Abstract:
Disclosed is a sliding mechanism for a handheld electronic device. The mechanism includes a first slider in a single piece metallic body, two elongated plastic rails, and a second slider. The single piece metallic body includes two opposite side portions that are bent toward each other and define two elongated spaces, each of which is partially surrounded by each bent side portion. Each elongated plastic rail includes a groove on a surface of the elongated plastic rail and is fitted into each elongated space such that the groove of one elongated plastic rail opposes the groove of the other elongated plastic rail. The second slider includes two edges slidably engaged with the grooves such that the second slider is slidable relative to the first slider.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application is a continuation application of U.S. application Ser. No. 11/650,641, filed Jan. 8, 2007, now pending, which is a continuation application under 35 U.S.C. § 365(c) of International Application No. PCT/KR2005/002046, filed Jun. 29, 2005 designating the United States. International Application No. PCT/KR2005/002046 was published in English as WO2006/006776 A1 on Jan. 19, 2006. This application further claims the benefit of the earlier filing dates under 35 U.S.C. § 365(b) of Korean Utility Model Application Nos. 20-2004-0019437 filed Jul. 8, 2004, 20-2004-0034247 filed Dec. 2, 2004, 20-2005-0006264 filed Mar. 8, 2004, 20-2005-0007326 filed Mar. 18, 2005 and 20-2005-0007928 filed Mar. 23, 2005. This application incorporates herein by reference the U.S. application Ser. No. 11/650,641, the International Application No. PCT/KR2005/002046 including the International Publication No. WO2006/006776 A1 and the Korean Utility Model Application Nos. 20-2004-0019437, 20-2004-0034247, 20-2005-0006264, 20-2005-0007326 and 20-2005-0007928 in their entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present disclosure relates to a slider assembly, and more particularly, to a slider assembly for use in a handheld electronic device such as a cellular phone. 
         [0004]    2. Discussion of Related Technology 
         [0005]    As shown in  FIG. 25 , a sliding-type cellular phone comprises a main body  1  on which a plurality of keys  3  are installed and a cover  2  installed slidably over a surface of the main body  1  on which the keys  3  are installed. A liquid crystal display  4  is installed on a front surface of the cover  2 . In the sliding-type cellular phone as described above, a slider assembly  100  shown in  FIG. 25  or  26  is installed between the main body  1  and the cover  2  to allow the cover  2  to be slid with respect to the main body  1 . 
         [0006]    The slider assembly shown in  FIG. 25  comprises a fixing plate  110  fixed to the main body  1 ; a sliding plate  170  fixed to a surface of the cover facing the main body; and an up/down positioning means  140  which includes one end hinged to the fixing plate  110  and the other end hinged to the sliding plate  120  to impart an elastic force to the cover  2  in a direction in which the cover is closed or opened with respect to a certain sliding point. The up/down positioning means includes a cylinder  141  in which a compression spring is received and a rod  142  which is installed to be movably received in the cylinder  141  while pushing the compression spring. As shown in the figure, an end of the cylinder  141  is hinged to the fixing plate  110 , and an opposite end of the rod  142  is hinged to the sliding plate  120 . 
         [0007]    Another type of exemplary slider assembly  100  is illustrated in  FIG. 26 . The slider assembly  100  shown in  FIG. 26  includes a fixing plate  110  fixed to the main body  1 ; a sliding plate  120  fixed to a surface of the cover facing the main body; and a pair of torsion springs  130  each having an end hinged to the fixing plate  110  and the other end hinged to the sliding plate. In the slider assembly shown in  FIG. 26 , the pair of torsion springs  130  are equivalent to the up/down positioning means. 
         [0008]    The exemplary slider assembly as described above does not include a function of restricting a sliding length of the sliding plate  120 . Accordingly, in order to adjust the upward/downward sliding stroke of the sliding plate  120 , a stopper (not shown) for restricting the movement of the sliding plate is installed at the main body or cover of the cellular phone. Further, as shown in  FIG. 25 , separate dampers  150  for absorbing the shock may be installed at both ends of the sliding plate that collides against the stopper when the cover of the cellular phone is slid. Therefore, a process for manufacturing the cellular phone is complicated, and thus, the production costs are increased. Meanwhile, the slider assembly of  FIG. 25  is superior to the slider assembly of  FIG. 26  using the torsion springs in view of their durability, but the former is more complicated and expensive than the latter because the spring and rod  142  is received and assembled in the cylinder  141  and the ends of the cylinder and rod is hingedly coupled to the fixing plate and the sliding plate, respectively. 
         [0009]    The slider assembly of in  FIG. 26  employs the torsion spring  130  as the up/down positioning means, and thus, the slide assembly can be manufactured through a simple process and at a low cost. However, since it is difficult to manufacture the torsion spring with constant elasticity, every cellular phone cannot have a constant urging force required for sliding the cover. Accordingly, there is a problem that the cellular phones with the uniform urging force required for sliding the cover cannot be manufactured. Further, if the torsion spring  130  is repeatedly used for a long time, excessive deformation is generated at a portion that connects linear and curved portions of the torsion spring  130 , and thus, the connecting portion is broken due to fatigue. Consequently, there is another problem in that a durability of the torsion spring is not good. 
         [0010]    The discussion in this section is to provide general background information, and does not constitute an admission of prior art. 
       SUMMARY 
       [0011]    An aspect of the present invention is to provide a slider assembly which can restrict a sliding length of a sliding plate by means of an up/down positioning means thereof without need to install additional stoppers on a main body or cover of a cellular phone. 
         [0012]    Another aspect of the present invention is to provide a slider assembly which uses a tension spring, as an elastic means for maintaining an up/down state of a sliding plate, instead of a torsion spring to improve its durability. 
         [0013]    A further aspect of the present invention is to provide a slider assembly in which a guide bush with a low coefficient of friction is installed in a guide groove of a sliding plate to prevent the guide groove of the sliding plate and a guide section of a fixing plate from being brought into direct contact with each other, whereby the durability can be improved and sliding noise can be reduced. 
         [0014]    A still further aspect of the present invention is to provide a slider assembly including a spring engaging section that is deformed to prevent an up/down positioning means from interfering with a flexible printed circuit board when the up/down positioning means is operated. 
         [0015]    A still further aspect of the present invention is to provide a slider assembly including a fixing plate and a sliding plate which are manufactured through the press working to save the production costs such that there is no need for additional machining processes for the next assembly. 
         [0016]    A still further aspect of the present invention is to provide a slider assembly in which a sliding plate is arranged such that an amount of deformation of a spring is minimized when the sliding plate is slid up and down, whereby the expected life span of the spring can be prolonged. 
         [0017]    A still further aspect of the present invention is to provide a slider assembly of which respective plates are made from stainless steel such that the slider assembly cannot be easily damaged from shock. 
         [0018]    A still further aspect of the present invention is to provide a slider assembly in which a guide bush with a low coefficient of friction is installed to a guide section of a fixing plate to prevent the guide section of the fixing plate and a wing section of a sliding plate from being brought into direct contact with each other, whereby the durability can be improved and noise can be reduced when the sliding plate is slid. 
         [0019]    A still further aspect of the present invention is to provide a slider assembly in which a shock-absorbing member made of a soft material is installed at both ends of a guide bush installed at a fixing groove of a fixing plate such that the guide bush can be prevented from being damaged due to shock generated when a cover of the cellular phone is opened or closed or when the cellular phone is dropped. 
         [0020]    A still further aspect of the present invention is to provide a slider assembly in which noise cannot be generated by installing a shock-absorbing member to further protrude from both ends of a fixing plate such that a cover of the cellular phone with a sliding plate installed thereon is brought into contact with the shock-absorbing member rather than the fixing plate even though the cover of the cellular phone is frequently slid. 
         [0021]    A still further aspect of the present invention is to provide a slider assembly in which a cover of a cellular phone can be firmly kept at its up or down state by installing a plurality of permanent magnets at predetermined positions on both ends of the fixing plate and sliding plate such that a certain repulsive or attractive force can be exerted thereto even though an elastic restoring force of a spring becomes weak due to repeated use for a long time. 
         [0022]    A still further aspect of the present invention is to provide a slider assembly in which a sliding plate can be slid smoothly and continuously even in a dead zone by further installing permanent magnets at one end of the sliding plate such that a repulsive or attractive force can be generated between the magnets installed on the fixing and sliding plates. 
         [0023]    A still further aspect of the present invention is to provide a sliding-type cellular phone comprising the slider assembly so configured. 
         [0024]    According to an aspect of the present invention, there is provided a slider assembly for a sliding type cellular phone, which comprises a fixing plate formed with a guide section for guiding a linear motion of a sliding plate and fixed to an surface of a main body of the sliding-type cellular phone, a sliding plate guided linearly by the guide section of the fixing plate and fixed to an opposite surface of a cover of the cellular phone, and an up/down positioning means having one end hinged to the fixing plate and the other end hinged to the sliding plate to change a direction of an urging force for pushing the sliding plate from a specific sliding location of the sliding plate, wherein the guide section of the fixing plate includes a pair of opposite and parallel fixing grooves, each formed by bending twice a side portion of the fixing plate, and a pair of guide bushes fitted and installed in the fixing grooves, respectively, each guide bush having a guide groove for receiving a side of the sliding plate and guiding a sliding motion of the sliding plate, and the sliding plate includes a pair of wing sections formed by bending both sides thereof, each wing section is inserted in the guide groove of the corresponding guide bush to be linearly slid along the guide groove. 
         [0025]    The slider assembly may further comprise dampers made of a material softer than the guide bush and installed at both longitudinal ends of the guide bush to protrude from a longitudinal end of the fixing plate for absorbing shock generated due to collision against the sliding plate fixed to the cover of the cellular phone. 
         [0026]    Preferably, a plurality of through holes are formed on a bent side of each fixing groove of the guide section, and protrusions are formed on surfaces of the guide bush and damper facing the fixing groove of the guide section are inserted and fixed in the through holes. Preferably, the guide bushes are made of polyoxymethylene (POM) and the dampers are made of urethane rubber. 
         [0027]    The slider assembly may further comprise a pair of first permanent magnets installed at both ends of the fixing plate, respectively, to face the sliding plate; and a pair of second permanent magnets fixedly installed at positions on the sliding plate where the sliding plate can be urged outward at an up or down position of the sliding plate due to repulsive or attractive forces generated between the second permanent magnets and the first permanent magnets installed at both ends of the fixing plate. 
