Abstract:
A vibration actuator comprising: a vibration portion which contacts a relative movement portion, and produces necessary vibration for a relative movement of the relative movement portion; a first member provided to hold the relative movement portion between the first member and the vibration portion, and moves relative to the vibration portion in response to movement of the relative movement portion with respect to the vibration portion; a second member which faces the first member via a rolling member, and supports the first member so that the first member is movable relative to the vibration portion; and a pressing member which generate a pressing force between the second member and the vibration portion so that the vibration portion and the relative movement portion are in contact with each othercome in contact with each other; and wherein the first member comprises a plastic substance.

Description:
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Applications No. 2009-126126 filed on May 26, 2009, and No. 2010-117169 filed on May 21, 2010. The content of the application is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vibration actuator and an electric device. 
     2. Description of the Related Art 
     There has been a vibration actuator wherein an vibrating element is made to vibrate using an electromechanical conversion element, and a moving element is made to rotate by these vibrations. In such an vibration actuator, a bearing is used in order to hold the moving element so as to be rotatable with respect to the vibrating element (for example, refer to Japanese Unexamined Patent Publication No. Hei 10-319300). Thus far, metal has been used as the material for this bearing. 
     SUMMARY OF THE INVENTION 
     However, when using metal as the bearing material, the cost becomes high, and the weight increases. 
     A problem to be solved by the present invention is to provide a vibration actuator which has favorable characteristics. 
     The present invention solves the above described problem by the following means. 
     According to the first aspect of the present invention, there is provided a vibration actuator comprising: a vibration portion which contacts a relative movement portion, and which produces necessary vibration for a relative movement of the relative movement portion; a first member which is provided so as to hold the relative movement portion between the first member and the vibration portion, and which moves relative to the vibration portion in response to movement of the relative movement portion with respect to the vibration portion; a second member which faces the first member via a rolling member, and which supports the first member so that the first member is movable relative to the vibration portion; and a pressing member which gives rise to a pressing force between the second member and the vibration portion so that the vibration portion and the relative movement portion are in contact with each othercome in contact with each other; and wherein the first member comprises a plastic substance. 
     The first member may comprise a connection portion which is capable of connecting to the outside, at an outer circumferential face in a direction of relative movement of the vibration portion and the relative movement portion, and in a direction orthogonal to the direction of the pressing force. 
     The connection portion may be a gear which transmits power. 
     The relative movement portion and the vibration portion may relatively rotate about a central rotation axis. 
     The rolling member may be provided between an outer circumferential face of the second member and an inner circumferential face of the first member. 
     The first member may face the second member in a direction of relative movement of the vibration portion and the relative movement portion, and a direction orthogonal to a direction of the pressing force. 
     The rolling member may be provided between the first member and the second member, when seen in a direction of the pressing force. 
     The vibration actuator may further comprise a vibration absorption member provided between the relative movement portion and the first member when seen in a direction of the pressing force. 
     The first member may be made of plastic. 
     The second member may comprise a plastic substance. 
     The rolling member may be a metal sphere. 
     The rolling member may be held by a retainer made of plastic. 
     According to the second aspect of the present invention, there is provided an electric device comprising the above mentioned vibration actuator. 
     Further, the above constitution may be suitably improved, or at least partially substituted with other constitutional elements. 
     According to the present invention, it is possible to provide a vibration actuator and electric device having favorable characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual drawing explaining the camera of one embodiment of the present invention; 
         FIG. 2  is a longitudinal cross section drawing of an ultrasonic motor; 
         FIG. 3  is a longitudinal cross section drawing of an ultrasonic motor according to the second embodiment of the present invention; 
         FIG. 4  is an enlarged drawing of the bearing portion in  FIG. 3 ; and 
         FIG. 5  is a longitudinal cross section drawing of the ultrasonic motor according to the third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     Below, the first embodiment of the present invention will be explained with reference to the drawings and the like. Further, in each of the following drawings, in order to facilitate the explanations and understanding, an XYZ Cartesian coordinate system is established. In this coordinate system, in the position of the camera when photographing an image in the landscape orientation with the photographer making the optical axis A horizontal (below referred to as the normal position), the direction towards the left side as seen by the photographer is the X-plus direction. Further, in the normal position, the upwards direction is the Y-plus direction. Furthermore, in the normal position, the direction towards the subject is the 1-plus direction. 
       FIG. 1  is a conceptual drawing explaining the camera  1  of the first embodiment. In the camera  1  of the first embodiment, an ultrasonic motor  10  is provided as an example of the vibration actuator. 
