Abstract:
The present invention is capable of increasing the thinness of a linear vibration motor equipped with a fixed shaft. The linear vibration motor is equipped with: a frame; one fixed shaft extending in one axial direction and affixed to the frame; a drive unit for driving a magnet in the one axial direction, and equipped with a coil affixed to the frame and the magnet, which is positioned so as to be parallel to the fixed shaft; a needle which is slidably supported in the one direction by the fixed shaft, and is equipped with the magnet and a spindle part connected to the magnet; and an elastic member for imparting an elastic force to the needle in opposition to the driving force of the drive unit, and positioned so as not to be coaxial with the fixed shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national phase application under 35 U.S.C. §371 of International Patent Application No. PCT/JP2015/071254, filed Jul. 27, 2015, and claims benefit of priority to Japanese Patent Application No. 2014-153354, filed Jul. 28, 2014. The entire contents of these applications are hereby incorporated by reference. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The present invention relates to a linear vibration motor for generating a vibration through causing a needle to undergo reciprocating vibration linearly through a signal input. 
       BACKGROUND 
       [0003]    A vibration motor (or a vibration actuator) is that which communicates, to a user of a communication device or to an operator who is holding any of a variety of electronic devices, the state of an input signal through a vibration, through generating a vibration through an incoming call on a communication device or through the transmission of an alarm on any of a variety of electronic devices, and is built into any of a variety of electronic devices, such as mobile information terminals, including mobile telephones. 
         [0004]    Among the various types of vibration motors under development, there is a known linear vibration motor that is able to generate relatively large vibrations through linearly reciprocating vibrations. This linear vibration motor employs a structure that is provided with a straight stationary shaft, and a needle is vibrated therealong, making it possible to achieve stabilized vibration with little noise produced by components striking each other, and making it possible to achieve resistance to damage, such as when there is a drop impact, through the needle being held by the stationary shaft. 
         [0005]    In the prior art for linear vibration motors that are equipped with stationary shafts there have been proposals for those wherein a driving portion is structured from a coil that is secured to a case and a magnet that is disposed within the coil, a needle is structured through connecting a weight portion to the magnet along the direction of vibration, a through hole is formed in the needle along the direction of vibration, and a single stationary shaft is passed through this through hole (See, for example, Japanese Unexamined Patent Application Publication No. 2012-16153), or two stationary shafts are provided along the direction of vibration, a driving portion made from a coil and a magnet is disposed between the two stationary shafts, and a needle that is provided with a weight portion and which is driven by the driving portion is supported by the two stationary shafts so as to be able to slide (See, for example, Japanese Unexamined Patent Application Publication No. 2011-97747), and the like. In each of these prior art technologies, coil springs are provided around the stationary shaft, and the needle is caused to undergo reciprocating vibration along the stationary shaft through the driving force by the driving portion in one direction and the elastic force of the coil spring in opposition to the driving force. 
       SUMMARY 
       [0006]    With smaller and thinner mobile electronic devices there is the need for smaller and thinner vibration motors to be equipped therein. In particular, in electronic devices such as smart phones that are equipped with flat panel displaying portions, space within the devices is limited in the direction of thickness, perpendicular to the plane of the display, so there is a strong need for thinner vibration motors to be equipped therein. 
         [0007]    When one considers reducing the thickness of a linear vibration motor that is provided with a stationary shaft, in the first of the prior art technologies described above, a through hole is formed along the direction of vibration in a needle wherein a weight portion is connected to a magnet along the direction of vibration, and thus a through hole is formed in the magnet itself, requiring the magnet to be adequately thick, in respect to the diameter of the stationary shaft, in order to secure an adequate volume for the magnet, to thereby produce the desired driving force. Moreover, the driving portion is structured through the provision also of a coil around the magnet, and thus there is a problem in that this is not completely compatible with reducing thickness. Moreover, while one may consider forming the through hole in the magnet itself through dividing into magnets on the left and the right of the stationary shaft, this would increase the number of components for the magnet, not only preventing good manufacturability, but also producing a problem in that it would be difficult to secure the magnet volume for producing an adequate driving force. 
         [0008]    In contrast, if two stationary shafts are provided and a driving portion is provided therebetween, as in the latter of the prior art technologies described above, it would not be necessary to form a through hole through the magnet, thus enabling the magnet to be made thinner. However, because two stationary shafts would be provided, there would be the need for high accuracy in aligning the shafts, so there would be a problem in that the manufacturing process would be complex, and if the accuracy of the alignment of the shafts were lacking, it would not be possible to produce stabilized vibration, because components would rattle or strike the interior of the guide hole through which the stationary shaft passes. 