         [0028]    The slider assembly may further comprise third permanent magnets fixedly installed at positions on the sliding plate, near a position where a direction of the urging force of the up/down positioning means is changed while the sliding plate is moved, such that repulsive or attractive forces are generated between the third permanent magnets and any one pair of the first permanent magnets of the fixing plate. 
         [0029]    Preferably, the up/down positioning means is a spring including one end pivotally fixed to the fixing plate and the other end pivotally fixed to the sliding plate. Alternatively, the up/down positioning means includes a first link slider having an end slidably fixed to the fixing plate, a second link slider having an end fixed to the sliding plate and restricted with respect to the first link slider to be slid in a longitudinal direction of the first link slider, a tension spring having both ends fixed to opposite ends of the first and second link sliders, and a restriction means for restricting a sliding length of the sliding plate while guiding a sliding motion of the first and second link sliders. 
         [0030]    The slider assembly may further comprise a pair of first permanent magnets installed at both ends of the fixing plate, respectively, to face the sliding plate; and a pair of second permanent magnets fixedly installed at positions on the cover of the cellular phone such that the sliding plate is kept stationary at an up or down position due to an attractive force generated between the first and second permanent magnets. 
         [0031]    The slider assembly may further comprise third permanent magnets fixedly installed at positions on the sliding plate, near a position where a direction of the urging force of the up/down positioning means is changed while the sliding plate is moved, such that repulsive or attractive forces are generated between the third permanent magnets and any one pair of the first permanent magnets of the fixing plate. 
         [0032]    Preferably, the up/down positioning means is a spring including one end pivotally fixed to the fixing plate and the other end pivotally fixed to the sliding plate. Alternatively, the up/down positioning means includes a first link slider having an end slidably fixed to the fixing plate, a second link slider having an end fixed to the sliding plate and restricted with respect to the first link slider to be slid in a longitudinal direction of the first link slider, a tension spring having both ends fixed to opposite ends of the first and second link sliders, and a restriction means for restricting a sliding length of the sliding plate while guiding a sliding motion of the first and second link sliders. 
         [0033]    According to another aspect of the present invention, there is provided a slider assembly for a sliding type cellular phone including a fixing plate formed with a guide section for guiding a linear motion of a sliding plate and fixed to an surface of a main body of the sliding-type cellular phone, a sliding plate guided linearly by the guide section of the fixing plate and fixed to an opposite surface of a cover of the cellular phone, and an up/down positioning means having one end hinged to the fixing plate and the other end hinged to the sliding plate to change a direction of an urging force for pushing the sliding plate from a specific sliding location of the sliding plate, wherein the up/down positioning means includes a first link slider having one end slidably fixed to the fixing plate, a second link slider having one end fixed to the sliding plate and restricted with respect to the first link slider to be slid in a longitudinal direction of the first link slider, a tension spring having both ends fixed to opposite ends of the first and second link sliders, and a restriction means for restricting a sliding length of the sliding plate while guiding a sliding motion of the first and second link sliders. 
         [0034]    Preferably, the restriction means comprises a guide slot with a predetermined length formed in one of the first and second link sliders in a longitudinal direction of the link slider, and a guide protrusion fixed to the other link slider and received in the guide slot to guiding a sliding motion of the other link slider. 
         [0035]    Preferably, the first and second link sliders have the same plate shape, the guide slot is formed through each link slider, the guide protrusion is a pin fixed to each link slider, and the pin has a head with a diameter greater than a width of the guide slot. Alternatively, the first and second link sliders have the same plate shape, the guide slot is formed through each link slider, the guide protrusion is a protrusion formed by partially cutting a portion of each link slider and bending the partially cut portion toward the corresponding guide slot, and the pin has a head with a diameter greater than a width of the guide slot. 
         [0036]    Preferably, each of the link sliders has spring engaging sections formed at the other end thereof and protruding from both sides thereof perpendicular to a longitudinal direction of the link slider, and a pair of springs are installed between the corresponding spring engaging sections of the first and second link sliders. 
         [0037]    The slider assembly may further comprises a pair of first permanent magnets installed at both ends of the fixing plate, respectively, to face the sliding plate; and a pair of second permanent magnets fixedly installed at positions on the sliding plate where the sliding plate can be urged outward at an up or down position of the sliding plate due to repulsive or attractive forces generated between the second permanent magnets and the first permanent magnets installed at both ends of the fixing plate. 
         [0038]    The slider assembly may further comprise third permanent magnets fixedly installed at positions on the sliding plate, near a position where a direction of the urging force of the up/down positioning means is changed while the sliding plate is moved, such that repulsive or attractive forces are generated between the third permanent magnets and any one pair of the first permanent magnets of the fixing plate. 
         [0039]    The slider assembly may further comprise a pair of first permanent magnets installed at both ends of the fixing plate, respectively, to face the sliding plate; and a pair of second permanent magnets fixedly installed at positions on the cover of the cellular phone such that the sliding plate is kept stationary at an up or down position due to an attractive force generated between the first and second permanent magnets. 
         [0040]    The slider assembly may further comprise third permanent magnets fixedly installed at positions on the sliding plate, near a position where a direction of the urging force of the up/down positioning means is changed while the sliding plate is moved, such that repulsive or attractive forces are generated between the third permanent magnets and any one pair of the first permanent magnets of the fixing plate. 
         [0041]    Preferably, the guide section of the fixing plate includes a pair of opposite and parallel fixing grooves, each formed by bending twice a side portion of the fixing plate, and a pair of guide bushes fitted and installed in the fixing grooves, respectively, each guide bush having a guide groove for receiving a side of the sliding plate and guiding a sliding motion of the sliding plate; and the sliding plate includes a pair of wing sections formed by bending both sides thereof, each wing section is inserted in the guide groove of the corresponding guide bush to be linearly slid along the guide groove. 
         [0042]    The slider assembly may further comprise dampers made of a material softer than the guide bush and installed at both longitudinal ends of the guide bush to protrude from a longitudinal end of the fixing plate for absorbing shock generated due to collision against the sliding plate fixed to the cover of the cellular phone, wherein a plurality of through holes are formed on a bent side of each fixing groove of the guide section, and protrusions are formed on surfaces of the guide bush and damper facing the fixing groove of the guide section are inserted and fixed in the through holes. Preferably, the guide bushes are made of polyoxymethylene (POM) and the damper is made of urethane rubber. 
         [0043]    According to a further aspect of the present invention, there is provided a sliding-type cellular phone which comprises a main body with a plurality of keys provided on a surface thereof, a cover slidably installed over the surface of the main body and having a crystal liquid display installed on a front surface thereof, and the foregoing slider assembly, the slider assembly fixedly installed between the main body and the cover, wherein the fixing plate of the slider assembly is fixedly installed at the main body, and the sliding plate of the slider assembly is installed at the cover. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0044]      FIG. 1  is a perspective view of a cellular phone including a slider assembly for a sliding-type cellular phone according to an embodiment of the present invention. 
           [0045]      FIG. 2  is a plan view of a slider assembly for the sliding-type cellular phone according to a first embodiment of the present invention. 
           [0046]      FIG. 3  is a perspective view of an up/down positioning means of the slider assembly according the first embodiment of the present invention. 
           [0047]      FIG. 4  is an exploded perspective view of the up/down positioning means shown in  FIG. 3 . 
           [0048]      FIG. 5  ( a ) to ( c ) are views illustrating the operating state of the embodiment shown in  FIG. 2 . 
           [0049]      FIG. 6  is a perspective view of an up/down positioning means of a slider assembly according a second embodiment of the present invention. 
           [0050]      FIG. 7  is a plan view of a slider assembly for a sliding-type cellular phone according to a third embodiment of the present invention. 
           [0051]      FIG. 8  is a sectional view taken along line A-A of  FIG. 7 . 
           [0052]      FIG. 9  is a perspective view of an up/down positioning means of a slider assembly according a fourth embodiment of the present invention. 
           [0053]      FIG. 10  is an exploded perspective view of the up/down positioning means shown in  FIG. 9 . 
           [0054]      FIG. 11  ( a ) to ( c ) are views illustrating the operation state of the slider assembly according to the third embodiment of the present invention shown in  FIG. 7 . 
           [0055]      FIG. 12  is a perspective view of an up/down positioning means of a slider assembly according a fifth embodiment of the present invention. 
           [0056]      FIG. 13  is a plan view showing a coupled state of a hinge section of the up/down positioning means of the slider assembly according to the third to fifth embodiments of the present invention. 
           [0057]      FIG. 14  is an exploded perspective view of a slider assembly for a sliding-type cellular phone according to a sixth embodiment of the present invention. 
           [0058]      FIG. 15  is a view showing a state where the slider assembly of the sixth embodiment shown in  FIG. 14  has been assembled. 
           [0059]      FIG. 16  is a plan view of a slider assembly for a sliding-type cellular phone according to a seventh embodiment of the present invention. 
           [0060]      FIG. 17  is an exploded perspective view of a fixing plate of the embodiment shown in  FIG. 16 . 
           [0061]      FIG. 18  is a perspective view of a sliding plate of the embodiment shown in  FIG. 16 . 
           [0062]      FIG. 19  is an exploded perspective view of a slider assembly for a sliding-type cellular phone according to an eighth embodiment of the present invention. 
           [0063]      FIG. 20  is an exploded perspective view of a fixing plate in a slider assembly for a sliding-type cellular phone according to a ninth embodiment of the present invention. 
           [0064]      FIG. 21  is a perspective view of a sliding plate in the slider assembly for the sliding-type cellular phone according to the ninth embodiment of the present invention. 
           [0065]      FIG. 22  is a sectional view of an up/down positioning means according to the ninth embodiment of the present invention, in which  FIG. 22  ( a ) is a sectional view showing a state before the sliding plate is pushed in one direction,  FIG. 22  ( b ) is a section view showing a state when a repulsive force between a third permanent magnet of the sliding plate and a first permanent magnet of the fixing plate is generated, and  FIG. 22  ( c ) is a sectional view showing a state after the sliding plate has been pushed in one direction. 
           [0066]      FIG. 23  is an exploded perspective view of a slider assembly for a sliding-type cellular phone according to a tenth embodiment of the present invention. 
