Abstract:
A vibration actuator with good driving performance, and a lens barrel and camera equipped therewith, is provided. There is provided a vibration actuator comprising: an electromechanical conversion element that is excited by a driving signal; a vibrating body including a joining face, to which the electromechanical conversion element is joined, and a driving face, at which a vibration wave is produced by the excitation; and a relative motion member that is pressingly touched against the driving face, is driven by the vibration wave, and relatively moves with respect to the vibrating body, wherein at a first and a second portion of the electromechanical conversion element in a direction parallel to the joining face and orthogonal to a direction of the relative movement of the vibrating body and the relative motion member, thickness in a direction orthogonal to the joining face differs between the first portion and the second portion.

Description:
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2008-029591 filed on Feb. 8, 2008. 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 to a lens barrel and camera equipped therewith. 
     2. Description of the Related Art 
     Heretofore, vibration actuators have been known in which expansion and contraction of an electromechanical conversion element is used to generate progressive vibration waves (hereinafter referred to as progressive waves) at a driving surface of a vibrating body, elliptical movements are produced at the driving surface by the progressive waves, and a relative motion member that pressingly touches against wave peaks of the elliptical movements is driven. 
     In recent years, reductions in size of these vibration actuators have been demanded. Among vibration wave actuators with configurations in which the resilient member has a substantially annular form and the relative motion member is rotatingly driven or the like, actuators with larger diametric direction widths produce greater driving force. When these vibration actuators are reduced in size, it is necessary to increase the diametric direction width of the resilient member in order to obtain driving force. Therefore, as the resilient member is reduced in size, there is a tendency for a ratio between the external diameter and the internal diameter of the resilient member to increase. 
     When the ratio between the external diameter and internal diameter of the resilient member increases, a difference between vibration amplitudes of the progressive waves at the outer periphery of the driving surface and vibration amplitudes of the progressive waves at the inner periphery becomes larger. Consequently, a problem arises in that driving of the relative motion member becomes unstable, losses of vibration occur, and driving efficiency of a vibration wave motor falls. 
     As a measure to reduce the difference between the vibration amplitudes of progressive waves at the outer periphery and the vibration amplitudes at the inner periphery, Patent Reference 1 discloses a technique of forming indentation portions (grooves) in the face of the relative motion member that touches against the vibrating body (a driving surface). The indentation portions do not reach as far as the outer periphery end of the vibrating body. Thus, thickness at the outer periphery of the vibrating body and thickness at the inner periphery are altered, and stiffnesses thereof with respect to bending displacements are altered (for example, see Japanese Unexamined Patent Publication No. H3-273874). 
     SUMMARY OF THE INVENTION 
     However, with the technique disclosed in Patent Reference 1, the thickness of a base portion of the vibrating body at the outer periphery is increased and stiffness with respect to bending displacements is larger. In this state, vibration characteristics differ between the inner periphery side and the outer periphery side. Consequently, there is a problem in that sufficient vibration amplitudes are not obtained and driving force is reduced. 
     An object of the present invention is to provide a vibration actuator with good driving performance, and a lens barrel and camera equipped therewith. 
     In order to achieve the object mentioned above, according to a first aspect of the present invention, there is provided a vibration actuator comprising: an electromechanical conversion element that is excited by a driving signal; a vibrating body including a joining face, to which the electromechanical conversion element is joined, and a driving face, at which a vibration wave is produced by the excitation; and a relative motion member that is pressingly touched against the driving face, is driven by the vibration wave, and relatively moves with respect to the vibrating body, wherein at a first portion and a second portion of the electromechanical conversion element in a direction that is parallel to the joining face and orthogonal to a direction of the relative movement of the vibrating body and the relative motion member, thickness in a direction orthogonal to the joining face differs between the first portion and the second portion. 
     The electromechanical conversion element and the vibrating body may be in substantially annular forms, the first portion may be an inner periphery portion of the electromechanical conversion element, and the second portion may be an outer periphery portion of the electromechanical conversion element. 