     The camera  1  is provided with a camera body  2  having an image sensor  8 , and a lens barrel  3 . The lens barrel  3  is an interchangeable lens which is detachable from the camera body  2 . Further, in the present embodiment, the lens barrel  3  is shown by an example which is an interchangeable lens, but without being limited to this, for example, the lens barrel may be one which is integrated with the camera body. 
     The lens barrel  3  is provided with the focusing lens  4 , cam tube  5 , idler gear  6 , ultrasonic motor  10 , and a case body  7  which encases them. 
     In the first embodiment, the ultrasonic motor  10  is disposed in the annular space between the cam tube  5  and the case body  7 . The ultrasonic motor  10  is a driving source which drives the focusing lens  4  during the focusing operation of the camera  1 . The ultrasonic motor  10  rotationally drives the cam tube  5  via the idler gear  6  engaged with the output gear  10 G of the ultrasonic motor  10 . 
     The cam tube  5  is provided to be movable in a direction parallel to the optical axis OA (Z axis direction) in the case body  7 , by rotational operation by the ultrasonic motor  10 . 
     The focusing lens  4  is held at the cam tube  5 . Then, focus point adjustment is carried out by moving in the optical axis OA direction by movement of the cam tube  5  by the driving of the ultrasonic motor  10 . 
     Further, while not shown in the drawings, the lens barrel  3  is provided with a plurality of lens groups in addition to the focusing lens  4 . 
     In  FIG. 1 , a object image is imaged at the imaging face of the image sensor  8  by the lens group including the focusing lens  4  provided in the lens barrel  3 . The imaged object image is converted to an electric signal by the image sensor  8 , and imaging data is obtained by A/D conversion of this signal. 
     Next, the ultrasonic motor  10  as the first embodiment is explained in detail with reference to  FIG. 2 . 
       FIG. 2  is a longitudinal (in the axial direction) cross section drawing of the ultrasonic motor  10 . 
     The ultrasonic motor  10  is provided with a support shaft  11  which is disposed to pass through its center, an vibrating element  12 , a rotating body  13  which is rotationally driven by the vibrating element  12 , a support body  14  which supports the vibrating element  12 , and a bearing  20  which supports the rotating body  13  so as to freely rotate. Further, the ultrasonic motor  10  is provided with a pressing spring  15  which pressure-energizes the vibrating element  12  towards the rotating body  13 , and a stopping washer  16  which regulates the position of the pressing spring  15  with respect to the support shaft  11 . In the present embodiment, the vibrating element  12  is a fixed side, and is formed so that does not rotate with respect to the support shaft  11 , while it rotationally drives the rotating body  13  with respect to the support shaft  11 . 
     The support shaft  11  is a shaft of a predetermined diameter, and at one end (the Z axis plus side) the flange  11 A having a large diameter is formed. At the other end of the support shaft  11 , the stopping washer  16  is mounted. The stopping washer  16  is provided so as to be unable to move towards the Z axis minus side by engaging with a retaining ring  17  which is an E ring or the like mounted at the outer end side of the support shaft  11 . 
     The vibrating element  12  is a member whose overall form is hollow, and is constituted by the elastic body  12 A and the piezoelectric body  12 B which is joined to the elastic body  12 A. 
     The elastic body  12 A is formed as a hollow annulus whose outer form is approximately circular, of a metal material having a high degree of resonance acuteness. The elastic body  12 A has a comb tooth portion  12 Aa, a base portion  12 Ab, and a flange portion  12 Ac, and the like. 
     The comb tooth portion  12 Aa has a plurality of grooves of a predetermined width in the circumferential direction with a predetermined spacing and to a predetermined depth, formed from a face of the side facing the rotating body  13  of the elastic body  12 A. The front face of the comb tooth portion  12 Aa (the face of the elastic body  12 A which faces the rotating body  13 ) press-contacts the rotating body  13  and is the driving, face  12 Ad which drives the rotating body  13 , and a lubricant surface treatment such as Ni—P (nickel-phosphorous) plating or the like is usually applied thereto. Further, the reason for providing the comb tooth portion  12 Aa is to bring the neutral plane of the progressing wave arising at the driving face  12 Ad by the expansion and contraction of the piezoelectric body  12 B as close as possible to the piezoelectric body  12 B side, an in this way to amplify the amplitude of the progressing wave of the driving face  12 Ad. 
     The base portion  12 Ab is the part on the opposite side of the comb tooth portion  12 Aa of the elastic body  12 A (on the Z axis minus side in the drawing) on which the grooves of the comb tooth portion  12 Aa are not formed, and is continuous in the circumferential direction of the elastic body  12 A. 
