Abstract:
There is provided a vibration motor including: a housing having one open surface; a permanent magnet disposed in an internal space of the housing and interacting with a coil to generate electromagnetic force; an elastic member formed in the housing; a mass member coupled to the elastic member to perform resonant movement through the electromagnetic force; a cover covering the one open surface of the housing; and an extension part extended from the one open surface of the housing in a height direction thereof and compressed with the cover to closely attach the housing and the cover to each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2012-0006924 filed on Jan. 20, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vibration motor, and more particularly, to a vibration motor capable of increasing coupling force between a housing and a cover. 
     2. Description of the Related Art 
     Generally, a vibration motor has a structure in which a rotor having an eccentric mass with respect to a shaft rotates to produce mechanical vibrations. Here, the rotor rotates by receiving current in a coil thereof through contact between a brush and a commutator. 
     However, a vibration motor using a brush and a commutator has disadvantages, in that mechanical friction between the brush and the commutator may be high, and electrical sparks may be generated through contact between the brush and the commutator, such that a lifespan of the motor may be shortened. 
     In addition, a vibration motor having this type of structure is inappropriate for use in an output device requiring a rapid response since it may take a certain amount of time to reach a target oscillation frequency. 
     As a motor for overcoming these disadvantages, there is provided a linear vibration motor. 
     The linear vibration motor may allow a mass member fixed to an elastic member, vibrated through electromagnetic force, to relatively rapidly generate a oscillation frequency desired by a user. 
     The linear vibration motor has a structure in which a housing and a cover are coupled to each other by welding. However, this coupling structure may be disadvantageous, in that a molten material may penetrate into the housing to change vibration characteristics of the linear vibration motor (for example, generate noise therein). 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a vibration motor capable of improving coupling force between a housing and a cover without causing a change in vibration characteristics thereof. 
     According to an aspect of the present invention, there is provided a vibration motor including: a housing having one open surface; a permanent magnet disposed in an internal space of the housing and interacting with a coil to generate electromagnetic force; an elastic member formed in the housing; a mass member coupled to the elastic member to perform resonant movement through the electromagnetic force; a cover covering the one open surface of the housing; and an extension part extended from the one open surface of the housing in a height direction thereof and compressed with the cover to closely attach the housing and the cover to each other. 
     The extension part may be compressed with the cover by curling. 
     The extension part may be continuously protruded along an edge of the one open surface of the housing. 
     The housing may have a step supporting the cover. 
     The extension part may have a relatively smaller thickness than that of the housing so as to be easily compressed with the cover. 
     A height h of the extension part may satisfy the following Equation 1:
 
0.13&lt; h−T 2&lt;0.50  Equation 1
 
     where T 2  indicates a thickness of the cover. 
     The housing may be formed of stainless steel or a cold rolled steel sheet. 
     The cover may have an inclined surface contacting an end portion of the extension part in a state in which the cover is coupled to the housing. 
     The cover may include a protrusion part protruded in a radial direction. 
     The housing may have a groove into which the protrusion part is fitted. 
     According to another aspect of the present invention, there is provided a vibration motor including: a housing having one open surface; a permanent magnet disposed in an internal space of the housing and interacting with a coil to generate electromagnetic force; a cover covering the one open surface of the housing; an elastic member formed on the cover; a mass member coupled to the elastic member to perform resonant movement through the electromagnetic force; and an extension part extended from the one open surface of the housing in a height direction thereof and compressed with the cover to closely attach the housing and the cover to each other. 
     The extension part may be compressed with the cover by curling. 
     The extension part may be continuously protruded along an edge of the one open surface of the housing. 
     The housing may have a step supporting the cover. 
     The extension part may have a relatively smaller thickness than that of the housing so as to be easily compressed with the cover. 
     A height h of the extension part satisfies the following Equation 1:
 
