Abstract:
A tactile feedback device includes a vibrating device and a touch sensor. The vibrating device comprises a flexible diaphragm and a film which deforms in response to the application of electrical energy thereto, the film being attached to the flexible diaphragm at two spaced locations with a major surface of the film facing a major surface of the flexible diaphragm. The vibrating device further includes a spacer located between the two spaced locations and ensuring that the major surface of the flexible diaphragm is spaced from the major surface of the film. The touch sensor is coupled to the diaphragm and generates an output signal in response to a touch operation. Means are provided to apply electrical energy to the film in response to the output signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of International application No. PCT/JP2015/065983, filed on Jun. 3, 2015, which claims priority to Japanese Patent Application No. 2014-118332, filed on Jun. 9, 2014, the entire contents of each of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a vibrating device including a diaphragm which is caused to vibrate when a driving voltage is applied to a piezoelectric film attached thereto, and a tactile feedback device which transmits the vibration of the vibrating device as tactile feedback to a user. 
       BACKGROUND ART 
       [0003]    A vibrating device which includes a diaphragm vibrated by driving a piezoelectric film is used in a flat speaker or a haptics device (a tactile sense presenting device) as described, for example, in WO2012-0157691. 
         [0004]      FIG. 9(A)  is a side view of a vibrating device  101  employing a conventional configuration, and  FIG. 9(B)  is a top view of the vibrating device  101 . The vibrating device  101  includes a piezoelectric film  102 , a diaphragm  103  and frame members  104  and  105 . The diaphragm  103  and the piezoelectric film  102  have rectangular shapes which are elongated in a length direction (the vertical direction as viewed in  FIG. 9(B) ). The piezoelectric film  102  is formed by stretching a PLLA (poly-L-lactic acid) film in a stretching direction (indicated by outlined arrows in  FIG. 9(B) ) and cutting the stretched PLLA film out in such a manner that the length direction of the piezoelectric film  102  forms a 45° angle with respect to the stretching direction. The piezoelectric film  102  formed in this way stretches and contracts in the width direction when a voltage is applied thereto. The frame members  104  and  105  are provided at opposite ends of the piezoelectric film  102  and extend in the length direction. Opposite ends of the diaphragm  103  are connected to the piezoelectric film  102  by the frame members  104  and  105 , respectively. The diaphragm  103  flexes such that a center of the diaphragm  103  in the width direction is spaced apart from the piezoelectric film  102  (see  FIG. 9(A) ) and that the frame members  104  and  105  apply a tensile force to the piezoelectric film  102  in the direction of the solid arrows in  FIG. 9( a ) . When an AC voltage is applied to the piezoelectric film  102 , it vibrates in the width direction and the curvature of the diaphragm  103  fluctuates along with this vibration. 
         [0005]    In the haptics device of  FIGS. 9(A) and 9(B) , a downward pressing force applied to the diaphragm  103  in the thickness direction may cause the diaphragm to flatten and become parallel to the piezoelectric film. When this happens, the diaphragm barely vibrates even when the piezoelectric film is vibrated in the width direction (the horizontal direction in  FIG. 9(A) ). As a result, it is difficult to provide the user with a tactile feedback. To prevent the diaphragm from being pushed and flattened, the diaphragm may be made thick and rigidity of the diaphragm may be improved. However, when this is done, the amount of the diaphragm bends becomes small and it is difficult to provide a tactile feedback to the user. 
         [0006]    It is therefore an object of the present invention to provide a vibrating device and a tactile sense presenting device which can bend a diaphragm in a thickness direction from a flat state and can easily increase the amount the diaphragm bends in response to the vibration of the piezoelectric film. 
       SUMMARY OF THE INVENTION 
       [0007]    A vibrating device according to the present invention includes a flexible diaphragm and a film which deforms in response to the application of electrical energy thereto. The film is attached to the flexible diaphragm at two spaced locations with a major surface of the film facing a major surface of the flexible diaphragm. A spacer is located between the two spaced locations and ensures that the major surface of the flexible diaphragm is spaced from the major surface of the film. 
         [0008]    The vibratory device preferably has a length, a width and a height. The flexible diaphragm and the film are spaced apart in the height direction and the flexible diaphragm is flexible in the height direction. The flexible diaphragm deforms in response to deformation of the film when electrical energy is applied to the vibratory film. More preferably the diaphragm vibrates in response to vibration of the film when an alternating electric voltage is applied to the vibratory film. 
