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CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Application No. 2005-99152, filed Oct. 20, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Aspects of the present invention relate to a hinge unit and an image forming apparatus having the same. More particularly, aspects of the present invention relate to a hinge unit capable of smoothly operating by applying a resilience that varies according to an open angle of a hinge unit, and an image forming apparatus having a cover connected to a main body of the image forming apparatus by the hinge unit.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, image forming apparatuses that include a scanning function, such as, for example, copiers, scanners, and multifunction apparatuses, scan a document and store an image read from the document as data or print out the image on a print medium such as paper.  
         [0006]      FIG. 1  shows a conventional multifunction apparatus as an example of an image forming apparatus. Referring to  FIG. 1 , the multifunction apparatus comprises a scan unit  2  formed at a main body  1  thereof to read images from a document placed on the scan unit  2 , a cover  3  covering the document, and a hinge unit  10  connecting the scan unit  2  and the cover  3 . An automatic document feeder (ADF)  4  may be further mounted to the cover  3  to automatically supply a plurality of sheets of the document to the scan unit  2 . In a high-speed multifunction apparatus or copier, a duplex ADF may be mounted to the cover  3 . However, a cover  3  having a duplex ADF is typically so heavy that a user cannot conveniently lift and lower the cover  3 .  
         [0007]     In a general image forming apparatus, the cover is typically able to pivot by approximately 80°. The moment generated by pivoting the cover does not regularly increase according to the open angle of the cover. As the cover is becomes more and more closed, in other words, as the open angle of the cover with respect to a scan unit becomes close to 0°, the moment and resilience for balancing increase. Therefore, it is hard to maintain the moment equilibrium according to the open angle with a typical hinge unit containing only one spring. Although a single spring is generally mounted to the hinge unit, a pair of springs may be mounted in parallel when greater force is required. However, when using one or two parallel springs, the design freedom of the apparatus is poor. An over-spec spring needs to be employed in order to apply spring forces differently according to various opening angles. However, an over-spec spring does not offer the user a good feeling in opening and closing the cover. In order to provide a favorable opening and closing operation of the cover requiring only a minor force when performing scanning or copying work, configuration of the spring of the hinge unit connecting the cover with the scan unit of the main body becomes an essential issue.  
         [0008]      FIG. 2  is a sectional view showing the structure of a hinge unit  10  mounted in the conventional image forming apparatus, as disclosed in Japanese Patent Publication No. 2003-129739. In the hinge unit  10 , two springs  11  and  12  are serially connected.  
         [0009]     Referring to  FIG. 2 , the hinge unit  10  comprises a cam base  30  connected to a cover  3 , a plunger  21  received in a hinge housing  20  to move back and forth and having a slanted face  22 , first and second springs  11  and  12  received in the hinge housing  20  and pushing the plunger  21 , and first and second cams  31  and  32  pivoting in association with the cam base  30  and contacting the slanted face  22 . In the above-structured hinge unit  10 , a resistant force as a reaction by the first cam  31  is applied to the slanted face  22  of the plunger  21  in the direction of a common normal of the point of contact with the first cam  31 . Therefore, the resistant force operates as a moment inclining the plunger  21  to the rotational direction (illustrated by an arrow) so that the plunger  21  may swerve from the first cam  31 , thereby increasing the torque in the open direction around a hinge shaft P. Accordingly, enough force can be obtained for popping up the cover  3 , and also for preventing the cam base  30  and the plunger  21  from deforming. However, the hinge unit  10  may become worn along the first and the second cams  31  and  32  and the slanted face  22  of the plunger  21 . The user still has to apply a great force to open and close the cover  3 , especially a heavy cover, and accordingly, the cover  3  cannot be smoothly pivoted.  
       SUMMARY OF THE INVENTION  
       [0010]     An aspect of the present invention is to solve the above and/or other problems and disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a hinge unit enabling a user to smoothly open and close a cover of an image forming apparatus with only a minor force, by applying resilience of different degrees according to an open angle of the cover.  
