Patent Publication Number: US-2022231588-A1

Title: Linear vibration motor and electronic apparatus using the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT/JP2020/043217 filed Nov. 19, 2020, which claims priority to each of Japanese Patent Application No. 2019-217457, filed Nov. 29, 2019, Japanese Patent Application No. 2019-235675, filed Dec. 26, 2019, Japanese Patent Application No. 2020-014403, filed Jan. 31, 2020, and Japanese Patent Application No. 2020-183652, filed Nov. 2, 2020, the entire contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a linear vibration motor and an electronic apparatus using the same. 
     BACKGROUND 
     An example of a linear vibration motor is described in U.S. Patent Application Publication No. 2016/0226361 (hereinafter “Patent Document 1”).  FIG. 22  is a disassembled perspective view of the linear vibration motor described in Patent Document 1. As shown, a linear vibration motor  300  includes a housing  301 , a vibrator  302 , a first guide  303 , a second guide  304 , and a coil  305 . The vibrator  302  includes a first magnet M 301 , a second magnet M 302 , and a third magnet M 303 . Moreover, a fourth magnet M 304  and a fifth magnet M 305  are fixed to the housing  301 . 
     The vibrator  302  vibrates along a first direction D 1  by the coil  305 , the first magnet M 301  serving as a driving magnet, and the first guide  303  and the second guide  304  that guide the movement of the vibrator  302 . The second magnet M 302  and the fourth magnet M 304  are disposed along the first direction D 1  to repel each other, and the third magnet M 303  and the fifth magnet M 305  are disposed along the first direction D 1  to repel each other. That is, the second magnet M 302  and the fourth magnet M 304 , and the third magnet M 303  and the fifth magnet M 305  constitute a magnetic spring mechanism for vibration of the vibrator  302  along the first direction D 1 . 
     By this magnetic spring mechanism, the vibration of the vibrator  302  is transferred to the housing  301  via the fourth magnet M 304  and the fifth magnet M 305 , and is sensed as the vibration of the linear vibration motor  300 . 
     In recent years, a linear vibration motor has been used as a vibration generator for skin sensory feedback or for confirming a key operation, an incoming call, or the like, by vibration in an electronic apparatus, such as a portable information terminal. In order to cause the linear vibration motor to generate sufficient vibration, it is necessary that the vibrator normally vibrates in one direction and unnecessary friction between the vibrator and a guide fixed to a housing is reduced. 
     For example, in the linear vibration motor  300  described in Patent Document 1, the vibrator  302  and each guide are engaged with each other with a protrusion provided on each side surface of the vibrator  302  fitting into a groove of each guide facing a corresponding one of the side surfaces. With this configuration, in a case where the dimensional accuracy of the width of the vibrator  302  is low and the width is shorter than the intended length, there is a possibility that the vibrator  302  rattles between the guides and the vibrator does not normally vibrate in one direction (that is, a first direction D 1 ). Whereas, in a case where the width of the vibrator  302  is longer than the intended length, there is a possibility that the vibrator  302  is excessively pressed against each guide and unnecessary friction with each guide occurs. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present disclosure to provide a linear vibration motor in which a vibrator can easily vibrate in one direction and unnecessary friction between the vibrator and a guide fixed to a housing may be reduced. Moreover, an electronic apparatus using the linear vibration motor is also provided in an exemplary aspect. 
     The present disclosure first focuses on a linear vibration motor. A first exemplary aspect of the linear vibration motor includes a housing, a vibrator, a first shaft, and a second shaft. The first shaft and the second shaft correspond to a guide fixed to the housing. The vibrator is accommodated in the housing, is configured to vibrate along a first direction, and has a first through-hole and a space each extending along the first direction. The first shaft and the second shaft are disposed along a second direction and are each fixed to the housing so as to slidably support the vibrator along the first direction. 
     In the first exemplary aspect of the linear vibration motor, the first shaft is fitted together by insertion into the first through-hole, and the second shaft is inserted into the space. The second shaft and part of a wall determining the space are in contact with each other in a third direction orthogonal to each of the first direction and the second direction. 
     A second exemplary aspect of the linear vibration motor includes, similarly to the first aspect, a housing, a vibrator, a first shaft, and a second shaft. In the second aspect of the linear vibration motor, the second shaft and part of the wall determining the space are in contact with each other with a second member containing a low-friction material in between in the third direction orthogonal to each of the first direction and the second direction. 
     The present disclosure also focuses on an electronic apparatus. The electronic apparatus according to the present disclosure includes the linear vibration motor according to the present disclosure and an apparatus housing. Moreover, the linear vibration motor is accommodated in the apparatus housing. 
     With the linear vibration motor according to the exemplary aspects of the present disclosure, a vibrator is configured to easily vibrate in one direction, and unnecessary friction between the vibrator and guides, that is, a first shaft and a second shaft, fixed to a housing is reduced. Further, the electronic apparatus according to the present disclosure is configured to generate vibration sufficient for skin sensory feedback and confirmation of a key operation, an incoming call, or the like since the linear vibration motor according to the present disclosure is used therein. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a linear vibration motor  100  illustrating a schematic form of the linear vibration motor according to the present disclosure. 
         FIG. 2  is a perspective view of the linear vibration motor  100  with a top plate portion  1   d  of a housing  1  thereof removed, placing a first shaft  3  on the front side. 
         FIG. 3  is a perspective view of the linear vibration motor  100  with the top plate portion  1   d  of the housing  1  thereof removed, placing a second shaft  4  on the front side. 
         FIG. 4(A)  is a perspective view of a first member  2   d  included in a vibrator  2  of the linear vibration motor  100 ,  FIG. 4(B)  is a front view of the first member  2   d , and  FIG. 4(C)  is a sectional view of the first member  2   d  in the direction of arrows, taken along a plane including a line A-A in  FIG. 4(B) . 
         FIG. 5  is a sectional view, corresponding to  FIG. 4(C) , schematically illustrating a change in the state of contact between the first member  2   d  and the second shaft  4  in a case where there is a variation in the width of the vibrator  2  in a second direction D 2 . 
         FIG. 6  is a sectional view, corresponding to  FIG. 4(B) , schematically illustrating a change in the state of contact between the first member  2   d  and the second shaft  4  in a case where the second shaft  4  is inclined relative to a first direction D 1 . 
         FIG. 7(A)  is a front view of a first modification of the first member  2   d ,  FIG. 7(B)  is a front view of a second modification of the first member  2   d ,  FIG. 7(C)  is a front view of a third modification of the first member  2   d , and  FIG. 7(D)  is a front view of a fourth modification of the first member  2   d.    
         FIG. 8(A)  is a perspective view of a fifth modification of the first member  2   d ,  FIG. 8(B)  is a front view of the fifth modification of the first member  2   d , and  FIG. 8(C)  is a sectional view of the fifth modification of the first member  2   d  in the direction of arrows, taken along a plane including a line B-B in  FIG. 8(B) . 
         FIG. 9  is a perspective view of the vibrator  2  including a sixth modification of the first member  2   d.    
         FIG. 10  is a perspective view, corresponding to  FIG. 3 , of a linear vibration motor  100 A that is a first modification of the linear vibration motor  100 . 
         FIG. 11(A)  is a front view of a second member  7  in the linear vibration motor  100 A,  FIG. 11(B)  is a sectional view of the second member  7  in the direction of arrows, taken along a plane including a line C-C in  FIG. 11(A) , and  FIG. 11(C)  is a sectional view, corresponding to  FIG. 11(B) , of a first modification of the second member  7  in the direction of arrows in the linear vibration motor  100 A. 
