Abstract:
Disclosed are a vibration generator, which can increase the vibration force of a vibration plate by additionally applying the mass of a mass body to the vibration plate, and an electronic device including the same. The vibration generator includes at least one piezoelectric element mounted inside the case and subjected to compression and expansion in response to input power, a vibration plate including a body elongated in a preset lengthwise direction and having the at least one piezoelectric element mounted thereon, and generating vibrations by the compression and expansion of the at least one piezoelectric element, and at least one mass part adding a preset magnitude of mass to the vibration plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2010-0072735 filed on Jul. 28, 2010 and Korean Patent Application No. 10-2010-0096466 filed on Oct. 4, 2010 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vibration generator and an electronic device including the same, and more particularly, to a vibration generator, capable of enhancing the vibration force of a vibration plate by additionally applying (adding) the mass of amass body to a vibration plate, and an electronic device including the same. 
     2. Description of the Related Art 
     Recently, the use of touch-type devices allowing for an inputting operation in electronic devices through a user&#39;s touch (e.g. finger contact) is generalized according to the demands of users who desire to use electronic appliances in a simpler manner. 
     Currently, a haptic feedback device follows the concept of providing an intuitional user inference experience and diversifying types of contact feedback, in addition to facilitating the concept of performing an inputting operation through a touch. 
     The haptic feedback device has many advantages: It can save space, accomplish an improvement in manipulation and simplicity, allow for a simple change in specification, have a high level of user recognition, and have good interworkability with IT devices. 
     With such advantages, the haptic feedback device is commonly employed in electronic devices used in home computers, traffic note issuing devices, public information services, medical equipment, for mobile communications purposes and the like. 
     In general, the related art electronic device uses a vibration motor to implement a haptic function. The vibration motor was devised to vibrate the entire electronic device body, so, in order to increase vibration force, the size of a mass body needs to be increased. 
     For this reason, the haptic feedback device and the electronic device having the same have an undesirably large volume. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a vibration generator enhancing the vibration force of a vibration plate by additionally applying the mass of a mass body to the vibration plate, and an electronic device including the same. 
     According to an aspect of the present invention, there is provided a vibration generator including: at least one piezoelectric element subjected to compression and expansion in response to input power; a vibration plate including a body elongated in a preset lengthwise direction and having the at least one piezoelectric element mounted thereon, and generating vibrations by the compression and expansion of the at least one piezoelectric element; and at least one mass part adding a preset magnitude of mass to the vibration plate. 
     The vibration generator may further include a mounting part extending from the vibration plate and having the at least one mass part mounted thereon to apply the mass of the at least one mass part to the vibration plate. 
     The mounting part may apply the mass of the at least one mass part to a central portion of the vibration plate in the lengthwise direction thereof. 
     The mass part may include a first mass body and a second mass body disposed to have the vibration plate placed therebetween, and adding mass thereof to the vibration plate. 
     The mounting part may include: a first mounting region on which the first mass body is mounted; a second mounting region on which the second mass body is mounted; a first connection portion connected between the central portion of the vibration plate and the first mounting region, and applying the mass of the first mass body to the vibration plate; and a second connection portion connected between the central portion of the vibration plate and the second mounting region, and applying the mass of the second mass body to the vibration plate. 
     The vibration generator may further include a receiving part receiving the vibration plate and the mounting part. 
     The vibration generator may further include a support part placed at each end of the body in the lengthwise direction, and supporting the body from the receiving part. 
     The mass body may be formed of a metallic material having a preset density. 
     The mass body may be formed of at least one metallic material of stainless steel (SUS) and tungsten. 
     The vibration plate may be formed of a metallic material. 
     The vibration plate may be formed of Invar. 
     The at least one piezoelectric element may be a monolayer piezoelectric element or a multilayer piezoelectric element. 
     The vibration generator may further include a connection part extending from the vibration plate and connected to the at least one mass body to apply the mass of the at least one mass body to the vibration plate. 
     The connection part may connect the at least one mass body to a central portion of the vibration plate in the lengthwise direction thereof to apply the mass of the at least one mass body to the central portion. 
     The mass part may include a first mass body and a second mass body having the vibration plate placed therebetween and adding mass thereof to the vibration plate. 
     The connection part may include: a first connection unit connected between the central portion of the vibration plate and the first mass body and applying the mass of the first mass body to the vibration plate; and a second connection unit connected between the central portion of the vibration plate and the second mass body and applying the mass of the second mass body to the vibration plate. 
     The vibration generator may further include a receiving part receiving the vibration plate, the connection part and the mass part. 
     According to another aspect of the present invention, there is provided an electronic device including: a display module displaying an image upon a user&#39;s selection; a case having an internal space receiving the display module; and a vibration generator including: at least one piezoelectric element mounted inside the case and subjected to compression and expansion in response to input power; a vibration plate including a body elongated in a preset lengthwise direction and having the at least one piezoelectric element mounted thereon, and generating vibrations by the compression and expansion of the at least one piezoelectric element; and at least one mass part adding a preset magnitude of mass to the vibration plate. 
     The vibration generator may be mounted on an inner surface of the case. 
     The vibration generator may be mounted on a bottom surface of the display module. 
     The display module may include: a touch panel receiving a user&#39;s contact as input; and a display panel contacting a bottom surface of the touch panel and providing an image corresponding to the contact on the touch panel. 
    
