance between line RL and the external force receiving unit  233  may increase moving from the upper portion of the external force applying unit  231  towards the middle portion of the external force applying unit (d 1 &gt;d 2 ). In an alternative exemplary embodiment, as shown in  FIG. 8A , the external force applying unit  231 ′ may be shaped differently to have a different adjusting profile  231   a ′. Specifically, as shown in  FIG. 8A , the distance between line RL and the external force receiving unit  233  may decrease and become smaller from a lower part to an upper part (d 1 ′&gt;d 2 ′). In yet another alternative exemplary embodiment, as shown in  FIG. 8B , the adjusting profile  231   a ″ may be different than  231   a  of  FIG. 5 and 231   a ′ of  FIG. 8A . As seen in  FIG. 8B , the adjusting profile  231   a ″ may be provided so that a predetermined height in a lower part (l) can have a uniform contact length and the contact length over length l can gradually decrease (d 1 ″=d 2 ″&gt;d 3 ″). 
     The pressing elastic member  235  causes the external force receiving unit  233  to come in contact with the external force applying unit  233 . Furthermore, the contact length d of the external force applying unit  233  determines the horizontal distance the external force receiving unit  233  moves when the external force receiving unit  233  is in contact with the external force applying unit  231 . The distance the external force receiving unit  233  moves determines the contact position of the external force receiving unit  233  with the printing medium loading plate  215 . Additionally, as already discussed above, the radius R of the elevation profile  233   b  of the external force receiving main body varies along the length of the external force receiving unit  233 . This variation in the radius R coupled with the distance the external force receiving unit  233  actually moves determines the amount by which the printing medium loading plate  215  is actually pressed. 
     An operating process of the printing medium supplying unit  200  according to an exemplary disclosed embodiment will now be described by referring to  FIGS. 3A to 7B . At first, as shown in  FIG. 6A , if a large number of printing mediums are loaded in the printing medium loading plate  215 , the elevation adjusting elastic member  217  contracts due to the weight of the printing medium. This contraction of the elevation adjusting elastic member  217  causes the printing medium loading plate  215  to move down towards the cassette main body  211 . 
     As seen in  FIG. 6A , the external force receiving unit  233  comes in contact with an upper part of the external force applying unit  231 . Specifically, the external force receiving unit  233  is in contact with the adjusting profile  231  a having a short contact length d. Furthermore, the pressing elastic member  235  exerts an elastic force to cause the external force applying unit  231  to move towards the pickup roller  223 . Also, the contact member  213  comes in contact with a point of the external force receiving unit  233  having a big contact radius R. Accordingly, the standby position of the printing medium loading plate  215  is a position X adjacent to the cassette main body  211 , and the height of the top-positioned printing medium is a position Y. 
     In this state, as shown in  FIG. 6B , if a printing signal is applied, the rotation shaft  221  rotates, the external force receiving unit  233  rotates together with the rotation shaft  221 , and a pressing force pressing the contact member  213  is withdrawn. The printing medium loading plate  215  elastically moves up depending on the withdrawal of the pressing force. Here, the supply position of the printing medium loading plate  215  becomes a position Y 1 ′. At position Y 1 ′, the top-positioned printing medium comes in contact with the pickup roller  223 . At this time, the elevation height of the printing medium loading plate  215  becomes a height difference h 1  of the top-positioned printing medium. 
     On the other hand, as shown in  FIG. 7A , if the loading amount of the printing medium loaded in the printing medium loading plate  215  is further reduced than the case shown in  FIG. 6A , the printing medium loading plate  215  has a relatively high standby position (X 2 &gt;X 1 ). That is, the contact length dm of the external force applying unit  231  pressing the external force receiving unit  233  toward the pressing elastic member  235  becomes bigger (dm&gt;df) than the case shown in  FIG. 6A  as the height of the printing medium loading plate  215  increases. This increase in contact length dm pressing the external force receiving unit  233  causes the external force receiving unit  233  to move towards the pressing elastic member  235 . This movement of the external force receiving unit  233  towards the pressing elastic member  235  causes the contact diameter Rm of the elevation profile  233   b  of the external force receiving unit  233  that presses the contact member  213  to become shorter (Rm&lt;Rf) than the case shown in  FIG. 6A . Because the contact diameter Rm becomes shorter, the height of the standby position of the printing medium loading plate  215  can increase (X 2 &gt;X 1 ). 