         FIG. 12  is a front view of a second modification of the second member  7  in the linear vibration motor  100 A. 
         FIG. 13  is a perspective view, corresponding to  FIG. 3 , of a linear vibration motor  100 B that is a second modification of the linear vibration motor  100 . 
         FIG. 14(A)  is a front view of the second member  7  in the linear vibration motor  100 B,  FIG. 14(B)  is a sectional view of the second member  7  in the direction of arrows, taken along a plane including a line D-D in  FIG. 14(A) , and  FIG. 14(C)  is a sectional view, corresponding to  FIG. 14(B) , of a first modification of the second member  7  in the direction of arrows in the linear vibration motor  100 B. 
         FIG. 15  is a front view of a second modification of the second member  7  in the linear vibration motor  100 B. 
         FIG. 16(A)  is a perspective view of a third modification of the second member  7  in the linear vibration motor  100 B,  FIG. 16(B)  is a front view of another form of the third modification of the second member  7 , and  FIG. 16(C)  is a front view of still another form of the third modification of the second member  7 . 
         FIG. 17  is a perspective view of the vibrator  2  in a state that a fourth modification of the second member  7  in the linear vibration motor  100 B is fitted into a groove T formed on another side surface of a substrate  2   a.    
         FIG. 18(A)  is a perspective view of the fourth modification of the second member  7 ,  FIG. 18(B)  is a perspective view of a state that the fourth modification of the second member  7  is fitted into the groove T formed on the other side surface of the substrate  2   a.    
         FIG. 19  is a perspective view of the vibrator  2  in a state that a fifth modification of the second member  7  in the linear vibration motor  100 B is fitted into the groove T formed on the other side surface of the substrate  2   a.    
         FIG. 20(A)  is a perspective view of the fifth modification of the second member  7 ,  FIG. 20(B)  is a perspective view of a state in which the fifth modification of the second member  7  is fitted into the groove T formed on the other side surface of the substrate  2   a.    
         FIG. 21  is a transparent perspective view of a portable information terminal  1000  that is a schematic form of the electronic apparatus according to the present disclosure. 
         FIG. 22  is an exploded perspective view of a conventional linear vibration motor  300  according to the background art. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Features of the present disclosure will be described with reference to the drawings. In the schematic forms and embodiments of the linear vibration motor to be described below, the same or common portions are denoted by the same reference signs in the drawings, and there may be a case where descriptions thereof are not repeated. 
     Schematic Form of Linear Vibration Motor— 
     A linear vibration motor  100  exhibiting a schematic form of the linear vibration motor according to the present disclosure will be described with reference to  FIG. 1  to  FIG. 5 . 
       FIG. 1  is a perspective view of the linear vibration motor  100 .  FIG. 2  is a perspective view of the linear vibration motor  100  with a top plate portion  1   d  of a housing  1  thereof removed, placing a first shaft  3  on the front side.  FIG. 3  is a perspective view of the linear vibration motor  100  with the top plate portion  1   d  of the housing  1  thereof removed, placing a second shaft  4  on the front side. 
     As illustrated in  FIG. 1  to  FIG. 3 , the linear vibration motor  100  includes the housing  1 , a vibrator  2 , the first shaft  3 , the second shaft  4 , a coil  5 , an extended wiring member  6  connected to the coil  5 , a fourth magnet M 4 , and a fifth magnet M 5 . 
     The housing  1  (from which the top plate portion  1   d  is removed) includes a bottom plate portion  1   a  extending in a first direction D 1  to be described later, and a first side surface  1   b  and a second side surface  1   c  formed by bending the bottom plate portion  1   a . That is, the bottom plate portion  1   a , the first side surface  1   b , and the second side surface  1   c  form a space in which the vibrator  2  is accommodated, and the top plate portion  1   d  serves as a lid member covering the space. The top plate portion  1   d  is in contact with each of the bottom plate portion  1   a , the first side surface  1   b , and the second side surface  1   c . As a material of the housing  1 , stainless steel, such as SUS304, may be used, for example. It is noted that the top plate portion and other portions may be made of different materials in alternative aspects. 
     In the linear vibration motor  100 , the first side surface  1   b  and the second side surface  1   c  are formed by bending the bottom plate portion  1   a  at a right angle. The first shaft  3  and the second shaft  4  each extend along the first direction D 1 , and are disposed along a second direction D 2  parallel to the bottom plate portion  1   a  and orthogonal to the first direction D 1 . As will be described later, the first shaft  3  and the second shaft  4  slidably support the vibrator  2  along the first direction D 1 . As a material of the first shaft  3  and the second shaft  4 , stainless steel, such as SUS304, may be used, for example. 
     The first shaft  3  and the second shaft  4  are each fixed to bridge a space between the first side surface  1   b  and the second side surface  1   c . It is noted that the method of fixing each shaft to the first side surface  1   b  and the second side surface  1   c  is not limited to the above. Further, each shaft may be fixed to a substrate  2   a  using a separate member, for example. 
     Furthermore, the fourth magnet M 4  is fixed to the first side surface  1   b  such that the array direction of the magnetic poles is parallel to the first direction D 1 , and the fifth magnet M 5  is fixed to the second side surface  1   c  with the array direction of the magnetic poles as same as above. For fixing the fourth magnet M 4  to the first side surface  1   b  and fixing the fifth magnet M 5  to the second side surface  1   c , an epoxy-based adhesive may be used, for example. 
     The housing  1  of the linear vibration motor  100  has a structure in which the surface orthogonal to each of the bottom plate portion  1   a , the first side surface  1   b , and the second side surface  1   c  is open as described above, but the shape is not limited thereto. For example, the housing  1  may have a sealed structure when the top plate portion is attached. It is noted that the housing  1  includes a fixing portion to fix the housing  1  in an electronic apparatus such as a portable information terminal, but the fixing portion is not illustrated (the same applies hereinafter). 
     As further shown, the vibrator  2  is accommodated in the space described above in the housing  1 . The vibrator  2  includes the substrate  2   a , a first sleeve  2   b , a second sleeve  2   c , and a first member  2   d , as well as a first magnet M 1 , a second magnet M 2 , and a third magnet M 3 . In the linear vibration motor  100 , the vibrator  2  is configured to vibrate along the first direction D 1  when a driving force to be described later is applied, from the coil  5  to be described later, to the first magnet M 1  serving as a driving magnet. 
     The substrate  2   a  has three protrusions on one side surface and two protrusions on another side surface, and has a rectangular parallelepiped shape extending in the first direction D 1  to be described later. It is noted that the number and arrangement of the protrusions are not limited to those described above. Further, in the linear vibration motor  100 , recesses, into which magnet for forming a magnetic spring mechanism to be described later are inserted, are each formed on one end surface and the other end surface of the substrate  2   a . In the linear vibration motor  100 , the recesses pass through from one main surface to another main surface of the substrate  2   a , but the present invention is not limited thereto. 
     One of the two protrusions provided on one side surface of the substrate  2   a  is provided with a groove that matches the outer shape of the first sleeve  2   b  and extends along the first direction D 1 . The other of the two protrusions is provided with a groove that matches the outer shape of the second sleeve  2   c  and extends along the first direction D 1 . The first sleeve  2   b  and the second sleeve  2   c  are fixed by being fitted into the grooves of the respective protrusions. That is, in the linear vibration motor  100 , the vibrator  2  has two through-holes (e.g., first through-holes) extending along the first direction D 1  on the one side surface side. Note that the through-hole referred to here is not limited to the sleeve illustrated in  FIG. 2 , and may be an annular shape that has a short length along the first direction D 1  in an alternative aspect. Further, part of the side surface of the through-hole may be open. Furthermore, the number of the through-holes forming the first through-hole is not limited to two in alternative aspects. 