           [0067]      FIG. 24  is a bottom view of the sliding-type cellular phone with the slider assembly according to the ninth and tenth embodiments of the present invention installed therein. 
           [0068]      FIG. 25  is a schematic view of an exemplary slider assembly. 
           [0069]      FIG. 26  is a schematic view of an exemplary slider assembly. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0070]    Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0071]      FIG. 1  is a perspective view of a cellular phone including a slider assembly for a sliding-type cellular phone according to an embodiment of the present invention,  FIG. 2  is a plan view of a slider assembly for the sliding-type cellular phone according to a first embodiment of the present invention,  FIG. 3  is a perspective view of an up/down positioning means of the slider assembly according the first embodiment of the present invention,  FIG. 4  is an exploded perspective view of the up/down positioning means shown in  FIG. 3 , and  FIG. 5  ( a ) to ( c ) are views illustrating the operating state of the embodiment shown in  FIG. 2 . 
         [0072]    The sliding-type cellular phone of  FIG. 1  comprises a main body  1  on which a plurality of keys  3  are installed, and a cover  2  installed slidably over a surface of the main body  1  on which the keys  3  are installed. A liquid crystal display  4  is installed on a front surface of the cover  2 . In the sliding-type cellular phone as described above, a slider assembly  100  is installed between the main body  1  and the cover  2 . In such a case, a fixing plate  10  is installed on the main body  1  and a sliding plate  20  is installed slidably on the cover  2 . 
         [0073]    The slider assembly of the sliding-type cellular phone according to this embodiment comprises a fixing plate  10  fixed to the main body of the cellular phone, a sliding plate  20  fixed to the cover, and an up/down positioning means  30  including one end hinged to the fixing plate  10  and the other end hinged to the sliding plate  20  to change a direction of a force for pushing the sliding plate  20  from a specific sliding location of the sliding plate  20 . Guide grooves  171  and guide bars  112  for guiding the sliding movement are formed at both sides of the fixing plate  10  and sliding plate  20 , as shown in  FIG. 26 . 
         [0074]    Referring to  FIGS. 3 and 4 , the up/down positioning means  30  comprises a pair of link sliders  31  with the same shape that can be restricted and slid with respect to each other, a pair of tension springs  32  fixed respectively to opposite ends of the link sliders, and guide protrusions  313  fixed to the link sliders  31 , respectively, each of which is received in a guide slot  312  formed on each link slider to restrict and guide the link sliders. In this embodiment, a guide pin formed with a head  313   a  and a neck  313   b  is used as the guide protrusion  313 . 
         [0075]    Each of the link sliders  31  is formed with a hinge section  311  which has a through hole formed therein and is hinged to the fixing or sliding plate  10  or  20  by fitting a pin into the through hole, the guide slot  312  spaced apart from the hinge section  311  and formed in a longitudinal direction at a certain length, and a pair of spring engaging sections  314  formed at the other end thereof opposite to the hinge section to protrude laterally outward from the other end. The hinge sections  311  are bent at two steps to be easily fixed to the fixing plate  10  and the sliding plate  20  and to allow the tension springs  32  to be installed in a space defined between the two hinge sections. 
         [0076]    In this embodiment, the guide slot  312  is composed of a guide pin-receiving portion  312   a  and a sliding guide portion  312   b.  The guide pin-receiving portion  312   a  of the guide slot  312  is formed adjacent to the hinge section  311  to have a width greater than a diameter of the head  313   a  of the guide pin  313  such that the guide pin  313  can be easily installed to or removed from the up/down positioning means. 
         [0077]    Further, the sliding guide portion  312   b  has an appropriate length to restrict a sliding length of the cover of the cellular phone. That is, since the movement of the guide pin  313  is restricted at an end of the sliding guide portion  312   b  opposite to the hinge section  311 , the sliding length of the sliding plate  20  is restricted. Accordingly, there is no need to install an additional stopper on the main body of the cellular phone for restricting the sliding motion of the sliding plate  20 . Further, the sliding length of the sliding plate  20  can be adjusted by changing a position where the guide pin  313  is fixed. 
         [0078]    In a pair of the link sliders  31  arranged to face each other, the guide pin  313  of the link slider  31  is received in the guide slot  312  of the corresponding link slider  31  to restrict and guide the sliding motion of each link slider  31  in only a longitudinal direction. Further, the guide pin  313  is composed of the head  313   a  and the neck  313   b  calked and fixed to the link slider  31 . In such a case, a diameter of the head  313   a  is greater than a width of the sliding guide portion  312   b  of the guide slot  312  to prevent the assembled up/down positioning means from being disassembled. 
         [0079]    Each of the pair of spring engaging sections  314  is formed with a hook recess  314   a  at a side facing away from the hinge section  311  such that a hook formed at an end of the tension spring  32  can be hooked into the hook recess. Further, as described in an embodiment shown in  FIG. 6 , through holes  314   b  can be formed on the spring engaging sections  314  to prevent the tension springs  32  from being separated from the spring engaging sections. 
         [0080]    As compared with an up/down positioning means using a torsion spring, the up/down positioning means  30  according to an embodiment of the present invention has improved durability since it uses the tension springs. Further, it is possible to manufacture a cellular phone in which a constant urging force for sliding the slider assembly is required. Furthermore, since the pair of the tension springs  32  are fixed symmetrically to the spring engaging sections  314  of the linker sliders  31 , the stable sliding motion of the link sliders  31  can be obtained. Since the tension spring  32  is fixed to the end of the link slider  31  to always impart an elastic force to the link slider  31  in a direction in which the entire length of the combined link sliders is increased, the sliding plate  20  can be always kept in a state where it is moved upward or downward (up/down) with respect to the fixing plate  10 . 
         [0081]    Hereinafter, the operation of the slider assembly according to this embodiment of the present invention will be described with reference to  FIG. 5  ( a ) to ( c ). 
         [0082]      FIG. 5  ( a ) shows a state where the two link sliders  31  are slid at a maximum distance from each other by a tension of the tension springs such that the entire length of the combined link sliders  31  is increased to the utmost. That is, the guide pin is brought into contact with an end of the guide slot away from the hinge section, and thus, the sliding motion of the slider link is restricted. The hinge section  311  of the first link slider of the up/down positioning means  30  is hinged to a middle portion of the fixing plate  10  by means of a pin, and the hinge section  311  of the second link slider is hinged to a middle portion of the sliding plate  20  by means of a pin. If a user pushes the sliding plate  20  leftward as viewed in the figure, the sliding plate  20  is slid and the tension springs  32  of the up/down positioning means are stretched while the respective link sliders  31  are pivoted on the pins, as shown in  FIG. 5  ( b ). A pair of link sliders  31  that are restricted and combined with each other are slid toward the hinge sections of the corresponding link sliders, respectively, so that a change in the entire length of the combined link sliders due to the sliding motion of the sliding plate  20  can be absorbed. In a state shown in  FIG. 5  ( b ), the tension of the tension spring  32  is maximized and the entire length of the link sliders  31  is minimized. Since the tension springs  32  are stretched until they are in such a state as shown in  FIG. 5  ( b ), a user continuously apply a certain force to move the sliding plate  20 . However, if the sliding plate  20  is slightly further moved leftward from the state shown in  FIG. 5  ( b ), the sliding plate  20  is automatically moved leftward due to elastic energy stored in the tension spring  32 . That is, while the pair of tension springs  32  are compressed, each of the tension springs pulls the link slider  31  fixed to the ends thereof to be closer to each other. Thus, the link slider  31  fixed to the sliding plate  20  pushes the sliding plate  20  which in turn is moved to such a state as shown in  FIG. 5  ( c ). The sliding motion of the sliding plate from the state shown in  FIG. 5  ( c ) to the state shown in  FIG. 5  ( a ) is repeated in the same manner as to be described above. At this time, since the neck  313   b  of the guide pin  313  is brought into contact with the end of the sliding guide portion  312   b  to restrict the movement of the sliding plate  20 , there is no need to provide an additional stopper in the main body of the cellular phone for restricting the sliding motion of the sliding plate  20 . 
         [0083]      FIG. 6  is a perspective view of an up/down positioning means of a slider assembly according a second embodiment of the present invention. The up/down positioning means of  FIG. 6  is different from that of  FIG. 4  in that the guide pin  313  is replaced with a guide protrusion  313  formed by partially cutting a certain portion of a guide slider  31  corresponding to a guide slot  312  adjacent to a hinge section  311  of another link slider  31  and then bending the partially cut portion toward a guide slot  312 . Further, a width of a head of the guide protrusion  313  so formed is greater than a width of the guide slot to prevent a pair of assembled link sliders from being separated from each other. 
         [0084]      FIG. 7  is a plan view of a slider assembly for the sliding-type cellular phone according to a third embodiment of the present invention,  FIG. 8  is a sectional view taken along line A-A in  FIG. 7 ,  FIG. 9  is a perspective view of an up/down positioning means of a slider assembly according a fourth embodiment of the present invention,  FIG. 10  is an exploded perspective view of the up/down positioning means shown in  FIG. 9 ,  FIG. 11  ( a ) to ( c ) are views illustrating an operation state of the slider assembly according to the third embodiment of the present invention shown in  FIG. 7 ,  FIG. 12  is a perspective view of an up/down positioning means of a slider assembly according a fifth embodiment of the present invention, and  FIG. 13  is a plan view showing a coupled state of a hinge section of the up/down positioning means of the slider assembly according to the third to fifth embodiments of the present invention. 
         [0085]    The slider assembly for the sliding-type cellular phone according to the third embodiment of the present invention comprises a fixing plate  10  fixed to the main body of the cellular phone, a sliding plate  20  fixed to a cover, and an up/down positioning means  30  including one end hinged to the fixing plate  10  and the other end hinged to the sliding plate  20  to change a direction of a force for pushing the sliding plate  20  from a specific sliding location of the sliding plate  20 . In order to prevent opposite sliding sides of the fixing plate  10  and sliding plate  20  from wearing out due to friction therebetween, guide bushes  122  are fitted into guide grooves  121  of the sliding plate  20 , respectively. 