0.13&lt; h−T 2&lt;0.50  Equation 1
 
     where T 2  indicates a thickness of the cover. 
     The housing may be formed of stainless steel or a cold rolled steel sheet. 
     The cover may have an inclined surface contacting an end portion of the extension part in a state in which the cover is coupled to the housing. 
     The cover may include a protrusion part protruded in a radial direction. 
     The housing may have a groove into which the protrusion part is fitted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, 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: 
         FIG. 1  is a cross-sectional view of a vibration motor according to an embodiment of the present invention; 
         FIG. 2  is an assembled perspective view showing a state of the vibration motor shown in  FIG. 1  before curling; 
         FIG. 3  is an enlarged cross-sectional view of part A shown in  FIG. 1 ; 
         FIG. 4  is an assembled perspective view showing a state of the vibration motor shown in  FIG. 1  after curling; 
         FIG. 5  is an enlarged cross-sectional view showing a state of part A shown in  FIG. 1  after curling; 
         FIG. 6  is a graph showing a relationship between a height of an extension part and unmating force described in Table 2; 
         FIG. 7  is a cross-sectional view of a vibration motor according to another embodiment of the present invention; 
         FIG. 8  is an assembled perspective view showing a state of the vibration motor shown in  FIG. 7  before curling; 
         FIG. 9  is an enlarged cross-sectional view of part B shown in  FIG. 7 ; and 
         FIG. 10  is an enlarged cross-sectional view showing a state of part B shown in  FIG. 7  after curling. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A small-sized vibration motor may receive a permanent magnet and a coil in a space formed by a housing and a cover and generate vibrations having a predetermined frequency through interaction between the permanent magnet and the coil. 
     Recently, as a magnitude of vibrations required in a portable terminal has gradually increased, and a oscillation frequency band required in the portable terminal has been specified, the development of a small-sized vibration motor having resistance to internal impacts and external impacts has been demanded. 
     That is, in the case of a small-sized vibration motor according to the related art, a housing and a cover may be separated from each other or may be partially separated from each other due to an internal impact or an external impact, such that it may be difficult to stably obtain a desired oscillation frequency band. 
     Meanwhile, in consideration of this problem, a scheme of welding a housing and a cover to each other has been proposed. However, this scheme has a problem, in that a material, molten during a welding process, may be introduced into the vibration motor to change characteristics of main components thereof. For example, the molten material introduced into the vibration motor may penetrate a space between a coil and a permanent magnet to thereby cause coil disconnection, thereby leading to a change in characteristics of the vibration motor (generation of noise). 
     According to embodiments of the present invention, provided to solve these problems, a small-sized vibration motor in which a housing and a cover may be stably coupled to each other may be provided. To this end, according to embodiments of the present invention, the housing and the cover are coupled to each other in a compression scheme (particularly, by curling), such that coupling force between the housing and the cover may be improved. 
     Particularly, according to embodiments of the present invention, the entire portion in which the housing and the cover are in contact with each other is compressed, such that the coupling force between the housing and the cover may be further improved. 
     Further, according to embodiments of the present invention, at least one of the housing and the cover is formed of a cold rolled steel sheet, such that a compression state may not be significantly changed due to external force. 
     Therefore, according to embodiments of the present invention, a joint between the housing and the cover may not be easily deformed due to an internal impact or an external impact, such that a oscillation frequency having a predetermined magnitude may be generated. 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     In describing the present invention below, terms indicating components of the present invention are named in consideration of functions thereof. Therefore, the terms used herein should not be understood as limiting the technical components of the present invention. 
       FIG. 1  is a cross-sectional view of a vibration motor according to an embodiment of the present invention;  FIG. 2  is an assembled perspective view showing a state of the vibration motor shown in  FIG. 1  before curling;  FIG. 3  is an enlarged cross-sectional view of part A shown in  FIG. 1 ;  FIG. 4  is an assembled perspective view showing a state of the vibration motor shown in  FIG. 1  after curling;  FIG. 5  is an enlarged cross-sectional view showing a state of part A shown in  FIG. 1  after curling;  FIG. 6  is a graph showing a relationship between a height of an extension part and unmating force described in Table 2;  FIG. 7  is a cross-sectional view of a vibration motor according to another embodiment of the present invention;  FIG. 8  is an assembled perspective view showing a state of the vibration motor shown in  FIG. 7  before curling;  FIG. 9  is an enlarged cross-sectional view of part B shown in  FIG. 7 ; and  FIG. 10  is an enlarged cross-sectional view showing a state of part B shown in  FIG. 7  after curling. 
     A vibration motor  100  according to an embodiment of the present invention may include a housing  110 , a cover  120 , an elastic member  130 , a permanent magnet  140 , a coil  150 , a mass member  160 , and a (flexible) circuit board  170 . In addition, the vibration motor  100  may further include impact absorbing members  180  and  182 . 
     The housing  110  may have a container shape in which it has a receiving space formed therein. For example, the housing  110  may have a cylindrical shape in which it has one open surface. However, this is only an example, and a shape of the housing  110  is not specifically limited. That is, the housing  110  may have a shape other than cylindrical. 
     The housing  110  may include a mounting part  112 . The mounting part  112  may be formed on a bottom surface of the housing  110  and fix the permanent magnet  140 . For example, the mounting part  112  may have a protrusion, protruded from a bottom surface of the housing  110  to a predetermined height. For reference, the mounting part  112  may have an adhesive applied thereto in order to stably fix the permanent magnet  140  to the housing  110 . 
     The housing  110  may be formed of a metallic material. For example, the housing  110  may be formed of a cold rolled steel sheet (SPCC) or stainless steel. The housing  110  formed of the above-described material may effectively protect components received therein from an external impact. Meanwhile, the above-mentioned material is only an example, and a material of the housing  110  is not limited. Therefore, the housing  110  may be formed of other materials having physical properties equal or similar to those of the cold rolled steel sheet or stainless steel. 
     The housing  110  may include an extension part  114  as shown in  FIGS. 2 and 3 . The extension part  114  may be formed on the one open surface of the housing  110  and be protruded lengthwise in a height direction (a Z axis direction, based on the accompanying drawings) of the housing  110 . Here, the extension part  114  may be a part of the housing  110  extended upwardly of a bottom surface of the cover  120  in a state in which the housing  110  and the cover  120  are coupled to each other. 
     The extension part  114  may have a thickness equal to a thickness T 1  of the housing  110 . However, the extension part  114  may have a thickness less than the thickness T 1  of the housing  110  so that the compression work (particularly, the curling work) may be easily performed. 
     The extension part  114  may have a first part  1142  and a second part  1144 . 
     The first part  1142  may be a part contacting an end surface of the cover  120 . That is, the first part  1142  may be a part of the housing  110  substantially enclosing a circumference of the cover  120 . Here, a height h 1  of the first part  1142  is equal to or greater than a thickness T 2  of the cover  120 . 
     The second part  1144  may be a part except for the first part  1142  in the extension part  114 . Here, the second part  1144  may be a part of the housing  110  extended upwardly of an upper surface of the cover  120  in a state in which the housing  110  and the cover  120  are coupled to each other. Here, a height h 2  of the second part  1144  may be less than the height h 1  of the first part  1144  and be equal to or greater than the thickness T 1  of the housing  110 . 
     The extension part  114  formed as described above may have a predetermined height h (h 1 +h 2 ) and cover an edge of the cover  120  through a curling process as shown in  FIGS. 4 and 5 . 
     Meanwhile, the height h of the extension part  114  may be selected from the following range. The following Table 1 shows several experiment numerals of a height h of the extension part  114  and a height h 2  of the second part  1144 , and the following Table 2 shows a relationship between a height of the extension part  114 ;  1142  and  1144  and unmating force. For reference, in the present specification, unmating force refers to a magnitude of force required for forcibly separating the cover  120  compressed with the housing  110  from the housing  110 . 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Note 
                 h (=h1 + h2) 
                 h2 
               
