Patent Publication Number: US-2022238789-A1

Title: Actuator and tactile sensation providing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 16/084,316, filed on Sep. 12, 2018, which is the U.S. National Stage of International Application No. PCT/JP2017/009614, filed on Mar. 9, 2017, which is based on and claims the benefit of priority from Japanese Patent Application No. 2016-060626, filed on Mar. 24, 2016, the entire contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an actuator and a tactile sensation providing apparatus. 
     BACKGROUND 
     An actuator that generates vibration has been provided in a touch sensor or the like. The actuator is, for example, a unimorph. The actuator vibrates an object of vibration, such as a touch sensor, thereby providing a tactile sensation to a user who touches the object of vibration. For example, large vibration of the actuator is required. 
     SUMMARY 
     An actuator according to an embodiment of the present disclosure includes a piezoelectric element, a vibration plate, and a support. The vibration plate has the piezoelectric element joined thereto and is configured to vibrate in accordance with displacement of the piezoelectric element. The support is configured to support the vibration plate. The angle between the vibration plate and the support is acute. The support is configured so that an end of the vibration plate is displaced more in a longitudinal direction than in a normal direction of the vibration plate in accordance with displacement of the piezoelectric element. 
     A tactile sensation providing apparatus according to an embodiment of the present disclosure includes an actuator that includes a piezoelectric element, a vibration plate, and a support. The vibration plate has the piezoelectric element joined thereto and is configured to vibrate in accordance with displacement of the piezoelectric element. The support is configured to support the vibration plate. The tactile sensation providing apparatus includes an object of vibration configured to provide a tactile sensation to a user by vibration of the vibration plate being transmitted to the object of vibration. The angle between the vibration plate and the support is acute. The support is configured so that an end of the vibration plate is displaced more in a longitudinal direction than in a normal direction of the vibration plate in accordance with displacement of the piezoelectric element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a main cross-section of an example configuration of a tactile sensation providing apparatus according to a first embodiment; 
         FIG. 2A  is a perspective view of an example configuration of an actuator  10  from the side joined to a housing; 
         FIG. 2B  is a perspective view of an example configuration of the actuator from the side joined to an object of vibration; 
         FIG. 3  is a functional block diagram illustrating an example of the schematic configuration of the tactile sensation providing apparatus according to the first embodiment; 
         FIG. 4A  illustrates an example cross-sectional shape of a frame when an actuator is not being driven; 
         FIG. 4B  illustrates an example cross-sectional shape of the frame when the actuator is being driven; 
         FIG. 5A  illustrates a cross-sectional shape of a frame when an actuator according to a comparative example is not being driven; 
         FIG. 5B  illustrates the cross-sectional shape of the frame when the actuator according to the comparative example is being driven; 
         FIG. 6  is a main cross-section of an example configuration of a tactile sensation providing apparatus according to a second embodiment; 
         FIG. 7A  illustrates an example cross-sectional shape of a joint between a vibration plate and a support; 
         FIG. 7B  illustrates an example cross-sectional shape of a joint between a vibration plate and a support; 
         FIG. 7C  illustrates an example cross-sectional shape of a joint between a vibration plate and a support; 
         FIG. 8A  illustrates an example cross-sectional shape of a frame in which a rib is provided in a support; 
         FIG. 8B  is a cross-section along the A-A line in  FIG. 8A ; 
         FIG. 9A  is a cross-section of an example frame in which fixing portions at either side are bent inward and connected; 
         FIG. 9B  is a plan view of an example frame in which fixing portions at either side are bent inward and connected; 
         FIG. 10A  illustrates example dimensions of each part when an actuator is not being driven; and 
         FIG. 10B  illustrates example dimensions of each part when an actuator is being driven. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     An actuator according to the present embodiment may be used in a variety of devices. A tactile sensation providing apparatus according to the present embodiment may be an on-vehicle device such as a car navigation system, a steering wheel, or a power window switch. The tactile sensation providing apparatus may also be a mobile phone, a smartphone, a tablet personal computer (PC), a notebook PC, or the like. The tactile sensation providing apparatus is not limited to these examples and may be any of a variety of electronic devices, such as a desktop PC, a household appliance, an industrial device or factory automation (FA) device, a dedicated terminal, or the like. The drawings referred to below are schematic illustrations. The dimensional ratios and the like in the drawings do not necessarily match the actual dimensions. 
