Abstract:
Disclosed herein is a vibration actuator. The vibration actuator excites a mass member by interaction between an electric field of a vibration coil provided in an inner space of a case and a magnetic field of a magnetic field unit disposed corresponding to the vibration coil. The vibration actuator comprises an elastic wire having a wire body fixed to the outer surface of the mass member and elastic ends fixed to the inner surface of the case. The elastic wire is connected between the case and the mass member for elastically supporting mass member. The present invention minimizes change of natural frequency due to manufacturing tolerance of raw materials to improve vibration characteristics of the vibration actuator, simplifies and reduces a manufacturing process to improve productivity of the vibration actuator, and improves durability to increase the service life of the vibration actuator.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Korean Application Number 2005-10702, filed Feb. 4, 2005, the disclosure of which is incorporated by reference herein in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a vibration actuator, and, more particularly, to a vibration actuator that is capable of minimizing change of natural frequency due to manufacturing tolerance of raw materials to improve vibration characteristics of the vibration actuator, simplifying and reducing a manufacturing process to improve productivity of the vibration actuator, and improving durability to increase the service life of the vibration actuator.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, a mobile communication device, such as a mobile phone or a pager, incorporates a vibration actuator that is capable of individually or simultaneously outputting sound or vibration. The vibration actuator outputs a voice signal, which is electrically or electronically received, or a previously inputted bell or melody as audible sound, or resonates at a specific frequency to output an incoming signal as vibration that a person can feel.  
         [0006]      FIG. 13  is a cross-sectional view illustrating a conventional vibration actuator  1 . As shown in  FIG. 13 , the conventional vibration actuator  1  comprises a case  1   a  formed in the shape of a hollow cylinder. The case  1   a  has an opened lower part, which is closed by a shield plate  2 . Also, the case  1   a  has an opened upper part, at which is securely mounted a diaphragm  3 , which is a sound-generation oscillating plate, by a supporting ring  13 , which is separately fixed to the case  1   a . Specifically, the outer-circumferential part of the diaphragm  3  is securely inserted in the inner wall of the case  1   a . To the center of the lower surface of the diaphragm  3  is securely fixed a voice coil  4 .  
         [0007]     Between the shield plate  2  and the diaphragm  3  is disposed a plate spring  5 , which comprises a spring body  5   a  having an opened center part and a plurality of elastic legs  5   b  extending from the spring body  5   a . The elastic legs  5   b  are securely fixed to the inner wall of the case  1   a.    
         [0008]     To the lower surface of the plate spring  5  is integrally attached an upper surface of a mass member  6 . The mass member  6  has a mounting hole  6   a  formed through the center thereof such that a yoke  7  is inserted in the mounting hole  6   a  of the mass member and an engaging protrusion  6   b  extending from the outer circumferential part thereof such that the engaging protrusion  6   b  is engaged with the inner circumferential surface of the case  1   a.    
         [0009]     On the upper surface of the yoke  7 , which is inserted in the mounting hole  6   a  of the mass member  6 , is mounted a vertically magnetized magnet member  8 . On the magnet member  8  is disposed an upper plate  9 . The yoke  7 , the magnet member  8 , and the upper plate  9  constitute a magnetic field unit  10 .  
         [0010]     On the upper surface of the shield plate  2  is mounted a vibration coil  11 , which is disposed directly under the yoke  7 .  
         [0011]     When electric current is supplied to the vibration coil  11 , the mass member  6 , including the magnetic field unit  10 , is excited by an elastic force of the plate spring  5  due to interaction between the electric field generated by the vibration coil  11  and the magnetic field generated by the magnetic field unit  10 . As a result, the vibration actuator is vibrated.  
         [0012]     When electric current is supplied to the voice coil  4 , the diaphragm  3  is oscillated due to interaction between the electric field generated by the voice coil  4  and the magnetic field generated by the magnetic field unit  10 . As a result, sound is generated from the vibration actuator.  
         [0013]     The plate spring  5  provided at the conventional vibration actuator  1  is manufactured by processing a thin metal sheet according to a pressing process and a wire discharging process. During the pressing process and the wire discharging process, minute defects and cracks are generated at the cut surface of the plate spring. As a result, fatigue lifetime of the plate spring  5  is decreased, and therefore, the service life of the vibration actuator  1  is reduced.  
         [0014]     When the thickness of the plate spring  5  is changed by approximately 1 μm, stiffness of the plate spring  5  is increased or decreased by 2 gf/mm. Such stiffness change of the plate spring  5  directly affects natural frequency of the plate spring  5 . For this reason, it is necessary to strictly control the thickness of the plate spring  5 , which elastically supports the entire vibrator, including the mass member  6  and the magnetic field unit  10 . However, it is difficult to strictly control the thickness of the plate spring  5  due to the manufacturing process of the plate spring  5 , and therefore, it is difficult to uniformly maintain the natural frequency of the vibration actuator  1 .  