     The flange portion  12 Ac is a portion of a small diameter which protrudes to a predetermined thickness at the inner circumference side of the elastic body  12 A. By this flange body  12 Ac, the vibrating element  12  is supported at the support body  14 . 
     The piezoelectric body  12 B has an approximately plate-like shape, and is joined by an adhesive to the face of the base portion  12 Ab side of the elastic body  12 A (the side of the elastic body  12 A at the opposite side to the rotating body  13 ). 
     The piezoelectric body  12 B is an electromechanical conversion element which converts electrical energy into mechanical energy. Further, in the present embodiment, a piezoelectric element is used as the piezoelectric body  12 B, but it is also possible to use an electrostrictive element or the like. 
     The piezoelectric body  12 B is provided with two electrodes, not shown in the drawing, for inputting a driving signal. 
     The flexible printed circuit board  12 C is disposed at the face at the opposite side of the elastic body  12 A of the piezoelectric body  12 B. 
     The wiring of the flexible printed circuit board  12 C is connected to the electrodes of the piezoelectric body  12 B. 
     The flexible printed circuit board  12 C has the function of providing a driving signal to the piezoelectric body  12 B. Progressing waves are generated at the driving face of the elastic body  12 A when the elastic body  12 A is excited by the expansion and contraction of the piezoelectric body  12 B, by the driving signal provided from this flexible printed circuit board  12 C. In the present embodiment, a four wave progressing wave is generated. 
     The rotating body  13  is a member which is rotationally driven by the progressing wave arising at the driving face  12 Ad of the elastic body  12 A. 
     The rotating body  13  is formed with an approximately discoid shape of a light metal such as aluminum or the like, and has a contact face  13 A which has an approximately annular shape and contacts the vibrating element  12  (the driving face  12 Ad of the elastic body  12 A), and a joining portion  13 B which has a cylindrical shape with a small diameter and joins to the bearing  20  (outer wheel  22 ). The contact face  13 A is given a surface treatment of alumite or the like to increase the abrasion resistance. 
     The joining portion  13 B of the rotating body  13  fits at the joining portion  22 A of the outer wheel  22  of the later described bearing  20  via the damping member  18  and is joined without allowing rotation relative to the outer wheel  22 . 
     The support body  14  which supports the vibrating element  12  has a main body portion  14 A of a predetermined outer diameter, a support portion  14 B which fits at the flange portion  12 Ac of the vibrating element  12 , and a pressing flange  14 C having a large diameter, which is formed between the main body portion  14 A and the support portion  14 B and exhibits an approximately discoid shape. Further, a mounting hole  14 D which fits the support shaft  11  so as to be slidably movable is formed at the central portion of the support body  14 . 
     The support body  14  fits the support shaft  11  at the mounting hole  14 D, and its support portion  148  fits to the flange portion  12 Ac of the vibrating element  12 , and in this way, the vibrating element  12  is concentrically supported about the support shaft  11 . 
     A pressing spring  15  is disposed between the pressing flange  14 C of the support body  14  and the stopping washer  16  mounted at the shaft end of the support shaft  11 . 
     The pressure spring  15  is a coil spring which gives rise to an elastic return force by compressive deformation, and it is disposed such that the main body portion  14 A of the support body  14  is fit at its inner circumference. Further, this elastic return force pressure-energizes the pressing flange  14 C (namely the support body  14 ) in a direction away from the stopping washer  16 . 
     The bearing  20  is provided with the inner wheel  21 , the outer wheel  22 , and the ball  23  disposed between the inner wheel  21  and the outer wheel  22 , and is constituted to allow free relative rotation between the inner wheel  21  and the outer wheel  22  with low friction by the rolling of the ball  23 . 
     The outer wheel  22  is provided with the joining portion  22 A at its inner circumference, which is joined with the rotating body  13 . Further, the output gear  10 G is formed at the outer circumference of the outer wheel  22 . In other words, the outer wheel  22  has the function of supporting the rotating body  13 , and the function of outputting the rotational power of the rotating body  13  to the outside. 
     The inner wheel  21  of the bearing  20  is fit to the support shaft  11  without allowing relative rotation, and one end face thereof (the Z axis plus side) abuts the flange  11 A of the support shaft  11 . 
     The joining portion  138  of the rotating body  13  is fit to the joining portion  22 A of the outer wheel  22  of the bearing  20 , and joined thereto via the damping member  18 . In this way, the bearing  20  supports the rotating body  13  so as to be freely rotatable. Further, the constitution of this bearing  20  will be explained later in more detail. 