         [0086]    Each of the guide bushes  122  is composed of a groove  122   a  in which a guide section  111  of the fixing plate  10 , a fixing protrusion  122   b  formed on one side thereof to be spaced apart by a certain interval, and an attaching surface  122   c  fitted into the guide groove  121  of the sliding plate  20 . Further, the guide bushes prevent the guide grooves  121  of the sliding plate  20 , which are repeatedly slid, from wearing out and can be used for a long time without frequent exchange. In addition, the guide bushes may be made of a wear resistant material with a low dynamic coefficient of friction, and preferably, from polyoxymethylene (POM) that has been generally used. 
         [0087]    Referring to  FIGS. 9 and 10 , the up/down positioning means  30  comprises a pair of link sliders  31  with the same shape that can be restricted and slid with respect to each other, a pair of tension springs  32  fixed respectively to ends of the link sliders  31 , and guide protrusions  313  fixed to the link sliders  31 , respectively, each of which is received in a guide slot  312  formed on each link slider  31  to restrict and guide the link sliders. In this embodiment, a guide pin formed with a head  313   a  and a neck  313   b  is used as the guide protrusion  313 . 
         [0088]    Each of the link sliders  31  comprises a hinge section  311  having a through hole  311   a  and hinged to the fixing or sliding plate  10  or  20  by fitting a pin P into the through hole, the guide slot  312  spaced apart from the hinge section  311  and formed in a longitudinal direction at a certain length, and a pair of spring engaging sections  314  formed at the other end thereof opposite to the hinge section  311  to protrude laterally outward from the other end. The hinge sections  311  are bent at two steps to be easily fixed to the fixing plate  10  and the sliding plate  20  and to allow the tension springs  32  to be installed in a space defined between the two hinge sections. 
         [0089]    In the fourth embodiment, the guide slot  312  is composed of a guide pin-receiving portion  312   a  and a sliding guide portion  312   b.  The guide pin-receiving portion  312   a  of the guide slot  312  is formed adjacent to the hinge section  311  to have a width greater than a diameter of the head  313   a  of the guide pin  313  such that the guide pin  313  can be easily installed to or removed from the up/down positioning means. 
         [0090]    In a pair of the link sliders  31  arranged to face each other, the guide pin  313  of the link slider  31  is received in the guide slot  312  of the corresponding link slider  31  to restrict and guide the sliding motion of each link slider  31  in only a longitudinal direction. Further, the guide pin  313  is composed of the head  313   a  and the neck  313   b  calked and fixed to the link slider  31 . In such a case, a diameter of the head  313   a  is greater than a width of the sliding guide portion  312   b  of the guide slot  312  to prevent the assembled up/down positioning means from being disassembled. 
         [0091]    Each of the pair of spring engaging sections  314  is formed with a hook recess  314   a  bent at a predetermined angle such that a hook formed at an end of the tension spring  32  can be caught into the hook recess. Further, a fixing protrusion  314   b  is formed at an end of the hook recess  314   a  so as to prevent the hook from being removed from the recess. In addition, as described in an embodiment shown in  FIG. 12 , through holes  314   c  can be formed on the spring engaging sections to prevent the tension springs  32  from being separated from the spring engaging sections 
         [0092]    The reason that the hook recess  314   a  is bent at the predetermined angle is that a flexible printed circuit board (PCB) installed on one surface of the fixing plate  10  can be operated without any interference with the up/down positioning means in order to prevent the malfunction of the cellular phone. 
         [0093]    As compared with an up/down positioning means using a torsion spring, the up/down positioning means  30  of this embodiment has improved durability since it uses the tension springs. Further, it is possible to manufacture a cellular phone in which a constant urging force for sliding the slider assembly is required. Furthermore, since the pair of the tension springs  32  are fixed symmetrically to the spring engaging sections  314  of the linker sliders  31 , the stable sliding motion of the link sliders  31  can be obtained. Since the tension spring  32  is fixed to the end of the link slider  31  to always impart an elastic force to the link slider  31  in a direction in which the entire length of the combined link sliders is increased, the sliding plate  20  can be always kept in a state where it is moved upward or downward (up/down) with respect to the fixing plate  10 . 
         [0094]    Hereinafter, the operation of the slider assembly according to the embodiment shown in  FIG. 7  will be described with reference to  FIG. 11  ( a ) to ( c ). 
         [0095]      FIG. 11  ( a ) shows a state where the two link sliders  31  are slid at a maximum distance from each other by a tension of the tension springs such that the entire length of the combined link sliders  31  is increased to the utmost. That is, the guide pin is brought into contact with an end of the guide slot away from the hinge section, and thus, the sliding motion of the slider link is restricted. The hinge section  311  of the first link slider of the up/down positioning means  30  is hinged to a middle portion of the fixing plate  10  by means of a pin, and the hinge section  311  of the second link slider is hinged to a middle portion of the sliding plate  20  by means of a pin. If a user pushes the sliding plate  20  leftward as viewed in the figure, the sliding plate  20  is slid and the tension springs  32  of the up/down positioning means are stretched while the respective link sliders  31  are pivoted on the pins, as shown in  FIG. 11  ( b ). A pair of link sliders  31  that are restricted and combined with each other are slid toward the hinge sections of the corresponding link sliders, respectively, so that a change in the entire length of the combined link sliders due to the sliding motion of the sliding plate  20  can be absorbed. In a state shown in  FIG. 11  ( b ), the tension of the tension spring  32  is maximized and the entire length of the link sliders  31  is minimized. Since the tension springs  32  are stretched until they are in such a state as shown in  FIG. 11  ( b ), a user continuously apply a certain force to move the sliding plate  20 . However, if the sliding plate  20  is slightly further moved leftward from the state shown in  FIG. 11  ( b ), the sliding plate  20  is automatically moved leftward due to elastic energy stored in the tension spring  32 . That is, while the pair of tension springs  32  are compressed, each of the tension springs pulls the link slider  31  fixed to the ends thereof to be closer to each other. Thus, the link slider  31  fixed to the sliding plate  20  pushes the sliding plate  20  which in turn is moved to such a state as shown in  FIG. 11  ( c ). The sliding motion of the sliding plate from the state shown in  FIG. 11  ( c ) to the state shown in  FIG. 11  ( a ) is repeated in the same manner as to be described above. At this time, since the neck  313   b  of the guide pin  313  is brought into contact with the end of the sliding guide portion  312   b  to restrict the movement of the sliding plate  20 , there is no need to provide an additional stopper in the main body of the cellular phone for restricting the sliding motion of the sliding plate  20 . 
         [0096]      FIG. 12  is a perspective view of an up/down positioning means of a slider assembly according the fifth embodiment of the present invention. The up/down positioning means of  FIG. 12  is different from that of  FIG. 9  in that the guide pin  313  is replaced a guide protrusion  313  by partially cutting a certain portion of a guide slider  31  corresponding to a guide slot  312  adjacent to a hinge section  311  of another link slider  31  and then bending the partially cut portion toward a guide slot  312 . Further, a width of a head of the guide protrusion  313  so formed is greater than a width of the guide slot to prevent a pair of assembled link sliders from being separated from each other. 
         [0097]      FIG. 13  is a plan view showing a coupled state of a hinge section of the up/down positioning means of the slider assembly according to the third to fifth embodiments of the present invention. Each of a pair of the link sliders  31  with the same shape, which can be restricted and slid with respect to each other, among the up/down positioning means  30  is formed with a hinge section  311  which has a through hole formed therein and is hinged to the fixing or sliding plate  10  or  20  by fitting a pin into the through hole. 
         [0098]    At this time, since the hinge section  311  coupled with the pin P is easily worn down due to friction therebetween when the link slider is pivoted on the pin, a bushing  40  made of a wear resistant material such as polyoxymethylene (POM) with a low dynamic coefficient of friction is inserted between the hinge section  311  and the pin P to prevent the hinge section from wearing out. 
         [0099]    The bushing  40  includes a through hole  42  formed at the center thereof, a contact surface  43  contacted with one side of the hinge section  311 , and a fixing protrusion  41  fitted and fixed into the through hole  311  la of the hinge section  311 . The bushing  40  and the hinge section  311  can be coupled with each other by the fixing protrusion  41  in the form of a key. Preferably, the fixing protrusion is in the form of a groove. When the hinge section is pivoted, an inner surface of the through hole  42  of the bushing  40  fitted and fixed into the hinge section  311  is brought into contact with the pin P. Thus, the hinge section  311  and the pin P can be prevented from wearing out. 
         [0100]      FIG. 14  is an exploded perspective view of a slider assembly for the sliding-type cellular phone according to a sixth embodiment of the present invention, and  FIG. 15  is a view showing a state where the slider assembly of the sixth embodiment shown in  FIG. 14  has been assembled. 
         [0101]    The slider assembly of the sixth embodiment comprises a fixing plate  10  fixed to a main body  1  of the cellular phone, a sliding plate  20  fixed to a cover  2 , two springs  50  each of which has one end hingedly fixed to the fixing plate  10  and the other end hingedly fixed to the sliding plate  20 , and sliding members  15  and  15 ′ for preventing the sliding portions of the fixing plate  10  and sliding plate  20  from wearing out. 
         [0102]    Both longitudinal side sections  14  and  14 ′ of the fixing plate  10  are bent twice by a press, and thus, parallel fixing grooves  13  and  13 ′ are formed at both side sections, respectively. A plurality of screw holes  12  are formed in the fixing plate  10  by a punching process such that the fixing plate  10  can be fixed to the main body  1  of the cellular phone. In particular, two supporting protrusions  11  and  11 ′ are formed on the fixing plate  10  along a straight line parallel to the fixing grooves  13  and  13 ′. Each of the supporting protrusions  11  and  11 ′ is formed by the press working to protrude toward the sliding plate  20  and has a circular outer circumferential surface and an expanded end portion  11   a.    
         [0103]    Further, the sliding members  15  and  15 ′ with guide grooves  15   b  and  15   b ′ formed thereon are inserted and installed in the fixing grooves  13  and  13 ′, respectively. The sliding member has the same length as the fixing groove. 
         [0104]    The sliding member is fixed to the fixing plate in such a manner that a pair of protrusions  15   a  and  15   a ′ formed on the sliding member  15  or  15 ′ at a certain interval are fitted and fixed into cutouts  14   a  and  14   a ′ formed at certain positions on the bent side section  14  or  14 ′ of the fixing plate  10 , respectively. Further, the sliding members prevent wing sections  23  and  23 ′ of the sliding plate  20 , which are repeatedly slid, from wearing out and can be used for a long time without frequent exchange. In addition, the sliding members may be made of a wear resistant material with a low dynamic coefficient of friction, and preferably, from polyoxymethylene (POM) that has been generally used. 