         [0015]     The mass member  6  is attached to the spring body  5   a  of the plate spring  5  by spot welding while the upper surface of the mass member  6  is in contact with the lower surface of the spring body  5   a  of the plate spring  5 , and ends of the elastic legs of the plate spring  5  are fixed to the inner circumferential surface of the case  1   a.    
         [0016]     The natural frequency of the vibration actuator  1  is sharply changed depending upon positions where the spot welding operation between the plate spring  5  and the mass member  6  has been performed, and therefore, the vibration characteristics of the vibration actuator  1  is deteriorated. Furthermore, the manufacturing process of the vibration actuator  1  is complicated, and therefore, productivity of the vibration actuator  1  is decreased.  
       SUMMARY OF THE INVENTION  
       [0017]     Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a vibration actuator that is capable of improving durability of an elastic member for elastically supporting a vibrator comprising a magnetic field unit and a mass member, thereby increasing the service life of the vibration actuator.  
         [0018]     It is another object of the present invention to provide a vibration actuator that is capable of uniformly maintaining natural frequency of an elastic member for elastically supporting a vibrator comprising a magnetic field unit and a mass member, thereby guaranteeing uniform performance of the vibration actuator and improving vibration characteristics of the vibration actuator.  
         [0019]     It is yet another object of the present invention to provide a vibration actuator that is capable of simplifying assembly of a mass member and an elastic member, thereby improving productivity of the vibration actuator.  
         [0020]     In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a vibration actuator for exciting a mass member by interaction between an electric field of a vibration coil provided in an inner space of a case and a magnetic field of a magnetic field unit disposed corresponding to the vibration coil, wherein the vibration actuator comprises: an elastic wire having a wire body fixed to the outer circumferential surface of the mass member and elastic ends fixed to the inner circumferential surface of the case, the elastic wire being connected between the case and the mass member for elastically supporting the mass member.  
         [0021]     Preferably, the mass member has a disposition groove formed, in a helical shape having at least one turn, at the outer circumferential surface thereof.  
         [0022]     Preferably, the elastic wire is composed of a coil spring comprising a coil body disposed in the disposition groove and elastic ends fixed to the inner circumferential surface of the case.  
         [0023]     Preferably, the wire body of the elastic wire is wound around the disposition groove of the mass member or forcibly fitted in the disposition groove of the mass member.  
         [0024]     Preferably, the mass member comprises: at least two mass disks having different diameters, the at least two mass disks being disposed while being vertically stacked; and a disposition groove provided between the at least two mass disks for allowing the middle part of the elastic wire to be disposed therein.  
         [0025]     Preferably, the mass member comprises: a hollow outer mass part having a disposition groove formed at the outer circumferential surface thereof, in a helical shape having at least one turn, and a center hole formed through the center thereof, the center hole having a predetermined size; and an inner mass part inserted in the center hole.  
         [0026]     More preferably, the mass member is made of a resin material having the disposition groove formed by molding.  
         [0027]     Preferably, the magnetic field unit comprises: a yoke fixed to the mass member; and a magnet mounted in the yoke. More preferably, the magnetic field unit further comprises: an upper plate disposed on the upper surface of the magnet.  
         [0028]     Preferably, the vibration actuator further comprises: a shield plate for closing an opened lower part of the case, the vibration coil being disposed on the upper surface of the shield plate.  
         [0029]     Preferably, the vibration actuator further comprises: a voice coil disposed at an opened upper part of the case for generating an electric field when electric current is supplied to the voice coil; and a diaphragm attached to the lower surface of the voice coil.  
         [0030]     In accordance with another aspect of the present invention, there is provided a vibration actuator for exciting a mass member by interaction between an electric field of a vibration coil provided in an inner space of a case and a magnetic field of a magnetic field unit disposed corresponding to the vibration coil, wherein the mass member has a disposition hole formed therein such that both ends of the disposition hole are exposed to the outside at the outer circumferential surface of the mass member, and the vibration actuator comprises: at least one elastic wire having a wire body disposed in the disposition hole of the mass member and elastic ends fixed to the inner circumferential surface of the case, the at least one elastic wire being connected between the case and the mass member for elastically supporting the mass member.  
         [0031]     Preferably, the mass member comprises: an upper mass member having an upper disposition groove formed at the lower surface thereof; and a lower mass member having a lower disposition groove formed at the upper surface thereof, the upper disposition groove and the lower disposition groove being vertically coupled with each other to form the disposition hole.  