     The damping member  18  is a member of approximately annular shape having a predetermined thickness and formed of an elastic body such as rubber or the like. 
     The damping member  18  is disposed between the end face of the joining portion  13 B of the rotating body  13 , and the end face of the joining portion  22 A of the outer wheel  22  of the bearing  20 , and joins the two without allowing relative rotation. The damping member  18  has the function of making the rotating body  13  and the outer wheel  22  of the bearing  20  integrally rotatable by its viscoelasticity, and the function of absorbing the vibrations of the rotating body  13  so that they are not transmitted to the outer wheel  22 . The damping member  18  is formed of, for example, butyl rubber, silicon rubber, propylene rubber, and the like. 
     In an ultrasonic motor  10  constituted as above, the vibrating element  12  is pressure-energized towards the rotating body  13  by the elastic return force of the pressing spring  15  via the support body  14 , and the driving face  12 Ad is press-contacted to the contact face  13 A by a predetermined force. Then, when two alternating current driving waveforms having different phases are input to the two electrodes of the piezoelectric body  12 B of the vibrating element  12 , a progressing wave is generated at the rotating body  13  side of the elastic body  12 A by the deformation of the piezoelectric body  12 B. The rotating body  13  (contact face  13 A) which press-contacts the vibrating element  12  (driving face  12 Ad) is friction driven to rotate by these progressing waves. The rotations of the rotating body  13  are transmitted to the outer wheel  22  of the bearing  20  via the damping member  18 , and the outer wheel  22 , namely the output gear  10 G, rotates, and the rotational power is output to the outside. 
     Next, a more detailed explanation will be given of the bearing  20  of the first embodiment. 
     As mentioned above, the bearing  20  is provided with the inner wheel  21 , the outer wheel  22 , and the ball  23 . Further, the bearing  20  is disposed at the right side (Z axis minus side) in  FIG. 2  of the flange  11 A with the inner wheel  21  fit to the support shaft  11  without allowing relative rotation, and receives the energizing force (the energizing force which pushes the vibrating element  12  to the rotating body  13 ) of the pressing spring  15  acting via the vibrating element  12  and the rotation body  13 , and supports the rotating body  13  so as to be freely rotatable. 
     Namely, at the Z axis minus side of the bearing  20 , the rotating body  13 , the vibrating element  12 , the support body  14 , and the pressing spring  15  are disposed in series in the axial direction of the support shaft  11 , and the pressing force generated from the pressing spring  15  which presses the vibrating element  12  to the rotating body  13  is act on the outer wheel  22 . 
     The inner wheel  21  is an annular shape having an inner diameter portion into which the support shaft  11  can fit, and is formed with a predetermined thickness in the radial direction. At its outer circumference, there is formed in the circumferential direction an inner rolling face  21 A where the ball  23  rolls. 
     The inner rolling face  21 A is formed with an arc-shaped cross sectional form conforming to the spherical surface of the ball  23 , and has the radial inner face portion  21 Ar which faces the outer side in the radial direction, and the thrust inner face portion  21 As orthogonal to the Z axis and which faces the Z axis minus direction. 
     The outer wheel  22  has a shape which is annular in outline, but as explained above, the output gear  10 G is formed at its outer circumference. At the inner circumference of the outer wheel  22 , the joining portion  22 A with which the rotating body  13  is joined, and the outer rolling face  22 B on which the ball  23  rolls, are respectively formed in the circumferential direction. 
     The joining portion  22 A has a recessed shape with a circular inner diameter into which the joining portion  13 B of the rotating body  13  can be inserted and fit, and is open at the side where the rotating body  13  of the outer wheel  22  is disposed (the Z axis minus side). 
     The outer rolling face  22 B is formed with an arc-shaped cross sectional form conforming to the spherical surface of the ball  23 , and has the radial outer face portion  22 Br which faces the inner side of the radial direction, and the thrust outer face portion  22 Br orthogonal to the Z axis and which faces the Z axis plus side. Namely, the outer wheel  22  is integrally formed with a portion (the joining portion  22 A) which holds the rotating body  13 . 
     The ball  23  is a rollable sphere interposed between the inner rolling face  21 A of the inner wheel  21 , and the outer rolling face  22 B of the outer wheel  22 , and a plurality are disposed around the whole circumference between the inner wheel  21  (inner rolling face  21 A) and the outer wheel  22  (outer rolling face  22 B). 
     Here, the inner wheel  21  and outer wheel  22  are manufactured of a substance having plasticity, in particular a plastic material which is easily moldable. However, without being limited to this, they may also be, for example, a thermoplastic material, a resin, a celluloid, a high polymer material and the like. 