         [0009]    The spacer preferably contacts both the diaphragm and the film both before electrical energy is applied to the film and after it is applied to the film. The spacer preferably includes a base portion facing the film and a plurality of protrusion portions facing the diaphragm. The base portion is preferably in contact with the film and the plurality of protrusions are preferably in contact with the diaphragm. 
         [0010]    The vibrating device preferably has a length, a width and a thickness extending perpendicular to one another and the spacer is elongated and extends in length direction of the vibrating device. Preferably the plurality of protrusions extend in the thickness direction of the vibrating device and a plurality of the spacers are aligned in the length direction of the vibrating device. 
         [0011]    In one embodiment, the diaphragm has a flat shape when electrical energy is not applied to the film. In others, it is curved. The film preferably comprises a chiral polymer film or a polyvinylidene fluoride film. 
         [0012]    As a result of the foregoing structures it is possible to reliably bend/vibrate the diaphragm in the thickness direction by driving the film even when the diaphragm is in a flat state. Further, even when the diaphragm is thin and not very rigid, a gap between the diaphragm and the film is maintained. Consequently, it is possible to make the diaphragm thin and less rigid and increase the amount of flexure in the diaphragm. 
         [0013]    The spacer is preferably provided between the diaphragm and the film and is in contact with the diaphragm and the film at all times. According to this configuration, the spacer can be sandwiched between and held by the diaphragm and the film. 
         [0014]    In some embodiments, a plurality of the spacers are preferably aligned in the length direction of the vibrating device. The positions of the spacers are such that they define nodes of a vibration of the diaphragm when electrical energy is applied thereto. The harmonic can be set to an appropriate frequency by adjusting the number and positions of the spacers. Generally, a vibrational frequency in a range of 100 Hz to 300 Hz is good for a tactile feedback on a finger (which means high sensitivity). Consequently, a vibrating device whose resonance frequency is less than 100 Hz can adjust the harmonic of the vibration caused by the diaphragm to a frequency of 100 Hz to 300 Hz by adjusting the numbers and the positions of the spacers. 
         [0015]    The diaphragm may have a flat shape when no electrical energy is applied to the film and yet, as a result of the use of the spacer, the diaphragm can be sufficiently bent to provide good tactile feedback to the user. As a result, it is possible to use the vibrating device for a wide range of uses. 
         [0016]    The foregoing vibrating device can be used in a tactile feedback device which includes a touch sensor coupled to the diaphragm and generating an output signal in response to a touch operation and means for applying electrical energy to the film in response to the output signal. 
         [0017]    According to the present invention, the vibrating device and the tactile feedback device can reliably bend the diaphragm in the thickness direction even when the diaphragm is in a flat state. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIGS. 1(A) and 1(B)  are a perspective view of and a partially broken plan view, respectively, of a top surface of a tactile feedback device according to a first embodiment. 
           [0019]      FIG. 2  is a perspective view of a spacer according to the first embodiment. 
           [0020]      FIGS. 3(A) and 3(B)  are side views illustrating a vibration mode of a vibrating device according to the first embodiment. 
           [0021]      FIGS. 4(A) and 4(B)  are side views of a vibrating device according to a second embodiment. 
           [0022]      FIGS. 5(A) and 5(B)  are a perspective view and a side view, respectively, of a vibrating device according to a third embodiment. 
           [0023]      FIGS. 6(A) and 6(B)  are a perspective view and a side view, respectively, of a vibrating device according to a fourth embodiment. 
           [0024]      FIGS. 7(A) and 7(B)  are side views illustrating a vibration mode of a harmonic produced in the vibrating device according to the third and fourth embodiments. 
           [0025]      FIGS. 8(A) and 8(B)  are a perspective view and a side view, respectively, of a vibrating device according to a fifth embodiment. 
           [0026]      FIGS. 9(A) and 9(B)  are views for explaining a conventional structure of a vibrating device. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    A plurality of embodiments for carrying out the present invention will be described with reference to some specific examples. Each embodiment is exemplary, and components described in different embodiments may be replaced or combined. 
