Abstract:
Disclosed herein is a vibration generator which is used to embody vibration for signal reception indication or a haptic function of wireless communication devices such as mobile phones. The vibration generator includes a casing which has a space therein, a stator which is provided in the casing and is provided with a coil along which current flows, a vibrator which is provided in the casing and is horizontally moved by electromagnetic force, an elastic body which is fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, and a residual vibration reducer which is provided between the vibrator and the casing to absorb vibration of the vibrator. Therefore, after the vibration of the vibrator is stopped, the time it takes to stop movement of the vibrator can be markedly reduced.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to vibration generators for embodying vibration for signal reception indication or a haptic function of wireless communication devices such as mobile phones and, more particularly, to a vibration generator and a method of manufacturing the vibration generator which includes a casing having a space therein, a stator provided in the casing and having a coil along which current flows, a vibrator provided in the casing at a position facing the stator such that the vibrator can be horizontally moved by electromagnetic force, an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, and a residual vibration reducer provided between the vibrator and the casing to absorb vibration of the vibrator, whereby when the operation of the vibration generator is interrupted, the movement of the vibrator can be rapidly stopped; contact noise caused during the vibration of the vibrator can be reduced; and even after a long period of time has passed, the weight, the magnet and the elastic body can be prevented from being undesirably moved from their correct positions; and the performance of the vibration generator can be uniformly maintained even in conditions such as free-fall conditions. 
         [0003]    2. Description of the Related Art 
         [0004]    As examples of conventional vibration generators for embodying vibration for signal reception indication or a haptic function of wireless communication devices such as mobile phones, there are a vibration motor in which an eccentric or eccentric-mass type weight is installed in a brush DC motor, a BLDC (Brushless DC) vibration motor in which an eccentric type weight is installed in a rotor, a coin type vibration motor, a vertical vibration motor using resonance, etc. However, the conventional vibration generators are problematic in that they cannot satisfactorily realize certain requirements, such as long life span, reliability, thinness, and high vibration force that are required by devices such as mobile phones. 
         [0005]    In an effort to overcome problems of vibration generators using brush DC motors, vertical vibration motors that vibrate upward and downward using resonance were proposed. Such vertical vibration motors can generate resonance vibration in a vibrator having an elastic body and a weight by causing oscillation in electromagnetic force using mutual interaction between the electromagnetic force and a magnetic field. However, the vertical vibration motors are mechanically problematic in that they have a vertically moving mechanism using an elastic body, and so they require a mechanical space in which the vibrators can move upward and downward, thus making it difficult to reduce the entire height of the vibration generator. 
         [0006]    Furthermore, in the case of the conventional vibration generators installed in devices such as mobile phones which require vibration functions, the coupling state among the elements of the vibration generator is not reliable. Thus, for example, when a user drops a mobile phone due to careless, elements of the vibration generator may be removed from its original position, or the performance thereof may deteriorate. Such a problem of dislocation of the elements is mainly in regard to dislocation of a weight from an elastic body. Further, typical weights are made of tungsten which has a comparatively high specific gravity. Due to the characteristic that the tungsten material has a high melting point, coupling of the weight to the elastic body by melting cannot provide 100% reliability with regard to the coupling. In addition, a method using a chemical material to couple the weight to the elastic body also cannot ensure 100% reliability. 
         [0007]    To solve the problems of the conventional vertical vibration generator, a horizontal vibration generator which horizontally vibrates was proposed in Korean Patent Application No. 2010-0090230, which was filed by the applicant of the present invention. 
         [0008]    The conventional vibration generator introduced by the applicant of the present invention includes a casing, a vibrator which is installed in the casing and provided with a weight, and an elastic body which has a ‘U’ shape and encloses the weight. A first end of the elastic body is fixed to the weight, and a second end thereof is fixed to the casing. This vibration generator is configured such that horizontal vibration occurs using a resonant phenomenon induced by oscillation of electromagnetic force having the same frequency as the natural frequency of the elastic body. Therefore, this conventional vibration generator is advantageous in that the life span thereof is increased, and the vibration force thereof can be increased despite having a thin structure. 
         [0009]    Recently, as the sizes of communication devices are increased, vibration generators that have strong vibration force are preferred. However, the vibration generators that have strong vibration force are problematic in that the time it takes to stop the vibration generator is increased as the vibration force thereof is increased. With regard to awareness obtained by alternation of motion and stop, as the time it takes to stop the vibration generator is increased in proportion to the time period for which the vibration generator has moved, it becomes difficult to realize the desired awareness function. The vibration generator introduced in the patent application of the present applicant does not have measures to cope with vibration response characteristic being deteriorated by an increase in the time it takes to stop the vibrator after the vibration of the vibration generator is stopped. Furthermore, there is no measure to cope with noise generated by contact between the vibrator and the casing or the other elements when the vibrator is vibrating. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a vibration generator which includes a casing having a space therein, a stator provided in the casing and having a coil along which current flows, a vibrator provided in the casing at a position facing the stator such that the vibrator can be horizontally moved by electromagnetic force, and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, wherein a residual vibration reducer is installed between the vibrator and the casing to absorb vibration of the vibrator in two stages, whereby when the operation of the vibration generator is interrupted, the movement of the vibrator can be rapidly stopped, and contact noise caused when the vibrator is vibrating can be reduced. 