     The thickness of the inner periphery portion in the direction orthogonal to the joining face may be thinner than the thickness of the outer periphery portion in the direction orthogonal to the joining face. 
     The thickness of the electromechanical conversion element in the direction orthogonal to the joining face may alter stepwise along the direction that is parallel to the joining face and orthogonal to the direction of relative movement of the vibrating body and the relative motion member. 
     The thickness of the electromechanical conversion element in the direction orthogonal to the joining face may alter stepwise along the direction that is parallel to the joining face and orthogonal to the direction of relative movement of the vibrating body and the relative motion member, due to the electromechanical conversion element being formed with a plurality of layers being stacked. 
     According to a second aspect of the present invention, there is provided a vibration actuator comprising: an electromechanical conversion element that is excited by a driving signal; a vibrating body including a joining face, to which the electromechanical conversion element is joined, and a driving face, at which a vibration wave is produced by the excitation; a relative motion member that is pressingly touched against the driving face, is driven by the vibration wave, and relatively moves with respect to the vibrating body; and an output portion that supplies the driving signal to the electromechanical conversion element, wherein at a first portion and a second portion of the electromechanical conversion element in a direction that is parallel to the joining face and orthogonal to a direction of the relative movement of the vibrating body and the relative motion member, a piezoelectric strain amount produced by the driving signal at the first portion differs from a piezoelectric strain amount produced by the driving signal at the second portion. 
     The electromechanical conversion element and the vibrating body may be in substantially annular forms, the first portion is an inner periphery portion of the electromechanical conversion element, and the second portion is an outer periphery portion of the electromechanical conversion element. 
     The piezoelectric strain amount produced at the inner periphery portion may be larger than the piezoelectric strain amount produced at the outer periphery portion. 
     A piezoelectric constant of a material that forms the first portion may differ from a piezoelectric constant of a material that forms the second portion. 
     A magnitude of an electric field produced at the first portion by the driving signal may differ from a magnitude of an electric field produced at the second portion by the driving signal. 
     In order to achieve the object mentioned above, according to a third aspect of the present invention, there is provided a lens barrel according to the above aspects of the vibration actuator. 
     In order to achieve the object mentioned above, according to a forth aspect of the present invention, a camera comprising the vibration actuator according to the above aspects of the vibration actuator. 
     The present invention may not be limited to the above description. The component of the embodiment described later may be modified as appropriate, and any other component may be substituted for at least a part of them. Further, constituent without any special limitation of its arrangement is not limited to arrangement disclosed in embodiments and may be arranged to the position where the function can be completed 
     According to the present invention, a vibration actuator with good driving performance, and a lens barrel and camera equipped therewith, can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view describing a camera of a first embodiment; 
         FIG. 2  is a cross-sectional view of an ultrasonic motor of the first embodiment; 
         FIG. 3  is a block diagram describing a driving device of the ultrasonic motor  10  of the first embodiment; 
         FIGS. 4A to 4C  are views showing a piezoelectric body of the first embodiment; 
         FIGS. 5A to 5C  are views showing a piezoelectric body of a second embodiment; 
         FIGS. 6A to 6C  are views showing a piezoelectric body of a third embodiment; and 
         FIGS. 7A to 7C  are views showing a piezoelectric body of a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Herebelow, preferred embodiments of the present invention are described with reference to the attached drawings and suchlike. The following embodiments describe an ultrasonic motor, which is offered as an example of the vibration actuator. 
     First Embodiment 
       FIG. 1  is a view describing the camera  1  of the first embodiment. 
     The first embodiment of the camera  1  is provided with a camera body  2  including an imaging device and a lens barrel  3  including a lens  7 . 
     The lens barrel  3  is an interchangeable lens which is detachable from the camera body  2 . In the present embodiment, the lens barrel  3  illustrates an example that is an interchangeable lens, but this is not to be limiting; for example, it may be a lens barrel that is integral with the camera body. 