         [0105]    The sliding plate  20  includes first bent sections  24  and  24 ′ that are formed on both sides of the sliding plate by bending a side portion of the sliding plate toward the fixing plate  10  through the press working, and the wing sections  23  and  23 ′ formed to extend outward by bending the first bending sections  24  and  24 ′ once more. A pair of the wing sections  23  and  23 ′ are fitted into the guide grooves  15   b  and  15   b ′ of the sliding members  15  and  15 ′, respectively, that are installed in the fixing grooves  13  and  13 ′ of the fixing plate  10 , respectively, such that the sliding plate can be slid in a longitudinal direction. Further, the sliding plate  20  is formed with two through holes  21  and  21 ′ in which one ends of the springs  30  and  30 ′ are inserted such that the springs are hingedly supported. In addition, a plurality of screw holes  22  are formed in the sliding plate  20  such that the sliding plate can be fixed to the cover. 
         [0106]    Each of the two springs  30  and  30 ′ is a coil spring, made of steel wire, of which both ends are extended. A spring portion  33  formed by winding several times the steel wire is formed at the center of the coil spring. One end  32  of the spring has a round shape such that it can surround a portion of the outer circumference of the circular supporting protrusion  11  of the fixing plate  10 . The other end  51  of the spring is bent first in a direction perpendicular to a plane defined by the circularly bent end  32  and then in a direction perpendicular to an extending direction of the first bent portion of the other end of the spring such that the second bent portion can be inserted in and pivoted on the through hole  21  of the sliding plate  20 . 
         [0107]      FIG. 15  is a view showing a state where the slider assembly of the sixth embodiment has been assembled. 
         [0108]    As shown in the figure, the wing sections  23  and  23 ′ formed at both sides of the sliding plate  20  are inserted in the respective guide grooves  15   b  and  15   b ′ of the sliding members  15  and  15 ′ installed in the fixing grooves  13  and  13 ′ formed at both sides of the fixing plate  10 , so that the sliding plate  20  can be slid in a longitudinal direction along the guide grooves  15   b  and  15   b ′. Further, one end of each of the two springs  50  surrounds a portion of the supporting protrusion  11  of the fixing plate  10  such that the spring can be pivoted with respect to the fixing plate, while the other end  51  of the spring is inserted in the through hole  21  of the sliding plate  20  such that the spring can be pivoted with respect to the sliding plate. Therefore, the sliding plate  20  is restricted by the springs  50  such that it is moved up and down within a predetermined distance. 
         [0109]    In addition, if the springs  50  are broken, the one end of the spring  50  surrounding the supporting protrusion  11  of the fixing plate  10  can be easily separated and removed from the fixing plate. Thus, the broken spring can be easily exchanged. 
         [0110]    In particular, the two supporting protrusions  11  and  11 ′ of the fixing plate  10  are disposed in a straight line parallel to the fixing grooves  13  and  13 ′, and the two through holes  21  and  21 ′ of the sliding plate  20  are also disposed in a straight line parallel to the wing section  23  to be inserted in the recess grooves  13  and  13 ′. That is, an imaginary straight line connecting the supporting protrusions  11  and  11 ′ is in parallel to the fixing grooves  13  and  13 ′, and the supporting protrusions  11  and  11 ′ are disposed such that a distance is as great as possible. When the sliding plate  20  is moved up and down, therefore, an amount of deformation of the spring becomes smaller, and thus, the life span of the spring  50  can be prolonged. Further, the one ends of the two springs  50  and  50 ′ are pivotally fixed to the same side with respect to the fixing groove  13 ′, and the other ends of the two springs are pivotally fixed to the same side with respect to the fixing groove  13 . Therefore, when the sliding plate is slid, an elastic force of each spring is applied in only one direction. Consequently, since the wing section  23  of the sliding plate  20  is slid along the fixing groove  13  of the fixing plate  10  in a state where the former is brought into contact with the latter, it is possible to prevent the cover from shaking from side to side when the cover is slid. 
         [0111]    Furthermore, until the center of the through hole  21  of the sliding plate  20  is coincident with the center of the supporting protrusion  11  of the fixing plate  10  after the sliding plate  20  has been moved, an elastic force of the spring  50  or  50 ′ is applied in a direction in which the sliding motion of the sliding plate is hindered. Once the sliding plate has passed through a position where the through hole is coincident with the supporting protrusion, an elastic force of the spring is applied in a direction in which the sliding motion of the sliding plate is promoted. Therefore, if a user wants to slide and open the cover, the user can merely apply a certain force to the cover only until the center of the through hole  21  or  21 ′ of the sliding plate  20  is coincident with the center of the supporting protrusion  11  or  11 ′ of the fixing plate  10 , because the cover is then slid automatically by the elastic force of the springs  50  and  50 ′. 
         [0112]      FIG. 16  is a plan view of a slider assembly for the sliding-type cellular phone according to a seventh embodiment of the present invention,  FIG. 17  is an exploded perspective view of a fixing plate of the embodiment shown in  FIG. 16 ,  FIG. 18  is a perspective view of a sliding plate of the embodiment shown in  FIG. 16 , and  FIG. 19  is an exploded perspective view of a slider assembly for the sliding-type cellular phone according to an eighth embodiment of the present invention. 
         [0113]    The slider assembly  100  for the sliding-type cellular phone according to the seventh embodiment of the present invention comprises a fixing plate  10  formed with a guide section for guiding a linear motion of a sliding plate and fixed to an surface of a main body of the sliding-type cellular phone, a sliding plate  20  guided linearly by the guide section of the fixing plate  10  and fixed to an opposite surface of a cover of the cellular phone, and an up/down positioning means  30  including one end hinged to the fixing plate  10  and the other end hinged to the sliding plate  20  to change a direction of a force for pushing the sliding plate  20  from a specific sliding location of the sliding plate  20 . Further, in order to prevent both sliding sides of the fixing plate  10  and sliding plate  20  from wearing out, guide bushes  14  and  14  are inserted and installed in fixing grooves  12  and  12 ′ of the fixing plate  10 , respectively. 
         [0114]      FIG. 17  is an exploded perspective view of the fixing plate  10 . Referring to this figure, each of both side sections  13  and  13  of the fixing plate  10  includes a pair of opposite and parallel fixing grooves  12  and  12 ′ formed by twice bending a side portion of the fixing plate through the press working, and a plurality of through holes  13   a  and  13   a ′ formed on the first bent side of the fixing grooves  12  and  12 ′. Further, the fixing plate  10  is formed with a plurality of screw holes for fixing the fixing plate to the main body  1  of the cellular phone and a hinge hole  11  into which one end of the up/down positioning means  30  is fitted. 
         [0115]    Each of the guide bushes  14  and  14 ′ fitted respectively into the fixing grooves  12  and  12 ′ in a longitudinal direction comprises a longitudinal guide groove  14   a  or  14   a ′ for receiving the wing section  23  or  23 ′ of the sliding plate  20  and guiding the sliding motion of the sliding plate, and a plurality of protrusions  14   a  or  14   b ′ formed on a surface corresponding to the through holes  13   a  or  13   a ′ of the fixing plate  10 . 
         [0116]    Each of dampers  15  and  15 ′ installed at both longitudinal ends of the guide bushes  14  or  14 ′ includes a protrusion  15  or  15 ′ fixed in the though hole  13   a  or  13   a ′ and protruding further from a longitudinal end of the fixing plate  10 , and a guide groove  15   b  or  15   b ′ for guiding the wing section  23  or  23 ′ of the sliding plate  20 . When the two dampers are installed at both ends of the guide bush  14  or  14 ′, the guide groove  14   a  or  14   a  of the guide bush  14  or  14 ′ and the guide groove  15   b  or  15   b ′ of the damper  15  or  15 ′ are aligned on the same line. 
         [0117]    The guide bushes  14  and  14 ′ prevent the fixing grooves of the fixing plate from wearing out due to friction with the wing sections  23  and  23 ′ of the sliding plate  20  which are repeatedly slid and can be made of a wear resistant material with a low dynamic coefficient of friction such that it can be used for a long time without frequent exchange. Preferably, the guide bushes are made of polyoxymethylene (POM) that has been generally used. Further, the dampers  15  and  15 ′ absorb shock generated when the sliding plate is slid and prevents the shock from being transferred to the guide bushes  14  and  14 ′ and thus the guide bushes from being damaged. Preferably, the dampers  15  and  15 ′ are made of urethane rubber with an excellent shock-absorbing property. 
         [0118]      FIG. 18  is a perspective view of the sliding plate  10 . Referring to this figure, the sliding plate  20  includes a plurality of screw holes used for fixing the sliding plate to the cover, a hinge hole  21  into which the other end of the up/down positioning means  30  is fitted, bent sections  22  and  22 ′ formed at both lateral sides of the sliding plate by bending side portions of the sliding plate toward the fixing plate  10  using a press, and wing sections  23  and  23 ′ formed by additionally bending portions of the bent sections to extend outward. A pair of the wing section  23  and  23 ′ are inserted into the guide grooves of the guide bush  14  and  14 ′ and damper  15  and  15 ′ installed in the fixing groove  12  and  12 ′ of the fixing plate  10 , respectively, such that the sliding plate can be slid up and down in a longitudinal direction. 
         [0119]      FIG. 19  is an exploded perspective view of the slider assembly of the eighth embodiment of the present invention. Referring to this figure, the up/down positioning means comprises a pair of link sliders  31  with the same shape that can be restricted and slid with respect to each other, a pair of tension springs  32  fixed respectively to ends of the link sliders  31 , and guide pins  313  fixed respectively to the link sliders  31 , each of which is received in a guide slot  312  formed on each link slider  31  to restrict and guide the link sliders and includes a head  313   a  and a neck  313   b.    
         [0120]    Each of the link sliders  31  comprises a hinge section  311  having a through hole and hinged to the fixing or sliding plate  10  or  20  by fitting a pin into the through hole, a guide slot  312  spaced apart from the hinge section  311  and formed in a longitudinal direction at a certain length, and a pair of spring engaging sections  314  formed at the other end thereof opposite to the hinge section  311  to protrude laterally outward from the other end. 