         [0011]    Another object of the present invention is to provide a vibration generator which includes a casing having a space therein, a stator provided in the casing and having a coil along which current flows, a vibrator provided in the casing at a position facing the stator such that the vibrator can be horizontally moved by electromagnetic force, and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, wherein a coil stopper is provided to limit the movement of the coil and protect the coil from the vibrator, whereby when an external impact, e.g., free fall shock or the like, is applied to the vibration generator, the stator (coil) can be prevented from being undesirably moved or damaged due to movement displacement of the vibrator. 
         [0012]    A further object of the present invention is to provide a vibration generator which includes a casing having a space therein, a stator provided in the casing and having a coil along which current flows, a vibrator provided in the casing at a position facing the stator such that the vibrator can be horizontally moved by electromagnetic force, and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, wherein a spacer for spacing a portion of the first end of the elastic body, fixed to the casing, apart from an inner surface of the casing is provided so that the elastic body is prevented from making contact with the casing, thereby enhancing resonant frequency, and preventing performance deterioration. 
         [0013]    Yet another object of the present invention is to provide a vibration generator which includes a casing having a space therein, a stator provided in the casing and having a coil along which current flows, a vibrator provided in the casing at a position facing the stator such that the vibrator can be horizontally moved by electromagnetic force, and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, wherein the vibrator includes a weight having an inner space therein, and a first magnet, yoke plate and a second magnet that are installed in the inner space of the weight, whereby the size of the main magnet (first magnet) can be reduced, thus making it possible to reduce the cost required to provide the magnet. 
         [0014]    Still another object of the present invention is to provide a vibration generator which includes a casing having a space therein, a stator provided in the casing and having a coil along which current flows, a vibrator provided in the casing at a position facing the stator such that the vibrator can be horizontally moved by electromagnetic force, and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, wherein the second end of the elastic body is fixed to the weight of the vibrator, and the first end of the elastic body is bent by a predetermined length and a surface of a overlapping portion of the bent first end is fixed to an inner surface of the casing so that the elastic body has an approximate “S” shape, thus making it possible for the elastic body to be comparatively long and slim, thereby reducing spatial constraints, and providing high vibration. 
         [0015]    Still another object of the present invention is to provide a method of manufacturing a vibration generator which can enhance the efficiency of the assembly process thanks to a simple assembly structure of the elements, and make the coupling between the elements more reliable, thus enhancing the reliability of products and reducing the production cost. 
         [0016]    In order to accomplish the above object, the present invention provides a vibration generator, including: a casing having a space therein; a stator provided in the casing, the stator comprising a coil along which current flows; a vibrator provided in the casing and facing the stator, the vibrator being horizontally moved by electromagnetic force; an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator; and a residual vibration reducer provided between the vibrator and the casing, the residual vibration reducer absorbing vibration of the vibrator. 
         [0017]    The residual vibration reducer may be disposed in a direction corresponding to a direction in which the vibrator vibrates. The residual vibration reducer may absorb vibration of the vibrator in two stages. 
         [0018]    The residual vibration reducer may include a fixed part which is fixed to the casing or the vibrator, and a movable part which extends from the fixed part and moves in response to the movement of the vibrator. 
         [0019]    The fixed part may be fixed to the vibrator, and the movable part may be bent from the fixed part and extend therefrom without being fixed to the casing or vibrator. 
         [0020]    The fixed part may be fixed to the casing, and the movable part may extend from the fixed part without being fixed to the casing or vibrator. 
         [0021]    The residual vibration reducer may be disposed on a side surface or a corner of the vibrator that corresponds to a direction opposite to the vibration direction of the vibrator, thus absorbing the vibration of the vibrator. 
         [0022]    The residual vibration reducer may include a fixed part which is fixed to the casing, and a movable part which perpendicularly extends from the fixed part and moves in response to the movement of the vibrator. 
         [0023]    The movable part may make contact with the weight of the vibrator. 
         [0024]    In another aspect, the present invention provides a vibration generator, including: a casing having a space therein; a stator provided in the casing, the stator comprising a coil along which current flows; a vibrator provided in the casing and facing the stator, the vibrator being horizontally moved by electromagnetic force; an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator; and a coil stopper limiting movement of the coil and protecting the coil from the vibrator. 
         [0025]    Furthermore, the coil stopper may enclose the periphery of the coil. 
         [0026]    The coil stopper may be open on one surface thereof. 
         [0027]    The coil stopper may be disposed in a central hollow space of the coil and protrude higher than the coil in the direction facing the vibrator. 