     The inner wheel  21  and the outer wheel  22  are respectively formed by injection molding or the like of a plastic material. As the plastic material, for example, polyacetal, polyether ether ketone, polybutylene terephthalate, polycarbonate and the like may be used. 
     On the other hand, the ball  23  is formed of a metal material such as a stainless alloy steel or the like, or a material such as a ceramic or the like. The outer wheel  22  has a lower hardness than the ball  23 , and a higher flexibility than the ball  23 . 
     In the bearing  20  with the above constitution, the outer wheel  22  can relatively rotate with respect to the inner wheel  21  mounted and fixed to the support shaft  11 , by the rolling of the balls  23 . 
     The power (thrust force Fs) by the energizing of the pressing spring  15  in the Z axis direction via the rotating body  13 , as well as the driving counterforce (radial force Fr) in a direction orthogonal to the rotation axis (=Z axis direction) when the output gear  10 G outputs the rotational power to the outside, act on the outer wheel  22  of the bearing  20 . 
     The thrust force Fs acts on the thrust inner face portion  21 As of the inner rolling face  21 A of the inner wheel  21  via the ball  23 , from the thrust outer face portion  22 B of the outer rolling face  22 B of the outer wheel  22 . In this way, the bearing  20  receives the thrust force Fs with the thrust inner face portion  21 As, and the outer wheel  22  is smoothly rotatable. 
     Further, the radial force Fr acts on the radial inner face portion  21 Ar of the inner rolling face  21 A of the inner wheel  21  via the ball  23 , from the radial outer face portion  22 Br of the outer rolling face  22 B of the outer wheel  22 . In this way, the bearing  20  receives the radial force Fr at the radial inner face portion  21 Ar, and the outer wheel  22  is smoothly rotatable without eccentricity. 
     In this way, the bearing  20  is provided with both functions of a thrust bearing and a radial bearing. 
     As described above, the bearing  20  is able to stably and rotatably support the rotating body  13  while resisting the thrust force Fs by the pressing spring  15  acts on the outer wheel  22  via the rotating body  13 . Further, it is able to allow the outer wheel  22  to stably rotate, preventing eccentricity, while resisting the radial force Fr arising when the output gear  10 G engages with and drives the gears of the side of the load to be driven. As a result, it is possible to output to the outside the rotational force with little fluctuation in speed, via the outer wheel (output gear  10 G). 
     In the present embodiment, the inner wheel  21  and outer wheel  22  of the bearing  20  are formed of a plastic material. Because of this, the outer wheel  22  and the output gear  10 G can be integrally formed, and can be manufactured at low cost. If the inner wheel  21  and the outer wheel  22  of the present embodiment were, for example, formed of metal as in the conventional manner, gear machining and cutting machining would be necessary, which would incur greatly higher costs. If they were constituted of different materials and assembled, the costs would also increase because of the increased number of parts and assembly stages. This does not occur in the present embodiment. Further, the constitution can be made light. In addition, what the ball  23  contacts is the inner wheel  21  and the outer wheel  22 , which are made of plastic, thus there is no mutual contact of metals, and it is possible to design the bearing  20  to be quiet when operating. 
     Further, in the present embodiment, the joining portion  22 A which joins to the rotating body  13  is formed at the inner diameter side of the outer wheel  22  which has the output gear  10 G formed on its outer diameter side. In this way, the overall length of the ultrasonic motor  10  can be shortened. In contrast, if the joining portion  22 A were not provided and the outer wheel  22  and the rotating body  13  were disposed in series, in order to maintain the same tooth width of the output gear  10 G as in the present embodiment, the length of the ultrasonic motor  10  in the axial direction would have to be increased. In the present embodiment, it is possible to compactly constitute an ultrasonic motor  10  having an output gear  10 G with a wide facewidth. 
     Second Embodiment 
     Next, the second embodiment of the present invention will be explained with reference to  FIG. 3  and  FIG. 4 . 
       FIG. 3  is a cross sectional drawing of the ultrasonic motor  110  according to the second embodiment.  FIG. 4  is a an enlarged drawing of a portion of the bearing  120  of  FIG. 3 . 
     The ultrasonic motor  110  shown in  FIG. 3 , in the same way as in the first embodiment, is used for an application such as the rotational driving of a cam tube  5  of a lens barrel  3 , but in the present embodiment it is constituted in a ring shape. 