         [0028]    The tactile feedback device  10  in the present embodiment is part of a touch sensor keyboard. The tactile feedback device  10  includes a control unit  11 , a driving unit  12 , a vibrating device  20  and a touch panel  30 . In addition, the tactile sense presenting device  10  may include a switch having a sheet shape, such as a membrane switch, in place of the touch panel  30 . A key position to be displayed or an indication can be arbitrarily changed using the touch panel  30 . 
         [0029]    The vibrating device  20  and the touch panel  30  are preferably thin in a thickness direction and are stacked in the thickness direction. The touch panel  30  is disposed at a top panel side in the thickness direction with respect to the vibrating device  20 . The touch panel  30  includes a plurality of touch sensors  31  exposed on the top panel of the tactile feedback device  10 . A plurality of touch sensors  31  are disposed at positions corresponding to a key alignment of the keyboard. Each touch sensor  31  outputs a respective detection signal to the control unit  11  when it detects a user&#39;s touch operation. 
         [0030]    The control unit  11  outputs a control signal to the driving unit  12  in response to an input detection signal received from one or more of the touch sensors  31 . The driving unit  12  outputs a drive voltage to the vibrating device  20  in response to the receipt of a control signal from the control unit  11 . The control unit  11  and the driving unit  12  cooperate to form a means for applying electrical energy to the film in response to the output signal. 
         [0031]    The vibrating device  20  includes a diaphragm  21 , a piezoelectric film  22  and a spacer  23 . The diaphragm  21  is preferably made of an elastically deformable material such as an acrylic resin PMMA. Other materials which can be used include a metal plate, PET, polycarbonate (PC), PLLA and glass. The diaphragm  21  is disposed above the piezoelectric film  22  in the thickness direction. The diaphragm  21  has a rectangular shape when seen from above, and has short sides which lie along a width direction and long sides which lie along a length direction. Further, the diaphragm  21  is preferably curved so that it protrudes toward the top surface of the tactile feedback device  10 . The top surface of the diaphragm  21  is joined to the touch panel  30 , for example with an adhesive or the like interposed therebetween. As a result, the touch panel  30  has a curved shape corresponding to the curved shape of the diaphragm  21 . 
         [0032]    The piezoelectric film  22  has two flat planar sections, each extending from an opposite side of spacer  23  and vibrates along those planar sections when electrically driven by an alternating voltage. The piezoelectric film can take other shapes, including the shape of a curved plane, as long as it vibrates in a manner that causes the diaphragm  21  to vibrate (more generally bend) with the vibration of the piezoelectric film. 
         [0033]    The piezoelectric film  22  is preferably composed of a film made of a piezoelectric material having electrodes (not illustrated) provided on the entirety of both principal surfaces of the film. The piezoelectric material of the piezoelectric film  22  is preferably, for example, poly-L-lactic acid (PLLA) which is chiral polymers, and is polyvinylidene fluoride (PVDF). The piezoelectric film  22  composed of PLLA and formed by following steps has piezoelectricity to stretch and contract in the length direction. The steps include stretching a film in a main stretching direction indicated by an outlined arrow in  FIG. 2(B) ; and then cutting the film in such a manner that its length direction extends approximately 45° with respect to the main stretching direction. 
         [0034]    Other films may be substituted for the piezoelectric film as long as the films have the property that the films cause vibration when electrically driven. For example, the “film” may be composed as a composite film or an electroactive film. Electroactive films are ones which cause a stress or displacement in the plane of the film when electrically driven. A composite film may be formed by adding a piezoelectric film, the electroactive film or piezoelectric ceramics to a base material such as a resin film. The composite film or the electroactive film may be composed of a piezoelectric film, piezoelectric ceramics, an electrostriction film, an electret film, an electrically driven elastomer, a urethane rubber, a silicon rubber, a fluororubber, a nitrile rubber, a diene rubber or a liquid crystal elastomer. 
         [0035]    The piezoelectric film  22  is disposed below the diaphragm  21  and connected to the diaphragm  21  at the opposite lateral edges thereof. More particularly, the lateral ends of the piezeolectic film  22  and the diaphragm  21  are connected together (e.g., glued together) along end areas  24  extending from the outermost edges of the piezoelectric film  22  and the diaphragm  21  inwardly towards the center of vibrating device  20  and terminate at spaced locations  25  shown in dotted lines in  FIG. 1(B)  of the diaphragm  21 . As a result, the piezoelectric film  22  is stretched between the two fixed end areas  24 . The vibrating device  20  and the tactile feedback device  10  are preferably supported on an installation surface of a table or the like at the two fixed end areas  24 . 