         [0028]    The coil stopper may enclose the periphery of the coil, and one side thereof may protrude towards the side surface of the vibrator. 
         [0029]    Further, the coil stopper may further include a protrusion for protecting the side surface of the vibrator from the casing. 
         [0030]    In addition, the coil stopper may be open on one surface thereof. 
         [0031]    The weight of the vibrator may have a protrusion protruding towards a surface of the coil that faces the weight. 
         [0032]    A magnetic fluid may be applied to the magnet to prevent interference which is caused when the vibrator vibrates. 
         [0033]    In a further aspect, the present invention provides a vibration generator, including: a casing having a space therein; a stator provided in the casing, the stator comprising a coil along which current flows; a vibrator provided in the casing and facing the stator, the vibrator being horizontally moved by electromagnetic force; an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator; and a spacer for spacing a portion of the first end of the elastic body, fixed to the casing, apart from an inner surface of the casing. 
         [0034]    The spacer may comprise a protruding part provided on an inner surface of the casing so that a portion of the first end of the elastic body is spaced apart from the inner surface of the casing by the protruding part. 
         [0035]    The spacer may comprise a plurality of embossments provided on the first end of the elastic body so that a portion of the first end of the elastic body is spaced apart from the inner surface of the casing by the embossments. 
         [0036]    The spacer may comprise a bending part formed by bending a portion of the first end of the elastic body so that a non-bent portion of the elastic body, other than the bent portion of the first end, is spaced apart from the inner surface of the casing by the bending part. 
         [0037]    The spacer may comprise a metal plate disposed between the elastic body and the casing so that a portion of the first end of the elastic body is spaced apart from the inner surface of the casing by the metal plate. 
         [0038]    The elastic body may be fixed to the spacer of the casing by welding the junction therebetween. 
         [0039]    In a still another aspect, the present invention provides a vibration generator, including: a casing having a space therein; a stator provided in the casing, the stator provided with a coil along which current flows; a vibrator provided in the casing and facing the stator, the vibrator being horizontally moved by electromagnetic force; and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, wherein the vibrator comprises a weight having an inner space therein, and a first magnet, yoke plate and a second magnet that are installed in the inner space of the weight. 
         [0040]    The yoke plate may have a receiving depression for receiving the second magnet. The second magnet may be installed in the receiving depression. 
         [0041]    The second magnet may comprise two second magnets. The two second magnets may be respectively disposed in medial portions of the opposite surface of the second-magnet-receiving depression. 
         [0042]    The second magnet may comprise four second magnets. The two second magnets may be respectively disposed in four corners of the second-magnet-receiving depression. 
         [0043]    The second magnet may comprise two second magnets. The two second magnets may be respectively disposed in two diagonally opposing corners of the second-magnet-receiving depression. 
         [0044]    The second magnet may comprise a planar plate having the same size as that of the first magnet. 
         [0045]    The second magnet may comprise a rubber magnet having elasticity. 
         [0046]    The second magnet may comprise a sintered magnet. The second magnet may comprise a magnet, one surface of which is four-pole magnetized. 
         [0047]    Further, a magnetic fluid may be applied to the upper surface of the second magnet that faces the inner surface of the casing. 
         [0048]    In yet another aspect, the present invention provides a vibration generator, including: a casing having a space therein; a stator provided in the casing, the stator comprising a coil along which current flows; a vibrator provided in the casing and facing the stator, the vibrator being horizontally moved by electromagnetic force; and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator, wherein the second end of the elastic body is fixed to the weight of the vibrator, and the first end of the elastic body is bent by a predetermined length and a surface of a overlapping portion of the bent first end is fixed to an inner surface of the casing. 
         [0049]    The elastic body may be partitioned into three surfaces which include a first end surface formed on the first end, a second end surface formed on the second end and a connection surface connecting the first end surface to the second end surface. The elastic body may be configured such that the connection surface does not make contact with the weight. 
         [0050]    In yet another aspect, the present invention provides a method of manufacturing a vibration generator including: a casing having a space therein; a vibrator installed in the casing and provided with a weight; an elastic body fixed in the casing; a magnetic field generating unit comprising a magnet for providing electromagnetic force to horizontally vibrate the vibrator, a coil spaced apart from the magnet by a predetermined distance, and an FPCB; and a cover assembled with the casing to cover an open surface of the casing, the method including: a first assembly process comprising disposing the magnet and the yoke plate in a magnet receiving depression formed in the weight to form the vibrator, fixing the vibrator to the elastic body, and fixing the elastic body in the casing, thus forming a first assembly; a second assembly process separately conducted from the first assembly process, the second assembly process comprising installing the FPCB and the coil in the cover, and installing a coil stopper to protect the coil from the vibrator, thus forming a second assembly; and a third assembly process assembling the first assembly manufactured through the first assembly process with the second assembly manufactured through the second assembly process. 