     The protrusion disposed at the central portion of the one side surface and the two protrusions provided on the other side surface are each provided with a groove extending along the first direction D 1  and having a shape that prevents each shaft from coming into contact with the protrusions. The first member  2   d , which will be described in detail later, is fixed to the central portion of the other side surface of the substrate  2   a.    
     The substrate  2   a  is also configured to function as a weight portion. The vibrator  2  may further include another weight portion different from the substrate  2   a  in an alternative aspect. 
     As the material of the substrate  2   a  and the other weight portion, tungsten (W) and an alloy containing the same, stainless steel such as SUS304, Al and an alloy containing the same, or the like may be used, for example. In order to increase the mass of the vibrator  2  and to transfer a large vibration to the housing  1  via the magnetic spring mechanism, it is preferable that the substrate  2   a  and the other weight portion be made of a material having large relative density such as tungsten (W). 
     A through-hole is provided in the central portion of the substrate  2   a , and the first magnet M 1  is inserted and fixed such that the first magnet M 1  and the coil  5  (to be described later) face each other. For fixing the first magnet M 1  to the substrate  2   a , an epoxy-based adhesive is used, for example. Inserting each magnet into the through-hole makes it easy to fix the magnet to the substrate  2   a . Further, the magnet may be fixed to the substrate  2   a  with high accuracy. It is noted that each of the magnets may be fixed to the substrate  2   a  without being inserted into the through-hole. 
     In the linear vibration motor  100 , the first magnet M 1  includes five magnets M 1   a , M 1   b , M 1   c , M 1   d , and M 1   e  arrayed along the first direction D 1 , and these magnets are disposed in a Halbach array, for example. However, it is also noted that the configuration of the first magnet M 1  is not limited to the above. 
     It is sufficient that the first magnet M 1  serving as a driving magnet includes at least one magnet that can apply a driving force for vibration of the vibrator  2  from the coil  5 , to be described later. In a case where the first magnet M 1  forms the Halbach array, it is sufficient that the first magnet M 1  includes an odd number of three or more magnets arrayed along the first direction D 1 . In the present disclosure, an array of driving magnets that concentrate a magnetic field, generated by driving magnets, between the driving magnets and a coil that drives the vibrator is broadly referred to as the Halbach array. Therefore, it is sufficient that the number of magnets forming the Halbach array is an odd number of three or more. 
     As a material of the first magnet M 1 , a Nd—Fe—B-based or a Sm—Co-based rare-earth magnet may be used, for example. It is noted that for the first magnet M 1 , it is preferable to use a Nd—Fe—B based rare-earth magnet that have strong magnetic force and is able to increase the driving force of the vibrator  2 . 
     The second magnet M 2  is inserted into and fixed to the recess of the one end surface of the substrate  2   a  such that the array direction of the magnetic poles is parallel to the first direction D 1 , and the second magnet M 2  and the fourth magnet M 4  fixed to the first side surface  1   b  of the housing  1  are disposed to face each other and magnetically repel each other. The third magnet M 3  is inserted into and fixed to the recess of the other end surface such that the array direction of the magnetic poles is parallel to the first direction D 1 , and the third magnet M 3  and the fifth magnet M 5  fixed to the second side surface  1   c  of the housing  1  are disposed to face each other and magnetically repel each other. 
     For example, the centers of gravity of the second magnet M 2 , the third magnet M 3 , the fourth magnet M 4 , and the fifth magnet M 5  are disposed on the same axial line parallel to the first direction D 1  in plan view. It is noted that it is sufficient that the second magnet M 2 , the third magnet M 3 , the fourth magnet M 4 , and the fifth magnet M 5  are disposed such that at least respective magnets partially overlap with each other when viewed from the first direction D 1 . The N-pole of the second magnet M 2  and the N-pole of the fourth magnet M 4  face each other, and the S-pole of the third magnet M 3  and the S-pole of the fifth magnet M 5  face each other. 
     With this configuration, the pair of the second magnet M 2  and the fourth magnet M 4  and the pair of the third magnet M 3  and the fifth magnet M 5  each form a magnetic spring mechanism for the vibration along the first direction D 1  of the vibrator  2 . For fixing the second magnet M 2  and the third magnet M 3  to the substrate  2   a , an epoxy-based adhesive may be used, for example. 
     Inserting each magnet into each recess makes it easy to fix the magnet to the substrate  2   a . Further, each magnet may be fixed to the substrate  2   a  with high accuracy. It is also noted that each magnet may be fixed to the substrate  2   a  without being inserted into the recess. 
     For the material of the second magnet M 2 , the third magnet M 3 , the fourth magnet M 4 , and the fifth magnet M 5 , a rare-earth magnet of a Nd—Fe—B-base or a Sm—Co-base, or the like may be used, for example. Moreover, for each magnet described above, it is preferable to use a Sm—Co-based rare-earth magnet having a small temperature change rate of magnetic force and capable of stably exhibiting a magnetic spring effect. 
     The coil  5  is formed by winding a conductor wire around a virtual winding axis. The coil  5  is fixed to the bottom plate portion  1   a  of the housing  1  such that the winding axis is parallel to the direction normal to the bottom plate portion  1   a  of the housing  1 , that is, the winding axis is orthogonal to the first direction D 1  and the second direction D 2 . In the linear vibration motor  100 , the coil  5  has a rectangular shape with rounded corners when viewed from the winding axis direction. 
     As the coil  5 , a coil obtained by winding a coated Cu wire having a diameter of 0.06 mm approximately 50 turns is used, for example. Moreover, the coil  5  is connected to a stabilized power supply via a power amplifier by the extended wiring member  6 , such as a flexible substrate, on which a wiring pattern is printed. The coil  5  is configured to apply a driving force to the first magnet M 1  so that the vibrator  2  is able to vibrate along the first direction D 1  by being energized via the extended wiring member  6 . In  FIG. 2  and  FIG. 3 , the winding wire of the coil  5  is not illustrated. 
     When a current flows through the coil  5 , because of an interaction with the magnetic field of the first magnet M 1 , Lorentz force in a direction orthogonal to each of the magnetic field direction and the current flow direction is applied to the coil  5 . Whereas, since the coil  5  is fixed to the housing  1  (i.e., the bottom plate portion  1   a ), reaction force to the Lorentz force is applied to the first magnet M 1 . Therefore, the coil  5  applies, by energization, a driving force along the first direction D 1  to the first magnet M 1 , and consequently to the vibrator  2 . That is, the first magnet M 1  functions as a driving magnet in the linear vibration motor  100 . 
     As described above, when the coil  5  has a rectangular shape when viewed from the winding axis direction, the direction of the Lorentz force is more likely to be aligned in the first direction D 1  than when the coil  5  has an annular shape. Therefore, the driving force along the first direction D 1  applied to the vibrator  2  is increased, and this achieves a preferable performance. 
     According to the exemplary aspect, the vibrator  2  is engaged with the first shaft  3  and the second shaft  4  as to be described below. First, the engagement between the vibrator  2  and the first shaft  3  will be described. As described above, the first sleeve  2   b  is fixed to one of the two protrusions provided on the one side surface of the substrate  2   a  of the vibrator  2 , and the second sleeve  2   c  is fixed to the other of the two protrusions provided on the one side surface of the substrate  2   a.    