     [Example Configuration of Tactile Sensation Providing Apparatus] 
     As illustrated in  FIG. 1 , a tactile sensation providing apparatus  1  according to the present embodiment includes an actuator  10 , a housing  20 , and an object of vibration  30 . 
     The actuator  10  includes a piezoelectric element  11 , a vibration plate  12 , supports  13 , fixing portions  14 , and a holder  15 . The actuator  10  is joined to the housing  20  by the fixing portions  14 . The actuator  10  has the object of vibration  30  joined thereto via the holder  15 . 
     Each portion of the actuator  10  is described with reference to  FIGS. 1, 2A, and 2B . 
     The piezoelectric element  11  is, for example, rectangular. The piezoelectric element  11  expands and contracts in the longitudinal direction in a variety of patterns in accordance with an applied voltage signal. The piezoelectric element  11  may have a different shape. The piezoelectric element  11  may be a piezoelectric film or piezoelectric ceramic. Piezoelectric ceramic can generate vibration having a greater vibration energy than piezoelectric film can. 
     The piezoelectric element  11  may be replaced with a magnetostrictor. A magnetostrictor expands and contracts in accordance with the applied magnetic field. A magnetostrictor is used together with a coil or the like that converts an applied voltage signal to a magnetic field. 
     The vibration plate  12  is a rectangular plate-shaped member having a predetermined thickness. The vibration plate  12  may have a different shape. The vibration plate  12  is, for example, a thin plate with elasticity. The vibration plate  12  may, for example, be made of metal, resin, or a composite material of metal, resin, and the like. The vibration plate  12  may be a thin metal plate. A thin metal plate is also referred to as a shim. The surface facing the housing  20  is also referred to as a first main surface  12   a . The surface facing the object of vibration  30  is also referred to as a second main surface  12   b.    
     The piezoelectric element  11  is provided on the first main surface  12   a  of the vibration plate  12 . The piezoelectric element  11  is arranged so that the longitudinal direction of the piezoelectric element  11  matches the longitudinal direction of the vibration plate  12 . The holder  15  is provided on the second main surface  12   b  of the vibration plate  12 . The piezoelectric element  11  and the holder  15  are each joined to the vibration plate  12  by a method such as adhesion. 
     A structure in which the piezoelectric element  11  is provided on the first main surface  12   a  of the vibration plate  12  is known as a monomorph. In a monomorph, the expansion and contraction of the piezoelectric element  11  provokes bending vibration of the vibration plate  12 . When only one end of the vibration plate  12  is supported by the housing  20 , the vibration plate  12  vibrates with the amplitude in the normal direction of the first main surface  12   a  being maximized at the other end of the vibration plate  12 . When both ends of the vibration plate  12  are supported by the housing  20 , the vibration plate  12  vibrates with the amplitude in the normal direction of the first main surface  12   a  being maximized near the center of the vibration plate  12 . 
     A support  13  is provided at each end of the vibration plate  12  in the longitudinal direction. The supports  13  maintain a clearance between the piezoelectric element  11  and the housing  20  to prevent the piezoelectric element  11  from hitting the housing  20  when the vibration plate  12  vibrates in accordance with displacement of the piezoelectric element  11 . The supports  13  are, for example, thin plates with elasticity like the vibration plate  12 . The supports  13  may be made of the same or different material as the vibration plate  12 . When both ends of the vibration plate  12  are supported, the vibration plate  12  vibrates in accordance with displacement of the piezoelectric element  11 , with the amplitude being maximized near the center of the vibration plate  12 . 
     One end of each support  13  is connected to the vibration plate  12 . The other end of each support  13  is connected to one of the fixing portions  14 . The fixing portions  14  may, for example, be fixed to the housing  20  by screwing, adhesion, or the like. The fixing portions  14  may, for example, be thin plates with elasticity like the vibration plate  12 . The fixing portions  14  may be made of the same or different material as the vibration plate  12 . 
     In the actuator  10  according to the present embodiment, the vibration plate  12 , the supports  13 , and the fixing portions  14  are integrally molded. The member in which the vibration plate  12 , the supports  13 , and the fixing portions  14  are integrally molded is also referred to below as a frame  10   a  of the actuator  10 . The frame  10   a  according to the present embodiment is entirely made of the same material. The frame  10   a  may, for example, be integrally molded by subjecting a thin sheet of metal to sheet-metal processing to bend the thin sheet. The frame  10   a  may be integrally molded by welding the vibration plate  12 , the supports  13 , and the fixing portions  14  together. The frame  10   a  may be made by integrally molding resin. 