         [0036]    Because the piezoelectric film  22  is stretched (i.e., is in a tensile state) between the fixed end areas  24 , a tensile force is transmitted from the piezoelectric film  22  to the diaphragm  21  causing the diaphragm  21  to elastically deform to attain a curved shape with a space being formed between the upper principle surface of the piezoelectric film  22  and the lower principle surface of the diaphragm  21 . Further, a spacer  23  is provided in a gap between the diaphragm  21  and the piezoelectric film  22 , preferably near a center position between the opposite end areas  24  as viewed in  FIG. 1(B) . The presence of the spacer  21  ensures that there will be a gap between the upper principle surface of the piezoelectric film  22  and the lower principle surface of the diaphragm  21  even when the piezoelectric film contracts and expands in response to the application of an alternating voltage. 
         [0037]      FIG. 2  is a perspective view of the spacer  23 . The spacer  23  is made of metal, PET or polycarbonate (PC), for example. The spacer  23  preferably has high rigidity to prevent attenuation of vibrations of the diaphragm  21  and the piezoelectric film  22 , and may be made of a material of a higher elastic modulus than those of the diaphragm  21  and the piezoelectric film  22 . The spacer  23  is sandwiched between and held by the diaphragm  21  and the piezoelectric film  22 , and is preferably fixed to at least one of the diaphragm  21  and the piezoelectric film  22  with an adhesive or the like interposed therebetween. The spacer  23  includes a base  25  and a plurality of protrusions  26  extending upwardly therefrom. The base  25  contacts or extends toward the piezoelectric film  22  and is elongated in the length direction. The protrusions  26  protrude from a top surface of the base  25  and contact or extend toward the bottom principle surface of the diaphragm  21 . By providing the protrusions  26  on the top surface of the spacer  23 , it is possible to reduce a contact area between the diaphragm  21  and the spacer  23 . Consequently, even when a finger or the like presses the vicinity of the center of the diaphragm  21  (as viewed in  FIG. 1(B) ) at a position directly above the spacer  23 , it is possible to prevent significant attenuation of vibration. The protrusions  26  are preferably provided at positions facing a frame portion between the touch sensors  31  on the touch panel  30 . 
         [0038]      FIG. 3(A)  is a side view illustrating a vibration mode of the vibrating device  20  in a state where a pressing force is not applied. The spacer  23  is in contact with both the lower surface of the diaphragm  21  and an upper surface of the piezoelectric film  22 . The dimension of the spacer  23  in the height direction is set to be slightly larger than a gap between the diaphragm  21  and the piezoelectric film  22  (near the center point between the spaced locations  25 ) under the condition that the spacer  23  is not provided and no voltage is applied to the piezoelectric film  22 . As a result, when a voltage is not applied to the piezoelectric film  22 , the spacer  23  pushes the piezoelectric film  22  downward in the thickness direction and the piezoelectric film  22  is deformed downwardly at a contact position with the spacer  23 . 
         [0039]    When an alternating voltage is applied to the piezoelectric film  22 , it repeatedly contracts and expands in the width direction. As a result, the tensile force T 1  transmitting from the piezoelectric film  22  to the diaphragm  21  cyclically increases and decreases. This causes a force component T 2  of the tensile force T 1  in a direction perpendicular to a surface of the fixed end areas  24  to also cyclically increase and decrease. Therefore, as indicated by dotted lines in  FIG. 3(A) , a flexure amount of the diaphragm  21  cyclically increases and decreases. As a result, the center of diaphragm  21  (as viewed in  FIG. 3(A) ) is cyclically displaced upward and downward. The spacer  23  moves with the film  22  and maintains a spacing between the top surface of the film  22  and the bottom surface of the diaphragm  21 . 