     In exemplary aspects, examples of the material for the first sleeve  2   b  and the second sleeve  2   c  include low-friction materials of a polyphenylene sulfide-base, an aromatic polyester base, which is a so-called liquid crystal polymer, a polyacetal-base, or the like, brass, Ni, or stainless steel such as SUS304. For purposes of this disclosure, the low-friction material refers to a material exhibiting dynamic friction coefficient of approximately 0.15 or less relative to carbon steel in a thrust type dynamic friction coefficient specified in JIS K7218. 
     The first shaft  3  is slidably fitted together by insertion into the first sleeve  2   b  and the second sleeve  2   c . For purposes of this disclosure, “fit together by insertion” means that the first shaft  3  is inserted and fitted into each sleeve in a state that looseness is suppressed within accuracy determined by a dimensional tolerance. With this configuration, the vibration of the vibrator  2  is restricted along the first direction D 1 . It is also noted that the engagement between the vibrator  2  and the first shaft  3  is not limited to the above. 
     Next, the engagement between the vibrator  2  and the second shaft  4  will be described. As described above, the vibrator  2  includes the first member  2   d  fixed to the central portion of the other side surface of the substrate  2   a . The first member  2   d  will be described in detail with reference to  FIGS. 4(A) -(C) and  FIG. 5 . 
       FIG. 4(A)  is a perspective view of the first member  2   d  included in the vibrator  2  of the linear vibration motor  100 .  FIG. 4(B)  is a front view of the first member  2   d .  FIG. 4(C)  is a sectional view of the first member  2   d  in the direction of arrows, taken along a plane including a line A-A in  FIG. 4(B)  and being orthogonal to the first direction D 1 .  FIG. 5  is a sectional view corresponding to  FIG. 4(C)  schematically illustrating a change in the state of contact between the first member  2   d  and the second shaft  4  when there is a variation in the width of the vibrator  2  in the second direction D 2 . It is noted that in  FIG. 4  and  FIG. 5 , the second shaft  4  is also illustrated so that the state of contact with the first member  2   d  may be understood. 
     In the linear vibration motor  100 , a groove T opening in the second direction D 2  is formed in the first member  2   d  in a state of being fixed to the other side surface of the substrate  2   a . The groove T is deeper than the diameter of the second shaft  4  and extends along the first direction D 1 . The width of the groove T along a third direction D 3  orthogonal to each of the first direction D 1  and the second direction D 2  increases from the central portion of the groove T toward the one end and the other end. It is noted that the change in the width of the groove T does not need to start from the central portion of the groove T, and may start from any portion inside the groove T. In other words, it is not necessary that the first member  2   d  is bilaterally symmetrical when viewed from the second direction D 2 . 
     That is, in the linear vibration motor  100 , the vibrator  2  has a space on the other side surface side extending along the first direction D 1 . The length of the space becomes longer along the third direction D 3  from the inside toward the one end and the other end. That is, in the first member  2   d  in  FIG. 3 , a protrusion of which height increases from the one end and the other end toward the central portion of the groove T is provided in the groove T. 
     It is noted that the sectional shape of the groove T may have various shapes as indicated in modifications to be described later in alternative aspects. The section of the groove T has a U-shape, but the shape of the groove T is not limited thereto. In the linear vibration motor  100 , a case where the space included in the vibrator  2  is the groove T has been described. However, the form of the space is not limited to the groove and may be a through-hole (i.e., a second through-hole), to be described later, that does not open in the second direction D 2 . 
     Examples of the material for the first member  2   d  include low-friction materials of a polyacetal-base, a polyetheretherketone-base, a fluororesin-base, a polyester-base, or the like. Here, the low-friction material refers to a material specified in the definition described above. Note that, without being limited to the above, a Cu—C-based metal bearing material or the like may be used, for example. 
     The second shaft  4  is inserted into the groove T. The second shaft  4  and part of the wall determining the groove T are in contact with each other in the third direction D 3  orthogonal to each of the first direction D 1  and the second direction D 2 . Specifically, as illustrated in  FIG. 4(B) , at the central portion in the longitudinal direction of the groove T, that is, at the portion where the width along the third direction D 3  is the shortest, at least one of the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing and the second shaft  4  are slidably in contact with each other. 
     That is, in the linear vibration motor  100 , the second shaft  4  and part of the wall determining the space described above are in contact with each other at a portion where the length of the space along the third direction D 3  is the shortest. As illustrated in  FIG. 4(B)  and  FIG. 4(C) , it is preferable that both of the side walls S 1  and S 2  be in contact with the second shaft  4 . 
     In the linear vibration motor  100 , as described above, the first shaft  3  is fitted together by insertion into the through-hole (i.e., the first through-hole) provided in the vibrator  2  extending along the first direction D 1 . This restricts the vibrator  2  to vibrate along the first direction D 1 . 
     Since the first member  2   d  has the structure described above, the second shaft  4  and the first member  2   d  are slidably in contact with each other as illustrated in  FIG. 5 . That is, even in a case where the width of the vibrator  2  is shorter than an intended width in the second direction D 2 , the second shaft  4  is reliably in contact with at least one of the side walls S 1  and S 2  of the groove T, as in  FIG. 5  where the second shaft  4  is virtually illustrated by a long broken line. Therefore, the vibrator  2  does not rattle between the first shaft  3  and the second shaft  4 . As a result, the vibrator  2  is configured to easily vibrate along the first direction D 1 . 
     Whereas, even in a case where the width of the vibrator  2  is longer than an intended width in the second direction D 2 , the vibrator  2  is can move in the second direction D 2 , as the second shaft  4  is virtually illustrated by a short broken line in  FIG. 5 . Therefore, the vibrator  2  is not excessively pressed against the first shaft  3  and the second shaft  4 . As a result, unnecessary friction between the vibrator  2  and each shaft is reduced. 
     Further, in the linear vibration motor  100 , as described above, the width of the groove T of the first member  2   d  increases from the central portion toward the one end and the other end of the groove T. The advantage of this structure will be described with reference to  FIG. 6 .  FIG. 6  is a sectional view corresponding to  FIG. 4(B) , schematically illustrating a change in the state of contact between the first member  2   d  and the second shaft  4  when the second shaft  4  is inclined relative to the first direction D 1 . 
     Due to a problem of the accuracy of assembling the second shaft  4  into the housing  1 , for example, the second shaft  4  may be inclined relative to the first direction D 1 , as in  FIG. 6  where the second shaft  4  is virtually illustrated by a long broken line or a short broken line. With the shape of the first member  2   d  described above, the second shaft  4  and the first member  2   d  may be brought into contact with each other with a small area of the central portion of the groove T. Therefore, even when the second shaft  4  is inclined relative to the first direction D 1 , the vibrator  2  is not excessively pressed against the second shaft  4 . As a result, excessive friction between the vibrator  2  and the second shaft  4  can be suppressed. 
     This structure can also suppress not only the excessive friction in the case above, but also the friction between the vibrator  2  and the second shaft  4  due to the deviation of the driving direction of the vibrator  2  from the first direction D 1 . As described above, when a current flows through the coil  5 , Lorentz force is applied to the coil  5  by the magnetic field of the first magnet M 1 , and the reaction force to the Lorentz force is applied to the first magnet M 1 . That is, the coil  5  applies a driving force along the first direction D 1  to the first magnet M 1 , and consequently to the vibrator  2  by energization. 