         [0121]    The hinge sections  311  are bent at two steps to be easily fixed to the fixing plate  10  and the sliding plate  20  and to allow the tension springs  32  to be installed in a space defined between the two hinge sections. The guide slot  312  is composed of a guide pin-receiving portion  312   a  and a sliding guide portion  312   b.  The guide pin-receiving portion  312   a  of the guide slot  312  is formed adjacent to the hinge section  311  to have a width greater than a diameter of the head  313   a  of the guide pin  313  such that the guide pin  313  can be easily installed to or removed from the up/down positioning means. 
         [0122]    In a pair of the link sliders  31  arranged to face each other, the guide pin  313  of the link slider  31  is received in the guide slot  312  of the corresponding link slider  31  to restrict and guide the sliding motion of each link slider  31  in only a longitudinal direction. Further, the guide pin  313  is composed of the head  313   a  and the neck  313   b  calked and fixed to the link slider  31 . In such a case, a diameter of the head  313   a  is greater than a width of the sliding guide portion  312   b  of the guide slot  312  to prevent the assembled up/down positioning means from being disassembled. 
         [0123]    Each of the pair of spring engaging sections  314  is formed with a hook recess  314   a  bent at a predetermined angle such that a hook formed at an end of the tension spring  32  can be caught into the hook recess. 
         [0124]    Since the pair of the tension springs  32  are fixed symmetrically to the spring engaging sections  314  in the linker sliders  31 , the stable sliding motion of the link sliders  31  can be obtained. Since the tension spring  32  is fixed to the end of the link slider  31  to always impart an elastic force to the link slider  31  in a direction in which the entire length of the combined link sliders is increased, the sliding plate  20  can be always kept in a state where it is moved upward or downward (up/down) with respect to the fixing plate  10 . 
         [0125]    The operation of the up/down positioning means according to this embodiment of the present invention will be briefly explained. The sliding motion of the link sliders is restricted when the entire length of the link sliders  31  combined by the tension of the tension springs is maximized. That is, the guide pin  313  is brought into contact with an end of the guide slot  312  opposite to the hinge section  311  to restrict the sliding motion of the slider link. The hinge section  311  of the first link slider of the up/down positioning means  30  is hinged to a middle portion of the fixing plate  10  by means of a pin, and the hinge section  311  of the second link slider is hinged to a middle portion of the sliding plate  20  by means of a pin. 
         [0126]    If a user pushes the sliding plate  20 , the sliding plate  20  is slid and the tension springs  32  of the up/down positioning means  30  are stretched while the respective link sliders  31  hinged thereto are pivoted on the pins. At the same time, a pair of the link sliders  31  that are restricted and combined with each other are slid toward the hinge sections of the corresponding link sliders, respectively, so that a change in the entire length of the combined link sliders due to the sliding motion of the sliding plate  20  can be absorbed. At this time, the tension of the tension spring  32  is maximized and the entire length of the link sliders  31  is minimized. 
         [0127]    As described above, the tension springs  32  are stretched up to a maximum stretched position, and thus, a user apply the force to the sliding plate  20  in order to further move the sliding plate. After the maximum stretched position, the sliding plate  20  will be automatically slid due to elastic energy stored in the tension springs  32  in a direction in which the user wants to push the sliding plate. That is, while the pair of tension springs  32  are compressed, each of the tension springs pulls the link slider  31  fixed to the ends thereof to be closer to each other. Thus, the link slider  31  fixed to the sliding plate  20  pushes the sliding plate  20 . 
         [0128]    With the up/down positioning means  30  according to an embodiment of the present invention, it is possible to manufacture a cellular phone in which a constant urging force for sliding the slider assembly is required. 
         [0129]      FIG. 19  is an exploded perspective view of the slider assembly for the sliding-type cellular phone according to the eighth embodiment of the present invention, in which the up/down positioning means of the slider assembly is different from that of the seventh embodiment of the present invention. 
         [0130]    The slider assembly of this embodiment comprises a fixing plate  10 ′ fixed to a main body of the cellular phone, a sliding plate  20 ′ fixed to a cover, an up/down positioning means including one end hinged to the fixing plate  10 ′ and the other end hinged to the sliding plate  20 ′, and guide bushes  14  and  14 ′ and dampers  15  and  15 ′ for preventing sliding portions of the fixing plate  10 ′ and sliding plate  20 ′ from wearing out. 
         [0131]    Two supporting protrusions  11  and  11 ′ are further formed on the fixing plate  10 ′ in a straight line parallel to the fixing grooves  12  and  12 ′. Each of the supporting protrusions  11  and  11 ′ is formed by the press working to protrude toward the sliding plate  20 ′ and has a circular outer circumferential surface and an extended end portion  11   a.    
         [0132]    In the meantime, the shape and function of the guide bushes  14  and  14 ′ and the dampers  15  and  15 ′ inserted in the fixing grooves  12  and  12 ′ in a longitudinal direction are the same as those described in the seventh embodiment. 
         [0133]    Further, the sliding plate  20 ′ includes first bent sections  22  and  22 ′ that are formed on both sides of the sliding plate by bending a side portion of the sliding plate toward the fixing plate  10 ′ through the press working, and wing sections  23  and  23 ′ formed to extend outward by bending the first bending sections  22  and  22 ′ once more. A pair of the wing sections  23  and  23 ′ are fitted into the guide grooves of the guide bushes  14  and  14 ′ and the dampers  15  and  15 ′, respectively, that are installed in the fixing grooves  12  and  12 ′ of the fixing plate  10 ′, respectively, such that the sliding plate can be slid up and down in a longitudinal direction. Further, the sliding plate  20 ′ is formed with two through holes  21  and  21 ′ in which one ends of the springs  50  and  50 ′ are inserted such that the springs are hingedly supported. In addition, a plurality of screw holes are formed in the sliding plate  20 ′ such that the sliding plate can be fixed to the cover. 
         [0134]    Each of the two springs  50  and  50 ′ serving as an up/down positioning means is a coil spring, made of steel wire, of which both ends are extended. A spring portion  53  formed by winding several times steel wire is formed at the center of the coil spring. One end  52  of the spring has a round shape such that it can surround a portion of the outer circumference of the circular supporting protrusion  11  of the fixing plate  10 ′. The other end  51  of the spring is bent first in a direction perpendicular to a plane defined by the circularly bent end  52  and then in a direction perpendicular to an extending direction of the first bent portion of the other end of the spring such that the second bent portion can be inserted in and pivoted on the through hole  21  of the sliding plate  20 ′. 
         [0135]    The operation of the up/down positioning means  50  of this embodiment will be briefly explained. That is, the wing sections  23  and  23 ′ formed at both sides of the sliding plate  20 ′ are inserted in the respective guide grooves  14   a,    14   a ′,  15   b  and  15   b ′ of the guide bushes  14  and  14 ′ and dampers  15  and  15 ′ installed in the fixing grooves  12  and  12 ′ formed at both sides of the fixing plate  10 ′, so that the sliding plate  20 ′ can be slid up and down in a longitudinal direction along the guide grooves  14   a,    14   a ′,  15   b  and  15   b ′. Further, one end  52  of each of the two springs  50  surrounds a portion of the supporting protrusion  11  of the fixing plate  10 ′ such that the spring can be pivoted with respect to the fixing plate, while the other end  51  of the spring is inserted in the through hole  21  of the sliding plate  20 ′ such that the spring can be pivoted with respect to the sliding plate. Therefore, the sliding plate  20 ′ is restricted by the springs  50  such that it is moved up and down within a predetermined distance. 
         [0136]    In particular, the two supporting protrusions  11  and  11 ′ of the fixing plate  10 ′ are disposed in a straight line parallel to the fixing grooves  12  and  12 ′, and the two through holes  21  and  21 ′ of the sliding plate  20 ′ are also disposed in a straight line parallel to the wing section  23  to be inserted in the recess grooves  12  and  12 ′. That is, an imaginary straight line connecting the supporting protrusions  11  and  11 ′ is in parallel to the fixing grooves  12  and  12 ′, and the supporting protrusions  11  and  11 ′ are disposed such that a distance is as great as possible. When the sliding plate  20 ′ is moved up and down, therefore, an amount of deformation of the spring  50  or  50 ′ becomes smaller, and thus, the life span of the spring  50  or  50 ′ can be prolonged. Further, the one ends of the two springs  50  and  50 ′ are pivotally fixed to the same side with respect to the fixing groove  13 ′, and the other ends of the two springs are pivotally fixed to the same side with respect to the fixing groove  13 . Therefore, when the sliding plate is slid, an elastic force of each spring is applied in only one direction. Consequently, since the wing section  23  of the sliding plate  20 ′ is slid along the fixing groove  12  of the fixing plate  10 ′ in a state where the former is brought into contact with the latter, it is possible to prevent the cover from shaking from side to side when the cover is slid. 
         [0137]    Furthermore, until the center of the through hole  21  of the sliding plate  20 ′ is coincident with the center of the supporting protrusion  11  of the fixing plate  10 ′ after the sliding plate  20 ′ has been moved, an elastic force of the spring  50  or  50 ′ is applied in a direction in which the sliding motion of the sliding plate is hindered. Once the sliding plate has passed through a position where the through hole is coincident with the supporting protrusion, an elastic force of the spring  50  or  50 ′ is applied in a direction in which the sliding motion of the sliding plate is promoted. Therefore, if a user wants to slide and open the cover, the user can merely apply a certain force to the cover only until the center of the through hole  21  of the sliding plate  20 ′ is coincident with the center of the supporting protrusion  11  of the fixing plate  10 ′, because the cover is then slid automatically by the elastic force of the springs  50  and  50 ′. 
         [0138]    In a case where the respective plates of this embodiment are made of stainless steel, the holes for assembling the slider assembly or the through holes for supporting the ends of the springs can be manufactured at one time through the press working. Therefore, the manufacture can be easily made and the production costs can also be saved. 
         [0139]    Further, the guide bushes prevent the wing sections of the sliding plate from wearing out and can be made of a wear resistant material with a low dynamic coefficient of friction, such as polyoxymethylene (POM), such that it can be used for a long time without frequent exchange. The dampers are preferably made of urethane rubber with an excellent shock-absorbing property such that they can absorb shock generated when the sliding plate is slid and prevent the shock from being transferred to the guide bushes and thus the guide bushes from being damaged. 