     If the printing signal is applied, the rotation shaft  221  rotates, and the pressing force of the external force receiving unit  233  pressing the contact member  213  is withdrawn. The printing medium loading plate  215  moves up to the supply position in which the top-positioned printing medium comes in contact with the pickup roller  223 . In this case, the elevation height of the printing medium loading plate  215  becomes smaller than the case shown in  FIG. 6B , in which a large number of printing mediums are loaded. However, the elevating height of the top positioned printing medium loading plate  215  is substantially the same as the case shown in  FIG. 6B  (h 1 ≈h 2 ). 
     Accordingly, in the printing medium supplying unit  200  disclosed above, although the elevating height of the printing medium loading plate  215  is gradually reduced as the loading amount of the printing medium decreases, the elevation height of the top positioned printing medium can be maintained to be the substantially same. Thus, when the printing medium loading plate  215  moves up and down, because the top-positioned printing medium moves by the same elevation height irrespective of the loading amount of the printing medium, an impact noise can be uniform. Also, because the top-positioned printing medium moves up and down by the same distance as would be the case where the elevation height was the least, (i.e., a lot of printing mediums are loaded), the generated impact noise can be minimized. 
     As discussed above, in the printing medium supplying unit  200 , the standby position and the supply position of the printing medium loading plate  215  vary depending on the loading amount of the printing medium. Specifically, these positions are maintained when the elastic force of the elevating adjusting elastic member  217  elastically supporting the printing medium loading plate  215  and the elastic force of the pressing elastic member  235  balance each other. Accordingly, in designing the printing medium supplying unit  200 , the elastic forces of the elevating adjusting elastic member  217  and the pressing elastic member  235  may be determined based on factors such as, for example, the shapes of the elevating profile  233   b  and the adjusting profile  231   a  and a maximum loading amount of the printing medium loaded in the printing medium loading plate  215 . 
       FIG. 9  is a schematic view illustrating a configuration of an image forming apparatus  100  including the printing medium supplying unit  200  according to an exemplary disclosed embodiment. As shown in  FIG. 9 , the image forming apparatus  100  includes the printing medium supplying unit  200 , an image forming unit  300 , a fusing unit  400 , and a discharging unit  500 . The image forming unit is configured to form an image on a printing medium. The fusing unit  400  is configured to fuse the image on the printing medium. The discharging unit  500  is configured to discharge the printing medium on which the image is completely formed to the outside. 
     Specifically, the image forming unit  300  applies a developer to the printing medium picked up by the pickup roller  223  to form an image. The fusing unit  400  applies heat and pressure to the printing medium to fuse the developer on the printing medium. The discharging unit  500  discharges the printing medium passing through the fusing unit  400  to an external unit that is configured to receive the printing medium with the image formed on the printing medium. 
     The printing medium supplying unit according to an exemplary disclosed embodiment may be mounted below the image forming apparatus. Alternatively, the disclosed printing medium supplying unit may be provided to a large sized printing apparatus that is commonly used to print advertising material, wall paper, etc. 
     As described above, the present disclosure provides a printing medium supplying unit and an image forming apparatus having the same, that is capable of gradually raising a standby position of a printing medium loading plate as a loading amount of a printing medium decreases. This gradual raising of the standby position of the printing medium loading plate may help maintain an elevation height of the printing medium loading plate to be uniform. This operation may also help reduce an impact noise and/or impact damage generated when the printing medium is supplied to the image forming unit. 
     Although a few exemplary embodiments of the present disclosure have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.