         [0051]    The first assembly process, to prevent the elastic body from being deformed, may further include attaching a main rubber to a surface of the weight that is not enclosed by the elastic body, and attaching a side rubber to a surface of the weight that is opposite to the surface thereof to which the main rubber. 
         [0052]    The second assembly process may further include attaching a guide rubber to an inner surface of the cover to prevent the elastic body from being deformed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0053]    The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0054]      FIG. 1  is an exploded perspective view illustrating a vibration generator according to an embodiment of the present invention; 
           [0055]      FIG. 2  is a perspective view showing the internal construction of an assembled vibration generator of  FIG. 1 ; 
           [0056]      FIGS. 3A through 3C  are views illustrating the operation of a residual vibration reducer of the vibration generator according to the present invention; 
           [0057]      FIG. 4  is a view illustrating a second embodiment of the residual vibration reducer installed in the vibration generator according to the present invention; 
           [0058]      FIG. 5  is a view illustrating a third embodiment of the residual vibration reducer installed in the vibration generator according to the present invention; 
           [0059]      FIG. 6  is a view illustrating a fourth embodiment of the residual vibration reducer installed in the vibration generator according to the present invention; 
           [0060]      FIG. 7  is an exploded perspective view of a second embodiment of a coil stopper of the vibration generator according to the present invention; 
           [0061]      FIG. 8  is a view illustrating the second embodiment of the coil stopper of the vibration generator according to the present invention; 
           [0062]      FIG. 9  is a view illustrating a third embodiment of the coil stopper of the vibration generator according to the present invention; 
           [0063]      FIG. 10  is a view illustrating a fourth embodiment of the coil stopper of the vibration generator according to the present invention; 
           [0064]      FIGS. 11A and 11B  are views illustrating a first embodiment of a spacer of the vibration generator according to the present invention; 
           [0065]      FIGS. 12A and 12B  are views illustrating a second embodiment of a spacer of the vibration generator according to the present invention; 
           [0066]      FIGS. 13A and 13B  are views illustrating a third embodiment of a spacer of the vibration generator according to the present invention; 
           [0067]      FIGS. 14A and 14B  are views illustrating a fourth embodiment of a spacer of the vibration generator according to the present invention; 
           [0068]      FIGS. 15A through 15C  are views illustrating several embodiments of the vibration generator according to the present invention; 
           [0069]      FIG. 16  is a sectional view of the vibration generator to illustrate application of a magnetic fluid according to the present invention; 
           [0070]      FIG. 17  is an exploded perspective view illustrating another embodiment of an elastic body of the vibration generator according to the present invention; 
           [0071]      FIG. 18  is a plan view showing an assembled state of  FIG. 17 ; 
           [0072]      FIG. 19  is a view showing a main rubber and a side rubber which are respectively attached to opposite side surfaces of the vibrator of the vibration generator according to the present invention; and 
           [0073]      FIG. 20  is a view showing a guide rubber attached to a cover of the vibration generator according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0074]    Hereinafter, a vibration generator according to the present invention will be described in detail with reference to the attached drawings. 
         [0075]    As shown in  FIGS. 1 and 2 , the vibration generator according to the present invention includes a casing  10  which is open on one surface thereof and has a space therein, a stator which is provided in the casing  10  and provided with a coil  41  along which current flows, a vibrator  20  which is provided in the casing  10  and is horizontally moved by electromagnetic force against the stator  40 , an elastic body  30  which is fixed at a first end thereof to the casing  10  and fixed at a second end thereof to the vibrator  20 , a cover  50  which covers the open surface of the casing  10 , a rubber body  51  which is installed on an outer surface of the cover  50  to protect elements from external impact, and a residual vibration reducer  60  which is provided between the vibrator  20  and the casing  10  and absorbs vibration of the vibration  20  in two stages. 
         [0076]    The casing  10  is made of a nonmagnetic electric conductor and has a rectangular container shape configured such that one surface thereof is open, the other surfaces thereof are closed to define a space therein, and four sides of the closed surface extend perpendicular to the closed surface and forms four sidewalls. 
         [0077]    The stator  40  includes a FPCB (flexible printed circuit board)  43  which applies an external electric signal to the coil  41 , the coil  41  which receives an external electric signal from the FPCB  43  and generates a magnetic field, and a coil stopper  42  which limits the movement of the coil  41 . The stator  40  is disposed at a position spaced apart from the vibrator  20  by a predetermined distance. The coil  41  forms a hollow structure which has an internal space in a central portion thereof and is configured in a circular or rectangular shape. Preferably, the coil  14  comprises a wound self bonding wire. A core may be installed in the internal space of the hollow structure formed by the coil  41  or may be omitted. The core is preferably made of metal that has magnetic permeability. 
         [0078]    As shown in  FIG. 1 , the vibrator  20  includes a weight  21 , and a first magnet  22 , a yoke plate  23  and a second magnet  24  which are installed in an internal space of the weight  21 . 