               
                   
                   
               
             
             
               
                   
                 Experimental Example 1 
                 0.30 
                 0.10 
               
               
                   
                 Experimental Example 2 
                 0.32 
                 0.12 
               
               
                   
                 Experimental Example 3 
                 0.34 
                 0.14 
               
               
                   
                 Experimental Example 4 
                 0.36 
                 0.16 
               
               
                   
                 Experimental Example 5 
                 0.38 
                 0.18 
               
               
                   
                   
               
             
          
         
       
     
     An experiment was performed while changing a height h of the extension part  114  and a height h 2  of the second part  1144  as shown in Table 1, and an optimal amount of coupling force between the housing  110  and the cover  120  was determined through the experiment. 
     That is, in the respective Experimental Examples, heights of the second part  1144  were set to be different according to heights h of the extension part  114 , and unmating force of the cover  120  was determined through the experimentation (for reference, in the present experiment, a thickness T 2  of the cover  120  may be substantially equal to a height h 1  of the first part  1142 ). For example, a ratio of a height of the second part  1144  to the total height h of the extension part  114  was 0.33% in Experimental Example 1, 0.28% in Experimental Example 2, 0.41% in Experimental Example 3, 0.44% in Experimental Example 4, and 0.47% in Experimental Example 5. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Unmating Force (kgf/mm) 
               