         [0009]    Moreover, because in both of the prior art technologies set forth above coil springs are provided around the stationary shafts, of necessity the diameters of the coil springs must be larger than the diameters of the stationary shafts. Because the diameters of the stationary shafts must, to some degree, be large to facilitate processing of components and in order to produce a stabilized vibration, there is a problem in that the provision of coil springs with diameters even larger than those would cause a reduction in thickness difficult. 
         [0010]    In the present invention, the handling of such problems is an example of the problem to be solved. That is, the object of the present invention is to enable a linear vibration motor that is provided with a shaft to be made thinner, and, furthermore, to enable the reduction in thickness while not increasing the number of components for the magnet, suppressing a reduction in the volume of the magnet, and ensuring a stabilized vibration. 
         [0011]    In order to achieve such an object, the linear vibration motor of the present invention is equipped with the following structures: 
         [0000]    A linear vibration motor comprising: a frame; a shaft provided protruding along an axial direction within the frame; a driving portion, comprising a magnet and a coil, which is secured to the frame, for driving the magnet along the axial direction; a needle, comprising the magnet and a weight portion that is connected to the magnet, supported by the shaft so as to be able to slide in the axial direction; and an elastic member for applying, to the needle, an elastic force that opposes the driving force of the driving portion, arranged off-axis from the shaft within the frame. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is an assembly perspective diagram illustrating the overall structure of a linear vibration motor according to an example according to the present invention. 
           [0013]      FIG. 2( a )  and  FIG. 2( b )  are explanatory diagrams illustrating the overall structure of a linear vibration motor according to an example according to the present invention (wherein  FIG. 2( a )  is a plan view wherein the cover plate has been removed,  FIG. 2( b )  is a cross-sectional view along the section A 1 -A 1  in (a), and (c) is a cross-sectional view along the section A 2 -A 2  in  FIG. 2( a ) ). 
           [0014]      FIG. 3( a )  and  FIG. 3( b )  are explanatory diagrams illustrating the overall structure of a linear vibration motor according to an example according to the present invention (wherein  FIG. 3( a )  is a cross-sectional view along the section B-B in  FIG. 3( a )  and  FIG. 3( b )  is a front view). 
           [0015]      FIG. 4  is an assembly perspective diagram illustrating the overall structure of a linear vibration motor according to another example according to the present invention. 
           [0016]      FIG. 5  is a cross-sectional diagram illustrating the overall structure of a linear vibration motor according to another example according to the present invention. 
           [0017]      FIG. 6  is a cross-sectional diagram illustrating the overall structure of a linear vibration motor according to another example according to the present invention. 
           [0018]      FIG. 7  is a cross-sectional diagram illustrating the overall structure of a linear vibration motor according to another example according to the present invention. 
           [0019]      FIG. 8  is an explanatory diagram illustrating the electronic device (a mobile information terminal) equipped with a linear vibration motor according to an example according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Examples according to the present invention will be explained below in reference to the drawings (where identical reference symbols in different drawings below indicate identical positions, and redundant explanations in the various drawings are omitted).  FIG. 1  through  FIG. 3  illustrate the overall structure of a linear vibration motor according to one example according to the present invention. The X direction in each of the drawings indicates the direction of vibration (the axial direction), the Y direction indicates the width direction, and the Z direction indicates the thickness (height) direction. The linear vibration motor  1  according to the present example of the present invention is to reduce the thickness in the Z direction. 
         [0021]    The linear vibration motor  1  comprises: a frame  2 ; one stationary shaft  3  that is secured to the frame  2  and that extends in the axial direction (the X direction in the figure); a needle  20  that is supported so as to be able to slide along the axial direction (the X direction in the figure) by the stationary shaft  3 ; a driving portion  10  for driving the needle  20  in the axial direction (the X direction in the figure); and an elastic member  8 . 
         [0022]    The frame  2  may have a frame structure that is able to secure a single stationary shaft  3  and able to contain the various components described below, and, in the illustrated example, is provided with side walls  2 B,  2 C,  2 D, and  2 E that are provided extending from the edges of a rectangular bottom face  2 A, and provided with shaft securing portions  2 B 1  and  2 C 1  for securing both ends of a stationary shaft  3  on the mutually opposing side walls  2 B and  2 C. Moreover, the frame  2 , as necessary, is provided with a cover plate  2 Q for covering that which is contained within the frame  2 . The cover plate  2 Q is formed in a rectangular plate shape that is attached to the top end faces of the side walls  2 B through  2 E. This frame  2  can be formed through machining a metal plate (for example, through performing a pressing process, like). 