         [0011]     Another aspect of the present invention is to provide an image forming apparatus having the above-mentioned hinge unit.  
         [0012]     According to an aspect of the present invention, there is provided a hinge unit comprising a lower frame connected to a scan unit of a main body of an image forming apparatus; an upper frame engaged with the lower frame through a hinge shaft and connected to a cover of the image forming apparatus; and first and second resilient members serially arranged within the upper frame, wherein, when the cover pivots toward the scan unit, the first resilient member displaces first and then the second resilient member displaces.  
         [0013]     According to an aspect of the present invention, the upper frame comprises a fixed holder mounted at one end thereof to receive the first resilient member; a first movable holder mounted to be opposed to the fixed holder, receiving the second resilient member, and moving along a length direction of the upper frame; and a second movable holder disposed between the first and the second resilient members to move along the length direction of the upper frame.  
         [0014]     According to an aspect of the present invention, the upper frame comprises a guide rail that guides sliding movement of the first and the second movable holders along the length direction of the upper frame.  
         [0015]     According to an aspect of the present invention, the upper frame further comprises a fixed member that prevents the fixed holder from being pushed outward.  
         [0016]     According to an aspect of the present invention, the lower frame comprises a link fixed in front of the hinge shaft to contact with the first movable holder.  
         [0017]     According to an aspect of the present invention, at least one of the fixed holder and the second movable holder comprises sidewalls on surfaces thereof opposite to each other. The fixed holder may have a sidewall that extends downward, that is, in the direction of the second movable holder. The second movable holder may have a sidewall that extends upward and/or downward, that is, in the direction of the fixed holder and/or in the direction of the first movable member. The total height of the sidewalls of the fixed holder and sidewalls of the second movable holder extending toward the fixed holder is equal to or greater than length of the first resilient member when the first member is completely compressed. In addition, the respective holders may include mounting parts for seating the first and second resilient members therein.  
         [0018]     Preferably, but not necessarily, the first and the second resilient members are springs, and the spring constant K 1  of the first resilient member is smaller than the spring constant K 2  of the second resilient member.  
         [0019]     An image forming apparatus according to another aspect of the present invention may comprise a main body including a scan unit, and a cover connected with a scan unit of the main body by the above-described hinge unit.  
         [0020]     According to another aspect of the present invention, a hinge unit of an image forming apparatus having a cover and a main body with a scan unit, comprises a lower frame connected to a scan unit of a main body of an image forming apparatus; an upper frame engaged with the lower frame through a hinge shaft and connected to a cover of the image forming apparatus; and a plurality of resilient members serially arranged within the upper frame, wherein an overall resilience of the hinge unit is controlled by selecting a resilience of individual resilient members of the plurality of serially arranged resilient members.  
         [0021]     According to another aspect of the present invention, an apparatus has a main body and a cover, wherein the cover is connected with the main body through a hinge unit, wherein the hinge unit comprises, a lower frame connected to the main body; an upper frame engaged with the lower frame through a hinge shaft and connected to the cover, and first and second resilient members serially arranged within the upper frame, wherein the first resilient member displaces before the second resilient member when the cover pivots toward the scan unit.  
         [0022]     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  
       [0023]     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:  
         [0024]      FIG. 1  is an exterior view of a conventional multifunction apparatus;  
         [0025]      FIG. 2  is a sectional view showing the structure of a conventional hinge unit;  
         [0026]      FIG. 3  is a perspective view showing the hinge unit as assembled;  
         [0027]      FIG. 4  is an exploded perspective view of  FIG. 3 ;  
         [0028]      FIG. 5  is a longitudinal-sectional view of  FIG. 3 ;  
         [0029]      FIG. 6  is a front view showing the detailed structure of resilient members of  FIG. 3 ;  
         [0030]      FIG. 7  is a view showing the structure of a hinge unit according to another embodiment of the present invention;  
         [0031]      FIGS. 8A through 8D  are views showing the operation of the hinge unit of  FIG. 7 ; and  
         [0032]      FIG. 9  is a graph illustrating relationships between loads and open angles of the cover with respect to the hinge unit. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0033]     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. Well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
         [0034]      FIGS. 3 through 6  are an assembled view, an exploded perspective view, a longitudinal-sectional view, and a front view, respectively, for showing a hinge unit according to an embodiment of the present invention. Referring to the drawings, the hinge unit  100  comprises a lower frame  110 , and an upper frame  120  connected to the lower frame  110  through a hinge shaft P.  