     The holder  15  may, for example, be made of a rubber material. The holder  15  is not limited to a rubber material and may be made of another material, such as metal. The holder  15  is provided on the second main surface  12   b  side of the vibration plate  12 . The holder  15  is joined to the vibration plate  12  using a method such as adhesion. The holder  15  is provided near the center on the second main surface  12   b  side. The position at which the holder  15  is provided is not limited to being near the center. The holder  15  may be provided at the portion where the amplitude of the vibration plate  12  is maximized. The holder  15  has the object of vibration  30  joined thereto by a method such as adhesion, for example. 
     The holder  15  may have a large elastic modulus in the vibration direction of the vibration plate  12 , i.e. in the normal direction of the first main surface  12   a , to efficiently transmit vibration of the vibration plate  12  to the object of vibration  30 . On the other hand, the holder  15  may have a small elastic modulus in a direction parallel to the first main surface  12   a  of the vibration plate  12 . This configuration can reduce the likelihood of damage to the tactile sensation providing apparatus  1  due to an external force. The elastic modulus is a constant indicating the relationship between an external force acting on a member and the amount of displacement of the member. The external force on the member corresponds to the product of the amount of displacement and the elastic modulus. In other words, the same external force produces a larger amount of displacement as the elastic modulus is smaller. 
     The housing  20  has the actuator  10  joined thereto by the fixing portions  14 . The housing  20  has a greater mass and a higher rigidity than the actuator  10  does. In the present embodiment, the housing  20  is considered to be a rigid body. The object of vibration  30  may, for example, be a touch sensor  50  provided in a device (see  FIG. 3 ) or a switch. The object of vibration  30  has the actuator  10  joined thereto by the holder  15 . When the housing  20  is considered to be a rigid body, the vibration generated by the actuator  10  is mainly transmitted to the object of vibration  30 . By the vibration being transmitted from the actuator  10  to the object of vibration  30 , the object of vibration  30  can provide a tactile sensation to the user that touches the object of vibration  30 . 
     [Example Operations of Tactile Sensation Providing Apparatus] 
     As illustrated in  FIG. 3 , the tactile sensation providing apparatus  1  further includes a controller  40 . The controller  40  may be constituted by a processor, microcomputer, or the like capable of executing application software. The controller  40  may appropriately include a storage unit or the like constituted by memory or the like capable of storing various information as necessary. 
     As illustrated in  FIG. 3 , the controller  40  connects to the actuator  10 . The controller  40  outputs a drive signal to the actuator  10 . The drive signal may be a voltage signal that is applied to the piezoelectric element  11  of the actuator  10 . 
     The piezoelectric element  11  expands and contracts in the longitudinal direction in accordance with the drive signal acquired from the controller  40 . The vibration plate  12  of the example actuator  10  illustrated in  FIGS. 1, 2A , and  2 B bends in accordance with displacement of the piezoelectric element  11 . When the piezoelectric element  11  is displaced by contracting in the longitudinal direction of the vibration plate  12 , the vibration plate  12  bends so that the second main surface  12   b  side becomes convex. When the piezoelectric element  11  is displaced by expanding in the longitudinal direction of the vibration plate  12 , the vibration plate  12  bends so that the first main surface  12   a  side becomes convex. Displacement of the piezoelectric element  11  is converted into vibration in the normal direction of the first main surface  12   a  of the vibration plate  12 . 
     In the present embodiment, the piezoelectric element  11  is displaced only in the contracting direction in response to application of a voltage signal. In this case, the vibration plate  12  oscillates between a state in which the second main surface  12   b  side is bent to become convex and a normal, straight state. The piezoelectric element  11  is not limited to being displaced in the contracting direction in response to application of a voltage signal. The piezoelectric element  11  may be configured to be displaced in the expanding direction in response to application of a voltage signal or to be displaced in both the expanding direction and the contracting direction. 
     In this way, the controller  40  drives the actuator  10  and vibrates the vibration plate  12 . Vibration of the vibration plate  12  is transmitted to the object of vibration  30  through the holder  15 . A tactile sensation is provided to the user touching the object of vibration  30  by vibration being transmitted to the object of vibration  30 . 