         [0032]     Preferably, the mass member comprises: an upper mass member; a lower mass member; and a disposition groove formed at one of the surfaces of the upper and lower mass members opposite to each other when the upper mass member and the lower mass member are coupled with each other to form the disposition hole. More preferably, one of the upper and lower mass members is composed of a plate for covering the disposition groove to form the disposition hole.  
         [0033]     More preferably, the disposition hole is formed in the shape of a straight line or a curved line.  
         [0034]     Preferably, the upper and lower mass members have the same size and weight, or the upper and lower mass members have different sizes and weights.  
         [0035]     Preferably, the upper and lower mass members are vertically coupled with each other by a plurality of coupling members, by welding, or by a bonding agent.  
         [0036]     Preferably, the elastic wire is composed of a wire comprising: a wire body disposed in the disposition hole of the mass member; and a pair of elastic ends extending along the outer circumferential surface of the mass member and securely fixed to the inner circumferential surface of the case. Alternatively, the elastic wire may be composed of at least two wires, each comprising: one end fixedly disposed in the disposition hole of the mass member; and an elastic end extending along the outer circumferential surface of the mass member and securely fixed to the inner circumferential surface of the case.  
         [0037]     Preferably, the mass member is a weight having at least two fixing holes formed at the outer circumferential surface thereof while being spaced uniformly apart in the circumferential direction, and the elastic wire is composed of at least two wires each having one end fixedly inserted in the corresponding fixing hole of the mass member and an elastic end extending along the outer circumferential surface of the mass member and securely fixed to the inner circumferential surface of the case.  
         [0038]     Preferably, the mass member is a weight comprising: an upper mass member having a mounting hole formed therethrough and an upper groove formed at the lower surface thereof; and a lower plate having a lower groove formed at the upper surface thereof such that the lower groove and the upper groove together form a disposition space where the elastic wire is disposed when the lower groove is vertically coupled with the upper groove, and the elastic wire is composed of at least two wires disposed between the upper mass member and the lower plate, each of the at least two wires having an elastic end extending along the outer circumferential surface of the mass member and securely fixed to the inner circumferential surface of the case.  
         [0039]     Preferably, the mass member is a weight comprising: an upper mass member having an upper mounting hole formed therethrough and an upper groove formed at the lower surface thereof; a lower mass member having a lower mounting hole formed therethrough, the lower mounting hole corresponding to the upper mounting hole, and a first intermediate groove formed at the upper surface thereof, which corresponds to the upper groove, the lower mass member being vertically coupled with the upper mass member; and a lower plate having a lower groove formed at the upper surface thereof, which corresponds to a second intermediate groove formed at the lower surface of the lower mass member, the lower plate being vertically coupled with the lower mass member, and the elastic wire is composed of a pair of upper and lower wires disposed between the upper mass member and the lower mass member and between the lower mass member and the lower plate, respectively, each of the upper and lower wires having an elastic end extending along the outer circumferential surface of the mass member and securely fixed to the inner circumferential surface of the case.  
         [0040]     Preferably, the mass member is a weight comprising: a mass body having a mounting hole formed through the center thereof; and a fixing groove formed at the upper surface of the mass body for allowing one end of the at least one elastic wire to be vertically inserted therein, and the elastic wire is composed of at least two wires each having an elastic end extending along the outer circumferential surface of the mass member and securely fixed to the inner circumferential surface of the case.  
         [0041]     Preferably, the magnetic field unit comprises: a yoke fixed to the mass member; and a magnet mounted in the yoke. More preferably, the magnetic field unit further comprises: an upper plate disposed on the upper surface of the magnet.  
         [0042]     Preferably, the vibration actuator further comprises: a shield plate for closing an opened lower part of the case, the vibration coil being disposed on the upper surface of the shield plate.  