         [0035]     The hinge unit may connect a cover of an image forming device with the scan unit of the main body of an image forming device. Aspects of the image forming device may be the same as those shown in  FIG. 1 , with respect to the main body  1 , the scanning unit  2 , the cover  3  and optional automatic document feeder  4 , except that the hinge unit according to embodiments of the present invention described herein replaces the conventional hinge unit  10  shown in  FIGS. 1 and 2 . The lower frame  110  of the hinge  100  is connected to a scan unit  2  mounted to a main body  1  ( FIG. 1 ) of an image forming apparatus. The lower frame  110  may comprise a fastening hole  114   a  on a bottom surface  114  thereof, to be connected with the scan unit  2  by a fastening member (not shown). The hinge shaft P is mounted to the lower frame  110  through a shaft hole formed in front of the hinge shaft P. In other words, the link  112  is placed so that it is offset from the hinge shaft P within the angle of rotation of the hinge  100 . The hinge shaft P and the link  112  may be formed as cylindrical bars. The link  112 , contacts and engages with a first movable holder  121  of the upper frame  120 .  
         [0036]     The upper frame  120  is connected to the cover  3  ( FIG. 1 ) of the image forming apparatus and coupled with the lower frame  110  by the hinge shaft P passing through a connection hole  120   a  formed at one side thereof. The upper frame  120  may be fixedly mounted to the cover  3  through a connection member  125 .  
         [0037]     The upper frame  120  comprises first and second resilient members  131  and  132  that are serially arranged. Although the number of the resilient member is not limited, it is preferable to serially arrange two resilient members  131  and  132 .  
         [0038]     The upper frame  120  has a fixed holder  123  formed at an upper side and a first movable holder  121  formed at a lower side opposite to the fixed holder  123 . As used herein, the term “lower side” of the upper frame  120  refers to the portion of the frame that is adjacent to the hinge shaft P and the term “upper side” of the upper frame  120  refers to the opposite portion of the upper frame  120 , that is, the portion that is farthest away from the hinge shaft P. The fixed holder  123  supports the first resilient member  131  so that the first resilient member  131  is not pushed out of the upper frame  120 . In addition, fixed members  126   a  and  126   b  may be provided to the upper frame  120  or the connection member  125  in order to prevent the fixed holder  123  from being pushed out of the upper frame  120 . Alternatively, the fixed holder  123  may be attached directly to the upper frame  120  or to the connection member  125 .  
         [0039]     The first and the second resilient members  131  and  132  are serially arranged between the fixed holder  123  and the first movable holder  121 . Preferably, but not necessarily, the first movable holder  121  has a mounting part  121   e  constructed by sidewalls of a bottom portion thereof to receive therein an end of the second resilient member  132 . Therefore, the second resilient member  132  can be stably received in the first movable holder  121  by the mounting part  121   e  of the first movable holder  121 . The fixed holder  123  may also have such a mounting part.  
         [0040]     In addition, a second movable holder  122  is formed between the first and the second resilient members  131  and  132 .  
         [0041]     The upper frame  120  may include guide rails  124   a  and  124   b  at both flanks along a length direction thereof that allow the first and the second movable holders  121  and  122  to slide in the length direction. The first and the second movable holders  121  and  122  comprise first guide grooves  121   a  and  121   b  and second guide grooves  122   a  and  122   b,  respectively, that allow the first and the second movable holders  121  and  122  to smoothly slide along the guide rails  124   a  and  124   b.    
         [0042]     In the hinge unit  100  of this embodiment, springs are employed for the first and the second resilient members  131  and  132 . According to this embodiment, it is preferred that a spring constant K 1  of the first resilient member  131  is less than a spring constant K 2  of the second resilient member  132  so that the first resilient member  131  operates first and the second resilient member  132  operates next.  
