Patent Publication Number: US-7909318-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 2008-0002562, filed on Jan. 9, 2008 in the Korean Intellectual 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 an image forming apparatus, and, more particularly, to an image forming apparatus having improved configuration of a paper supply device. 
     2. Description of the Related Art 
     An image forming apparatus is an apparatus to form an image on a printing medium. Examples of the image forming apparatus include, e.g., printers, copiers, facsimiles, and devices with some combination of functions of these. 
     An image forming apparatus includes a paper supply device to supply a printing medium (hereinafter, referred to as “paper” for convenience of description, but the present invention is not limited to paper) to a printing unit of the image forming apparatus. 
     The paper supply device includes a paper loading member, in which paper is loaded. The paper loading member generally takes the form of a cassette or a tray. The paper supply cassette can hold a plurality of sheets of paper therein, and is frequently used in an automatic paper supply mechanism. The paper supply tray conveniently supplies a sheet of paper or a special sheet of paper, and is frequently used as a manual paper supply mechanism. 
       FIG. 1  illustrates an example of an image forming apparatus having both a paper supply cassette and paper supply tray. As shown in  FIG. 1 , the image forming apparatus  1  includes a paper supply cassette  2  detachably mounted to a lower portion of a body  1   a , and a paper supply tray  3  arranged above, and in parallel with, the paper supply cassette  2 . 
     The paper supply tray  3  is arranged in the body  1   a , and the body  1   a  has a paper input opening  4  through which a single sheet of paper can be placed on the paper supply tray  3 . 
     The image forming apparatus  1  further includes a pickup roller  5  located above the paper supply cassette  2  and paper supply tray  3  and a pickup pad  6  disposed opposite the pickup roller  5  designed to prevent simultaneous delivery of two sheets of paper. 
     The pickup roller  5  is commonly used to pick up paper loaded in both the paper supply cassette  2  and paper supply tray  3 . More specifically, when a printing operation is performed using the paper supply cassette  2  as shown in  FIG. 1A , the pickup roller  5  picks up paper P 1  loaded in the paper supply cassette  2  sheet by sheet. Also, when a printing operation is performed using a paper supply tray  3  as shown in  FIG. 1B , the pickup roller  5  picks up paper P 2  placed on the paper supply tray  3 . 
     The above-described image forming apparatus  1  has an advantage of reducing the size of the apparatus as a result of arranging the paper supply cassette  2  and paper supply tray  3  in parallel. However, there is a risk that the paper loaded in the paper supply cassette  2  can be picked up by the pickup roller  5  even when it is intended to perform a printing operation using the paper supply tray  3 , resulting in a simultaneous delivery of two sheets of paper. 
     For example, a printing operation using the paper supply cassette  2  frequently causes a situation, in which the paper P 1  loaded in the paper supply cassette  2  is caught between the pickup roller  5  and the pickup pad  6  as shown in  FIG. 1C . If the paper P 2  is supplied from the paper supply tray  3  in this state, the paper P 1  and paper P 2  are picked up together by rotation of the pickup roller  5 , thereby being delivered together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects and advantages of the embodiments 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: 
         FIGS. 1A-1C  are views schematically illustrating a conventional image forming apparatus having both a paper supply cassette and a paper supply tray; 
         FIG. 2  is a view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention; 
         FIG. 3  is a view illustrating supply of paper from a first paper supply unit of the image forming apparatus of  FIG. 2 ; 
         FIG. 4  is a view illustrating supply of paper from a second paper supply unit of the image forming apparatus of  FIG. 2 ; 
         FIG. 5  is a perspective view illustrating relevant portions of the paper supply device of  FIG. 4 ; 
         FIG. 6  is an exploded perspective view illustrating a paper supply cassette and a pickup guide according to an embodiment of the present invention; and 
         FIG. 7  is a perspective view illustrating a paper supply tray according to and embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS 
     Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. While the embodiments are described with detailed construction and elements to assist in a comprehensive understanding of the various applications and advantages of the embodiments, it should be apparent however that the embodiments can be carried out without those specifically detailed particulars. Also, well-known functions or constructions will not be described in detail so as to avoid obscuring the description with unnecessary detail. It should be noted that in the drawings, the dimensions of the features are not intended to be to true scale, and may be exaggerated for the sake of allowing greater understanding. 
       FIG. 2  shows an illustrative example of an image forming apparatus according to an embodiment of the present invention. As shown in  FIG. 2 , the image forming apparatus  10  includes a body  10   a , a paper supply device  20 , a printing device  30 , and a paper discharge device  90 . 