    
     
       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 schematic exploded perspective view illustrating a vibration generator according to an exemplary embodiment of the present invention; 
         FIG. 2A  is a partial perspective view illustrating the vibration generator of  FIG. 1 ; 
         FIG. 2B  is a front view illustrating the vibration generator of  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating a piezoelectric element employed in the vibration generator of  FIG. 1 , according to an exemplary embodiment of the present invention; 
         FIG. 4  is a view illustrating how a vibration plate of the vibration generator vibrates; 
         FIG. 5  is a schematic exploded perspective view illustrating a vibration generator according to another exemplary embodiment of the present invention; 
         FIG. 6A  is a partial perspective view illustrating the vibration generator of  FIG. 5 ; 
         FIG. 6B  is a front view of the vibration generator of  FIG. 5 ; 
         FIG. 7  is a perspective view illustrating a piezoelectric element, employed in the vibration generator of  FIG. 5 , according to another exemplary embodiment of the present invention; 
         FIG. 8  is a graph showing the resonant frequency of a vibration generator according to the present invention; 
         FIG. 9  is a schematic perspective view illustrating an electronic device according to an exemplary embodiment of the present invention; 
         FIG. 10  is a schematic cross-sectional view illustrating the electronic device of  FIG. 9 ; and 
         FIG. 11  is a cross-sectional view illustrating an electronic device according to another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
       FIG. 1  is a schematic exploded perspective view illustrating a vibration generator according to an exemplary embodiment of the present invention.  FIG. 2A  is a partial perspective view illustrating the vibration generator according to this exemplary embodiment of the present invention, and  FIG. 2B  is a front view illustrating the vibration generator according to this exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 ,  2 A and  2 B, a vibration generator  100 , according to an exemplary embodiment of the present invention, may include a vibration plate  110 , at least one piezoelectric element  120 , amass part  130 , a mounting part  140  and a receiving part  150 . 
     The vibration plate  110  includes a body having a preset length, and may vibrate due to its body being bent when vibrations are applied thereto. The mounting part  140  may be formed at a central portion of the body in the lengthwise direction of the body. Here, term ‘central portion’ may refer to a portion covering the center and the vicinity of the center of the body in the lengthwise direction. 
     Furthermore, respective support parts  111  and  112  may be placed at both ends of the body in the lengthwise direction thereof. The support parts  111  and  112  contact the receiving part  150  to thereby support the body. 
     The mounting part  140  may be configured as at least one part or may be configured as two parts  141  and  142  having the vibration plate  110  interposed therebetween. As for the mounting part  140 , first and second mounting regions  141   a  and  142   a  having a predetermined area may be placed parallel to each other while having the vibration plate  110  interposed therebetween. Also, a first connection portion  141   b  may be formed to connect the first mounting region  141   a  with the central portion of the body of the vibration plate  110 , and a second connection portion  142   b  may be formed to connect the second mounting region  142   a  with the central portion of the body of the vibration plate  110 . 
     The mass part  130  may be mounted on the mounting part  140  in order to add a preset magnitude of mass to the vibration plate  110 . The mass part  130  may include a mass body corresponding to the mounting region of the mounting part  140 . Since the mounting portion  140  has the first and second mounting regions  141   a  and  142   a , the mass part  130  may also include first and second mass bodies  131  and  132 . 
     The first mass body  131  may be mounted on the first mounting region  141   a , and the second mass body  132  may be mounted on the second mounting region  142   a . In this way, the mass of the first and second mass bodies  131  and  132  may be applied to the central portion of the body of the vibration plate  110 . That is, the mass of the mass body  130  is applied to the vibration plate  110  through a neck structure. Accordingly, the mass can be added while achieving a reduction in the thickness thereof and suppressing the loss of driving force. 
     The at least one piezoelectric element  120  may be mounted on the top surface of the body of the vibration plate  110 , preferably in the lengthwise direction of the body. The at least one piezoelectric element  120  is repetitively compressed and expanded in response to applied external power to thereby cause the vibration plate  110  to be bent up and down as shown in  FIG. 4  and thus vibrated accordingly, which, as a result, generates vibration force. At this time, the mass part  130  may increase the vibration force by adding its mass to the central portion on which the displacement of the vibration plate  110  reaches the maximum level. 
     Namely, the vibration force may be increased by increasing the mass of the vibration plate  110  or increasing the driving displacement, as expressed in equation 1 below:
 