         [0140]      FIG. 20  is an exploded perspective view of a fixing plate of a slider assembly for the sliding-type cellular phone according to a ninth embodiment of the present invention; FIG.  21  is a perspective view of a sliding plate of the slider assembly for the sliding-type cellular phone according to the ninth embodiment of the present invention;  FIG. 22  is a sectional view of an up/down positioning means according to the ninth embodiment of the present invention, in which  FIG. 22  ( a ) is a sectional view showing a state before the sliding plate is pushed in one direction,  FIG. 22  ( b ) is a section view showing a state when a repulsive force between a third permanent magnet of the sliding plate and a first permanent magnet of the fixing plate is generated, and  FIG. 22  ( c ) is a sectional view showing a state after the sliding plate has been pushed in one direction;  FIG. 23  is an exploded perspective view of a slider assembly for the sliding-type cellular phone according to a tenth embodiment of the present invention; and  FIG. 24  is a bottom view of the sliding-type cellular phone with the slider assembly according to the ninth and tenth embodiments of the present invention installed therein. 
         [0141]    The slider assembly for the sliding-type cellular phone according to this embodiment of the present invention comprises a fixing plate  10  formed with a guide section for guiding a linear motion of a sliding plate and fixed to an surface of a main body of the sliding-type cellular phone, a sliding plate  20  guided linearly by the guide section of the fixing plate  10  and fixed to an opposite surface of a cover of the cellular phone, and an up/down positioning means  30  including one end hinged to the fixing plate  10  and the other end hinged to the sliding plate  20  to change a direction of a force for pushing the sliding plate  20  from a specific sliding location of the sliding plate  20 . Further, in order to prevent both sliding sides of the fixing plate  10  and sliding plate  20  from wearing out, guide bushes  14  and  14 ′ are inserted and installed in fixing grooves  12  and  12 ′ of the fixing plate  10 , respectively. 
         [0142]      FIG. 20  is an exploded perspective view of the fixing plate  10 . Referring to this figure, each of both side sections  13  and  13 ′ of the fixing plate  10  includes a pair of opposite and parallel fixing grooves  12  and  12 ′ formed by twice bending a side portion of the fixing plate through the press working, and a plurality of through holes  13   a  and  13   a ′ formed on the first bent side of the fixing grooves  12  and  12 ′. Further, a pair of first permanent magnets  16  or  16 ′ are provided on predetermined positions of each of side ends of the fixing plate  10 , and the fixing plate  10  is formed with a plurality of screw holes for fixing the fixing plate to the main body  1  of the cellular phone and a hinge hole  11  into which one end of the up/down positioning means  30  is fitted. 
         [0143]    Each of the guide bushes  14  and  14 ′ inserted respectively into the fixing grooves  12  and  12 ′ in a longitudinal direction comprises a longitudinal guide groove  14   a  or  14   a ′ for receiving the wing section  23  or  23 ′ of the sliding plate  20  and guiding the sliding motion of the sliding plate, and a plurality of protrusions  14   b  or  14   b ′ formed on a surface corresponding to the through holes  13   a  or  13   a ′ of the fixing plate  10 . 
         [0144]    Each of dampers  15  and  15 ′ installed at both longitudinal ends of the guide bushes  14  or  14 ′ includes a protrusion  15  or  15 ′ fixed in the though hole  13   a  or  13   a ′ and protruding further from a longitudinal end of the fixing plate  10 , and a guide groove  15   b  or  15   b ′ for guiding the wing section  23  or  23 ′ of the sliding plate  20 . When the two dampers are installed at both ends of the guide bush  14  or  14 ′, the guide groove  14   a  or  14   a  of the guide bush  14  or  14 ′ and the guide groove  15   b  or  15   b ′ of the damper  15  or  15 ′ are aligned on the same line. 
         [0145]    The guide bushes  14  and  14 ′ prevent the fixing grooves of the fixing plate from wearing out due to friction with the wing sections  23  and  23 ′ of the sliding plate  20  which are repeatedly slid and can be made of a wear resistant material with a low dynamic coefficient of friction such that it can be used for a long time without frequent exchange. Preferably, the guide bushes are made of polyoxymethylene (POM) that has been generally used. Further, the dampers  15  and  15 ′ absorb shock generated when the sliding plate is slid and prevents the shock from being transferred to the guide bushes  14  and  14 ′ and thus the guide bushes from being damaged. Preferably, the dampers  15  and  15 ′ are made of urethane rubber with an excellent shock-absorbing property. 
         [0146]      FIG. 21  is a perspective view of the sliding plate  20 . Referring to this figure, the sliding plate  20  includes a plurality of screw holes used for fixing the sliding plate to the cover, a hinge hole  21  into which the other end of the up/down positioning means  30  is fitted, bent sections  22  and  22 ′ formed at both lateral sides of the sliding plate by bending side portions of the sliding plate toward the fixing plate  10  using the press working, and wing sections  23  and  23 ′ formed by additionally bending portions of the bent sections to extend outward. A pair of the wing section  23  and  23 ′ are inserted into the guide grooves of the guide bush  14  and  14 ′ and damper  15  and  15 ′ installed in the fixing groove  12  and  12 ′ of the fixing plate  10 , respectively, such that the sliding plate can be slid up and down in a longitudinal direction. 
         [0147]    Second permanent magnets  24  and  24 ′ are installed at positions on the sliding plate  20  where the sliding plate  20  can be urged outward at the up/down position of the sliding plate  20  due to repulsive or attractive forces generated between the second permanent magnets and the first permanent magnets  16  and  16 ′ installed at both ends of the fixing plate  10 . Further, third permanent magnets  25  and  25 ′ are installed at positions where a direction of an urging force of the sliding plate  20  slid along the fixing plate  10  is changed, such that repulsive or attractive forces are generated between the third permanent magnets and the first permanent magnets  16  and  16 ′. 
         [0148]    In a case where the first permanent magnets  16  and  16 ′ of the fixing plate  10  have N-polarity, the second permanent magnets  24  and  24 ′ of the sliding plate  20  corresponding to the first permanent magnets can have N-polarity or S-polarity. If the second permanent magnets  24  and  24 ′ have N-polarity, a repulsive force is generated between the first permanent magnets  16  and  16 ′ and the second permanent magnets  24  and  24 ′, and thus, the first and second permanent magnets repel each other. At this time, the first permanent magnets  16  and  16 ′ of the fixing plate  10  is located at an outer side of the second permanent magnets  24  and  24 ′ of the sliding plate  20 . 
         [0149]    On the other hand, if the second permanent magnets  24  and  24 ′ have S-polarity, an attractive force is generated between the first and second permanent magnets, and thus, the first permanent magnets  16  and  16 ′ and the second permanent magnets attract each other. At this time, the first permanent magnets  16  and  16 ′ of the fixing plate  10  is located at an inner side of the second permanent magnets  24  and  24 ′ of the sliding plate  20 . 
         [0150]    As described above, since a repulsive force is exerted when the polarities of the magnets of the fixing plate  10  and sliding plates  20  are the same as each other and an attractive force is exerted when the polarities of the magnets of the fixing plate and sliding plate are different from each other, the arrangement of the magnets can be made properly in various ways according to positions of the first permanent magnets  16  and  16 ′ of the fixing plate  10  and the second permanent magnets  24  and  24 ′ of the sliding plate  20 . 
         [0151]    The operation of the slider assembly of this embodiment will be described with reference to  FIG. 22 .  FIG. 22  ( a ) shows a state where the fixing plate  20  (→ 10 ) is placed at a lower portion of the sliding plate  20 . In such a state, the second permanent magnet  24  of the sliding plate  20  having N-polarity is located at an inner side of the first permanent magnet  16  of the fixing plate  10  having N-polarity, and thus, the repulsive force is generated between the first and second permanent magnets. Therefore, unless a certain force is applied downward to the sliding plate  20 , the state shown in  FIG. 22  is maintained because the first and second permanent magnets  16  and  24  repel each other. 
         [0152]    As shown in  FIG. 22  ( b ), if the sling plate  20  is pushed downward, the sliding plate  20  is moved by the up/down positioning means. At this time, while the sliding plate  20  is moved, it is stopped in a moment at a position (i.e., a dead zone) in which the direction of the urging force of the up/down positioning means is changed. In order to prevent this phenomenon from occurring, the third permanent magnet  25  is further installed at a position on the sliding plate  20 , at which the dead zone is created, to generate a repulsive force between the first and third permanent magnets  16  and  25 . Therefore, if the sliding plate  20  is pushed downward and then reaches near the position of the dead zone, the sliding plate  20  is smoothly moved at the dead zone in a direction in which the direction of the urging force is changed, due to a repulsive force generated between the third and first permanent magnets  25  and  16 . 
         [0153]    Furthermore, even though an attractive force is generated between the first and second permanent magnets  16  and  25  due to their polarity difference, the sliding plate can smoothly pass through the dead zone without stopping at the dead zone. 
         [0154]    If the fixing plate  10  is placed at an upper portion of the sliding plate  20  that has passed through the dead zone as described above, a repulsive force is generated between the first permanent magnet  16  provided at an upper end of the fixing plate  10  and the second permanent magnet  24  provided at an upper end of the sliding plate  20 . Therefore, unless a certain force is applied upward to sliding plate  20 , a current state is maintained because the first and second permanent magnets  16  and  24  repel each other. 
         [0155]      FIG. 23  is an exploded perspective view of a slider assembly for the sliding-type cellular phone according to the tenth embodiment of the present invention. 
         [0156]    The slider assembly of this embodiment comprises a fixing plate  10 ′ fixed to a main body of the cellular phone, a sliding plate  20 ′ fixed to a cover, an up/down positioning means including one end hinged to the fixing plate  10 ′ and the other end hinged to the sliding plate  20 ′, and guide bushes  14  and  14 ′ and dampers  15  and  15 ′ for preventing sliding portions of the fixing plate  10 ′ and sliding plate  20 ′ from wearing out. 
         [0157]    Further, first permanent magnets  16  and  16 ′ are installed at both ends of the fixing plate  10 ′, respectively, and second permanent magnets  24  and  24  are installed at positions on the sliding plate  20 ′ where the sliding plate  20 ′ can be urged outward due to repulsive or attractive forces generated between the second permanent magnets and the first permanent magnets  16  and  16 ′. In addition, third permanent magnets  25  and  25 ′ are installed at certain positions on the sliding plate  20 ′, near a position where the direction of an urging force of the up/down positioning means is changed while the sliding plate is moved, such that repulsive or attractive forces are generated between the third permanent magnets and any one pair of the first permanent magnets  16  and  16 ′ of the fixing plate  10 ′. 