     As illustrated in  FIG. 3 , for example, the controller  40  may connect to the touch sensor  50 . In this case, the controller  40  may output a drive signal to the actuator  10  in response to a signal acquired from the touch sensor  50 . The touch sensor  50  may be the object of vibration  30  of the tactile sensation providing apparatus  1 . In this case, a touch by the user on the object of vibration  30  is detected by the touch sensor  50 . The controller  40  vibrates the object of vibration  30  when the user is touching the object of vibration  30 . This configuration allows the tactile sensation providing apparatus  1  to provide a tactile sensation to the user touching the object of vibration  30 . The touch sensor  50  may be provided as a separate structure from the object of vibration  30  of the tactile sensation providing apparatus  1 . 
     [Shape of Frame] 
     The frame  10   a  of the actuator  10  elastically deforms in response to driving of the actuator  10 . As illustrated in  FIG. 4A , the vibration plate  12  does not deform when the actuator  10  is not being driven. As illustrated in  FIG. 4B , when the actuator  10  is driven, the vibration plate  12  bends in accordance with driving of the actuator  10  to become convex at the second main surface  12   b  side. 
     As illustrated in  FIG. 4A , each support  13  is arranged so that when the actuator  10  is not driven, the end of the support  13  at the side connected to the vibration plate  12  is further outward than the end at the side connected to the fixing portion  14 . The supports  13  arranged in this way are also referred to as being inclined outward. In this case, the angle between the vibration plate  12  and the support  13  is acute. 
     The support  13  is arranged so that the angle between the normal direction of the vibration plate  12  and the support  13  becomes α. The angle (α) is also referred to as a given angle (α). The given angle (α) is assumed to be a positive value when the support  13  is inclined outward relative to the normal direction of the vibration plate  12 . The given angle (α) is measured in radians. Unless otherwise noted, the units of angles in the explanation below are radians. The given angle (α) is assumed to satisfy −π≤α&lt;π to uniquely represent the direction in which the support  13  is arranged. 
     The length of the support  13  is H. In this case, the distance between the end of the vibration plate  12  and the fixing portion  14  is H cos α. The distance between the end of the vibration plate  12  and the fixing portion  14  is assumed to be the length of a perpendicular from the end of the vibration plate  12  to a surface including the fixing portion  14 . 
     As illustrated in  FIG. 4B , the vibration plate  12  bends when the actuator  10  is being driven. The displacement of the central portion of the vibration plate  12  relative to the ends is Δx (Δx&gt;0) assuming that the displacement from the first main surface  12   a  side towards the second main surface  12   b  side is positive. In accordance with the bending of the vibration plate  12 , the upper end of the support  13  is pulled by the vibration plate  12 . The upper end of the support  13  corresponds to the end on the side connected to the vibration plate  12 . When the support  13  is pulled by the vibration plate  12 , the angle between the normal direction of the vibration plate  12  and the support  13  becomes β. The angle (β) is also referred to as a displacement angle (β). The displacement angle (β) is assumed to be a positive value when the support  13  is inclined outward. Like the range of the given angle (α), the displacement angle (β) is assumed to satisfy −π≤β&lt;π. The length of the support  13  is H, as in  FIG. 4A . In this case, the distance between the end of the vibration plate  12  and the fixing portion  14  is H cos β. 
     When comparing  FIG. 4A  and  FIG. 4B , the change (Δy) in distance between the end of the vibration plate  12  and the fixing portion  14  due to driving of the actuator  10  is given by Equation (1) below. 
       Δ y=H (cos β−cos α)  (1)
 
     In Equation (1), α&gt;β&gt;0 and H&gt;0. Hence, Δy&gt;0. 
     The displacement of the actuator  10  transmitted to the object of vibration  30  is the sum of the displacement (Δx) of the central portion of the vibration plate  12  and the change (Δy) in the distance between the end of the vibration plate  12  and the fixing portion  14 . Since Δy&gt;0, the displacement of the actuator  10  transmitted to the object of vibration  30  can be increased as compared to when the angle between the support  13  and the normal direction of the vibration plate  12  does not change (Δy=0). 
     Comparative Example 
     As illustrated in  FIGS. 5A and 5B , a frame  10   b  of an actuator  10  according to a comparative example is a member in which a vibration plate  12 , supports  13 , and fixing portions  14  are integrally molded, like the frame  10   a  illustrated in  FIG. 1  and the like. The frame  10   b  has a different cross-sectional shape than the frame  10   a  does. As illustrated in  FIG. 5A , the vibration plate  12  does not deform when the actuator  10  is not being driven. As illustrated in  FIG. 5B , when the actuator  10  is driven, the vibration plate  12  bends in accordance with driving of the actuator  10  to become convex at the second main surface  12   b  side. 