     Further, the bearing  120  in the ultrasonic motor  110  of the present embodiment is constituted in approximately the same way as the bearing  20  in the previously described first embodiment, and detailed explanations of identical constituent elements are omitted. 
     The ultrasonic motor  110  is provided with a support ring  111 , an vibrating element  112 , a rotating body  113 , a bearing  120 , a pressing portion  115 , and a fixing ring  116 . Further, the ultrasonic motor  110  is provided with the first damping member  112 , the second damping member  119 , and the like. 
     The vibrating element  112  is provided with the elastic body  112 A and the piezoelectric body  112 B. 
     The elastic body  112 A is a member of approximately annular shape, and at one end face, the piezoelectric body  112 B is provided, and at the other face, the comb tooth portion  112 Aa is formed, wherein a plurality of grooves are cut and formed. A progressing wave is generated by the vibrations of the piezoelectric body  112 E at the tip end faces of the comb tooth portion  112 Aa, which form the driving face  112 Ad which drives the rotating body  113 . 
     The piezoelectric body  112 B has the function of converting electrical energy into mechanical energy. This piezoelectric body  1128  has electrodes, not shown in the drawings, which are connected to the flexible printed circuit board, and is excited by driving electric power provided from this flexible printed circuit board. 
     The rotating body  113  is member having an approximately annular shape, and has the contact face  113 A having an approximately annular shape and which contacts the vibrating element  112  (the driving face  112 Ad of the elastic body  112 A), and the joining portion  113 B having a cylindrical shape which joins to the bearing  120  (the outer wheel  122 ). 
     In the rotating body  113 , the joining portion  113 B is fit with the joining portion  122 A of the outer wheel  122  of the bearing  120  described later, and thus is joined without allowing rotation relative to the outer wheel  122  via the first damping member  118 . 
     The first damping member  118  is a member of an approximately annular shape formed using rubber or the like. This first damping member  118  has the function of making the rotating body  113  and the outer wheel  122  of the bearing  120  integrally rotatable by its viscoelasticity, and the function of absorbing vibrations of the rotating body  113  so that they are not transmitted to the outer wheel  122 . 
     The bearing  120 , in the same way as the bearing  20  in the first embodiment described above, is provided with the inner wheel  121 , the outer wheel  122 , and the ball  123  disposed between the inner wheel  121  and the outer wheel  122 , and is constituted such that the inner wheel  121  and outer wheel  122  can freely rotate relative to each other with low friction by the rolling of the ball  123 . 
     However, the joining portion  122 A of the outer wheel  122 , to which the rotating body  113  is joined, is at the outer circumference side of the outer wheel  122 , and the joining portion  113 B of the rotating body  113  is fit to the outer circumference. 
     Further, at the outer circumference of the outer wheel  122 , the output projection  110 P protrudes. The output projection  110 P engages with, for example, a fork shaped engaging member provided at a member to be driven, and has the function of rotationally driving a member to be driven via the engaging portion. 
     Namely, the outer wheel  122  has the function of supporting the rotating body  113 , and the function of outputting to the outside the rotational driving force of the rotating body  113 . 
     At the bearing  120 , the inner wheel  121  is fit to the support ring  111  without allowing relative rotation, and one end face (at the Z axis plus side) is provided so as to abut the flange  111 A of the support ring  111 . 
     At the joining portion  122 A of the outer wheel  122  of the bearing  120 , the joining portion  113 B of the rotating body  113  is fit, and is joined via the first damping member  118 . In this way, the bearing  120  supports the rotating body  113  so as to be freely rotatable. 
     The inner rolling face  121 A of the inner wheel  121  of the bearing  120  has a radial inner face portion  121 Ar and a thrust inner face portion  121 As, and the outer rolling face  122 B of the outer wheel  122  has a radial outer face portion  122 Br and a thrust outer face portion  122 Bs. In this way, the bearing  120  is able to receive either of the thrust force Fs or the radial force Fr. 
     Further, the inner wheel  121  and the outer wheel  122  of the bearing  120  are respectively formed by injection molding or the like by a plastic material. As the plastic material, for example, polyacetal, polyether ether ketone, polybutylene terephthalate, polycarbonate and the like can be used. 
     On the other hand, the ball  123  is formed of a material such as a stainless alloy steel or a ceramic or the like. 
     The pressing portion  115  is a part which generates a pressing force to press-contact the vibrating element  112  and the rotating body  113 , and is provided with the pressure plate  115 A and a plurality of (two in the present embodiment) plate springs  115 B. The pressure plate  115 A receives the elastic return force generated by the plate springs  115 B, and is a plate having an approximately annular shape. 