     The printing device  30  prints an image on paper supplied from the paper supply device  20 . The image forming apparatus of this example is an electro-photographic type color image forming apparatus, and the printing device  30  includes photosensitive members  40 K,  40 C,  40 M, and  40 Y, a light scanning device  50 , a developing device  60 , a transfer device  70 , and a fixing device  80 . It should be apparent however, the present embodiment is not so limited to any particular type of image forming apparatus, and could be practiced in any image forming apparatus that uses print medium for recording visual images. 
     The body  10   a  defines the overall external appearance of the image forming apparatus, and supports a variety of elements installed therein. 
     The paper supply device  20  supplies paper to the printing device  30 . A detailed description of the paper supply device  20  will follow. 
     The light scanning device  50  irradiates light beams, corresponding to image information, to the photosensitive members  40 K,  40 C,  40 M, and  40 Y, to form electrostatic latent images on the surfaces of the photosensitive members  40 K,  40 C,  40 M, and  40 Y. 
     The developing device  60  supplies toner to the electrostatic latent images formed on the photosensitive members  40 K,  40 C,  40 M, and  40 Y, so as to form visible images. The developing device  60  may include four developers  60 K,  60 C,  60 M, and  60 Y, each of which receive toner of different color, for example, black toner K, cyan toner C, magenta toner M, and yellow toner Y, respectively. 
     Each of the developers  60 K,  60 C,  60 M, and  60 Y may include a feed roller  61  and a developing roller  62 . The feed roller  61  supplies toner to the developing roller  62 , and the developing roller  62  supplies the toner to the associated photosensitive member so as to develop the electrostatic latent image into the visible image. 
     The transfer device  70  may include an intermediate transfer drum  71  and a transfer roller  72 . The visible images formed on the photosensitive members  40 K,  40 C,  40 M, and  40 Y are sequentially transferred to the intermediate transfer drum  71  such that they overlap one another. The resulting overlapped color image is transferred to paper, which passes through a gap between the transfer roller  72  and the intermediate transfer drum  71 . 
     The paper, having passed through the transfer device  70 , is introduced to the fixing device  80 . The fixing device  80  may include a heating roller  81  and a pressing roller  82 . While the paper medium, to which the image was transferred, passes through the gap between the heating roller  81  and the pressing roller  82 , the image is fixed to the paper by heat and pressure. 
     The paper, having passed through the fixing device  80 , is guided to the paper discharge device  90 , and in turn, is discharged from the body  10   a  by a discharge roller  91 . 
       FIG. 3  is a view illustrating supply of paper from a first paper supply unit provided in the image forming apparatus of  FIG. 2 .  FIG. 4  is a view illustrating supply of paper from a second paper supply unit provided in the image forming apparatus of  FIG. 2 . 
     As shown in  FIGS. 3 and 4 , the paper supply device  20  includes a first paper supply unit  100   a , in which a plurality of sheets of paper P 1  can be loaded, and a second paper supply unit  100   b , which allows a user to manually supply a sheet of paper P 2 . Hereinafter, paper loaded in the first paper supply unit  100   a  is referred to as first paper P 1 , and paper disposed on the second paper supply unit  100   b  is referred to as second paper P 2 . 
     When no second paper P 2  is disposed on the second paper supply unit  100 , the image forming apparatus  10  performs a printing operation by supplying the first paper P 1 , loaded in the first paper supply unit  100   a , to the printing device  30 . When the second paper P 2  is put on the second paper supply unit  100   b , the image forming apparatus  10  performs a printing operation by supplying the second paper P 2  to the printing device  30 . 
     The first paper supply unit  100   a  may take the form of a paper supply cassette  110  detachably mounted to the body  10   a.    
     The second paper supply unit  100   b  may take the form of a paper supply tray  120  mounted in the body  10   a . The paper supply tray  120  is located close to the paper supply cassette  110  above the paper supply cassette  110 . The body  10   a  has a paper input opening  11  through which paper can be placed on the paper supply tray  120 . 
     In the case where the first paper supply unit  100   a  and second paper supply unit  100   b  are arranged in parallel, the first paper P 1  and second paper P 2  can be delivered to the printing device  30  along the same paper supply path  21 , and various supply elements in the paper supply path can be shared by the first paper P 1  and the second paper P 2 . This may advantageously reduce the size of the image forming apparatus  10 . 