         [0079]    The weight  21  is made of metal having a comparatively high specific gravity and has an internal space which is a through hole. The first magnet  22 , the yoke plate  23  and the second magnet  24  are successively installed in the internal space of the weight  21 . 
         [0080]    The yoke plate  23  is disposed between the first magnet  22  and the second magnet  24  and functions as a rail through which lines of magnetic force generated from N poles of the first and second magnets  22  and  24  enters S poles of them. The yoke plate  23  is made of magnetic material, wherein the higher the magnetic permeability of the magnetic material, the better. 
         [0081]    The elastic body  30  has a “U” shape, and the first end thereof is fixed to the casing  10 . The elastic body  30  functions to make the vibrator  20  horizontally vibrate using a resonant phenomenon induced by means of applying the same frequency as that of the natural frequency of the vibrator  20  thereto. 
         [0082]    The FPCB  43  is elastically connected to the coil  41  and applies an external electric signal to the coil  41  to form a magnetic field around the coil  41 . Although, in  FIG. 1 , the FPCB  43  is illustrated as being installed on an inner surface of the cover  50  that is coupled to the open surface of the casing  10 , the present invention is not limited to the embodiment of  FIG. 1  and can be modified into any shape or construction, so long as it can apply an external electric signal to the coil  41  to form a magnetic field around the coil  41 . 
         [0083]    The residual vibration reducer  60  is installed between the vibrator  20  and the casing  10  on a surface of the vibrator  20  that corresponds to the direction in which the vibrator  20  moves. The residual vibration reducer  60  is configured to absorb vibration of the vibrator  20  in two stages. 
         [0084]    As shown in  FIG. 2 , in a first embodiment, the residual vibration reducer  60  includes a fixed part  61  which is fixed to a surface of the vibrator  20  that corresponds to the direction vibrator  20  moves, and a movable part  62  which extends from the fixed part  61  and is moved by movement of the vibrator  20 . The fixed part  61  is fixed to the surface of the vibrator  20  that corresponds to the movement direction of the vibrator  20 . The movable part  62  is bent from the fixed part  61  and extends a predetermined length. The movable part  62  is neither fixed to the casing  10  nor the vibrator  20 . 
         [0085]    The operation of the first embodiment of the residual vibration reducer  60  will be explained with reference to  FIGS. 3A through 3  C. 
         [0086]      FIG. 3A  illustrates an initial state of vibration of the vibrator  20  in the casing  10 .  FIG. 3B  illustrates a process in which the vibrator  20  is moved towards the right sidewall of the casing  10 .  FIG. 3C  illustrates a state in which the vibrator  20  further moves and reaches the inner surface of the right sidewall of the casing  10 . 
         [0087]    As shown in  FIG. 3B , during the process in which the vibrator  20  is moved towards the right sidewall of the casing  10 , the movable part  62  of the residual vibration reducer  60  comes into contact with the inner surface of the right sidewall of the casing  10  and primarily absorbs vibration of the vibrator  20 . 
         [0088]    Thereafter, as shown in  FIG. 3C , when the vibrator  20  further moves and reaches the inner surface of the right sidewall of the casing  10 , the movable part  62  and the fixed part  61  of the residual vibration reducer  60  become linear and secondarily absorb impact applied from the vibrator  20  to the casing  10 . 
         [0089]    Preferably, the residual vibration reducer  60  is made of rubber or the like to more effectively absorb the vibration of the vibrator  20 . 
         [0090]    In a second embodiment of the residual vibration reducer  60 , as shown in  FIG. 4 , the residual vibration reducer  60  is configured such that the first part  61  is fixed to the casing  10 , and the movable part  62  extends from the fixed part  61  and is neither fixed to the casing  10  nor the vibrator  20 . In this embodiment, when the vibrator  20  is moved towards the right sidewall of the casing  10 , the movable part  62  of the residual vibration reducer  60  comes into contact with a right side surface of the vibrator  20  and primarily absorbs vibration of the vibrator  20 . When the vibrator  20  further moves and reaches the inner surface of the right sidewall of the casing  10 , the movable part  62  and the fixed part  61  of the residual vibration reducer  60  become a linear line and secondarily absorb impact applied from the vibrator  20  to the casing  10 . 
         [0091]    In a third embodiment of the residual vibration reducer  60 , as shown in  FIG. 5 , the fixed part  61  of the residual vibration reducer  60  is fixed to the surface of the vibrator  20  that corresponds to the movement direction of the vibrator  20 . The movable part  62  linearly extends from the fixed part  61  without being fixed to the vibrator  20 . In this case, when the movable part  62  comes into contact with the corresponding corner of the casing  10 , the residual vibration reducer  60  primarily absorbs vibration of the vibrator  20 . When the vibrator  20  further moves and reaches the inner surface of the right sidewall of the casing  10 , the movable part  62  and the fixed part  61  of the residual vibration reducer  60  secondarily absorb vibrational impact applied from the vibrator  20  to the casing  10 . 