 F=m*x*w 2  (Equation 1)
 
where F denotes vibration force, m denotes the mass of a vibration plate, x denotes the displacement of the vibration plate, and w denotes a vibration frequency of the vibration plate.
 
     As referred to above, the at least one piezoelectric element  120  may be mounted. However, as shown in  FIG. 3 , a plurality of piezoelectric elements  120  may be mounted on the top of the body of the vibration plate  110 , and the piezoelectric element  120  may have a monolayer or a multilayer structure. In the case in which a multilayer piezoelectric element is used, a sufficient level of power to drive the piezoelectric element can be obtained even at a low voltage level, and therefore, driving power having a low voltage level may be used. 
     Meanwhile, the vibration generator according to exemplary embodiments of the present invention may be configured in various ways, and one of the embodiments will now be described with reference to the accompanying drawings. 
       FIG. 5  is a schematic exploded perspective view illustrating a vibration generator according to another exemplary embodiment of the present invention,  FIG. 6A  is a partial perspective view illustrating the vibration generator according to this exemplary embodiment of the present invention, and  FIG. 6B  is a front view of the vibration generator according to this exemplary embodiment of the present invention.  FIG. 7  is a perspective view illustrating a piezoelectric element, employed in the vibration generator of  FIG. 5 , according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 5 ,  6 A and  6 B, a vibration generator  200 , according to another exemplary embodiment of the present invention, may include a vibration plate  210 , at least one piezoelectric element  220 , a mass part  230 , a connection part  240 , and a receiving part  250 . 
     The vibration plate  210  includes a body having a preset length, and may vibrate due to its body being bent when vibrations are applied thereto. The connection portion  240  may be formed at the central portion of the body in the lengthwise direction of the body. 
     Furthermore, respective support parts  211  and  212  may be placed at both ends of the body in the lengthwise direction thereof. The support parts  211  and  212  contact the receiving part  250  to thereby support the body. 
     The connection part  240  may be configured as at least one unit or may be configured as two units  241  and  242  having the vibration plate  210  placed therebetween. Namely, the connection part  240  may include a first connection unit  241  connecting a first mass body  231  with the central portion of the body of the vibration plate  210 , and a second connection unit  242  connecting the second mass body  232  with the central portion of the body of the vibration plate  210 . Here, the first and second connection units  241  and  242  may be disposed parallel to each other while having the vibration plate  210  placed therebetween. 
     The mass part  230  is connected to the connection part  240  to thereby be able to add a preset magnitude of mass to the vibration plate  210 , and may include a mass body corresponding to the connection units of the connection part  240 . That is, since the connection part  240  includes the first and second connection units  241  and  242 , the mass part  230  may include first and second mass bodies  231  and  232 . 
     The first mass body  231  is connected to the first connection unit  241 , and the second mass body  232  may be connected to the second connection unit  242 . That is, the first and second connection units  241  and  242  extend from the central portion of the body of the vibration plate  210  and are connected to the first and second mass bodies  231  and  232 , respectively, so as to apply the mass of the first and second mass bodies  231  and  232  to the central portion of the body of the vibration plate  210 . That is, since the first and second connection units  241  and  242  extend from the vibration plate  210  to have a neck structure, the mass can be added to the vibration plate  210  while minimizing the thickness thereof and the loss of driving force therein. 
     The at least one piezoelectric element  220  may be mounted on the top surface of the body of the vibration plate  210 , preferably in the lengthwise direction of the body of the vibration plate  210 . 
     As described, the at least one piezoelectric element  220  may be mounted. However, as shown in  FIG. 7 , a plurality of piezoelectric elements  220  may be mounted on the top of the body of the vibration plate  210 , and the piezoelectric element  220  may have a monolayer or multilayer structure. 
       FIG. 8  is a graph showing the resonant frequency of a vibration generator according to the present invention. 
     Referring to  FIG. 8 , the resonant frequency of the vibration generator according to the invention may be varied according to the purpose of using the vibration generator. That is, in the case in which the vibration generator is employed for use in a cellular phone, the resonant frequency of the vibration generator may be set to fall within the range of 150 Hz to 200 Hz as indicated by curve ‘B’ of the graph, if an alarm function for calls, text messages and the like is considered to be important, whereas the resonant frequency thereof may be set to be within a band over 200 Hz as indicated by graph A of the graph if the use of a haptic function is considered to be important. 
     The resonant frequency is determined by the mass and rigidity of the vibration plate, as expressed by equation 2 below: 
                   Fn   =       k   m               (     Equation   ⁢           ⁢   2     )               
where Fn denotes a resonant frequency, m denotes the mass of a vibration plate, and k denotes the rigidity of the vibration plate.
 