     As illustrated in  FIG. 5A , the supports  13  of the frame  10   b  are arranged to lie in the normal direction of the vibration plate  12  when the actuator  10  is not being driven. In other words, the supports  13  are orthogonal to the vibration plate  12  in  FIG. 5A . The length of the support  13  is H. In this case, the distance between the end of the vibration plate  12  and the fixing portion  14  is the same as the length (H) of the support  13 . 
     As illustrated in  FIG. 5B , the vibration plate  12  bends when the actuator  10  is being driven, so that the central portion of the vibration plate  12  is displaced relative to the ends by Δx at the second main surface  12   b  side. As in  FIG. 4B , the relationship Δx&gt;0 is satisfied assuming that the displacement from the first main surface  12   a  side towards the second main surface  12   b  is positive. In accordance with the bending of the vibration plate  12 , the upper end of the support  13  is pulled by the vibration plate  12 . The upper end of the support  13  corresponds to the end on the side connected to the vibration plate  12 . The displacement angle of the support  13  is β. Under the above-described assumption, the relationship β&lt;0 holds. The length of the support  13  is H, as in  FIG. 4A . In this case, the distance between the end of the vibration plate  12  and the fixing portion  14  is H cos β. 
     When comparing  FIG. 5A  and  FIG. 5B , the change (Δy) in distance between the end of the vibration plate  12  and the fixing portion  14  due to driving of the actuator  10  is given by Equation (2) below. 
       Δ y=H (cos β−1)  (2)
 
     In Equation (2), cos β&lt;1 and H&gt;0. Hence, Δy&lt;0. 
     The displacement of the actuator  10  transmitted to the object of vibration  30  is the sum of the displacement (Δx) of the central portion of the vibration plate  12  and the change (Δy) in the distance between the end of the vibration plate  12  and the fixing portion  14 . Since Δy&lt;0, the displacement of the actuator  10  transmitted to the object of vibration  30  is smaller than in the example (Δy&gt;0) of the cross-sectional shape of the frame  10   a  according to the present embodiment. The displacement of the actuator  10  transmitted to the object of vibration  30  is also smaller than when the angle between the support  13  and the normal direction of the vibration plate  12  does not change (Δy=0). 
     The support  13  has a given angle (α) in the cross-sectional shape of the frame  10   a  according to the present embodiment. In other words, the angle between the vibration plate  12  and the support  13  is acute. The displacement of the actuator  10  transmitted to the object of vibration  30  does not increase when the angle between the vibration plate  12  and the support  13  is a right angle, as in the cross-sectional shape of the frame  10   b  according to the comparative example. The displacement of the actuator  10  transmitted to the object of vibration  30  does not increase when the angle between the vibration plate  12  and the support  13  is obtuse, either. The frame  10   a  according to the present embodiment allows an increase in the displacement of the actuator  10  transmitted to the object of vibration  30 . 
     Second Embodiment 
     In the first embodiment, the entire frame  10   a  of the actuator  10  is made of the same material. In the second embodiment, the vibration plate  12  and the supports  13  are made of different materials. The configuration example of a tactile sensation providing apparatus  1  according to the second embodiment illustrated in  FIG. 6  has similarities to and differences from  FIG. 1 . The differences from  FIG. 1  are described below. 
     The vibration plate  12  and the fixing portions  14  of the present embodiment may, for example, be thin plates with elasticity as in the first embodiment. The material of the vibration plate  12  and the material of the fixing portions  14  may be the same or different. The supports  13  may be pillars made of curable resin, for example. The supports  13  may be members with a large elastic modulus in the normal direction of the vibration plate  12 . The supports  13  may be made of another material, such as metal. The supports  13  are configured to elastically deform at the joint with the vibration plate  12  and the joint with the fixing portion  14 . The supports  13  can incline by elastically deforming at these joints. 