         [0040]      FIG. 3(B)  is a side view for explaining a vibration mode of the vibrating device  20  in a state where a pressing force produced by a touch operation or the like is applied. In a state where a pressing force T 3  of a user&#39;s finger or the like is applied to the diaphragm  21  and the diaphragm  21  is pushed into a roughly flat shape, an elastic force of the vibrating device  20  produces a reaction force T 4  with respect to the pressing force T 3  which is felt by the user&#39;s finger or the like. In this state, the spacer  23 , and with it the piezoelectric film  22 , are pushed downward. This causes the piezoelectric film  22  to be bent more than it is bent when the pressing force T 3  is not applied. Even when the diaphragm  21  and the diaphragm  21  is pushed by the pressing force T 3  into a roughly flat shape, the spacer  23  ensures that a gap between the diaphragm  21  and the piezoelectric film  22  is maintained and the piezoelectric film  22  is kept in a state where it is stretched in a direction crossing the surface (i.e., not parallel with the plane) of the fixed end area  24 . Consequently, even when the diaphragm  21  is in a flat state, the force component T 2  of the tensile force T 1  works in a direction perpendicular to the surface of the fixed end area  24 . 
         [0041]    As a result, when an AC voltage is applied to the piezoelectric film  22 , the tensile force T 1  transmitted from the piezoelectric film  22  to the diaphragm  21  and the force component T 2  of the tensile force T 1  cyclically increases and decreases, and the diaphragm  21  cyclically flexes significantly. Thus, the reaction force T 4  transmitting from the diaphragm  21  to the user&#39;s finger or the like which pushes the diaphragm  21  cyclically fluctuates, so that it is possible to provide a tactile feedback to the user who performs the touch operation. Consequently, even if the position of a key displayed on the touch panel  30  is arbitrarily changed, a touch operation applied to the changed key position will receive a tactile feedback so that it is possible to improve operability and an operational feeling of the touch keyboard. 
         [0042]    Because the spacer  23  maintains a gap between the diaphragm  21  and the piezoelectric film  22 , it is possible to make the diaphragm  21  thin, suppress rigidity of the diaphragm  21  and make the flexure amount of the diaphragm  21  large compared to the conventional technique. 
         [0043]    In the present embodiment, the diaphragm  21  and the piezoelectric film  22  are connected to each other at opposite ends thereof (i.e., at the fixed ends  24 ) so that it is possible to suppress the number of members which compose the vibrating device. 
         [0044]    The tactile feedback device and the vibrating device according to the present invention may employ different configurations from the above configurations. For example, one end of the diaphragm and one end of the piezoelectric film in the width direction may be directly connected, and the other ends in the width direction may be connected with each other with a support member interposed therebetween. 
         [0045]    In the present embodiment, the piezoelectric film  22  which is a single layer is stretched on the diaphragm  21 . However, the piezoelectric film  22  may be pasted on a film (exciter film) which is a base material such as a resin film, and the exciter film may be stretched on the diaphragm  21  to compose the tactile sense presenting device and the vibrating device according to the present invention. Further, piezoelectric ceramics may be added to the exciter film and the exciter film is stretched on the diaphragm  21  to compose the tactile feedback device and the vibrating device according to the present invention. In this case, a pair of exciter films may be prepared, one end of each exciter film may be connected to the piezoelectric ceramics, and the other end of each exciter film may be connected to the diaphragm  21 . Further, a plurality of pairs of exciter films may be prepared, and configured to be connected with one piezoelectric ceramics. 
         [0046]    In the foregoing embodiment, the spacer  23  is provided with base  25  and protrusions  26 . However, the spacer  23  may have other shapes and the protrusions  26  may be omitted. Protrusions are, however, preferred since they can reduce the contact area between the spacer  23  and the diaphragm  21 . When the contact area between the spacer  23  and the diaphragm  21  is smaller, the spacer  23  is prevented from constraining vibration of the diaphragm  21  and the diaphragm  21  can be better vibrated. Further, the protrusions  26  are not limited to columnar shapes illustrated in  FIG. 2  and may have other shapes such as semispherical shapes or conical shapes. The protrusions  26  may also have a blade shape protruding upwardly toward the diaphragm  21  in the thickness direction and extending along the width direction of the spacer  23  as viewed in  FIG. 2 . Still further, the protrusions  26  may have cross sections of polygonal shapes such as a quadrangular prism shape. Moreover, the base  25  of the spacer  23  may have a shape different from a cuboid shape. 