     Between the pressing portion  115  and the vibrating element  112 , the second damping member  119  is provided. 
     The second damping member  119  is formed of a non-woven fabric or felt or the like. This second damping member  119  is a member which prevents transmission of the vibrations of the vibrating element  112  to the pressing portion  115  side, and is provided between the piezoelectric body  112 B and the pressing plate  115 A. 
     The fixing ring  116  has a disc-shaped major diameter, and is provided at the end portion of the support ring  111 . The fixing ring  116  is a member which receives the counter force of the pressing force by the pressing portion  115  which makes the vibrating element  112  press-contact the rotating body  113 . Further, the fixing ring  116  has the function of coupling the ultrasonic motor  11  with the rotation of an external operating means (for example, a focus operation ring, zoom operation ring or the like), not shown in the drawings. 
     At the rear face side (the z axis minus side) of the fixing ring  116 , the electric power supply portion  130  is formed. 
     The electric power supply portion  130  is connected to the piezoelectric body  112 B of the vibrating element  112  via the flexible printed circuit board  131 , and provides driving electric power to the piezoelectric body  112 B via the flexible printed circuit board  131 . 
     In the ultrasonic motor  110  constituted as above, the vibrating element  112  is pressure energized towards the rotating body  113  by the pressing force of the pressing portion  115 , and the driving face  112 Ad is press-contacted with a predetermined force with the contact face  113 A. Then, when two alternating current driving waveforms having different phases are applied to the two electrodes of the piezoelectric body  112 B of the vibrating element  112 , a progressing wave is generated at the rotating body  113  side of the elastic body  112 A by the deformation of the piezoelectric body  112 B. The rotating body  113  (contact face  113 A) which press-contacts the vibrating element  112  (driving face  112 Ad) is friction driven by this progressing wave and rotates. The rotation of the rotating body  113  is transmitted to the outer wheel  122  of the bearing  120  via the first damping member  118 , and the outer wheel  122 , namely the output projection  110 P rotates (revolves) and outputs the rotation power to the outside. 
     The bearing  120  is able to stably and rotatably support the rotating body  113  while resisting the thrust force Fs by the pressing portion  115  applied to the outer wheel  122  via the rotating body  113 . Further, it is able to allow the outer wheel  122  to stably rotate, preventing eccentricity, while resisting the radial force Fr arising when the output projection  110 P drives the member to be driven. As a result, it is possible to output to the outside the rotational force with little fluctuation in speed, via the outer wheel (output projection  110 P). 
     Further, in the same way as for the above described first embodiment, the inner wheel  121  and the outer wheel  122  of the bearing  120  are formed of a plastic material. Because of this, the constitution can be light, and further, it is possible to integrally mold the output projection  110 P protruding at the outer circumference as described above, and it can be manufactured at low cost. 
     Third Embodiment 
     Below, the third embodiment of the present invention will be described with reference to the drawings.  FIG. 5  is a longitudinal (axial direction) cross section drawing of the ultrasonic motor  210  of the third embodiment. 
     The third embodiment is approximately the same as the second embodiment, but differs in the point that the balls  123  are held by the retainer  125 . The other parts are the same as for the second embodiment, and thus are assigned the same reference numbers, and explanations thereof are omitted. 
     The retainer  125  is an annular member extending along the entire circumference of the gap between the inner wheel  121  and the outer wheel  122 . Further, as shown in  FIG. 5 , in the retainer  125 , a cross section parallel to the central axis of the retainer  125  is inclined by a prescribed angle with respect to this central axis. Namely, the retainer  125  has a shape wherein a part of the side face of a cone has been cut out to a predetermined width. The side face of the retainer  125  is provided with a plurality of holes, and the balls  123  are rotatably held in these holes. 
     The retainer  125  is made of plastic, and is formed by injection molding or the like. As the plastic material, for example, polyacetal, polyether ether ketone, polybutylene terephthalate, polycarbonate and the like can be used. 
     According to the present embodiment, the balls  123  are held by the retainer  125 , thus the spacing of the balls  123  is held constant, and it is possible to prevent the balls from contacting each other. In this way, because the balls do not contact each other, there is no generation of contact sounds arising from the balls rubbing with or colliding against each other. Accordingly, it is possible to achieve further silencing of the ultrasonic motor  210  when operating. 
     Further, because the retainer  125  can be manufactured of plastic, its manufacturing cost can be made low. In addition, the number of the balls  123  can be reduced and the assembling operation becomes simple and easy. 
     The above embodiments have the following effects. 