     As expressed by equation 2 above, the resonant frequency may be set to be low by increasing the mass of the vibration plate or decreasing the rigidity thereof. 
     The rigidity of the vibration plate may be increased or reduced according to the length, thickness, width, mechanical and physical measures and the like of the vibration plate, as expressed by equation 3 below: 
                   k   ∝     C   ×     EI     L   3                 (     Equation   ⁢           ⁢   3     )               
where k denotes the rigidity of a vibration plate, E denotes Young&#39;s modulus, I denotes a moment of inertia, L denotes the effective length of the vibration plate, and C denotes a preset constant.
 
     The vibration plate  110  may be formed of a preset metallic material. Furthermore, the vibration plate  110  may be formed of a metallic material such as tungsten and stainless steel (SUS) having a high density per unit area. In addition, the vibration plate  110  may be formed of a material, such as Invar, having a similar thermal expansion coefficient to that of the piezoelectric element  120 . The piezoelectric element  120  may suffer from piezoelectric deterioration, which means deterioration in electrical properties caused by thermal stress under high temperature or thermal shock. Since a reduction in thermal stress can be achieved by a sufficiently small difference between the thermal expansion coefficients of the piezoelectric element and the vibration plate, the vibration plate may be desirably formed of a material having a similar thermal expansion coefficient to that of the piezoelectric element, such as Invar, in terms of the prevention of piezoelectric determination. 
     The vibration plate  110 , the piezoelectric element  120 , the mass part  130  and the mounting part  140 , or the vibration plate  210 , the piezoelectric element  220 , the mass part  230  and the connection part  240  are accommodated by the respective receiving parts  150  and  250  to thereby be utilized for various electronic devices. 
       FIG. 9  is a schematic perspective view illustrating an electronic device according to an exemplary embodiment of the present invention.  FIG. 10  is a schematic cross-sectional view illustrating the electronic device of  FIG. 9 , and  FIG. 11  is a cross-sectional view illustrating an electronic device according to another exemplary embodiment of the present invention. 
     As shown in  FIG. 9 , an electronic device  1000 , according to an exemplary embodiment of the preset invention, may display an image upon a user&#39;s selection. Referring to  FIG. 10 , the electronic device  1000  may include a display module displaying an image upon a user&#39;s selection, and a case  400  having an internal space receiving the display module. The display module may include a touch panel  200  providing the pressure of a user&#39;s contact pressure, and a display panel  300  mounted on the bottom of the touch panel  200  to provide an image upon the user&#39;s selection. The vibration generator  100 , according to the exemplary embodiments of the present invention, is mounted on the inner surface of the case  400  to thereby provide vibration depending on the user&#39;s selection. As shown in  FIG. 11 , the vibration generator  100  may be mounted on the bottom of the display panel  300  to thereby directly provide vibration to the display module. 
     As described above, driving force is increased by adding mass to the point of the vibration plate in which the displacement is the highest. Thus, the vibration device and the electronic device including the same, according to the exemplary embodiments of the present invention, can achieve a reductions in weight, thickness and size, as compared to the case in which driving force is increased by increasing the mass of the entire vibration plate. 
     As set forth above, according to exemplary embodiments of the invention, the mass of a mass body is additionally applied to the vibration plate to thereby increase the vibration force of the vibration plate. 
     While the present invention has been shown and described in connection with the exemplary 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.