         [0047]    In the foregoing embodiment, the spacer  23  is in contact with the diaphragm  21  and the piezoelectric film  22  even when the piezoelectric film  22  is not driven and a tension is applied from the spacer  23  to the piezoelectric film  22 . However, the present invention is not limited to this example. For example, the spacer  23  may be set to the substantially same height as the interval between the diaphragm  21  and the piezoelectric film  22  in case where the piezoelectric film  22  is not driven. In this case, even in a state where the spacer  23  is not in contact with both the piezoelectric film  22  when the piezoelectric film  22  is not driven, a tension is not applied from the spacer  23  to the piezoelectric film  22 . Consequently, compared to a case where the tension is applied from the spacer  23  to the piezoelectric film  22  at all times, it is possible to reduce a load applied to the piezoelectric film  22  and prevent shape deterioration and characteristics deterioration of the piezoelectric film  22 . 
         [0048]    Next, a vibrating device according to a second embodiment of the present invention will be described. 
         [0049]      FIG. 4(A)  is a side view illustrating a state where a pressing force is not applied to a vibrating device  20 A according to the second embodiment. The vibrating device  20 A includes a diaphragm  21 , a piezoelectric film  22  and a spacer  23 A. The spacer  23 A has a dimension smaller than a spacing between the diaphragm  21  and the piezoelectric film  22  in the case where the spacer  23 A is not provided, and is fixed to either the piezoelectric film  22  or the diaphragm  21  using an adhesive or the like. In the preferred embodiment, the spacer is fixed to the piezoelectric film  22 . As a result, where the pressing force is not applied to the vibrating device  20 A, the spacer  23 A is not in contact with the diaphragm  21  and the piezoelectric film  22  is flat. 
         [0050]      FIG. 4(B)  is a side view illustrating a state where a pressing force is applied to the vibrating device  20 A according to the second embodiment. When a relatively large pressing force T 3  is applied to the diaphragm  21 , the diaphragm  21  is pushed into a roughly flat shape. When this occurs the spacer  23 A contacts both the diaphragm  21  and the piezoelectric film  22  and pushes the piezoelectric film  22  downward. Thus, the piezoelectric film  22  is bent into a downwardly protruding shape around a contact position with the spacer  23 A. Hence, the spacer  23 A maintains a gap between the diaphragm  21  and the piezoelectric film  22  and, even when the diaphragm  21  is flattened by the pressing force T 3 , the piezoelectric film  22  is kept in a state where it is stretched in a direction that is not parallel to the plane (which could be a curved plane) of the diaphragm  21 . 
         [0051]    With this structure, the vibrating device  20 A can vibrate the diaphragm  21  by driving the piezoelectric film  22  when the pressing force T 3  is applied to the diaphragm  21  to push the diaphragm  21  in a roughly flat shape. Consequently, it is possible to provide a tactile feedback to a user who performs the touch operation. 
         [0052]    Further, when the spacer is not in contact with the diaphragm before a pressing force is applied, vibration of the diaphragm is not constrained by the spacer even when the pressing force is applied. As a result, the time it takes for the vibration of the diaphragm to rise from zero to a desired amplitude is short. This makes it possible to provide a more reliably tactile feedback to an operator who performs the touch operation. 
         [0053]    Next, a vibrating device according to a third embodiment of the present invention will be described with reference to  FIGS. 5(A) and 5(B) . The vibrating device  20 B includes a diaphragm  21 B, a piezoelectric film  22 B, a spacer  23 B and fixed portions  24 B. As in the foregoing embodiments, the diaphragm  21 B and the piezoelectric film  22 B are connected at opposed fixed end areas  24 B. The unstressed shape of the diaphragm  21 B and the prestressed state of the piezoelectric film  22 B are chosen to ensure that the diaphragm  21 B lies in a flat plane before any excitation voltage is applied to the piezoelectric film  22 B. More specifically, an initial shape of the diaphragm  21 B in a state where the diaphragm  21 B is not connected with the piezoelectric film  22 B is a downwardly protruding shape. The tensile force of the piezoelectric film  22 B is set such that the diaphragm  21 B is deformed into a flat shape by the tensile force applied by the piezoelectric film  22 B and an external force applied by the spacer  23 B. 