         [0043]     To ensure the orderly operation of the first and the second resilient members  131  and  132 , and to prevent the resilient members from popping out of the upper frame  120 , the fixed holder, and first and second movable holders may further include sidewalls. Holders having sidewalls are shown as the first movable holder  221 , second movable holder,  222  and fixed holder  223  in the embodiment shown in  FIG. 7 . In the embodiment shown in  FIG. 7 , the other structures are the same as those of the hinge unit  100  of  FIG. 3  except that the holders  221  to  223  include sidewalls, respectively. For convenient explanation, only the holders  221  to  223  and the resilient members  131  and  132  are illustrated in  FIG. 7 .  
         [0044]     In the hinge unit  200  according to the embodiment of  FIG. 7 , one or both of the second movable holder  221  and the fixed holder  223  may comprise sidewalls on surfaces thereof opposite to each other. As shown in  FIG. 7 , sidewalls  222   c  and  223   c  may be formed on circumferences or perimeters of both the second movable holder  222  and the fixed holder  223  to be opposed to each other. Preferably, a total height of the fixed holder sidewall  223   c  and the movable holder sidewall  222   c  is equal to or greater than a height of the first resilient member when the first resilient member  131  is completely compressed, so that the operation of the first resilient member  131  is followed by that of the second resilient member  132 . More particularly, when the first resilient member  131  is compressed, the movable holder sidewall  222   c  and the fixed holder sidewall  223   c  come into contact with each other, thereby restraining the operation of the first resilient member  131  and promoting the operation of the second resilient member  132 .  
         [0045]     Sidewalls  221   c  to  223   c  of the respective holders  221  to  223  comprise mounting parts  221   e  to  223   e,  respectively, to stably receive the resilient members  131  and  132 . The second movable holder  222  may further comprise another sidewall  222 &#39; c  formed on a lower part thereof.  
         [0046]     The above-structured hinge unit is applicable to various devices mounting a cover, such as the image forming apparatus having the cover  3  hingedly connected to the main body  1  comprising the scan unit  2  and to the scan unit  2  of the main body  1 . Especially, the hinge unit according to embodiments of the present invention may be used for an image forming apparatus having a relatively heavy cover mounting an automatic document feeder (ADF)  4  ( FIG. 1 ) thereon. The hinge unit may be used with other apparatuses having a heavy cover, such as, for example, a chest freezer.  
         [0047]     Hereinbelow, the operations and effects of the hinge unit according to embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0048]      FIGS. 8A through 8D  show the operation of the hinge unit applied to the image forming apparatus according to the embodiment of  FIG. 7 . For convenient explanation, only the holders  221  to  223  and the two springs  131  and  132  are illustrated. It is to be understood that the upper frame  120  of the hinge unit  200  is fixed to the cover of the image forming apparatus, and the lower frame  110  is fixed to the scan unit of the main body and that the remaining features of the hinge unit  200  may be as shown, for example, in  FIGS. 3-5 . Moreover, it is to be understood that aspects of the image forming device may be the same as those shown in  FIG. 1 , with respect to the main body  1  and the cover  3 , except that the hinge unit according to  FIGS. 3-8  replaces the conventional hinge unit  10  shown in  FIGS. 1 and 2 .  
         [0049]     Generally, the cover  3  of the image forming apparatus is opened and closed pivoting by approximately 80°. The moment generated by pivot of the cover  3  is not regularly increased according to an open angle of the cover  3 . As the cover  3  is being closed, in other words, as the open angle of the cover  3  with respect to a scan unit is becoming 0°, the moment and resilience for balancing increase. In the hinge unit of  FIG. 8 , the two springs  131  and  132  are arranged in a serial manner so as to balance the moment according to the open angle of the cover  3 .  
         [0050]     Presuming that ‘K1’ denotes a spring constant of the first spring  131  and ‘K2’ denotes a spring constant of the second spring  132 , the springs wherein K 1  is smaller than K 2  are used so that the first spring  131  is displaced ahead of the second spring.  