         [0023]    The stationary shaft  3  is a straight circular column or square column member that has rigidity necessary to produce a stable vibration of the needle  20 . Here the stationary shaft  3  is a single unit, so that there will be no need to align axes. 
         [0024]    The driving portion  10  is provided with a magnet  4  that structures a portion of the needle  20 , and a coil  6  that is secured to the frame  2 . The magnet  4  is disposed in parallel to the stationary shaft  3  within the frame  2 , where the stationary shaft  3  extends along the axial direction (the X direction in the figure) without passing through the magnet  4 . 
         [0025]    In the magnet  4 , two flat rectangular magnet pieces  4 A and  4 B that have polarities along the axial direction (the X direction in the figure) are disposed with identical poles facing each other, connected with a spacer yoke  4 C interposed therebetween. If necessary, a reinforcing plate  5  is secured to a side face of the magnet  4  to increase the rigidity of the magnet  4  thereby. 
         [0026]    In the coil  6 , an electric wire is wound along the Y and Z directions around the magnet  4  wherein the direction of the magnetic pole faces the X direction, with the top face and/or bottom face of the coil  6  and, if necessary, a side face thereof as well, secured to the inner surface of the frame  2 . Securing of the coil  6  to the frame  2  may be through securing directly to the frame  2 , or the coil  6  may be wound onto a coil bobbin with the coil bobbin secured to the frame  2 . The magnet  4  is driven in the X direction through the application of an electric current to the coil  6 . In the example that is illustrated, the magnet  4  and the stationary shaft  3  are provided on the inside of the coil  6 ; however, if there is extra space in the Y direction in the figure, the stationary shaft  3  may instead be provided outside of the coil  6 . 
         [0027]    The needle  20  is provided with the magnet  4  and weight portions  7  that are connected to the magnet  4 . In the example that is illustrated, weight portions  7  are connected to both sides of the magnet  4  in the axial direction (the X direction in the figure). Additionally, the needle  20  is supported so as to be able to slide in the axial direction (the X direction in the figure) through the stationary shaft  3  passing through a guide hole  7 A that is formed in the weight portions  7 . The weight portions  7  may be structured through, for example, a metal material with a high specific gravity, and in the example that is illustrated, are shaped essentially as rectangular solids wherein the height in the Z direction is greater than the thickness of the magnet  4 . 
         [0028]    Instead of the example that is illustrated, a structure may be used wherein a bearing is connected to the needle  20 , and the bearing is supported so as to be able to slide on the stationary shaft  3 ; however, the efficiency with which the space in the Y direction is used can be increased through the provision of a guide hole  7 A directly in the weight portions  7 , with the stationary shaft  3  passing through the guide hole  7 A, as in the example that is illustrated, enabling a reduction in the width of the linear vibration motor  1 . Moreover, providing the guide hole  7 A directly in the weight portion  7  makes it is possible to eliminate the bearing, the connecting member for connecting the bearing to the needle  20 , and the like, enabling a reduction in the number of components. 
         [0029]    Elastic members  8  are disposed off-axis from the stationary shaft  3  within the frame  2 , to apply, to the needle  20 , an elastic force that opposes the driving force of the driving portion  10 . In the example that is illustrated, coil springs that extend and compress along the axial direction (the X direction) are used as the elastic members  8 , where the elastic members  8  are disposed coaxially on both sides of the needle  20  in the direction of vibration, where, in this example, two elastic members  8  are disposed between the weight portion  7  and the side walls  2 B and  2 C. 
         [0030]    In the example that is illustrated, the axis of the elastic members  8  is disposed so as to be parallel to the axis of the stationary shaft  3 . Additionally, ends of the elastic members  8  engage supporting protrusions  2 P that are provided on the side walls  2 B and  2 C, and the other ends of the elastic members  8  are inserted into attachment recessed portions  7 C that are provided in the weight portions  7 , and are engaged to supporting protrusions  7 C 1  within the attachment recessed portions  7 C. 
         [0031]    The operation of such a linear vibration motor  1  will be explained. When not driven, the needle  20  stands still in the vibration center position wherein the elastic forces of the two elastic members  8  are in equilibrium. When an electric current of a vibration generation signal is inputted into the coil  6 , a driving force is applied to the magnet  4  in the X direction, and the needle  20  undergoes reciprocating vibration along the stationary shaft  3  through the driving force and the elastic repulsive force of the elastic member  8 . The vibration generation signal preferably is an AC current of a resonant frequency that is determined by the mass of the needle  20  and the coefficient of elasticity of the elastic members  8 . 