     However, the coil  5  is not a complete rectangle but has rounded corners, and there may be a case where a portion corresponding to each side of the rectangle is not exactly orthogonal to the first direction D 1 . Therefore, the direction of the reaction force to the Lorentz force that the vibrator  2  receives may slightly fluctuate from the first direction D 1 . As a result, as schematically illustrated in  FIG. 5  and  FIG. 6 , the relative positional relationship between the vibrator  2  and the second shaft  4  can change during the vibration of the vibrator  2 . 
     In a case where the first member  2   d  has the structure in  FIG. 4 , the deviation of the relative positional relationship between the vibrator  2  and the second shaft  4 , caused by the fluctuation of the reaction force to the Lorentz force, can be absorbed by the effect described above. As a result, the friction between the vibrator  2  and the second shaft  4  is suppressed. 
     Various modifications of the first member  2   d  will be described with reference to  FIGS. 7( a )-( d )  and  FIGS. 8( a )-( c ) .  FIG. 7(A)  is a front view of a first modification of the first member  2   d .  FIG. 7(B)  is a front view of a second modification of the first member  2   d .  FIG. 7(C)  is a front view of a third modification of the first member  2   d .  FIG. 7(D)  is a front view of a fourth modification of the first member  2   d . In these figures, the second shaft  4  is also illustrated so that the state of contact with the first member  2   d  may be understood. 
     In the first modification, the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing have a flat surface when viewed from the second direction D 2 . That is, in the first modification, the first member  2   d  and the second shaft  4  are in contact with each other along two lines extending in the first direction D 1 . Also in this case, the vibrator  2  does not rattle between the first shaft  3  and the second shaft  4 , and the vibrator  2  is not excessively pressed against the first shaft  3  and the second shaft  4 . Therefore, the vibrator  2  is configured to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft can be reduced. 
     In the second modification, the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing have a saw-tooth shape when viewed from the second direction D 2 . That is, in the second modification, the first member  2   d  and the second shaft  4  are in contact with each other in a minute region. Therefore, in the second modification, slidability is higher than that of the first modification. In the second modification, the first member  2   d  and the second shaft  4  are in contact with each other at four portions, but the number of contact portions is not limited thereto. Also in this case, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. 
     In the third modification, the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing have a trapezoidal shape when viewed from the second direction D 2 . That is, in the third modification, the first member  2   d  and the second shaft  4  are in contact with each other along two lines extending in the first direction D 1 . Note that, in the third modification, the two lines serving as the contact portions are shorter than those in the first modification. Therefore, in the third modification, slidability is higher than that of the first modification. Also in this case, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. 
     In the fourth modification, the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing have an arc shape when viewed from the second direction D 2 . That is, in the fourth modification, the first member  2   d  and the second shaft  4  are in contact with each other in a minute region. Therefore, in the fourth modification, slidability is higher than that of the first modification. Also in this case, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft is also reduced. 
     Further, in the fourth modification, the deviation of the relative positional relationship between the vibrator  2  and the second shaft  4 , caused by the inclination of the second shaft  4  relative to the first direction D 1  and the fluctuation of the reaction force to the Lorentz force, may be absorbed. 
       FIG. 8(A)  is a perspective view of a fifth modification of the first member  2   d .  FIG. 8(B)  is a front view of the fifth modification of the first member  2   d .  FIG. 8(C)  is a sectional view of the fifth modification of the first member  2   d  in the direction of arrows, taken along a plane including a line B-B in  FIG. 8(B)  and being orthogonal to the first direction D 1 . In these figures, the second shaft  4  is also illustrated so that the state of contact with the first member  2   d  may be understood. 
     In the fifth modification of the first member  2   d , a through-hole H (second through-hole) penetrating through the first member  2   d  along the first direction D 1  is formed in the first member  2   d . That is, also in the fifth modification, the vibrator  2  has a space on the other side surface side extending along the first direction D 1 . The length of the space becomes longer along the third direction D 3  from the inside toward the one end and the other end. That is, in the fifth modification of the first member  2   d , protrusions of which heights increase from one end and the other end toward the central portion of the through-hole H are provided in the through-hole H. The shape of the through-hole H is not limited to the shape illustrated in  FIG. 8(B) , for example. 
     Also in the fifth modification, as illustrated in  FIG. 8(B) , at the central portion in the longitudinal direction of the groove T, at least one of the upper side wall S 1  and the lower side wall S 2  of the through-hole H in the drawing and the second shaft  4  are slidably in contact with each other. That is, also in the linear vibration motor  100  in which the fifth modification of the first member  2   d  is used, the second shaft  4  and part of the wall determining the space described above are in contact with each other, at a portion where the length of the space along the third direction D 3  is the shortest. As illustrated in  FIG. 8(B)  and  FIG. 8(C) , it is preferable that both of the side walls S 1  and S 2  be in contact with the second shaft  4 . 
     Also in the fifth modification, similar to the example of the first member  2   d  in  FIG. 3 , the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. Further, in the fifth modification, the deviation of the relative positional relationship between the vibrator  2  and the second shaft  4 , caused by the inclination of the second shaft  4  relative to the first direction D 1  and the fluctuation of the reaction force to the Lorentz force, may be absorbed. 
       FIG. 9  is a perspective view of the vibrator  2  including a sixth modification of the first member  2   d . In  FIG. 9 , the first shaft  3  and the second shaft  4  are also illustrated so that the state of engagement between the vibrator  2  and the first shaft  3 , and between the vibrator  2  and the second shaft  4  may be understood. 
     In the sixth modification of the first member  2   d , the first member  2   d  is a sleeve that has the same shape and is made of the same material as those of the first sleeve  2   b  and the second sleeve  2   c . The first sleeve  2   b  and the second sleeve  2   c  are fitted into a groove provided on one side surface side of the substrate  2   a  along the first direction D 1 , and the first member  2   d  is fitted into a groove provided on the other side surface side of the substrate  2   a  along the first direction D 1 . In  FIG. 9 , each groove provided in the substrate  2   a  is open to the lower side in the drawing in the third direction D 3 . Therefore, the first sleeve  2   b , the second sleeve  2   c , and the first member  2   d  in the respective grooves, and the first shaft  3  and the second shaft  4  are naturally invisible, but are illustrated in a see-through state. 
     As described above, the first shaft  3  is slidably fitted together by insertion into the first sleeve  2   b  and the second sleeve  2   c . Whereas the second shaft  4  is slidably fitted together by insertion into the first member  2   d  that is a sleeve having the same shape and the same material as those of the first sleeve  2   b  and the second sleeve  2   c . Here, the first member  2   d  is fitted into the groove on the other side surface side of the substrate  2   a , such that the first member  2   d  configured to be inclined in the third direction D 3  when external force is applied. 
     As described above, it is possible that the second shaft  4  becomes inclined relative to the first direction D 1  due to a problem of the accuracy of assembling the second shaft  4  into the housing  1 . Here, it is assumed that the first member  2   d  is fitted into the groove on the other side surface side of the substrate  2   a  such that the first member  2   d  may be inclined. In the case above, even when the second shaft  4  is inclined relative to the first direction D 1 , the first member  2   d  is inclined in accordance with the inclination of the second shaft  4 , by the force generated when the vibrator  2 , into which the first shaft  3  and the second shaft  4  are fitted together by insertion, is attached to the housing  1 . As a result, the vibrator  2  is not excessively pressed against the second shaft  4 . Further, as a result, excessive friction between the vibrator  2  and the second shaft  4  is suppressed. 