         [0158]    Two supporting protrusions  11  and  11 ′ are further formed on the fixing plate  10 ′ in a straight line parallel to the fixing grooves  12  and  12 ′. Each of the supporting protrusions  11  and  11 ′ is formed by the press working to protrude toward the sliding plate  20 ′ and has a circular outer circumferential surface and an extended end portion  11   a.    
         [0159]    In the meantime, the guide bushes  14  and  14 ′ and the dampers  15  and  15 ′ inserted in the fixing grooves  12  and  12 ′ in a longitudinal direction are the same as those described in the ninth embodiment. 
         [0160]    Further, the sliding plate  20 ′ includes first bent sections  22  and  22 ′ that are formed on both sides of the sliding plate by bending a side portion of the sliding plate toward the fixing plate  10 ′ through the press working, and wing sections  23  and  23 ′ formed to extend outward by bending the first bending sections  22  and  22 ′ once more. A pair of the wing sections  23  and  23 ′ are fitted into the guide grooves of the guide bushes  14  and  14 ′ and dampers  15  and  15 ′, respectively, that are installed in the fixing grooves  12  and  12 ′ of the fixing plate  10 ′, respectively, such that the sliding plate can be slid up and down in a longitudinal direction. Further, the sliding plate  20 ′ is formed with two through holes  21  and  21 ′ in which one ends of the springs  50  and  50 ′ are inserted such that the springs are hingedly supported. In addition, a plurality of screw holes are formed in the sliding plate  20 ′ such that the sliding plate can be fixed to the cover. 
         [0161]    Each of the two springs  50  and  50 ′ serving as an up/down positioning means is a coil spring, made of steel wire, of which both ends are extended. A spring portion  53  formed by winding steel wire several times is formed at the center of the coil spring. One end  52  of the spring has a round shape such that it can surround a portion of the outer circumference of the circular supporting protrusion  11  of the fixing plate  10 ′, The other end  51  of the spring is bent first in a direction perpendicular to a plane defined by the circularly bent end  52  and then in a direction perpendicular to an extending direction of the first bent portion of the other end of the spring such that the second bent portion can be inserted in and pivoted on the through hole  21  of the sliding plate  20 ′. 
         [0162]    The operation of the up/down positioning means  50  of this embodiment will be briefly explained. That is, the wing sections  23  and  23 ′ formed at both sides of the sliding plate  20 ′ are inserted in the respective guide grooves  14   a,    14   a ′,  15   b  and  15   b ′ of the guide bushes  14  and  14 ′ and dampers  15  and  15 ′ installed in the fixing grooves  12  and  12 ′ formed at both sides of the fixing plate  10 ′, so that the sliding plate  20 ′ can be slid up and down in a longitudinal direction along the guide grooves  14   a,    14   a ′,  15   b  and  15   b ′. Further, one end  52  of each of the two springs  50  surrounds a portion of the supporting protrusion  11  of the fixing plate  10 ′ such that the spring can be pivoted with respect to the fixing plate, while the other end  51  of the spring is inserted in the through hole  21  of the sliding plate  20 ′ such that the spring can be pivoted with respect to the sliding plate. Therefore, the sliding plate  20 ′ is restricted by the springs  50  and  50 ′ such that it is moved up and down within a predetermined distance. 
         [0163]    In particular, the two supporting protrusions  11  and  11 ′ of the fixing plate  10 ′ are disposed in a straight line parallel to the fixing grooves  12  and  12 ′, and the two through holes  21  and  21 ′ of the sliding plate  20 ′ are also disposed in a straight line parallel to the wing section  23  to be inserted in the recess grooves  12  and  12 ′. That is, an imaginary straight line connecting the supporting protrusions  11  and  11 ′ is in parallel to the fixing grooves  12  and  12 ′, and the supporting protrusions  11  and  11 ′ are disposed such that a distance is as great as possible. When the sliding plate  20 ′ is moved up and down, therefore, an amount of deformation of the spring  50  or  50 ′ becomes smaller, and thus, the life span of the spring  50  or  50 ′ can be prolonged. Further, the one ends of the two springs  50  and  50 ′ are pivotally fixed to the same side with respect to the fixing groove  13 ′, and the other ends of the two springs are pivotally fixed to the same side with respect to the fixing groove  13 . Therefore, when the sliding plate is slid, an elastic force of each spring is applied in only one direction. Consequently, since the wing section  23  of the sliding plate  20 ′ is slid along the fixing groove  12  of the fixing plate  10 ′ in a state where the former is brought into contact with the latter, it is possible to prevent the cover from shaking from side to side when the cover is slid. 
         [0164]    Furthermore, until the center of the through hole  21  of the sliding plate  20 ′ is coincident with the center of the supporting protrusion  11  of the fixing plate  10 ′ after the sliding plate  20 ′ has been moved, an elastic force of the spring  50  or  50 ′ is applied in a direction in which the sliding motion of the sliding plate is hindered. Once the sliding plate has passed through a position where the through hole is coincident with the supporting protrusion, an elastic force of the spring  50  or  50 ′ is applied in a direction in which the sliding motion of the sliding plate is promoted. Therefore, if a user wants to slide and open the cover, the user can merely apply a certain force to the cover only until the center of the through hole  21  of the sliding plate  20 ′ is coincident with the center of the supporting protrusion  11  of the fixing plate  10 ′, because the cover is then slid automatically by the elastic force of the springs  50  and  50 ′. 
         [0165]    Hereinafter, a sliding-type cellular phone including the above slider assembly will be described. 
         [0166]      FIG. 24  is a bottom view of the sliding-type cellular phone including the slider assembly according to the ninth and tenth embodiments of the present invention. Referring to this figure, the sliding-type cellular phone  1000  comprises the slider assembly which includes a fixing plate  10  installed on a main body  1 , a sliding plate  20  installed on a cover  2 , and an up/down positioning means  30  for allowing the sliding plate  20  to be moved. 
         [0167]    A pair of first permanent magnets  16  and  16 ′ are installed at each of both ends of the fixing plate  10 , and a pair of third permanent magnets  25  and  25 ′ are installed at positions on the sliding plate  20  where a dead zone is created, such that a repulsive or attractive force is generated between the first permanent magnets  16  and  16 ′ and the third permanent magnets  25  and  25 ′. Even in the dead zone, therefore, the sliding plate  20  can be smoothly and continuously moved in a direction in which the direction of an urging force of the up/down positioning means is changed. 
         [0168]    Second permanent magnets  2   a  and  2   a ′ are installed at both ends of the cover  2  of the cellular phone, at which the sliding plate  20  is installed, to face the first permanent magnets  16  and  16 ′, such that an attractive force is generated between the first and second permanent magnets. That is, if the cover  2  of the cellular phone is pushed upward, the cover  2  is firmly kept stationary in a state where the cover has been opened, because an attractive force is generated between the first permanent magnets  16  and  16 ′ provided at a lower end of the fixing plate  10  and the second permanent magnets  2  and  2 ′ provided at a lower end of the cover  2  due to their polarity difference. 
         [0169]    On the other hand, if the cover  2  of the cellular phone is pushed downward, the cover  2  is firmly kept stationary in a state where the cover is closed, because an attractive force is generated between the first permanent magnets  16  and  16 ′ provided at an upper end of the fixing plate  10  and the second permanent magnets  2  and  2 ′ provided at an upper end of the cover  2  of the cellular phone due to their polarity difference. 
         [0170]    According to embodiments of the present invention so configured, since the up/down positioning means of the slider assembly can restrict a sliding length of the sliding plate, an additional stopper for restricting the sliding length needs not be installed on the main body or cover of the sliding-type cellular phone. Therefore, the manufacturing costs can be saved. 
         [0171]    Since a tension spring are is used as an elastic means for maintaining an up/down state of the sliding plate instead of a torsion spring, the durability of the slider assembly can be improved. Further, it is possible to provide a cellular phone with more uniform urging force required for pushing the cover upward or downward as compared with a case where the torsion spring is used. 
         [0172]    Since the sliding member with a low coefficient of friction is installed in the guide groove of the sliding plate that is slid along the fixing plate, the durability of the sliding plate can be improved and sliding noise can also be reduced. In addition, since the spring engaging section is formed to prevent the up/down positioning means from interfering with the flexible printed circuit board mounted within the cellular phone, any inconvenience due to the malfunction of the cellular phone can be eliminated and the cellular phone can be used for a long time. 
         [0173]    In addition, the manufacturing costs and working hour can be saved and the productivity can also be enhanced by providing the slider assembly including a fixing plate and a sliding plate which are manufactured through the press working such that there is no need for additional machining processes for the next assembly. 
         [0174]    According to embodiments of the present invention, there is an advantage in that the durability can be improved and the sliding noise can also be reduced, since the sliding member with a low coefficient of friction is installed in the fixing groove of the fixing plate that is slid along the sliding plate. 
         [0175]    Since the slider assembly is configured such that an amount of deformation of the spring is minimized when the sliding plate is slid up and down, the expected life span of the spring can be prolonged. Further, since the respective fixing and sliding plates are made of stainless steel, the plates cannot be easily damaged from shock, whereby the durability can also be increased. 
         [0176]    Since a shock-absorbing member made of a soft material is further installed at both ends of the guide bushes, the guide buses are not broken due to shock generated when the cover of the cellular phone is opened or closed or when the cellular phone is dropped. Thus, the cellular phone can be used for a long time and incidental expenses can be saved. Further, since the sliding plate installed on the cover of the cellular phone is brought into contact with the shock-absorbing member rather than the fixing plate even though the cover with the sliding plate installed thereon is frequently slid, noise due to the shock is not generated. 
         [0177]    According to embodiments of the present invention, since the permanent magnets are further installed at predetermined positions on the sliding plate to correspond to the permanent magnets installed on the fixing plate, the sliding plate can be smoothly and continuously slid up and down. Further, since a plurality of permanent magnets are installed at both ends of the fixing plate and sliding plate to generate an attractive or repulsive force between the magnets, the cover of the cellular phone can be firmly kept at its up or down state even though the spring in the up/down positioning means is weakened.