     The paper supply device  20  may include a pickup roller  130 , a pickup pad  140 , at least one feed roller  150 , a pickup guide  160 , and a delivery roller  170 . The pickup roller  130  picks up the first paper P 1  loaded in the paper supply cassette  110  and delivers it to the paper supply path  21 . The pickup pad  140  is disposed opposite the pickup roller  130  and is used to pick up the first paper P 1  sheet by sheet. The feed roller(s)  150  delivers the second paper P 2 , disposed on the paper supply tray  120 , along the paper supply path  21 . The pickup guide  160  guides the first paper P 1  or second paper P 2  to be delivered to the paper supply path  21 . The delivery roller  170  is located between the pickup roller  130  and the printing device  30 . 
     When the first paper P 1  is picked up from the paper supply cassette  110 , the pickup pad  140  is brought into contact with the pickup roller  130  as shown in  FIG. 3 . However, when the second paper P 2  is supplied from the paper supply tray  120 , the pickup pad  140  is spaced apart from the pickup roller  130 , to have a gap G with the pickup roller  130  as shown in  FIG. 4 . 
     As shown in  FIG. 4 , the second paper P 2 , which is delivered by the feed roller(s)  150 , can be moved to the delivery roller  170  by passing through the gap G. Therefore, even if the second paper P 2  is supplied from the paper supply tray  120  in a state wherein the first paper P 1  is caught between the pickup roller  130  and the pickup pad  140 , there is less likelihood of paper P 1  and P 2  being simultaneously delivered to the printing device  30 . 
     Hereinafter, the position of the pickup pad  140  when the pickup pad  140  comes into contact with the pickup roller  130  is referred to as the first position, and the position of the pickup pad  140  when the pickup pad  140  is spaced apart from the pickup roller  130  is referred to as the second position. 
       FIG. 5  is a perspective view illustrating the configuration of the relevant portions of  FIG. 4 .  FIG. 6  is a perspective view illustrating a paper supply cassette and a pickup guide according to an embodiment of the present invention. 
     As shown in  FIGS. 3 to 5 , the paper supply cassette  110  includes a cassette body  111  to receive paper, and a knockup plate  112  to support the first paper P 1  loaded in the paper supply cassette  110 . 
     The knockup plate  112  is rotatably supported in the cassette body  111 . The knockup plate  112  is coupled to the cassette body  111  via a hinge shaft  112   a  provided at a trailing end thereof, and the leading end of the knockup plate  112  pivotally rotates to move in upward and downward direction. 
     The pickup roller  130  is located above the leading end of the knockup plate  112 . The pickup roller  130  is installed on a shaft  180 , which is rotatably supported by the body  10   a . The shaft  180  rotates upon receiving power from a drive motor (not shown) provided in the body  10   a.    
     The pickup roller  130  includes a pickup rotating member  131  to pick up the first paper P 1  disposed on the knockup plate  112 , and a pair of idle rollers  132  provided on both sides of the pickup rotating member  131  to freely rotate. 
     The pickup rotating member  131  includes a contact portion  131   a , which is brought into contact with the first paper P 1  during only a portion of the rotational period of the pickup rotating member  131 . The contact portion  131   a  protrudes outward in a radial direction of the idle rollers  132 . When the contact portion  131   a  of the pickup rotating member  131  comes into contact with the first paper P 1  as shown in  FIG. 3 , the idle rollers  132  are spaced apart from the first paper P 1 . However, when the contact portion  131   a  of the pickup rotating member  131  does not come into contact with the first paper P 1 , the idle rollers  132  come into contact with the first paper P 1 . 
     The idle rollers  132  press the pickup pad  140  with a predetermined pressure when the first paper P 1 , picked up by the pickup rotating member  131 , passes over the pickup pad  141  located at a first position. This allows only the uppermost sheet of the first paper P 1  disposed on the knockup plate  112  to be delivered to the delivery roller  170 . 
     The paper supply device  20  includes a lifter  190  to move the knockup plate  112  up and down. The lifter  190  includes an elastic member  191  to elastically bias the knockup plate  112  upward, and a pair of cams  192 , which are coupled on both ends of the shaft  180  such that the pickup roller  130  is interposed therebetween, the cams  192  rotating together with the pickup roller  130 . 
     The cams  192  press both sidewalls  112   b  of the knockup plate  112  for a specific duration of the rotating period of the shaft  180 , thereby pivotally rotating the knockup plate  112  downward. Guide rollers  113  can be installed to both the sidewalls  112   b  of the knockup plate  112 , to allow the cams  192  to efficiently press the knockup plate  112 . 
     If the cams  192  are further rotated and thus, are spaced apart from the knockup plate  112 , the knockup plate  112  is pivotally rotated upward by the elastic member  191 . 