     In the description above, a case where each groove provided to the substrate  2   a  opens in the third direction D 3  has been described. However, when each of the grooves opens in the second direction D 2 , the first member  2   d  may be inclined in the second direction D 2 . That is, in this case, the first member  2   d  is inclined in accordance with the inclination of the second shaft  4  relative to the second direction D 2 , and the excessive friction between the vibrator  2  and the second shaft  4  may similarly be suppressed. 
     First Modification of Schematic Form of Linear Vibration Motor— 
     A linear vibration motor  100 A that is a first modification of the linear vibration motor  100  being a schematic form of the linear vibration motor according to the present disclosure, will be described with reference to  FIG. 10  and  FIGS. 11( a )-( c ) . 
       FIG. 10  is a perspective view of the linear vibration motor  100 A that is the first modification of the linear vibration motor  100 , corresponding to  FIG. 3 .  FIG. 11(A)  is a front view of a second member  7  in the linear vibration motor  100 A.  FIG. 11(B)  is a sectional view of the second member  7  in the direction of arrows, taken along a plane including a line C-C in  FIG. 11(A)  and being orthogonal to the first direction D 1 .  FIG. 11(C)  is a sectional view of the first modification of the second member  7  in the direction of arrows in the linear vibration motor  100 A, corresponding to  FIG. 11(B) . In  FIGS. 11( a )-( c ) , the second shaft  4  is also illustrated to indicate the state of contact with the first member  2   d.    
     The linear vibration motor  100 A differs from the linear vibration motor  100  in the manner of engagement between the vibrator  2  and the second shaft  4 . Since other configurations are basically the same as those of the linear vibration motor  100  described above, repetitive description will be omitted. 
     In the linear vibration motor  100 A, the second member  7  containing a low-friction material is provided in a cylindrical shape at the central portion of the second shaft  4 . Further, on the other side surface of the substrate  2   a  of the vibrator  2 , there is formed a groove T that opens in the second direction D 2 , has a depth larger than the diameter of the second shaft  4 , and extends along the first direction D 1 . That is, in the linear vibration motor  100 A, the groove T corresponds to the space extending along the first direction D 1 . 
     The second shaft  4  and part of the wall determining the groove T are in contact with each other in the third direction D 3 . Specifically, as illustrated in  FIG. 11(B) , at the central portion in the longitudinal direction of the groove T, at least one of the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing and the second shaft  4  are slidably in contact with each other via the second member  7 . As illustrated in  FIG. 11(B) , both of the side walls S 1  and S 2  are preferably in contact with the second member  7 . 
     For the second member  7 , low-friction materials of a polyacetal-base, a polyetheretherketone-base, a fluororesin-base, a polyester-base, or the like may be used, for example. Here, the low-friction material is specified in the definition described in the description of the material used for the first member  2   d.    
     As further shown, the second member  7  has a cylindrical shape in  FIG. 10 ,  FIG. 11(A) , and  FIG. 11(B) , but it is noted that the shape of the second member  7  is not limited thereto. That is, it is sufficient that the second member  7  has a shape in which at least one of the upper side wall S 1  and the lower side wall S 2  of the groove T and the second shaft  4  are indirectly and slidably in contact with each other. For example, as illustrated in  FIG. 11(C) , the second member  7  may have a shape with a portion that cannot come into contact with the groove T removed. Further, the position where the second member  7  is provided is not limited to the central portion of the second shaft  4 . Furthermore, a plurality of second members  7  may be provided to the second shaft  4 . The width of the second member  7  in the first direction D 1  is preferably equal to or less than 2 mm. 
     Also, in the linear vibration motor  100 A, the vibrator  2  does not rattle between the first shaft  3  and the second shaft  4 , and the vibrator  2  is not excessively pressed against the first shaft  3  and the second shaft  4 . Therefore, the vibrator  2  can be configured to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft is reduced. Further, since the number of components is reduced as compared with the linear vibration motor  100 , assembling accuracy and the efficiency of assembling work may be improved. 
     A second modification of the second member  7  in the linear vibration motor  100 A will be described with reference to  FIG. 12 .  FIG. 12  is a front view of the second modification of the second member  7 . 
     Also in the second modification, the second member  7  containing a low-friction material is provided to the central portion of the second shaft  4 . It is noted that the outer shape of the second member  7  of the second modification is a barrel shape extending along the first direction D 1 . That is, the second member  7  has a cylindrical shape in which the sectional area decreases from the central portion toward one end and the other end of the second member  7 . Also, in the second modification, the position where the second member  7  is provided is not limited to the central portion of the second shaft  4 . Further, a plurality of second members  7  may be provided to the second shaft  4 . 
     As shown in the second modification, the second member  7  and the second shaft  4  are in contact with each other in a minute region. Therefore, in the second modification, slidability is higher than that of the second member  7  in a cylindrical shape. Also in this case, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. 
     Further, in the second modification, the deviation of the relative positional relationship between the vibrator  2  and the second shaft  4 , caused by the inclination of the second shaft  4  relative to the first direction D 1  and the fluctuation of the reaction force to the Lorentz force, may be absorbed. 
     Second Modification of Schematic Form of Linear Vibration Motor— 
     A linear vibration motor  100 B that is a second modification of the linear vibration motor  100  being a schematic form of the linear vibration motor according to the present disclosure, will be described with reference to  FIG. 13  and  FIGS. 14( a )-( c ) . 
       FIG. 13  is a perspective view of the linear vibration motor  100 B that is the second modification of the linear vibration motor  100 , corresponding to  FIG. 3 .  FIG. 14(A)  is a front view of the second member  7  in the linear vibration motor  100 B.  FIG. 14(B)  is a sectional view of the second member  7  in the direction of arrows, taken along a plane including a line D-D in  FIG. 14(A)  and being orthogonal to the first direction D 1 .  FIG. 14(C)  is a sectional view of a first modification of the second member  7  in the direction of arrows in the linear vibration motor  100 B, corresponding to  FIG. 14(B) . 
     Similar to the linear vibration motor  100 A, the linear vibration motor  100 B differs from the linear vibration motor  100  in the manner of engagement between the vibrator  2  and the second shaft  4 . Since other configurations are basically the same as those of the linear vibration motor  100 , repetitive description will be omitted. 
     Similar to the linear vibration motor  100 A, also in the linear vibration motor  100 B, on the other side surface of the substrate  2   a  of the vibrator  2 , there is formed a groove T that opens in the second direction D 2 , has a depth larger than the diameter of the second shaft  4 , and extends along the first direction D 1 . That is, also in the linear vibration motor  100 B, the groove T corresponds to the space extending along the first direction D 1 . 
     The second member  7  containing a low-friction material is provided to the central portion in the longitudinal direction of the groove T. In the linear vibration motor  100 B, the second member  7  includes two plate-shaped members  7   a  and  7   b  facing each other in the third direction D 3 . The plate-shaped member  7   a  is provided to the upper side wall S 1  and the plate-shaped member  7   b  is provided to the lower side wall S 2  in the drawing. 
     The second shaft  4  and part of the wall determining the groove T are in contact with each other in the third direction D 3 . Specifically, as illustrated in  FIG. 14(B) , at the central portion in the longitudinal direction of the groove T, at least one of the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing and the second shaft  4  are slidably in contact with each other via the second member  7 . As illustrated in  FIG. 14(B) , both of the plate-shaped members  7   a  and  7   b  are preferably in contact with the second shaft  4 . 
     For the second member  7  in the linear vibration motor  100 B, low-friction materials of a polyacetal-base, a polyetheretherketone-base, a fluororesin-base, a polyester-base, and the like may be used, for example. Here, the low-friction material is specified in the definition described in the description of the material used for the first member  2   d.    