         [0043]     Preferably, the vibration actuator further comprises: a voice coil disposed at an opened upper part of the case for generating an electric field when electric current is supplied to the voice coil; and a diaphragm attached to the lower surface of the voice coil. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0045]      FIG. 1  is an assembled perspective view illustrating a vibration actuator according to a first preferred embodiment of the present invention;  
         [0046]      FIG. 2  is an exploded perspective view illustrating the vibration actuator according to the first preferred embodiment of the present invention;  
         [0047]      FIGS. 3   a ,  3   b ,  3   c ,  3   d  and  3   e  are perspective views respectively illustrating assembly of a mass member and an elastic wire provided at the vibration actuator according to the first preferred embodiment of the present invention;  
         [0048]      FIG. 4  is an assembled perspective view illustrating a vibration actuator according to a second preferred embodiment of the present invention;  
         [0049]      FIG. 5  is an exploded perspective view illustrating the vibration actuator according to the second preferred embodiment of the present invention;  
         [0050]      FIGS. 6   a  and  6   b  are an exploded perspective view and an assembled plan view respectively illustrating an example of a mass member and an elastic wire provided at the vibration actuator according to the second preferred embodiment of the present invention;  
         [0051]      FIGS. 7   a  and  7   b  are an exploded perspective view and an assembled plan view respectively illustrating another example of a mass member and an elastic wire provided at the vibration actuator according to the second preferred embodiment of the present invention;  
         [0052]      FIGS. 8   a  and  8   b  are an exploded perspective view and an assembled plan view respectively illustrating still another example of a mass member and an elastic wire provided at the vibration actuator according to the second preferred embodiment of the present invention;  
         [0053]      FIGS. 9   a  and  9   b  are an assembled perspective view and an exploded perspective view respectively illustrating an example of a mass member and an elastic wire provided at a case of the vibration actuator according to the present invention;  
         [0054]      FIGS. 10   a  and  10   b  are an assembled perspective view and an exploded perspective view respectively illustrating another example of a mass member and an elastic wire provided at the case of the vibration actuator according to the present invention;  
         [0055]      FIGS. 11   a  and  11   b  are an assembled perspective view and an exploded perspective view respectively illustrating another example of a mass member and an elastic wire provided at the case of the vibration actuator according to the present invention;  
         [0056]      FIGS. 12   a  and  12   b  are an assembled perspective view and an exploded perspective view respectively illustrating another example of a mass member and an elastic wire provided at the case of the vibration actuator according to the present invention; and  
         [0057]      FIG. 13  is a cross-sectional view illustrating a conventional vibration actuator. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0058]     Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.  
         [0059]      FIG. 1  is an assembled perspective view illustrating a vibration actuator  100  according to a first preferred embodiment of the present invention, and  FIG. 2  is an exploded perspective view illustrating the vibration actuator  100  according to the first preferred embodiment of the present invention.  
         [0060]     The vibration actuator  100  according to the first preferred embodiment of the present invention is incorporated in a wireless communication device for vertically exciting a vibrator due to interaction between an electric field and a magnetic field to generate an incoming signal as vibration that a person can feel, and to generate a voice signal or a previously inputted bell or melody as audible sound. As shown in  FIGS. 1 and 2 , the vibration actuator  100  comprises a case  110 , a vibration coil  120 , a mass member  130 , a magnetic field unit  140 , and an elastic wire  150 .  
         [0061]     The case  110  is an accommodating member having an inner space of a predetermined size defined therein such that a plurality of components is accommodated in the inner space of the case  110 .  
         [0062]     The case  110  has an opened lower part, to which a shield plate  115  is fixed to protect the inner space, which may be formed in the shape of a circle or an oval according to the form of the wireless communication terminal, from the outer environment.  
         [0063]     The vibration coil  120  is disposed on the upper surface of the shield plate  115 , which corresponds to the magnetic field unit  140 , for generating an electric field having a predetermined strength such that the vibration coil  120  outputs vibration due to interaction between the electric field of the vibration coil  120  and a magnetic field generated by the magnetic field unit  140 .  
         [0064]     The mass member  130  is a weight vertically movably disposed in the inner space of the case  110  via the elastic wire  150 . At the outer circumferential surface of the mass member  130  is formed a disposition groove  132 , in which a wire body  151  of the elastic wire  150  is disposed, while being exposed to the outside.  
         [0065]     The elastic wire  150  is an elastic member disposed between the case  110  and the mass member  130 . The wire body  151  of the elastic wire  150  is disposed in the disposition groove  132  formed at the outer circumferential surface of a mass body  131  of the mass member  130  for elastically supporting the mass member  130  in the inner space of the case  110 . The elastic wire  150  also has elastic ends  152 , which are fixed to the inner circumferential surface of the case  110 .  
         [0066]     As shown in  FIG. 3   a ,  3   b  or  3   c , the elastic wire  150  may be composed of a coil spring comprising a wire body  151 ;  151   a ;  151   b  disposed in a disposition groove  132 ;  132   b ;  132   b  formed, in a helical shape having at least one turn, at the outer circumferential surface of a mass body  131 ;  131   a ′  131   b  of the mass member  130 , and elastic ends  152 ;  152   a ;  152   b  fixed to the inner circumferential surface of the case  110 .  