         [0054]    The fixed portions  24 B are provided, respectively, near the opposite ends of the diaphragm  21 B and the piezoelectric film  22 B which are connected with each other. The fixed portions  24 B protrude downward in the thickness direction of the vibrating device  20 B. The fixed portions  24 B are preferably supported on an installation surface of a table or the like, and prevent the diaphragm  21 B and the piezoelectric film  22 B from directly contacting the installation surface. 
         [0055]    In the vibrating device  20 B, the spacer  23 B is disposed near the center location as viewed in  FIG. 5(B)  between the piezoelectric film  22 B and the diaphragm  21 B. It contacts the lower surface of the diaphragm  21 B and the upper surface of the piezoelectric film  22 B to secure a gap of a predetermined size between the diaphragm  21 B and the piezoelectric film  22 B. As a result, the spacer  23 B pushes the piezoelectric film  22 B downward in the thickness direction, and the piezoelectric film  22 B is caused to protrude downward at the position where the spacer  23 B contacts the piezoelectric film. 
         [0056]    Thus, even when the diaphragm  21 B is in a flat state, the piezoelectric film  22 B is stretched in a direction crossing a surface of the diaphragm  21 B. Consequently, the diaphragm  21 B cyclically flexes in response to a driving voltage being applied to the piezoelectric film  22 B ensuring that a tactile feedback is provided to the user who performs a touch operation. Thus, by providing the spacer  23 B, the vibrating device  20 B can vibrate the diaphragm  21 B even when it is not in a curved shape. Consequently, it is possible to increase the degree of freedom of the shape of the diaphragm  21 B. 
         [0057]    Next, a vibrating device according to a fourth embodiment of the present invention will be described with reference to  FIGS. 6(A) and 6(B) . The vibrating device  20 C includes a diaphragm  21 C, a piezoelectric film  22 C, spacers  23 C and  24 C and fixed portions  25 C. The diaphragm  21 C and the piezoelectric film  22 C are connected to each other at the opposed fixed end areas  24 C and an initial shape of the diaphragm  21 C and a tensile force of the piezoelectric film  22 C are set such that the diaphragm  21 C maintains a flat shape without curving. Fixed portions  25 C protrude downward from the fixed end areas  24 C. The spacers  23 C and  24 C are aligned at predetermined intervals in the width direction of the vibrating device  20 C (i.e., the horizontal direction in  FIG. 6(B) ), and contact with a lower surface of the diaphragm  21 C and an upper surface of the piezoelectric film  22 C to ensure a predetermined gap between the diaphragm  21 C and the piezoelectric film  22 C. Hence, the piezoelectric film  22 C is pushed downward and is bent by the spacers  23 C and  24 C forming two laterally outward and one central planar section. 
         [0058]    The diaphragm  21 B is initially in a flat state and the two laterally outward planar sections of the piezoelectric film  22 C are stretched in a direction crossing a surface of the diaphragm  21 C. Consequently, the diaphragm  21 C is bent cyclically upward and downward as a result of a driving voltage applied to the piezoelectric film  22 C. This provides a tactile feedback to a user who performs a touch operation. 
         [0059]      FIGS. 7(A) and 7(B)  are views for explaining vibrations caused by a vibrating device  20 B according to the third embodiment and the vibrating device  20 C according to the fourth embodiment, specifically the vibrating devices  20 B and  20 C have resonance frequencies determined according to dimensions of diaphragms  21 B and  21 C in the width direction (the horizontal direction as viewed in  FIGS. 7(A) and 7(B) ). Hence, when a drive signal of a frequency matching the resonance frequencies is applied to the vibrating devices  20 B and  20 C, the centers of the vibrating devices  20 B and  20 C in the width direction serve as nodes and as antinodes, respectively, and opposite ends of the vibrating devices  20 B and  20 C are fixed ends. Further, such a harmonic that contact positions with spacers  23 B,  23 C and  24 C in the diaphragms  21 B and  21 C serve as nodes of the vibration is superimposed on the vibrations of the diaphragms  21 B and  21 C. 