     (1) In the ultrasonic motor  10 ,  110 , or  210 , the outer wheel  22  or  122  is made of a substance having plasticity such as a plastic material or the like, and has a lower hardness and higher flexibility than the balls  23  or  123  which are constituted of a metal material or the like. Because of this, when the ultrasonic motor  10 ,  110 , or  210  is driven, the outer wheel  22  or  122  and the balls  23  or  123  contact stably and flexibly, and thus the driving of the ultrasonic motor  10 ,  110  or  210  can be designed to be stable and quiet. 
     (2) In the ultrasonic motor  10 ,  110 , or  210 , for the bearing  20  or  120  rotatably supporting the rotating body  13  or  113 , the inner rolling face  21 A or  121 A of the inner wheel  21  or  121  has the radial inner face portion  21 Ar or  121 Ar, and the outer rolling face  22 B or  122 B of the outer wheel  22  or  122  has the radial outer face portion  22 Br or  122 Br, and because of this, the outer wheel  22  or  122  can be rotated stably while preventing eccentricities, while resisting the radial force Fr. Further, the outer wheel  22  is formed of a plastic material. Because of this, the degree of freedom in shaping is high, and complex shapes can be also integrally molded, and can be manufactured at low cost. 
     (3) At the outer circumference of the outer wheel  22  or  122  of the bearing  20  or  120 , the output gear  10 G or output projection  110 P which outputs rotational power to the outside is provided. Because of this, there is no need to provide a separate member for output, and the constitution can have a low cost by reducing the number of parts and the number of assembly steps. 
     (4) In the bearing  20  or  120  which rotatably supports the rotating body  13  or  113 , the inner rolling face  21 A or  121 A of the inner wheel  21  or  121  has the thrust inner face portion  21 As or  121 As, and the outer rolling face  22 B or  122 B of the outer wheel  22  has the thrust outer face portion  22 Bs or  122 Bs, and because of this, the outer wheel  22  or  122  can be supported to be stably rotatable while resisting the thrust force Fs by the pressing spring  15  or pressing portion  115  operating on the outer wheel  22  or  122  via the rotating body  113 . 
     (5) By disposing the damping member  18  or  118  between the outer wheel  22  or  122  of the bearing  20  or  120 , and the rotating body  13  or  113 , the vibrations of the rotating body  13  or  113  are absorbed and is it possible to suppress their transmission to the outer wheel  22 . 
     (6) The inner wheel  21  or  121  of the bearing  20  or  120  is formed of a plastic material. Because of this, the degree of freedom in shaping is high, and complex shapes can also be integrally molded, and can be manufactured at low cost. 
     (7) The camera  1  carries out focus point adjustment by moving the cam tube  5  by the driving of the ultrasonic motor  10  or  110 . By this means, smooth focus point adjustment is possible. 
     (8) Furthermore, in the case of the constitution wherein the balls  123  are held by the retainer  125 , there is no generation of contact noise arising from the balls  123  rubbing against or colliding with each other, and it is possible to achieve further silencing of the ultrasonic motor  210 . Further, by manufacturing the retainer  125  of plastic, the manufacturing costs can be reduced. 
     (Modifications) 
     The present invention is not limited to the above explained embodiments, and many modifications and variations such as those shown below are possible, and these are also within the scope of the present invention. 
     (1) In the embodiments, explanations were given showing as an example an ultrasonic motor  10  or  110  where the rotating body  13  or  113  rotates as an vibration actuator. However, as the form of the vibration actuator, this is not a limitation, and it may be an ultrasonic motor having a form wherein the support shaft rotates, or an ultrasonic motor of a linear type. 
     (2) In the embodiments, explanations were given showing as an example an ultrasonic motor  10  or  110  as a vibration actuator, but without being limited to this, for example, it may also be a vibration actuator using vibrations outside of the ultrasonic region. 
     (3) In the embodiments, an example is shown where the ultrasonic motor  10  or  110  is used as a driving source for the focus point adjustment of the lens barrel  3 , but without being limited to this, for example, it may also be a driving source of a zooming operation of a lens barrel  3 , or a driving source of a hand shake correction mechanism which corrects hand shake by driving a part of the imaging system of the camera. Furthermore, it may also be applied to a video camera, a mobile phone, or the like. 
     (4) In the third embodiment, an explanation was given for an example wherein the balls  123  of the second embodiment are held by the retainer  125 , but without being limited to this, for example, the balls  23  in the first embodiment may also be held by a retainer. 
     Further, the embodiments and modifications may be used in appropriate combinations, but detailed explanations are omitted. Further, the present invention is not limited by the embodiments explained above.