         [0067]     The assembly of the mass member  130  and the elastic wire  150  is made as follows. The wire body  151 ;  151   a ;  151   b  may be wound around the disposition groove  132 ;  132   a ;  132   b  of the mass member  130 , or the wire body  151 ;  151   a ;  151   b  may be forcibly fitted in the disposition groove  132 ;  132   a ;  132   b  of the mass member  130 .  
         [0068]     As shown in  FIG. 3   d , the mass member  130  may comprise: at least two mass disks  131   c  and  133   c  having different diameters, the at least two mass disks  131   c  and  133   c  being disposed while being vertically stacked; and a disposition groove  132  provided between the at least two mass disks  131   c  and  133   c  for allowing the wire body  151  of the elastic wire  150  to be disposed therein.  
         [0069]     As shown in  FIG. 3   e , the mass member  130  may comprise: a hollow outer mass part  131   d  having a disposition groove  132   d  formed at the outer circumferential surface thereof, in a helical shape having at least one turn, for allowing the wire body  151  of the elastic wire  150  to be disposed therein and a center hole  134   d  formed through the center thereof, the center hole  134   d  having a predetermined size; and an inner mass part  133   d  inserted in the center hole  134   d.    
         [0070]     The outer mass part  131   d  may be made of a resin material having the disposition groove  132   d  and the center hole  134   d  formed by molding. Preferably, the outer mass part  131   d  made of the resin material may contain powder having high specific gravity, such as tungsten, to amplify a vertical exciting force together with the inner mass part  133   d , which is made of a material having high specific gravity.  
         [0071]     The magnetic field unit  140  disposed in the inner space of the case  110  comprises: a yoke  141  integrally fixed to the mass member  130  elastically supported by the elastic member  150 ; and a vertically magnetized magnet  142  mounted in the yoke  141 . Preferably, the magnetic field unit  140  further comprises: an upper plate  143  disposed on the upper surface of the magnet  142  for concentrating magnetic flux discharged from the magnet  142 , which generates a magnetic force having a predetermined strength.  
         [0072]     At the opened upper part of the case  110  is preferably disposed a voice coil  160  for generating an electric field having a predetermined strength, when electric current is supplied to the voice coil  160 , to output sound along with vibration. To the lower surface of the voice coil  160  is also preferably attached a diaphragm  170 .  
         [0073]     The diaphragm  170  is an oscillating plate having a thickness of 19 μm to 50 μm, which is manufactured by pressing a film material, such as polyetherimide (PEI), polyethylene terephthalate (PET) or polycarbonate (PC), at a high temperature of approximately 200° C. and at high pressure. The outer circumferential part of the diaphragm  170  is located at an inner upper end  117   a  of the case  110 , and is fixedly supported by a supporting ring  117 .  
         [0074]     At a predetermined position of the outer circumferential surface of the case  110  is mounted a terminal part  112  for supplying electric current having different frequency bands to the vibration coil  120  and the voice coil  160 . At the inner circumferential surface of the case  110  are mounted a plurality of engagement protrusions  114  having groove-shaped or hole-shaped engagement parts formed at the outer surfaces thereof, which correspond to the elastic ends  152  of the elastic wire  150 , such that the elastic ends  152  of the elastic wire  150  can be easily and quickly engaged into the engagement parts of the engagement protrusions  114 , respectively.  
         [0075]      FIG. 4  is an assembled perspective view illustrating a vibration actuator  200  according to a second preferred embodiment of the present invention,  FIG. 5  is an exploded perspective view illustrating the vibration actuator  200  according to the second preferred embodiment of the present invention, and  FIGS. 6   a  and  6   b  are an exploded perspective view and an assembled plan view respectively illustrating an example of a mass member and an elastic wire provided at the vibration actuator  200  according to the second preferred embodiment of the present invention.  
         [0076]     As shown in FIGS.  4  to  6 , the vibration actuator  200  according to the second preferred embodiment of the present invention comprises: a case  210 , a vibration coil  220 , a mass member  230 , a magnetic field unit  240 , and an elastic wire  250 , which are identical in construction to the components of the vibration actuator  100  according to the second preferred embodiment of the present invention, and therefore, a detailed description thereof will not be given.  
         [0077]     The mass member  230 , which is elastically supported by the elastic wire  250 , is a weight vertically movably disposed in the inner space of the case  210 . The mass member  230  has a mass body  231 . In the mass body  231  of the mass member  230  is formed a disposition hole  132 , both ends of which are exposed to the outside at the outer circumferential surface of the mass body  231  of the mass member  230 .  