         [0092]    As such, the residual vibration reducer  60  is installed between the vibrator  20  and the casing  10  at a position corresponding to the movement direction of the vibrator  20  and thus forms the structure which absorbs vibration of the vibrator  20  in two stages. 
         [0093]    That is, the movable part  62  of the residual vibration reducer  60  primarily reduces elastic force generated from the vibrator  20  in the movement direction of the vibrator  20 , thus absorbing vibration of the vibrator  20 . The fixed part  61  of the residual vibration reducer  60  secondarily reduces the elastic force so that the vibrator  20  can be stopped in a short time. Thereby, the residual vibration reducer  60  can reduce residual vibration of the vibrator  20  that is vibration generated by the elastic force after the electromagnetic force is turned off, thus stopping the vibration  20  in a short time. In other words, a residual vibration duration for which residual vibration occurs can be reduced. Here, vibration force reduction is not caused. 
         [0094]    Furthermore, because the residual vibration reducer  60  is installed on the vibrator  20  or on the surface of the casing  10  that faces the vibrator  20  with respect to the movement direction of the vibrator  20 , the movable part  62  and the fixed part  61  function to reduce contact noise between the casing  10  and the vibrator  20  while coming into contact with the vibrator  20  or the surface of the casing  10  that faces the vibrator  20  with respect to the movement direction of the vibrator  20 . 
         [0095]    In a fourth embodiment of the residual vibration reducer  60 , as shown in  FIG. 6 , the residual vibration reducer  60  for absorbing vibration of the vibrator  20  is disposed on a sidewall or corner of the casing  10  that faces the direction perpendicular to the movement direction of the vibrator  20 . 
         [0096]    The residual vibration reducer  60  has a “T” shape and includes a fixed part  61  which is fixed on the casing  10 , and a movable part  62  which extends perpendicular to the fixed part  61  and moves in response to the movement of the vibrator  20 . An end of the movable part  62  makes contact with the weight  12  of the vibrator  20  to reduce vibration of the vibrator  20 . 
         [0097]    Next, the coil stopper  42 , which limits movement of the coil  41  that is one of the elements of the stator  40  of the vibration generator and protects the coil  41  from the vibrator  20 , will be described below. 
         [0098]    The coil stopper  42  functions to limit the movement of the coil  41  to prevent the coil  41  from being damaged when the coil  41  of the stator  40  is moved by movement of the stator  40  in response to displacement of the vibrator  20  when external impact, e.g., free fall shock or the like, is applied to the vibration generator. 
         [0099]    It is preferable that the coil stopper  42  for protecting the coil  41  protrude higher than the coil  41 . The coil stopper  42  is formed by plastic injection molding and fixed to the coil  41  by means of a thermosetting adhesive applied to the inner or outer surface of the coil  41 . 
         [0100]    In a first embodiment of the coil stopper  42 , as shown in  FIG. 1 , the coil stopper  42  is configured to enclose the periphery of the coil  41  and be open on one surface of the periphery of the coil  41 . 
         [0101]    In a second embodiment of the coil stopper  42 , as shown in  FIGS. 7 and 8 , the coil stopper  42  is installed in the central hollow space of the coil  41  and protrudes higher than the coil  41  in the direction facing the vibrator  20 . 
         [0102]    In a third embodiment of the coil stopper  42 , as shown in  FIG. 9 , the coil stopper  42  encloses the periphery of the coil  42  and has at one side thereof a protruding part  42   a  that faces a side surface of the vibrator  20 . 
         [0103]    In a fourth embodiment of the coil stopper  42 , as shown in  FIG. 10 , the coil stopper  42  has at one side thereof a protrusion part  42   a  that faces a side surface of the vibrator  20  in the same manner as that of the third embodiment and has at other sides thereof protrusions  42   b  for protecting the corresponding side surfaces of the vibrator  20  from the casing. 
         [0104]    The portion of the weight  21  that does not correspond to the coil stopper  42  may be inclined to one side because of a gap formed therebetween. Therefore, to maintain the balance, the weight  21  of the vibrator  20  may have a protrusion (not shown) on a surface thereof that faces the coil  41 . 
         [0105]    Furthermore, in the vibrator  20 , a magnetic fluid may be applied to the surface of the magnet  22  or  24  that is received in the magnet receiving depression of the weight to prevent the coil from snapping because of interference of the vibrator  20  or/and prevent the magnet  22  or  24  from colliding with the inner surface of the corresponding sidewall of the casing  10 . 
         [0106]    Next, in the vibration generator according to the present invention, a spacer for spacing a portion of a first end of the elastic body  30  that is fixed to the casing  10  apart from the inner surface of the corresponding sidewall of the casing  10  will be described below. 
         [0107]    The elastic body  30  includes the spacer for preventing the elastic body  30  from touching the casing  10 , so that an increase in resonant frequency and performance degradation can be prevented. 