         [0032]    Given such a linear motor  1 , the stationary shaft  3  does not pass through the magnet  4 , making it possible to secure a magnet volume that is able to produce an adequate driving force through a magnet  4  that is thin in the Z direction and wide in the Y direction, regardless of the diameter of the stationary shaft  3 . This enables the production of a thin linear vibration motor  1  able to produce a sufficient driving force. In contrast, in a type wherein the stationary shaft passes through the magnet, as it does in the prior art, the thickness of the magnet must be quite large when compared to the stationary shaft in order to produce an adequate driving force, and is coiled therearound, making it difficult to reduce adequately the thickness when considering the diameter of the stationary shaft and the driving force. 
         [0033]    Moreover, in the linear vibration motor  1  according to the example of the present invention, disposing the magnet  4  in parallel to the stationary shaft  3  on one side thereof, makes it possible to secure the magnet volume for producing an adequate driving force without dividing the magnet  4 . This makes it possible to produce a linear vibration motor  1  wherein a needle  20  is supported so as to be able to slide on a stationary shaft  3  in a structure wherein there is no increase in the number of components of the magnet  4  and wherein it is possible to prevent a reduction in the volume of the magnet  4 . 
         [0034]    Furthermore, disposing the elastic members  8  off-axis in relation to the stationary shaft  3  enables a reduction in the diameter of the elastic members  8  regardless of the diameter of the stationary shaft  3 . When the diameter of the elastic member  8  is reduced, the elastic force may be set arbitrarily through the selection of the material for the elastic members  8  and through providing many elastic members  8  in parallel. This can also reduce the thickness of a linear vibration motor  1  that is equipped with a stationary shaft  3 . 
         [0035]    Additionally, in the example that is illustrated, as is shown in  FIG. 2 ( a ) , the stationary shaft  3  is disposed on either the left or right side relative to the axis  0  of the needle, along the axial direction of the needle  20  (the X direction in the figure). The space in the Y direction for disposal of the magnet  4  can be increased through the provision of the stationary shaft  3  to the side of the needle  20  in this way. This makes it possible to secure the volume for producing the desired driving force, through increasing the width of the magnet  4  in the Y direction, when the thickness of the magnet  4  in the Z direction is reduced. 
         [0036]    At this time, one may consider the needle  20  rotating around the stationary shaft  3  that is disposed shifted to the left or the right side of the needle  20  and the other side, on the left or the right of the needle  20 , rotating upward or downward. In contrast, a slide bearing portion  21  with which the needle  20  makes sliding contact is provided on the inner surface of the frame  2  on the other side, the left or the right, and a sliding protrusion  7 B for contacting the slide bearing portion  21  is provided on the surface of the weight portion  7  of the needle  20 . Given this, when the slide bearing portion  21  is formed from a resin material, or the like, this can preserve stabilized vibration through enabling suppression of the production of noise, or the like, when the other side of the needle  20  contacts the inner surface of the frame  2 . 
         [0037]    When the position of the magnet  4  that is connected to the weight portion  7  of the needle  20  is shifted upward or downward, the needle  20  can be stuck to either the top or bottom side of the frame  2  through magnetic attraction that acts between the magnet  4  and the frame  2 , and thus when such a connecting position for the magnet  4  is used, the slide bearing portion  21  and the sliding protrusion  7 B, described above, need be provided on only one side, either the top or the bottom. 
         [0038]      FIG. 4  through  FIG. 7  are explanatory diagrams illustrating linear vibration motors according to other examples according to the present invention. Identical reference symbols are assigned to parts that are identical to the example set forth above, and redundant explanations are omitted. The linear vibration motor  1  illustrated in  FIG. 4  and  FIG. 5  is provided with a movable shaft  30  that is secured to the needle  20  side within the frame  2 , instead of the stationary shaft  3  that is described above. The movable shaft  30  is secured to the needle  20 , to move along the axial direction together with the needle  20 . A bearing  31  for supporting the movable shaft  30  so as to be able to slide is provided in the frame  2 . The bearing  31  is attached to a bearing supporting member  32 , and secured to the bottom face  2 A of the frame  2 . 