         [0078]     Specifically, the disposition hole  232  of the mass member  230  comprises: an upper disposition groove  233   a  formed at the lower surface of an upper mass member  233  constituting the mass member  230 ; and a lower disposition groove  234   a  formed at the upper surface of a lower mass member  234  also constituting the mass member  230 . The upper disposition groove  233   a  and the lower disposition groove  234   a  are vertically coupled with each other to form the disposition hole  232 .  
         [0079]     In this case, the mass member  230  comprises: the upper mass member  233  having the upper disposition groove  233   a  formed at the lower surface thereof; and the lower mass member  234  having the lower disposition groove  234   a  formed at the upper surface thereof, which is opposite to the lower surface of the upper mass member  233  where the upper disposition groove  233   a  is formed. The upper mass member  233  and the lower mass member  234  are coupled with each other to form the disposition hole  232 . Alternatively, one of the upper and lower mass members  233  and  234  may be composed of a plate material for covering the upper disposition groove  233   a  or the lower disposition groove  234   a  to form the disposition hole  232 .  
         [0080]     Preferably, the disposition hole  232  is formed in the shape of a straight line or a curved line.  
         [0081]     Also, the upper and lower mass members  233  and  234 , which are coupled with each other to constitute the mass member  230 , may have the same size, and therefore, the upper and lower mass members  233  and  234  may have the same weight. Alternatively, the upper and lower mass members  233  and  234  may have different sizes, and therefore, the upper and lower mass members  233  and  234  may have different weights.  
         [0082]     The upper and lower mass members  233  and  234  are vertically coupled with each other by a plurality of coupling members. However, the upper and lower mass members  233  and  234  may be vertically coupled with each other by other means. For example, the upper and lower mass members  233  and  234  may be vertically coupled with each other by welding, or the upper and lower mass members  233  and  234  may be vertically coupled with each other by a bonding agent.  
         [0083]     The elastic wire  250 , which is disposed between the case  210  and the mass member  230  for elastically supporting the mass member  230 , comprises: a wire body  251  disposed in the disposition hole  232  formed in the mass body  231  of the mass member  230 ; and elastic ends  252  extending from the wire body  251  and engaged in engagement protrusions  214  formed at the inner circumferential surface of the case  210 .  
         [0084]     As shown in  FIGS. 6   a  and  6   b , the elastic wire  250  may be composed of a wire comprising: a wire body  251  disposed in the disposition hole  232  of the mass member  230 ; and a pair of elastic ends  252  extending along the outer circumferential surface of the mass member  230  and fixed to the inner circumferential surface of the case  210 .  
         [0085]     Preferably, the elastic ends  252  of the elastic wire  250  are securely fixed to the inner circumferential surface of the case  210 , while being spaced apart from each other by an angular distance of 180 degrees, to maximize elasticity of the elastic wire  250 , which is necessary to elastically support the mass member  230 .  
         [0086]     As shown in  FIGS. 7   a  and  7   b , the elastic wire  250  may be composed of at least two wires comprising: inner ends  251   a  fixedly disposed in at least two disposition holes  232   a  formed at a mass body  231   a  constituting the upper and lower mass members  233  and  234  such that the outer end of the disposition holes  232   a  is exposed to the outside at the outer circumferential surface of the mass body  231  of the mass member  230 ; and elastic ends  252   a  extending along the outer circumferential surface of the mass body  231   a  of the mass member  230  and fixed to the inner circumferential surface of the case  210 .  
         [0087]     In the illustrated drawings, the disposition holes  232   a  formed by vertical coupling of the upper and lower disposition grooves  233   a  and  234   a  formed at the upper and lower mass members  233  and  234  do not communicate with each other, although the disposition holes  232   a  may communicate with each other.  
         [0088]     Preferably, the elastic ends  252   a  of the elastic wire  250  are securely fixed to the inner circumferential surface of the case  210 , while being spaced uniformly apart from each other, to maximize elasticity of the elastic wire  250 , which is necessary to elastically support the mass member  230 .  
         [0089]     As shown in  FIGS. 8   a  and  8   b , the mass member  230 , which is elastically supported by the elastic member  250  in the case  210 , is a weight having at least two fixing holes  232   b  formed at the outer circumferential surface of a mass body  231   b  thereof while being spaced uniformly apart in the circumferential direction. The elastic wire  250  is composed of at least two wires each having one end  251   b  fixedly inserted in the corresponding fixing hole  232   b  and the other end  252   b  extending along the outer circumferential surface of the mass member  230  and securely fixed to the inner circumferential surface of the case  210 .  
         [0090]     Preferably, the elastic ends  252   b  of the elastic wire  250  are securely fixed to the inner circumferential surface of the case  210 , while being spaced uniformly apart from each other, to maximize elasticity of the elastic wire  250 , which is necessary to elastically support the mass member  230 .  