     As shown in  FIGS. 3 to 6 , the pickup guide  160  is installed at the rear side of the paper supply cassette  110 . A pad holder  200  is installed, in a vertically movable manner, to the pickup guide  160  at a position corresponding to the pickup roller  130 . 
     The pad holder  200  includes a holder body  201  to support the pickup pad  140 , and an elastic member  202  to elastically bias the holder body  201  upward. 
     The holder body  201  is formed, at an upper end thereof, with a pad receiving portion  203  to receive the pickup pad  140 . Also, the holder body  201  is formed, at a lower end thereof, with an interference piece  204  protruding toward the knockup plate  112 . To allow the interference piece  204  to extend to the knockup plate  112 , the cassette body  111  is formed with an opening  111   a.    
     The interference piece  204  interferes with the leading end of the knockup plate  112  when the knockup plate  112  is pivotally rotated downward. Accordingly, the holder body  201  is moved downward in conjunction with the knockup plate  112  when the knockup plate  112  is pivotally rotated downward. As a result, the pickup pad  140  can be spaced apart from the pickup roller  130 . 
     The elastic member  202  is installed between the holder body  201  and the pickup guide  160 . If the knockup plate  112 , which press the interference piece  204  of the holder body  201 , is pivotally rotated upward, the holder body  201  is moved upward by an elastic force of the elastic member  202 , thereby allowing the pickup pad  140  to come into contact with the pickup roller  130 . 
       FIG. 7  is a perspective view of the paper supply tray according to an embodiment of the present invention. 
     As shown in  FIGS. 4 to 7 , the paper supply tray  120  includes a paper supply plate  121  fixedly mounted in the body  10   a , a guide film  122  extending from an end of the paper supply plate  121  toward the pickup roller  130 , and a pair of adjusting guides  123 , which are movable left and right such that a distance therebetween coincides with a width of the second paper P 2  disposed on the paper supply plate  121 . 
     The at least one feed roller  150  is disposed on the paper supply plate  121 . The feed roller  150  is rotatably installed in the body  10   a , and rotates upon receiving power from a drive motor (not shown). In the present embodiment, the at least one feed roller  150  includes first and second feed rollers  151  and  152 , but any number of the feed rollers can be appropriately provided to suit a particular design. 
     The paper supply plate  121  is provided with a first backup roller  124  and a second backup roller  125 . The first backup roller  124  and second backup roller  125  are rotatably engaged with the first feed roller  151  and second feed roller  152 , respectively, such that the second paper P 2 , disposed on the paper supply plate  121 , is delivered to the delivery roller  170  by rotation thereof. 
     The guide film  122  may be made of a flexible material, and extends with a slant toward the bottom of the pickup roller  130  from the paper supply plate  121  mounted in the body  10   a . In the present embodiment, the second paper P 2  disposed on the paper supply tray  120  is not picked up by the pickup roller  130 , but directly passes through the gap between the pickup roller  130  and the pickup pad  140  so as to be delivered to the delivery roller  170 . Accordingly, if the guide film  122  is excessively tilted, a paper jam may occur in the vicinity of the pickup guide  160  where a paper delivery path has a steep gradient. Therefore, the tilt angle θ of the guide film  122  relative to a horizontal plane is preferably less than 3°. 
     The delivery roller  170  is arranged, together with a third backup roller  171 , in the paper supply path  21  downstream of the pickup roller  130 . The third backup roller  171  is rotatably engaged with the delivery roller  170 , and delivers the paper by rotation thereof, and in conjunction with the delivery roller  170 , to the transfer roller  72 . In particular, in the case of the second paper P 2  supplied from the paper supply tray  120 , after being delivered to the delivery roller  170  by the first feed roller  151  and second feed roller  152 , the paper P 2  pauses between the delivery roller  170  and the third backup roller  171 , so as to be delivered to the transfer roller  72  at the appropriate time. 
     The delivery roller  170  may be a registration roller  170   a  to align the first paper P 1  supplied from the paper supply cassette  110  or the second paper P 2  supplied from the paper supply tray  120 . 
     A first paper sensor  211  may be provided at the front side of the first feed roller  151 . If the first paper sensor  211  senses a leading end of the second paper P 2  as the second paper P 2  is supplied to the paper supply tray  120 , a controller (not shown) of the image forming apparatus  10  drives the first feed roller  151  and second feed roller  152 , to deliver the second paper P 2 . 
     A second paper sensor  212  is disposed between the second feed roller  152  and the pickup roller  130 . The second paper sensor  212  is used to confirm normal delivery of the second paper P 2  supplied from the paper supply tray  120 . For example, if the second paper sensor  212  does not sense any paper after the first paper sensor  211  senses the paper, a paper jam may have occurred between the first paper sensor  211  and the second paper sensor  212 . 