     In  FIG. 13 ,  FIG. 14(A) , and  FIG. 14(B) , when viewed from the second direction D 2 , the second member  7  is the two plate-shaped members  7   a  and  7   b  that are disposed so as to face each other with the second shaft  4  interposed therebetween, but is not limited thereto. For example, the second member  7  may include a plurality of pairs of two plate-shaped members having the positional relationship described above along the first direction D 1 . For purposes of this disclosure, it is noted that “two plate-shaped members face each other” means that the two plate-shaped members at least partially overlap with each other when viewed from the third direction D 3 . That is, it is sufficient that the second member  7  has a form in which at least one of the upper side wall S 1  and the lower side wall S 2  of the groove T and the second shaft  4  are indirectly and slidably in contact with each other. 
     For example, as illustrated in  FIG. 14(C) , the second member  7  may have a U-shape in which the plate-shaped members  7   a  and  7   b  are connected to each other at the bottom of the groove T. Further, the position where the second member  7  is provided is not limited to the central portion in the longitudinal direction of the groove T. The width of the second member  7  in the first direction D 1  is preferably equal to or less than 2 mm. 
     Also, in the linear vibration motor  100 B, the vibrator  2  does not rattle between the first shaft  3  and the second shaft  4 , and the vibrator  2  is not excessively pressed against the first shaft  3  and the second shaft  4 . Therefore, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. Further, since the second member  7  is provided to the groove T side, assembling accuracy and the efficiency of assembling work may be improved. 
     A second modification of the second member  7  in the linear vibration motor  100 B will be described with reference to  FIG. 15 .  FIG. 15  is a front view of the second modification of the second member  7 . 
     In the second modification, the section of the plate-shaped members  7   a  and  7   b  is bow-shaped when viewed from the second direction D 2 . The plate-shaped members  7   a  and  7   b  may have a plate-shape of which section orthogonal to the second direction D 2  is an arc-shape, or a disk-shape of which any section parallel to the third direction D 3  is an arc-shape, for example. 
     In the second modification, the second member  7  and the second shaft  4  are in contact with each other in a minute region. Therefore, in the second modification, slidability is higher than that of the second member  7  in a cylindrical shape. Also in this case, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. 
     Further, in the second modification, the deviation of the relative positional relationship between the vibrator  2  and the second shaft  4 , caused by the inclination of the second shaft  4  relative to the first direction D 1  and the fluctuation of the reaction force to the Lorentz force, may be absorbed. 
     A third modification of the second member  7  in the linear vibration motor  100 B will be described with reference to  FIGS. 16(A) -(C). In particular,  FIG. 16(A)  is a perspective view of the third modification of the second member  7  in the linear vibration motor  100 B.  FIG. 16(B)  is a front view of another form of the third modification of the second member  7 .  FIG. 16(C)  is a front view of still another form of the third modification of the second member  7 . 
     In the third modification, the second member  7  includes three plate-shaped members  7   a ,  7   b   1 , and  7   b   2 . The plate-shaped member  7   a  is provided to the upper side wall S 1  of the groove T in the drawing, and the plate-shaped members  7   b   1  and  7   b   2  are provided to the lower side wall S 2  with a distance therebetween. That is, when viewed from the second direction D 2 , the three plate-shaped members  7   b   1 ,  7   a , and  7   b   2  are disposed at positions of apexes of a triangle that are shifted from each other in the first direction D 1  with the second shaft  4  interposed therebetween. It is noted that the plate-shaped member provided to the upper side wall S 1  and the plate-shaped member provided to the lower side wall S 2  may partially overlap with each other in an exemplary aspect. 
     In the third modification, when viewed from the third direction D 3 , the plate-shaped member  7   a  is disposed at the center of the distance between the plate-shaped member  7   b   1  and the plate-shaped member  7   b   2 , but is not limited thereto in alternative aspects. The second member  7  may further include another plate-shaped member. For example, as illustrated in  FIG. 16(B) , the second member  7  may be disposed in a zigzag manner with the second shaft  4  interposed therebetween. Further, as illustrated in FIG.  16 (C), when viewed from the third direction D 3 , a plurality of plate-shaped members provided to the lower side wall S 2  may be disposed between two plate-shaped members provided to the upper side wall S 1  of the groove T. With regard to the positions where the plate-shaped members are placed, the upper side wall S 1  and the lower side wall S 2  may be reversed with respect to the description above. 
     It is also noted that the number of plate-shaped members provided to each of the upper side wall S 1  and the lower side wall S 2  is not particularly limited. That is, when viewed from the second direction D 2 , it is sufficient that the plate-shaped member provided to the upper side wall S 1  and the plate-shaped member provided to the lower side wall S 2  of the groove T is disposed at positions shifted from each other in the first direction D 1  with the second shaft  4  interposed therebetween. 
     Also, in the linear vibration motor  100 B including the second member  7  of the third modification, the vibrator  2  can be configured to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. 
     A fourth modification of the second member  7  in the linear vibration motor  100 B will be described with reference to  FIG. 17  and  FIGS. 18(A) -(B).  FIG. 17  is a perspective view of the vibrator  2  in a state that the fourth modification of the second member  7  in the linear vibration motor  100 B is fitted into the groove T formed on the other side surface of the substrate  2   a .  FIG. 18(A)  is a perspective view of the fourth modification of the second member  7 .  FIG. 18(B)  is an enlarged view of a dotted line portion A in  FIG. 17 , and is a perspective view of a state that the fourth modification of the second member  7  is fitted into the groove T formed on the other side surface of the substrate  2   a . In  FIG. 18(B) , the second shaft  4  is also illustrated so that the state of contact with the second member  7  may be understood. 
     In the fourth modification, the second member  7  is a member of which section orthogonal to the first direction D 1  is a U-shape when fitted into the groove T of the substrate  2   a . Here, the distance between one end and the other end of the second member  7  in the section before being fitted into the groove T is wider than that after being fitted into the groove T. That is, the second member  7  is elastically deformed when fitted into the groove T, and comes into contact with the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing. This configuration enables the second member  7  to be fixed in the groove T.  FIG. 17  illustrates a case where the second member  7  is disposed at the central portion in the longitudinal direction of the groove T. 
     The second shaft  4  is, in the third direction D 3 , slidably in contact with at least one of the portion contacting with the upper side wall S 1  and the portion contacting with the lower side wall S 2  of the groove T in the U-shaped second member  7 . It is noted that as illustrated in  FIG. 18(B) , it is preferable that both of the portions described above in the second member  7  and the second shaft  4  be in contact with each other. 
     Examples of the material for the second member  7  according to the fourth modification include stainless steel such as SUS304, phosphor bronze, and a resin material of a polyacetal-base or the like. Metal materials such as stainless steel and phosphor bronze have high strength, and a resin material of a polyacetal-base or the like has a low dynamic friction coefficient as described above. Note that, the slidability may be improved by coating the surface of a metal material such as stainless steel or phosphor bronze with a film of a resin material such as polytetrafluoroethylene. 
     In the fourth modification, the second member  7  is disposed at the central portion in the longitudinal direction of the groove T, but is not limited thereto. Further, a plurality of second members  7  may be disposed in the groove T. The width of the second member  7  in the first direction D 1  is preferably equal to or less than 2 mm. 
     Also, in the linear vibration motor  100 B including the second member  7  of the fourth modification, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. 