     In the present embodiment, the vibration plate  12  and the supports  13  are different materials that are integrally molded together. For example, the vibration plate  12  and the supports  13  may be integrally molded by being welded together. The vibration plate  12  and the supports  13  may be integrally molded by molding resin that becomes the supports  13  around a metal vibration plate  12 . The vibration plate  12  and the supports  13  may be integrally molded by engaging supports  13  made of resin with fitting portions provided in a metal vibration plate  12 . The vibration plate  12  and the supports  13  may be integrally molded by applying primer to a joining face provided on a surface of a metal vibration plate  12  and molding resin onto the joining face. The vibration plate and the supports  13  may be integrally molded by performing microfabrication on a joining face provided on a surface of a metal vibration plate  12  and molding resin onto the joining face. 
     The vibration plate  12  and the supports  13  made of different materials are integrally molded in the actuator  10  according to the second embodiment. As compared to when the vibration plate  12  and the supports  13  are configured as separate components, the second embodiment allows a reduction in the number of components and assembly steps while the supports  13  reduce attenuation of the vibration of the vibration plate  12  generated in accordance with displacement of the piezoelectric element  11 . Not using adhesive between the vibration plate  12  and the supports  13  can lengthen the mean time between failure (MTBF) and improve the yield at the time of assembly. 
     As in the first embodiment, the angle between the vibration plate  12  and the support  13  is acute in the actuator  10  according to the second embodiment. The displacement of the actuator  10  transmitted to the object of vibration  30  can be further increased as compared to when the angle between the vibration plate  12  and the support  13  is not acute. 
     Other Embodiments 
     A notch  16  may be provided at the inside of the joint, as illustrated in  FIG. 7A . The inside of the joint corresponds to the side that connects to the first main surface  12   a  of the vibration plate  12 . A notch  16  may be provided at the outside of the joint, as illustrated in  FIG. 7B . The outside of the joint corresponds to the side that connects to the second main surface  12   b  of the vibration plate  12 .  FIG. 7C  illustrates a comparative example in which a notch  16  is not provided on the inside or the outside of the joint. 
     The joint between the vibration plate  12  and the support  13  in  FIGS. 7A and 7B  bends more easily than the example illustrated in  FIG. 7C  by virtue of the notch  16  being provided. By the joint bending more easily, the upper portion of the support  13  is pulled towards the vibration plate  12  more easily. This prevents bending of the vibration plate  12  from being impeded when the actuator  10  is driven. 
     The notch  16  illustrated in  FIGS. 7A and 7B  may be provided in the joint between the support  13  and the fixing portion  14 . This configuration can increase the difference between the given angle (α) and the displacement angle (β) of the support  13 . 
     As illustrated in  FIGS. 8A and 8B , a rib  13   a  may be provided on the support  13 . Provision of the rib  13   a  in the support  13  as illustrated in  FIG. 8B  increases the rigidity of the support  13  relative to the normal direction of the vibration plate  12 . In other words, this configuration reduces the amount of deformation of the support  13  due to the force acting on the support  13  as a reaction to the force that the actuator  10  exerts on the object of vibration  30 . The vibration generated by the actuator  10  thus tends to be absorbed less at the support  13  side. Consequently, the vibration generated by the actuator  10  can be transmitted more efficiently to the object of vibration  30 . 
     As illustrated in  FIGS. 7A, 7B, 8A, and 8B , the supports  13  may be configured so that the ends of the vibration plate  12  are displaced more in the longitudinal direction than in the normal direction of the vibration plate  12  in accordance with expansion and contraction of the piezoelectric element  11 . When the supports  13  are configured for smaller displacement of the ends of the vibration plate  12  in the normal direction of the vibration plate  12 , the vibration of the vibration plate  12  is efficiently transmitted to the object of vibration  30 . When the supports  13  are configured for greater displacement of the ends of the vibration plate  12  in the longitudinal direction of the vibration plate  12 , attenuation of the vibration of the vibration plate  12  is reduced. 
     As illustrated in  FIGS. 9A and 9B , the frame  10   a  may be configured so that the fixing portions  14  at either side connect with each other by being bent inward. The cross-sectional shape of the frame  10   a  becomes trapezoidal as a result of the fixing portions  14  being connected as in  FIG. 9A . Consequently, the frame  10   a  becomes stronger. In  FIG. 9B , screw holes  14   a  are provided beside the fixing portions  14 . Provision of the screw holes  14   a  facilitates screwing of the fixing portions  14  to the housing  20 . 
     (Example of Calculating Displacement) 
     With reference to  FIGS. 10A and 10B , an example of the method for calculating the displacement of the central portion of the vibration plate  12  when the actuator  10  is driven is described. 