         [0091]     The engagement protrusions  214  having groove-shaped or hole-shaped engagement parts formed at the outer surfaces thereof, which correspond to the elastic ends  252 ;  252   a ;  252   b  of the elastic wire  250 , are mounted at the inner circumferential surface of the case  210  such that the elastic ends  252 ;  252   a ;  252   b  of the elastic wire  250  can be easily and quickly engaged into the engagement parts of the engagement protrusions  214 , respectively.  
         [0092]      FIGS. 9   a  and  9   b  are an assembled perspective view and an exploded perspective view respectively illustrating an example of a mass member  330  and an elastic wire  350  provided at a case  310  of the vibration actuator according to the present invention. As shown in  FIGS. 9   a  and  9   b , a plurality of engaging protrusions  314 , in which elastic ends of the elastic wire  350  are engaged, are mounted at the inner circumferential surface of the case  310 .  
         [0093]     In the illustrated drawings, the case  310  has an oval inner space, although the inner space of the case  310  may be formed in the shape of a circle based on forms of wireless communication devices.  
         [0094]     The mass member  330  comprises: an upper mass member  333  having a mounting hole  339  formed through the center of a mass body thereof such that a magnetic field unit  340  is inserted in the mounting hole  339  of the upper mass member  333  and an upper groove  333   a  formed at the lower surface thereof; and a lower plate  334  having a lower groove  334   a  formed at the upper surface thereof such that the lower groove  334   a  and the upper groove  333   a  together form a disposition space where the elastic wire  350  is disposed when the lower groove  334   a  is vertically coupled with the upper groove  333   a , the lower plate  334  partially covering the mounting hole  339 .  
         [0095]     The elastic wire  350  is composed of at least two wires comprising: wire bodies  351  disposed in a disposition part formed between the upper mass member  333  and the lower plate  334 ; and elastic ends  352  extending along the outer circumferential surfaces of the upper mass member  333  and the lower plate  334  and fixed to a plurality of engagement protrusions  314  formed at the inner circumferential surface of the case  310 , respectively.  
         [0096]     Consequently, the mass member  330 , which comprises the upper mass member  333  and the lower plate  334 , is elastically supported by elastic forces of the elastic wire  350  composed of the at least two wires, which is disposed between the case  310  and the mass member  330 , such that the mass member  330  can be vertically moved.  
         [0097]      FIGS. 10   a  and  10   b  are an assembled perspective view and an exploded perspective view respectively illustrating another example of a mass member  330  and elastic wires  350  provided at the case  310  of the vibration actuator according to the present invention. As shown in  FIGS. 9   a  and  9   b , the case  310  has a plurality of insertion holes  314   a  formed therethrough from the inner circumferential surface thereof to the outer circumferential surface thereof for allowing elastic ends of the elastic wires  350  to be inserted therethrough.  
         [0098]     The mass member  330  comprises: an upper mass member  335  having an upper mounting hole  335   a  formed through the center of a mass body thereof such that a magnetic field unit  340  is inserted in the upper mounting hole  335   a  of the upper mass member  335  and an upper groove  335   b  formed at the lower surface thereof; a lower mass member  336  having an lower mounting hole  336   a  formed therethrough, the lower mounting hole  336   a  corresponding to the upper mounting hole  335   a , and a first intermediate groove  336   b  formed at the upper surface thereof, which corresponds to the upper groove  335   b , such that a wire body  353  of an elastic wire  350  is disposed in the first intermediate groove  336   b  of the lower mass member  336 , the lower mass member  336  being vertically coupled with the upper mass member  335 ; and a lower plate  337  having a lower groove  337   a  formed at the upper surface thereof, which corresponds to a second intermediate groove (not shown) formed at the lower surface of the lower mass member  336 , such that a wire body  353  of another elastic wire  350  is disposed in the second intermediate groove of the lower mass member  336 , the lower plate  337  being vertically coupled with the lower mass member  336  for partially covering the upper mounting hole  335   a  and the lower mounting hole  336   a.    
         [0099]     The elastic wires  350  disposed between the upper mass member  335  and the lower mass member  336  and between the lower mass member  336  and the lower plate  337 , respectively, comprise a pair of upper and lower wires each having a wire body  353  fixedly disposed between the upper mass member  335  and the lower mass member  336  and between the lower mass member  336  and the lower plate  337 , respectively, and an elastic end  354  extending along the outer circumferential surfaces of the upper mass member  335  and the lower mass member  336  and fixedly inserted in the corresponding insertion hole  314   a  formed at the inner circumferential surface of the case  310 .  