         [0108]    In a first embodiment of the spacer, as shown in  FIGS. 11A and 11B , the spacer comprises a protruding part  10   a  which is provided on the inner surface of the casing  10  so that a portion of the first end of the elastic body  30  is spaced apart from the inner surface of the casing  10  by the protruding part  10   a.  That is, as shown in  FIG. 11B , the protruding part  10   a  protrudes from a portion of the inner surface of the casing  10 , and a portion of the first end of the elastic body  30  makes contact with the protruding part  10   a,  but the other portion of the first end of the elastic body  30  is spaced apart from the inner surface of the casing  10  by a predetermined gap g. 
         [0109]    In a second embodiment of the spacer, as shown in  FIGS. 12A and 12B , a plurality of embossments  30   a  are provided on the first end of the elastic body  30  so that a portion of the first end of the elastic body  30  is spaced apart from the inner surface of the casing  10  by the embossments  30   a  by a predetermined gap g. 
         [0110]    In a third embodiment of the spacer, as shown in  FIGS. 13A and 13B , a bending part  30   b  is formed by bending a portion of the first end of the elastic body  30  so that the other portion of the first end of the elastic body  30  that is not bent is spaced apart from the inner surface of the casing  10  by the bending part  30   b  by a predetermined gap g. 
         [0111]    In a fourth embodiment of the spacer, as shown in  FIGS. 14A and 14B , a metal plate  31  is interposed between the elastic body  30  and the casing  10  so that a portion of the first end of the elastic body  30  can be spaced apart from the inner surface of the casing  10  by the metal plate  31  by a predetermined gap g. 
         [0112]    In the above-mentioned embodiments of the spacer, the elastic body  30  may be fixed to the spacer of the casing  10  by welding the junction therebetween. 
         [0113]    Next, the vibrator  20  of the vibration generator according to the present invention which uses a size-reduced main magnet ( 22 , first magnet) to reduce the cost for providing the magnet will be described below. 
         [0114]    As shown in  FIGS. 1 ,  15 A through  15 C, to reduce the cost for providing the magnet, the vibrator  20  includes the weight  21 , the first magnet  22  which is installed in the internal receiving space of the weight  21 , the yoke plate  23  and the second magnet  24 . 
         [0115]    In a first embodiment of the vibrator  20 , as shown in  FIG. 1 , the first magnet  22 , the yoke plate  23  and the second magnet  24  which have the same planar shape and the same size are disposed in the receiving depression of the weight and successively stacked on top of one another. 
         [0116]    Alternatively, as shown in  FIGS. 15A through 15C , the vibrator  20  may be configured such that the yoke plate  23  has a receiving space for the second magnet  24  and the second magnet  24  is installed in the receiving space. 
         [0117]      FIG. 15A  illustrates an example in which two second magnets  24  are provided and second magnet receiving spaces are respectively formed in the medial portions of opposite side surfaces of the yoke plate  23  so that the two second magnets  24  are installed in the opposite side surfaces of the yoke plate  23 . 
         [0118]      FIG. 15B  illustrates an example in which four second magnets  24  are provided and second magnet receiving spaces are respectively formed in the four corners of the yoke plate  23  so that the four second magnets  24  are installed in the four corners of the yoke plate  23 . 
         [0119]      FIG. 15C  illustrates an example in which two second magnets  24  are provided and second magnet receiving spaces are respectively formed in two diagonally opposing corners of the yoke plate  23  so that the two second magnets  24  are respectively installed in the two diagonally opposing corners of the yoke plate  23 . 
         [0120]    In each embodiment, the second magnet  24  may comprise a rubber magnet that has a predetermined elasticity, or a sintered magnet. 
         [0121]    Furthermore, in each embodiment, the second magnet  24  comprises a magnet, one surface of which is four-pole magnetized. 
         [0122]    As shown in  FIG. 16 , a magnetic fluid  25  is applied to an upper surface of the second magnet  24 . The magnetic fluid  25  functions as a damper to absorb contact impact between the vibrator  20  and the corresponding inner surface of the casing  10 . By virtue of the magnetic fluid  25 , contact between the inner surface of the casing  10  and the vibrator  20  can be more effectively prevented from being caused when vertical vibration occurs. 
         [0123]    Next, the structure of the elastic body  30 , which is able to have an increased length and achieve slimness to overcome spatial constraints and provide high vibration, will be described with reference to  FIGS. 17 and 18 . 
         [0124]    As shown in  FIGS. 17 and 18 , the first end of the elastic body  30  is fixed to the weight  21  of the vibrator  20 . The second end of the elastic body  30  is bent by a predetermined length, and the surface of the overlapping portion of the second end thereof is fixed to the inner surface of the casing  10 . Overall, the elastic body  30  forms an approximate S shape. 
         [0125]    Unlike the typical elastic body shown in  FIG. 1 , etc., because a modification of the elastic body shown in  FIGS. 17 and 18  has an approximate S shape, the elastic body  30  is configured to be comparatively long and slim, thus reducing spatial constraints, and providing high vibration. 