         [0060]    As illustrated in  FIG. 7(A) , the spacer  23 B is in contact with the center of the diaphragm  21 B in the width direction (and the vicinity thereof), so that the vibrating device  20 B causes vibration of such a harmonic that this contact position serves as a node of the vibration. That is, vibration of a second harmonic whose wavelength is equal to the width dimension of the diaphragm  21 B is superimposed on the vibration of the vibrating device  20 B. 
         [0061]    As illustrated in  FIG. 7(B) , the spacers  23 C and  24 C are aligned at an appropriate interval in the width direction of the diaphragm  21 C, so that the vibrating device  20 C causes vibration of such a harmonic that contact positions with the spacers  23 C and  24 C serve as nodes of the vibration. That is, the vibration of a third harmonic is superimposed on the vibration of the vibrating device  20 C, and the dimension of the diaphragm  21 C in the width direction is 1.5 times as large as wavelength of the third harmonic. 
         [0062]    Hence, the vibrating device  20 B according to the third embodiment and the vibrating device  20 C according to the fourth embodiment differ in frequencies of harmonics produced by the diaphragms  21 B and  21 C even when the dimensions of the diaphragms  21 B and  21 C in the width direction are equal. Generally, a frequency of vibration within a range of 100 Hz to 300 Hz is good for a tactile feedback on a finger (which means high sensitivity). Consequently, when resonance frequencies of the diaphragms  21 B and  21 C are frequencies lower than 100 Hz, it is possible to adjust the harmonics of the vibrations caused by the diaphragms  21 B and  21 C to frequencies of 100 Hz to 300 Hz by adjusting the number of and the positions of the spacers. Consequently, even when the resonance frequencies of the diaphragms  21 B and  21 C are lower than 100 Hz, it is possible to provide good tactile feedback to the user&#39;s finger or the like. 
         [0063]    Next, a vibrating device according to a fifth embodiment of the present invention will be described with reference to  FIGS. 8(A) and 8(B) . The vibrating device  20 D includes a diaphragm  21 D, a plurality of piezoelectric films  22 D and a spacer  23 D. Each of the piezoelectric films  22 D preferably has a rectangular shape in plan view. Each piezoelectric film  22 D has a width direction which is shorter than its length direction, and are aligned in parallel to one another (See  FIG. 8(A) ). The length of each of the piezoelectric films  22 D is substantially the same as the width of the diaphragm  21 D, and is provided with fixed end areas  24 D which are connected with the diaphragm  21 D. The spacer  23 D is in contact with a lower surface of the diaphragm  21 D and upper surfaces of the plurality of piezoelectric films  22 D and extends in the length direction of the vibrating device  20 D over the plurality of piezoelectric films  22 D so as to ensure a predetermined spacing between the diaphragm  21 D and the plurality of piezoelectric films  22 D. As a result, a plurality of piezoelectric films  22 D are pushed downward in a thickness direction and are bent by the spacer  23 D. 
         [0064]    In the vibrating device  20 D, the shape of each piezoelectric film  22 D is a strip (rectangular) shape which is elongated in its length direction (the width direction of the vibrating device  20 D). Therefore, when driven, each piezoelectric film  22 D stretches or contracts primarily in its length direction. Consequently, by vibrating the diaphragm  21 D including a plurality of these piezoelectric films  22 D, it is possible to effectively vibrate the diaphragm  21 D in its width direction. The spacer  23 D ensures that the diaphragm  21 D will be vibrated when the diaphragm  21 D is pressed downwardly. Consequently, even when the tactile feedback device is composed of the vibrating device  20 D, it is possible to present a tactile feedback to a user who performs the touch operation. 
         [0065]    In the foregoing embodiment, a single spacer is disposed across a plurality of piezoelectric films. Alternatively, a plurality of shorter spacers may be individually disposed on respective piezoelectric films. By disposing a plurality of spacers on a plurality of piezoelectric films, it is possible to individually adjust a tension to be applied to each piezoelectric film, and therefore to more effectively vibrate the diaphragm. 
         [0066]    Further, like the configuration illustrated in  FIGS. 6(A) and 6(B) , a plurality of spacers may be aligned in the length direction of each piezoelectric film in the present embodiment. 
         [0067]    The present invention can be carried out as described above, yet the present invention can be carried out while employing configurations other than the above configurations as long as these configurations correspond to the claims. For example, the vibrating device according to the present invention may be used for other devices than the tactile sense presenting device such as a flat speaker.