         [0100]     Consequently, the mass member  330 , which comprises the upper mass member  335 , the lower plate  336 , and the lower plate  337 , is elastically supported by elastic forces of the elastic wires  350 , which are disposed between the case  310  and the mass member  330 , such that the mass member  330  can be vertically moved.  
         [0101]      FIGS. 11   a  and  11   b  are an assembled perspective view and an exploded perspective view respectively illustrating another example of a mass member  330  and an elastic wire  350  provided at the case  310  of the vibration actuator according to the present invention. As shown in  FIGS. 11   a  and  11   b , a plurality of engaging protrusions  314   c , in which elastic ends of the elastic wire  350  are engaged, are mounted at the inner circumferential surface of the case  310 .  
         [0102]     The mass member  330  is a weight comprising: a mass body  331  having a mounting hole  339   c  formed through the center thereof such that a magnetic field unit  340  is inserted in the mounting hole  339   c  of the mass member  330 ; and fixing grooves  332  formed at the upper surface of the mass body  331  for allowing ends  355  of the elastic wire  350  to be vertically inserted therein.  
         [0103]     The elastic wire  350 , which elastically supports the mass member  330  in the case  310 , is composed of at least two wires each having one end  351  fixedly inserted in the corresponding fixing groove  332  of the mass member  330  and the other end  352 , which is an elastic end, extending along the outer circumferential surface of the mass member  330  and engaged in the corresponding engagement protrusion  114  of the case  310 .  
         [0104]     As shown in  FIGS. 11   a  and  11   b , the elastic ends  352  of the elastic wire  350  are inserted into insertion holes  315  formed at the side surfaces of the engaging protrusions  314   c  of the case  310  in the circumferential direction. Alternatively, the elastic ends  352  of the elastic wire  350  may be vertically fitted into a fitting grooves  315   a  formed at the upper surfaces of the engaging protrusions  314   c  of the case  310 , as shown in  FIGS. 12   a  and  12   b.    
         [0105]     When an electric field having a predetermined strength is generated by the vibration coil  120 ;  220  as electric current having a low frequency of 120 to 300 Hz to the vibration coil  120 ;  220  of the vibration actuator  100 ;  200  with the above-stated construction according to the present invention, the mass member  130 ;  230 , including the magnetic field unit  140 , is vertically vibrated in the inner space of the case  110 ;  210  by interaction between the electric field generated by the vibration coil  120 ;  220  and the magnetic field generated by the magnetic field unit  140 , since the mass member  130 ;  230  is elastically supported by the elastic wire  150 ;  250  whose wire body is fixed to the mass member  130 ;  230  and whose elastic ends are fixed to the case  110 ;  210 . The vibration is transmitted to the case  110 ;  210  via the elastic wire  150 ;  250  such that the vibration actuator  100 ;  200  is vibrated.  
         [0106]     When an electric field having a predetermined strength is generated by the voice coil  160 ;  260  as electric current having a high frequency of 200 Hz or more to the voice coil  160 ;  260  of the vibration actuator  100 ;  200 , the diaphragm  170 ;  270  is minutely oscillated by interaction between the electric field generated by the vibration coil  120 ;  220  and the magnetic field generated by the magnetic field unit  140 , since the voice coil  160 ;  260  is mounted to the diaphragm  170 ;  270  disposed at the opened upper part of the case  110 ;  210 . Consequently, sound or voice is generated.  
         [0107]     As apparent from the above description, the disposition groove is formed at the outer circumferential surface of the mass body of the mass member including the magnetic field unit, or the disposition hole is formed in the mass body of the mass member, and the elastic ends of the elastic wire disposed in the disposition groove or the disposition hole are fixed to the inner circumferential surface of the case such that the mass member elastically supported in the case. Consequently, the present invention has the effect of improving durability due to high fatigue strength of the metal wire used in manufacturing springs, and therefore, increasing the service life of the vibration actuator.  
         [0108]     According to the present invention as described above, change of the natural frequency of elastic member due to manufacturing tolerance is minimized while the natural frequency of the elastic member for elastically supporting a vibrator comprising the magnetic field unit and the mass member is constantly maintained. Consequently, the present invention has the effect of guaranteeing good quality while equalizing quality of mass-produced vibration actuators, and improving vibration characteristics of the vibration actuator.  
         [0109]     Furthermore, assembly of the mass member and the elastic wire, which elastically supports the mass member, is more easily and conveniently accomplished. Consequently, the present invention has the effect of simplifying and reducing a manufacturing process of the vibration actuator, and therefore, improving productivity of the vibration actuator.  
         [0110]     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.