         [0126]    Furthermore, the elastic body  30  is partitioned into three surfaces which include a first end surface formed on the first end, a second end surface formed on the second end and a connection surface connecting the first end surface to the second end surface. The elastic body  30  is configured such that the connection surface does not make contact with the weight  21 . That is, as shown in  FIG. 18 , the first end surface formed on the first end is brought into contact with the weight  21  and is fixed thereto. The surface of the overlapping portion formed by bending a predetermined length of the second end is brought into contact with the inner surface of the casing  10  and is fixed thereto. However, the connection surface makes no contact with the weight  21 . 
         [0127]    Meanwhile, a vibration generator manufacturing method according to the present invention relates to a method for manufacturing a vibration generator that includes: a casing which has a space therein; a vibrator  20  which is provided in the casing  10  and has a weight  21 ; an elastic body  30  which is fixed in the casing  10 ; a magnetic field generating unit which includes magnets  22  and  24  for providing electromagnetic force to horizontally vibrate the vibrator  20 , a coil  41  spaced apart from the magnets  22  and  24  by a predetermined distance, and an FPCB  43 ; and a cover  50  which is assembled with the casing  10  to cover the open surface of the casing  10 . 
         [0128]    With regard to the process of manufacturing the vibration generator having the above-mentioned construction, the vibration generator manufacturing method according to the present invention has several separate assembly processes, including a first assembly process through which a first assembly is completed, a second assembly process through which a second assembly is completed, and a third assembly process during which the first assembly manufactured through the first assembly process is assembled with the second assembly manufactured through the second assembly process. 
         [0129]    The first assembly process includes disposing the magnets  22  and  24  and the yoke plate  23  in the magnet receiving depression formed in the weight  21  to form the vibrator  20 , fixing the vibrator  20  to the elastic body  30 , and fixing the elastic body  30  in the casing  10 , thus forming the first assembly. The second assembly process includes installing the FPCB  43  and the coil  41  in the cover  50 , and installing a coil stopper  42  to protect the coil  41  from the vibrator  20 , thus forming the second assembly. 
         [0130]    To prevent the elastic body  30  from being deformed, the first assembly process, as shown in  FIG. 19 , may further include attaching a main rubber  26  to a surface of the weight  21  that is not enclosed by the elastic body  30 , and attaching a side rubber  27  to a surface of the weight  21  that is opposite to the surface to which the main rubber is attached. The reason for this is to prevent the elastic body  30  from being deformed by contact impact between the weight  21  and the casing  10  in the case where space around the weight  21  and the elastic body  30  is comparatively large. 
         [0131]    As shown in  FIG. 20 , the second assembly process may further include attaching a guide rubber  52  to the inner surface of the cover  50  to prevent the elastic body  30  from being deformed. The reason for this is to minimize empty space between the weight  21  and the cover  50  and thus prevent the elastic body  30  from being deformed. 
         [0132]    As described above, the present invention a vibration generator which includes a casing having a space therein, a stator provided in the casing and having a coil along which current flows, a vibrator provided in the casing at a position facing the stator such that the vibrator can be horizontally moved by electromagnetic force, and an elastic body fixed at a first end thereof to the casing and fixed at a second end thereof to the vibrator. A residual vibration reducer is installed between the vibrator and the casing to absorb vibration of the vibrator in two stages, whereby when the operation of the vibration generator is interrupted, the movement of the vibrator can be rapidly stopped, and contact noise caused when the vibrator is vibrating can be reduced. 
         [0133]    Furthermore, a coil stopper is provided to limit the movement of the coil and protect the coil from the vibrator, whereby when external impact, e.g., free fall shock or the like, is applied to the vibration generator, the stator (coil) can be prevented from being undesirably moved or damaged due to movement displacement of the vibrator. 
         [0134]    In addition, a spacer for spacing a portion of the first end of the elastic body, fixed to the casing, apart from an inner surface of the casing is provided so that the elastic body is prevented from making contact with the casing, thereby enhancing resonant frequency, and preventing performance deterioration. 
         [0135]    The vibrator includes a weight having an inner space therein, and a first magnet, yoke plate and a second magnet that are installed in the inner space of the weight, whereby the size of the main magnet (first magnet) can be reduced, thus making it possible to reduce the cost required to provide the magnet. 
         [0136]    The second end of the elastic body is fixed to the weight of the vibrator, and the first end of the elastic body is bent by a predetermined length and a surface of a overlapping portion of the bent first end is fixed to an inner surface of the casing so that the elastic body has an approximate “S” shape, thus making it possible for the elastic body to be comparatively long and slim, thereby reducing spatial constraints, and providing strong vibration. 
         [0137]    Furthermore, the vibration generator manufacturing method according to the present invention can enhance the efficiency of the assembly process thanks to a simple assembly structure of the elements, and make the coupling between the elements more reliable, thus enhancing the reliability of products and reducing the production cost. 
         [0138]    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.