         [0039]    In the example illustrated in  FIG. 4  and  FIG. 5 , the movable shaft  30  is secured to a weight portion  7  of the needle  20 . The movable shaft  30  is a single shaft, and is borne on bearings  31  on both end portions thereof. In the example that is illustrated, a magnet  4  that is the driving portion  10  is arranged in parallel to the movable shaft  30  within the frame  2 . Here the magnet  4  is structured from three magnet pieces  4 X,  4 Y, and  4 Z, where these are connected with spacer yokes  4 C therebetween. The magnet pieces  4 X,  4 Y, and  4 Z are magnetized along the axial direction of the movement shaft  30 , where neighboring magnet pieces  4 X and  4 Y (and  4 Y and  4 Z) are magnetized in mutually opposing directions. Given this, two coils  6  that form the driving portion  10  are wound in series, and in mutually opposing directions, around the two spacer yokes  4 C. 
         [0040]    The elastic members  8  that are disposed off-axis from the movable shaft  30  are disposed two on each side of the axis of the movable shaft  30 , for a total of four elastic members  8 , with the axes thereof parallel to the axis of the movable shaft  30 . With this plurality of elastic members  8 , one end each (the stationary end of each) is supported on a respective supporting protrusion  2 P that is provided on the side wall  2 B or  2 C of the frame  2 , with the other end (the movable end) of each supported on a supporting protrusion  7 D that is provided in an end portion of the weight portion  7 . 
         [0041]    The example illustrated in  FIG. 6  is a modified example of the example illustrated in  FIG. 4  and  FIG. 5 , wherein, in the linear vibration motor  1 , the movable shaft  30  is divided into two shafts  30 A and  30 B, disposed along the axial direction. That is, the axes of the shafts  30 A and  30 B are coaxial. By dividing the movable shaft  30  in this way, and secured one of the shafts  30 A to one of the weight portions  7  and securing the other shaft  30 B to the other shaft portion  7 , the magnet  4  that is provided between the pair of weight portions  7  can be provided so as to be wide in the Y direction that is perpendicular to the movable shaft  30 , enabling the driving force to be increased thereby. 
         [0042]    The example illustrated in  FIG. 7  is an example wherein the example illustrated in  FIG. 6  is further modified, where, in the linear vibration motor  1 , shafts  3 A and  3 B, which are divided along the axial direction, form a stationary shaft  3  that is secured to the frame  2 . That is, the axes of the shafts  3 A and  3 B are coaxial. In these shafts  3 A and  3 B, one end is supported on a side wall  2 B or  2 C of the frame  2 , and the other end is a free end, where the free end is inserted slidably into a guide hole  7 A that is formed in a weight portion  7 . The stationary end portions of the shafts  3 A and  3 B are supported stably by supporting portions  2 B 1  and  2 C 1  that are separated in the axial direction from the side walls  2 B and  2 C of the frame  2 . 
         [0043]    As explained above, in the linear vibration motor  1  according to the present example of the present invention the needle  20  vibrates along the shaft that is provided protruding from the frame  2  (the stationary shaft  3  or the movable shaft  30 ), making it possible to produce a stabilized vibration and possible to produce resistance to damage when there is a drop impact, or the like. Given this, the elastic members  8  are provided off-axis from the shaft (the stationary shaft  3  or the movable shaft  30 ) within the frame  2 , thus enabling the diameter of the elastic members  8 , which are formed from coil springs, to not be set so as to be larger than the diameter of the shaft, enabling the thickness to be reduced commensurately. This enables the linear vibration motor  1  that is provided with a shaft (a stationary shaft  3  or a movable shaft  30 ) to be made thinner, while having no increase in the number of components of the magnet  4  and while suppressing a reduction in the volume of the magnet  4 . 
         [0044]      FIG. 8  shows a mobile information terminal  100  as an example of an electronic device equipped with a linear vibration motor  1  according to an example according to the present invention. The mobile information terminal  100  that is equipped with the linear vibration motor  1  that can produce a stabilized vibration and for which the thickness can be reduced enables the user to be notified through a stabilized vibration that does not tend to produce noise, when there is an incoming call in a communication function or at the beginning or end of an operation such as an alarm function. Moreover, this makes it possible to produce a mobile information terminal  100  with high mobility and which facilitates design performance, through reducing the thickness of the linear vibration motor  110 . Furthermore, because the linear vibration  1  is of a compact shape wherein the various components are contained within a frame  2  of a rectangular shape wherein the thickness is suppressed, it can be mounted, with excellent space efficiency, within a thinner mobile information terminal  100 . 
         [0045]    While examples according to the present invention were described in detail above, referencing the drawings, the specific structures thereof are not limited to these examples, but rather design variations within a range that does not deviate from the spirit and intent of the present invention are also included in the present invention. Moreover, insofar as there are no particular contradictions or problems in purposes or structures, or the like, the technologies of the various examples described above may be used together in combination.