             
          
           
               
                   
                 Note 
                 Min 
                 Max 
                 Max − Min 
               
               
                   
                   
               
               
                   
                 Experimental Example 1 
                 3.16 
                 4.24 
                 1.08 
               
               
                   
                 Experimental Example 2 
                 5.32 
                 6.39 
                 1.07 
               
               
                   
                 Experimental Example 3 
                 7.42 
                 7.77 
                 0.35 
               
               
                   
                 Experimental Example 4 
                 8.13 
                 8.27 
                 0.14 
               
               
                   
                 Experimental Example 5 
                 8.17 
                 8.38 
                 0.21 
               
               
                   
                   
               
             
          
         
       
     
     In the experiment results, it was confirmed that unmating force in Experimental Examples 3 to 5 is relatively larger than unmating force in Experimental Examples 1 and 2. Particularly, it was confirmed that a difference between minimum unmating force and maximum unmating force is relatively small in Experimental Examples 3 and 4 (See  FIG. 6 ). Therefore, it may be confirmed that an optimal ratio of the height of the second part  1144  to the total height h of the extension part  114  is in the range of 0.40 to 0.45%. 
     In addition, the height h of the extension part  114  may satisfy Equation 1. For reference, in Equation 1, the height h of the extension part  114  may be h 1 +h 2 .
 