         [0051]     In  FIG. 8A , the state is shown in which the cover  3  is completely open so that no force is applied to the movable holders  221  and  222 . When the cover  3  begins to be closed, the second movable holder  222  and the fixed holder  223  are pushed in an angular direction by the rotation of the upper frame  120  about the hinge shaft P. The cover  3  begins to generate a large moment with respect to the hinge shaft P due to its own weight. Correspondingly, resilience is generated by the link  112  ( FIG. 3 ). The link  112  restrains the movement of the first movable holder  221  in the angular direction, thereby hindering closing of the cover and pushes the first movable holder  221  in the direction of the fixed member  223 . Since the spring constant K 1  of the first spring  131  is smaller than the spring constant K 2  of the second spring  132 , the second movable holder is also pushed in the direction of the fixed member  223 . The second spring  132  remains uncompressed while the first spring begins to be compressed, as shown in  FIG. 8B . Since the springs  131  and  132  are serially arranged, the total spring constant in the state of  FIG. 8B  can be expressed as (K tot )=(K1×K2)/(K1+K2).  
         [0052]     When the cover  3  is closed by more than a predetermined angle, the first spring  131  becomes compressed completely, and the fixed holder sidewall  223   c  and the movable holder sidewall  222   c  are brought into contact with each other, as shown in  FIGS. 8C and 8D . As a result, the first spring  131  cannot compress any more and only the second spring  132  can generate resilience. The total spring constant (K tot ) in the state of  FIG. 8D  is equal to K 1 .  
         [0053]     As described above, in the operation of the hinge unit according to aspects of the present invention, the first spring  131  is operated when the open angle of the cover is more than a predetermined angle and then the second spring  132  is operated when the open angle is less than the predetermined angle. Accordingly, the moment caused by the weight of the cover  3  can be properly offset. The resilience of the hinge unit is illustrated in  FIG. 9  according to the open angle of the cover  3 .  
         [0054]      FIG. 9  is a graph for showing the relationships between loads and the open angles of the cover with respect to the hinge unit wherein the two springs are serially arranged. As shown in  FIG. 9 , when a pivoting angle of the cover is relatively large, for example, at the beginning of closing the cover, a minor force needs to be applied to the cover. However, when the pivoting angle of the cover is relatively small, for example, when the cover is almost closed, a greater force should be applied to the cover.  
         [0055]     Therefore, according to embodiments of the present invention, since the spring constants of the resilient members of the hinge unit are properly applied, the cover can be prevented from closing spontaneously or from slamming down too hard when it is closed. Also, the user can comfortably open and close the cover during scanning and copying of works.  
         [0056]     As can be appreciated from the hinge unit according to embodiments of the present invention, extent of resilience of the resilient members can be controlled according to the open angle of the cover by serially connecting a plurality of the resilient members, thereby properly offsetting the moment by the weight of the cover. In addition, the feeling to the user when opening and closing the cover is improved.  
         [0057]     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. For example, a plurality of other resilient members may be applied instead of the first and the second resilient members between the fixed holder and the first movable holder. Furthermore, more movable holders may be added in order to securely mount the plurality of resilient members. Therefore, technical protection range of the invention should be defined by the appended claims.

Summary:
A hinge unit applies resilience differently according to the angle at which the hinge unit is opened, and an image forming apparatus has a cover attached by the hinge unit. The hinge unit includes a lower frame connected to a scan unit of a main body of an apparatus; an upper frame engaged with the lower frame through a hinge shaft and connected to a cover; and first and second resilient members serially arranged within the upper frame. When the cover pivots toward the scan unit at less than a predetermined angle, the hinge unit provides relatively minor resistance, whereas when the cover pivots toward the scan unit at the predetermined angle or greater, the hinge unit provides relatively greater resistance, thereby appropriately coping with the moment by weight of the cover. As a result, the improved hinge unit may enable a user to open and close the cover more comfortably.