     Further, when the material is a metal, the fourth modification of the second member  7  may be manufactured only by cutting a bent thin plate-shaped metal member. Therefore, the height along the third direction D 3  when fitted into the groove T of the substrate  2   a  may be suppressed, and consequently, the thickness of the vibrator  2  may be reduced. Whereas, when the material is a resin, a molded article with a predetermined shape may be manufactured in advance by molding or the like. Therefore, the form accuracy of the second member  7  may be increased, and consequently, the variation in friction between the vibrator  2  and each shaft may be reduced. In the fourth modification, the second member  7  is fixed by being fitted into the groove T of the substrate  2   a  regardless of the material thereof. This configuration makes it easy to assemble the vibrator  2  and the manufacturing cost may be reduced. 
     A fifth modification of the second member  7  in the linear vibration motor  100 B will be described with reference to  FIG. 19  and  FIGS. 20(A) -(B).  FIG. 19  is a perspective view of the vibrator  2  in a state that the fifth modification of the second member  7  in the linear vibration motor  100 B is fitted into the groove T formed on the other side surface of the substrate  2   a .  FIG. 20(A)  is a perspective view of the fifth modification of the second member  7 .  FIG. 20(B)  is an enlarged view of a dotted line portion B in  FIG. 19 , and is a perspective view of a state that the fifth modification of the second member  7  is fitted into the groove T formed on the other side surface of the substrate  2   a . In  FIG. 20(B) , the second shaft  4  is also illustrated so that the state of contact with the second member  7  may be understood. 
     In the fifth modification, the second member  7  is a cylindrical member of which section orthogonal to the first direction D 1  is an oval shape when fitted into the groove T of the substrate  2   a . Here, the oval shape includes an oblong shape, an elliptical shape, an ovoid shape and the like. The width of the section along the third direction D 3  before being fitted into the groove T is wider than that after being fitted into the groove T. That is, the second member  7  is elastically deformed when fitted into the groove T, and comes into contact with the upper side wall S 1  and the lower side wall S 2  of the groove T in the drawing. This configuration enables the second member  7  to be fixed in the groove T.  FIG. 19  illustrates a case where the second member  7  is disposed at the central portion in the longitudinal direction of the groove T. 
     The second shaft  4  is, in the third direction D 3 , slidably in contact with at least one of the portion contacting with the upper side wall S 1  and the portion contacting with the lower side wall S 2  of the groove T in the cylindrical second member  7 . It is also noted that as illustrated in  FIG. 20(B) , it is preferable that both of the portions in the second member  7  described above and the second shaft  4  be in contact with each other. As the material of the second member  7  according to the fifth modification, the same material as that of the fourth modification may be used. 
     Also in the fifth modification, the second member  7  may be disposed at any portion in the longitudinal direction of the groove T. Further, the plurality of second members  7  may be disposed in the groove T. The width of the second member  7  in the first direction D 1  is preferably equal to or less than 2 mm. 
     Also, in the linear vibration motor  100 B including the second member  7  of the fifth modification, the vibrator  2  may be made to easily vibrate along the first direction D 1 , and unnecessary friction between the vibrator  2  and each shaft may be reduced. 
     Further, when the material is a metal, the fifth modification of the second member  7  may also be manufactured only by cutting a thin cylindrical member. Therefore, the height of the fifth modification of the second member  7  along the third direction D 3  when fitted into the groove T of the substrate  2   a  may be suppressed, and consequently, the thickness of the vibrator  2  may be reduced. Whereas, when the material is a resin, a molded article with a predetermined shape may be manufactured in advance by extrusion molding or the like. Therefore, the form accuracy of the second member  7  may be increased, and consequently, the variation in friction between the vibrator  2  and each shaft may be reduced. Further, also in the fifth modification, the second member  7  is fixed by being fitted into the groove T of the substrate  2   a  regardless of the material thereof. This makes it easy to assemble the vibrator  2 . Further, the manufacturing cost may be reduced. 
     Schematic Form of Electronic Apparatus— 
     A portable information terminal  1000  shown a schematic form of an electronic apparatus using the linear vibration motor according to the present disclosure will be described with reference to  FIG. 21 . 
       FIG. 21  is a transparent perspective view of the portable information terminal  1000 . As shown, the portable information terminal  1000  includes an apparatus housing  1001 ; the linear vibration motor  100  according to the present disclosure as described above; and an electronic circuit (not illustrated) related to transmission and reception, and information processing. The apparatus housing  1001  includes a first portion  1001   a  and a second portion  1001   b . The first portion  1001   a  is a display and the second portion  1001   b  is a frame. The linear vibration motor  100  is accommodated in the apparatus housing  1001 . 
     In the portable information terminal  1000 , the linear vibration motor  100  according to the present disclosure is used as a vibration generator for skin sensory feedback or for confirming a key operation, an incoming call, or the like by vibration. The linear vibration motor used in the portable information terminal  1000  is not limited to the linear vibration motor  100 , and may be any linear vibration motor according to the present disclosure. 
     With the linear vibration motor according to exemplary aspect of the present disclosure, as described above, a vibrator is configured to easily vibrate in one direction, and unnecessary friction between the vibrator and a guide fixed to the housing is reduced. Therefore, the portable information terminal  1000  is able to generate vibration sufficient for skin sensory feedback and confirmation of a key operation, an incoming call, or the like. 
     In the linear vibration motor according to the present disclosure, as a mechanism for transferring the vibration of the vibrator  2  to the housing  1 , a magnetic spring mechanism achieved by a pair of the second magnet M 2  and the fourth magnet M 4  and a pair of the third magnet M 3  and the fifth magnet M 5  has been described, but the mechanism for transferring the vibration of the vibrator  2  to the housing  1  is not limited thereto. For example, instead of the magnetic spring mechanism, a mechanical spring mechanism, such as a coil spring or a plate spring, can be used. 
     As an example of a schematic form of an electronic apparatus in which the linear vibration motor according to the present disclosure is used, a portable information terminal provided with a display is described, but the electronic apparatus is not limited thereto. The electronic apparatus according to the present disclosure need not include a display. 
     Examples of the electronic apparatus according to the present disclosure include mobile phones, smartphones, portable video game machines, video game machine controllers, virtual reality (VR) device controllers, smart watches, tablet type personal computers, notebook type personal computers, remote controllers used to operate televisions, or the like, touch panel displays for automatic teller machines, or the like, various toys, and the like. 
     In general, it is noted that the exemplary embodiments disclosed in this description are illustrative, and the invention according to the present disclosure is not limited to the embodiments and modifications described above. Various applications and modifications can be added within the range described above. 
     The invention according to the present disclosure is applied to a linear vibration motor used as a vibration generator for skin sensory feedback, or for confirming a key operation, an incoming call, or the like by vibration in an electronic apparatus, for example. The skin sensory feedback includes expressing a tactile image corresponding to an action in a video game (such as opening and closing of a door, operation of a steering wheel of an automobile, for example) by vibration of a controller, for example. Note that, the skin sensory feedback may be other than the above. 
     In general, it is also noted that the present invention may also be applied to a linear vibration motor used as an actuator of a robot or the like, for example. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100  LINEAR VIBRATION MOTOR 
               1  HOUSING 
               2  VIBRATOR 
               2   d  FIRST MEMBER 
               3  FIRST SHAFT 
               4  SECOND SHAFT 
               5  COIL 
               6  EXTENDED WIRING MEMBER 
               7  SECOND MEMBER 
             D 1  FIRST DIRECTION 
             D 2  SECOND DIRECTION 
             D 3  THIRD DIRECTION 
             M 1  FIRST MAGNET