       FIG. 10A  illustrates example dimensions of each part when the actuator  10  is not being driven. The longitudinal dimension of the piezoelectric element  11  is L. The piezoelectric element  11  is disposed at a distance (M) from each end of the vibration plate  12 . The longitudinal dimension of the vibration plate  12  is L+2M. The length of the support  13  is H. The angle (given angle) formed by the support  13  and the normal direction of the vibration plate  12  is α. The ends of the supports  13  connected to the fixing portions  14  are fixed by the fixing portions  14 . The supports  13  are pivotable about the ends of the supports  13 . 
       FIG. 10B  illustrates example dimensions of each part when the actuator  10  is being driven. As a result of contraction of the piezoelectric element  11 , the vibration plate  12  bends to become convex at the side of the second main surface  12   b  (see  FIG. 1 ). The shape of the vibration plate  12  and the support  13  when the actuator  10  is not being driven is indicated in  FIG. 10B  by dashed double-dotted lines. The displacement (Δx) of the central portion of the vibration plate  12  relative to the ends, which correspond to the joints between the vibration plate  12  and the supports  13 , is given by Equation (3) below. 
       Δ x=M  sin θ+ρ(1−cos θ)  (3)
 
     In Equation (3), ρ is the radius of curvature when the vibration plate  12  bends, and θ is the difference in the angle between the bent state and the unbent state at the ends of the vibration plate  12 . The interior angle of the bent portion of the vibration plate  12 , i.e. the interior angle of the sector having the bent portion as an arc, is expressed as 2θ. The radius of curvature (ρ) and the interior angle (2θ) are determined by factors such as the amount of displacement of the piezoelectric element  11  or the ratio between the thickness of the piezoelectric element  11  and the thickness of the vibration plate  12 . 
     When the radius of curvature (ρ) or the interior angle (2θ) of the bent portion is known, the displacement angle (β) of the support  13  can be calculated with Equation (4) below. 
       β=α− M (1−cos θ)/ H   (4)
 
     Here, an approximation based on a Taylor expansion of a trigonometric function is used, taking α, β, and θ to be minute values. By the approximation, the relationships sin α≈α, sin β≈β, sin θ≈θ, and sin θ≈L/2ρ hold. 
     When the support  13  is parallel to the normal direction of the vibration plate  12 , the displacement angle (β) of the support  13  becomes 0 in accordance with the radius of curvature (ρ) and the interior angle (2θ). When β=0 in Equation (4), the given angle (α) satisfies the relationship in Equation (5) below. 
       α= M (1−cos θ)/ H   (5)
 
     In  FIG. 10B , bending of the vibration plate  12  causes the supports  13  to become parallel to the normal direction of the vibration plate  12  when the actuator  10  is not driven. In this case, the change (Δy) in the distance between the end of the vibration plate  12  and the fixing portion  14  is given by Equation (6) below. 
       Δ y=H (1−cos θ)  (6)
 
     The displacement (Δz) of the central portion of the vibration plate  12  is the sum of Δx and Δy. Accordingly, the displacement (Δz) of the central portion of the vibration plate  12  illustrated in  FIG. 10B  is given by Equation (7) below, which is based on Equation (3) and Equation (6). 
       Δ z=M  sin θ+ρ(1−cos θ)+ H (1−cos θ)  (7)
 
     On the basis of Equation (1), the relationship Δy&gt;0 is satisfied when the given angle (α) and the displacement angle (β) satisfy the relationship cos α&lt;cos β. Here, the relationship α&gt;β is satisfied in the actuator  10  according to the first embodiment and the like. Hence, Δy&gt;0 if β≥0. It follows that Equation (8) below represents a sufficient condition on the given angle (α) for the relationship Δy&gt;0 to be satisfied. 
       α≥ M (1−cos θ)/ H   (8)
 
     Accordingly, an appropriate setting of the given angle (α) of the support  13  to satisfy Equation (8) can increase the amplitude of the central portion of the vibration plate  12 . 
     The tactile sensation providing apparatus  1  and the actuator  10  according to the present embodiment can increase the generated vibration. 
     Although embodiments of the present disclosure have been described through drawings and examples, it is to be noted that various changes and modifications will be apparent to those skilled in the art on the basis of the present disclosure. Therefore, such changes and modifications are to be understood as included within the scope of the present disclosure.