0.13 mm&lt; h−T 2&lt;0.50 mm   Equation 1
 
     As the height of the extension part  114  is increased, unmating force is correspondingly increased. However, when the height of the extension part  114  exceeds a maximum value of Equation 1, a wrinkle may be formed in the extension part  114  during the curling process. On the other hand, when the height of the extension part  114  is less than a minimum value of Equation 1, the extension part  114  may not be stably compressed with the cover  120 . 
     Therefore, in order to firmly couple the housing  110  and the cover  120  to each other, the height of the extension part  114  may be set to satisfy Equation 1. 
     The cover  120  may be disposed on the one open surface of the housing  110  and close the one open surface. To this end, the cover  120  may have a cross-sectional shape with a size equal to that of the one open surface. 
     The cover  120  may be formed of a metallic material. For example, the cover  120  may be formed of a cold rolled steel sheet or stainless steel, similar to the housing  110 . However, the cover  120  is not limited to being formed of the above-mentioned material, but may be formed of other materials. 
     The cover  120  may include a protrusion part  122  extended in one direction (an −X axis direction based on  FIG. 2 ). The protrusion part  122  may support the circuit board  170  extended outwardly of the housing  110 . Meanwhile, although a separate reference numeral is not used in the accompanying drawings, a groove through which the protrusion part  122  may be extended may be formed in the housing  110 . 
     The elastic member  130  may be formed in the housing  110 . More specifically, the elastic member  130  may have one end fixed to the housing  110  and the other end connected to a bracket  162 . The elastic member  130 , disposed as described above, may always return the bracket  162 , moving in a vertical direction (a Z axis direction based on  FIG. 1 ) by external force, to its original position. 
     The elastic member  130  may be formed of a coil spring. However, the elastic member  130  is not limited to being formed of the coil spring. For example, the elastic member  130  may be formed of a leaf spring or other springs. 
     The permanent magnet  140  may be disposed on the mounting part  112 . The permanent magnet  140  may be disposed at the center of the elastic member  130  and allow the bracket  162  to vibrate in the vertical direction through interaction with the coil  150 . 
     The permanent magnet  140  may be provided with a yoke  142 . The yoke  142  may allow magnetic flux formed by the interaction between the permanent magnet  140  and the coil  150  to flow smoothly. The yoke  142  may have a plate shape and may be formed of a magnetic material. For reference, the yoke  142  may be fixed to the permanent magnet  140  by an adhesive, or the like. 
     The coil  150  may be formed on the bracket  162 . For example, the coil  150  may be adhered to the bracket  162  or wound around the bracket  162 . 
     The coil  150  may be electrically connected to the circuit board  170  and form a magnetic field through current supplied from the circuit board  170 . Here, a magnitude and a direction of the magnetic field formed by the coil  150  may be changed according to a magnitude and a direction of the current supplied from the circuit board  170 . 
     The coil  150  may reciprocate the bracket  162  in the vertical direction (the Z axis direction based on  FIG. 1 ) through the interaction with the permanent magnet  140  to generate vibrations having a predetermined frequency. Here, the frequency may be adjusted by a spring constant of the elastic member  130  and mass of the mass member  160 . 
     The coil  150  may have a hole larger than a cross-sectional shape of the permanent magnet  140 . Therefore, when the bracket  162  moves downwardly, the permanent magnet  140  may be disposed in the coil  150 . 
     The mass member  160  may be formed on the bracket  162  and move in the vertical direction together with the bracket  162 . 
     The mass member  160  may be formed of a material having a predetermined mass. For example, the mass member  160  may be formed of a metallic material. However, the mass member  160  is not limited to being formed of the metallic material, but may be formed of other materials. 
     For reference, although the mass member  160  and the bracket  162  are shown as separated members in the accompanying drawings, the mass member  160  and the bracket  162  may be formed integrally with each other as needed. 
     The circuit board  170  may be disposed on the cover  120 . The circuit board  170  may be electrically connected to the coil  150  and supply current to the coil  150 . 
     The circuit board  170  may be extended outwardly of the housing  110  through the protrusion part  122 . Here, the extended part of the circuit board  170  may be provided with a terminal connected to an external device. 
     The circuit board  170  may be a flexible board that may freely move. For example, the circuit board  170  may be manufactured in a film form. Since the circuit board  170  having this form may move freely, the circuit board  170  may stably maintain a state in which it is connected to the coil  150  regardless of vertical movement of the bracket  162 . 
     The impact absorbing members  180  and  182  may be formed on the housing  110  and the cover  120 . More specifically, a first impact absorbing member  180  may be formed along the circumference of the mounting part  112 , and a second impact absorbing member  182  may be formed on one surface (a lower surface based on  FIG. 1 ) of the cover  120 . 
     Here, the first impact absorbing member  180  may block the housing  110  and the bracket  162  from being indirect contact with each other at the time of downward movement of the bracket  162 . In addition, the second impact absorbing member  182  may block the bracket  162  and the cover  120  from being in direct contact with each other at the time of upward movement of the bracket  162 . 
     The vibration motor  100  formed as described above may stably protect internal components from an external impact since the housing  110  and the cover  120  are firmly coupled to each other by curling. 
     Hereinafter, a vibration motor according to another embodiment of the present invention will be described with reference to  FIGS. 7 through 10 . 
     A vibration motor  100  according to another embodiment of the present invention may be different from the vibration motor  100  according to the previous embodiment of the present invention in terms of the shapes of a housing  110  and a cover  120 . 
     The housing  110  may have a step  116  as shown in  FIG. 9 . The step  116  may be formed at a boundary at which an inner wall of the housing  110  and an extension part  114  are connected to each other. The step  116  formed as described above may stably support an edge of the cover  120 . In addition, the step  116  may firmly fix the edge of the cover  120  to the extension part  114  after curling. 
     The cover  120  may include an inclined part  1242  and a flat part  1244 . More specifically, the edge  124  of the cover  120  may include the inclined part  1242  and the flat part  1244  as shown in  FIGS. 8 and 9 . The inclined part  1242  may be bent downwardly from a body of the cover  120 , and the flat part  1244  may be extended from an end of the inclined part  1242  in a horizontal direction. 
     Here, the flat part  1244  of the cover  120  may be covered by the extension part  114 , and the inclined part  1242  of the cover  120  may contact an end portion of the extension part  114 . Therefore, the cover  120  according to the present embodiment may be relatively firmly coupled to the extension part  114 . 
     In the vibration motor  100  configured as described above, a gap between a surface of the cover  120  and the extension part  114  is reduced, in a state in which the housing  110  and the cover  120  are coupled to each other (See  FIG. 10 ), whereby air tightness and coupling force between the housing  110  and the cover  120  may be significantly improved. 
     Meanwhile, although the permanent magnet  140  is formed in the housing  110  and the coil  150  is formed on the cover  120  in the accompanying drawings, positions of these members may be reversed. 
     That is, according to another embodiment of the present invention, the coil  150  may be formed in the housing  110  and the permanent magnet  140  may be formed on the cover  120 . 
     As set forth above, according to embodiments of the present invention, a housing and a cover may be firmly coupled to each other. Therefore, vibration characteristics of a vibration motor may be constantly maintained. 
     While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.