     A third paper sensor  213  is disposed between the pickup roller  130  and the delivery roller  170 . As the third paper sensor  213  senses the paper to be introduced to the delivery roller  170 , the controller (not shown) of the image forming apparatus controls the delivery roller  170  on the basis of the signal from the third paper sensor  213 . 
     Hereinafter, an example of paper supply operation of the image forming apparatus according to the embodiment of the present invention will be described with reference to  FIGS. 3 to 5 . 
     In an idle state, i.e., waiting for a print operation, the cams  192  installed to the shaft  180  press the knockup plate  112  as shown in  FIG. 5 . Accordingly, the knockup plate  112  is kept in a downwardly pivotally rotated state. The pad holder  200 , which cooperates with the knockup plate  112 , is also kept in a downwardly moved state. As a result, the pickup pad  140 , installed at the upper end of the pad holder  200 , is spaced apart from the pickup roller  130  and is kept at the second position. 
     First, supply of the paper P 1  from the paper supply cassette  110  will be described. If a printing command is inputted in the above-described idle state, the shaft  180  is rotated, causing the cams  192  to be spaced apart from the knockup plate  112 . Thereby, the leading end of the knockup plate  112  is pivotally rotated upward by the elastic member  191  which elastically supports the knockup plate  112 . 
     As the leading end of the knockup plate  112  is pivotally rotated upward, an uppermost sheet of the first paper P 1  disposed on the knockup plate  112  is brought into contact with the pickup roller  130 . Also, the holder body  201  of the pad holder  200  is moved upward by the elastic member  202 , causing the pickup pad  140  to come into contact with the pickup roller  130 . 
     If the pickup roller  130  is further rotated in the above-described state, the uppermost paper P 1  is picked up by the pickup roller  130 , and is delivered toward the delivery roller  170 . In this case, the pickup pad  140  is pressed toward the pickup roller  130 , to prevent simultaneous delivery of two sheets of paper. 
     Next, supply of the second paper P 2  from the paper supply tray  120  will be described. If the second paper P 2  is placed on the paper supply tray  120  in the above-described idle state, the first paper sensor  211  senses the leading end of the second paper P 2 . 
     If the first paper sensor  211  senses the second paper P 2 , the controller (not shown) of the image forming apparatus  10  controls a drive motor (not shown) such that no power is applied to the shaft  180 . Thus, the cams  192  continue pressing the knockup plate  112 , the pad holder  200  is in a downwardly moved state, and the pickup pad  140  is spaced apart from the pickup roller  130  to maintain a gap G between the pickup pad  140  and the pickup roller  130 . 
     As the first feed roller  151  and second feed roller  152  rotate in the above-described state, the second paper P 2  disposed on the paper supply plate  121  is delivered to the guide film  122 , and is introduced into the gap G between the pickup roller  130  and the pickup pad  140  by guidance of the guide film  122 . In this case, even if paper is caught between the pickup roller  130  and the pickup pad  140 , the gap G between the pickup roller  130  and the pickup pad  140  can prevent simultaneous delivery of two sheets of paper toward the printing device  30 . 
     The second paper P 2 , having passed through the gap G between the pickup roller  130  and the pickup pad  140 , is delivered to the delivery roller  170  by the first feed roller  151  and second feed roller  152 . 
     If the third paper sensor  213  senses the leading end of the second paper P 2  as the second paper P 2  accesses the delivery roller  170 , the controller of the image forming apparatus  10  controls the delivery roller  170  such the delivery roller  170  rotates after a first predetermined time t 1  elapses, and stops after a second predetermined time t 2  elapses (t 2 &gt;t 1 ). 
     The second paper P 2  is continuously delivered by the feed rollers  151  and  152  for the first predetermined time t 1 , but the delivery roller  170  is not rotated for the first predetermined time t 1 . Thereby, the leading end of the second paper P 2  delivered to the delivery roller  170  is caught and aligned by the delivery roller  170 . 
     If the delivery roller  170  rotates after the first predetermined time t 1  elapses, the leading end of the second paper P 2  aligned by the delivery roller  170  is introduced into a gap between the delivery roller  170  and the third backup roller  171 . 
     Subsequently, if the delivery roller  170  stops after the second predetermined time t 2  elapses, the leading end of the second paper P 2  is kept in a waiting state in which it is caught between the delivery roller  170  and the third backup roller  171 , so as to be delivered toward the transfer roller  72  at the appropriate time. 
     Although 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.