     The lens barrel  3  is provided with the lens  7 , a cam tube  6 , gears  4  and  5 , the ultrasonic motor  10  and so forth. In the present embodiment, the ultrasonic motor  10  is used as a drive source that drives the lens  7  when focus-driving the camera  1 . The driving force provided from the ultrasonic motor  10  is transmitted to the cam tube  6  via the gears  4  and  5 . The lens  7  is retained in the cam tube  6 . The lens  7  is a focusing lens that is moved in a direction substantially parallel to an optical axis direction (the direction of arrow O shown in  FIG. 1 ) by the driving force of the ultrasonic motor  10  and implements focus point adjustment. 
     In  FIG. 1 , an image of a object is focused at an imaging plane of an imaging element  8  by an unillustrated lens group (including the lens  7 ) which is provided inside the lens barrel  3 . The object image imaged by the imaging element  8  is converted to electronic signals and these signals are A/D-converted. Thus, image data is obtained. 
       FIG. 2  is a cross-sectional view of the ultrasonic motor  10  of the first embodiment. 
     The ultrasonic motor  10  of the first embodiment is provided with an vibrator  11 , a moving element  15 , an output shaft  18 , a pressing member  19  and so forth. The ultrasonic motor  10  is fixed at the vibrator  11  side thereof, and has a form in which the moving element  15  is rotatingly driven. 
     The vibrator  11  is a member with a substantially annular shape, which includes a vibrating body  12  and the piezoelectric body  13 , which is joined to the vibrating body  12 . 
     The vibrating body  12  is formed of a metallic material with a large resonance peak sharpness, and the shape thereof is substantially annular. This vibrating body  12  includes a combtooth portion  12   a , a base portion  12   b  and a flange portion  12   c.    
     At the combtooth portion  12   a , a plural number of grooves are formed by cutting into a face at a side thereof that is opposite from a face at which the piezoelectric body  13  is joined. Distal end faces of the combtooth portion  12   a  pressingly touch against the moving element  15 , and form a driving face  12   d  that drives the moving element  15 . A lubricating surface treatment is applied to this driving face, such as Ni—P (nickel-phosphorus) plating or the like. The reason for providing the combtooth portion  12   a  is to bring a neutral plane of progressive vibration waves, which are produced at the driving face  12   d  by expansion and contraction of the piezoelectric body  13 , as close as possible to the piezoelectric body  13  side, thus amplifying the amplitudes of the progressive waves at the driving face  12   d.    
     The base portion  12   b  is a portion that is continuous in the circumferential direction of the vibrating body  12 . The piezoelectric body  13  is joined to a face (a joining face  12   e ) of the base portion  12   b  at the opposite side thereof from the combtooth portion  12   a.    
     The flange portion  12   c  is a brim-form portion protruding inward in the diametric direction of the vibrating body  12 , and is disposed centrally in the thickness direction of the base portion  12   b . The vibrator  11  is fixed to a fixing member  16  by this flange portion  12   c.    
     The piezoelectric body  13  is an electromechanical conversion element that converts electrical energy to mechanical energy. In the present embodiment, a piezoelectric element is used as the piezoelectric body  13 , but an electrostriction element or the like could be used. The piezoelectric body  13  is divided, along the circumferential direction of the vibrating body  12 , into ranges into which driving signals of two phases (an A phase and a B phase) are inputted (see  FIG. 4B ). In each phase, elements (electrode portions D 2  to D 5  and D 6  to D 9 , which will be described later) are arranged, and polarizations thereof are alternatively with difference of ½-wavelength. A ¼-wavelength gap is provided between the A phase and the B phase. The piezoelectric body  13  is joined to the vibrating body  12 , using an adhesive or the like. Details of the piezoelectric body  13  will be described later. 
     Wiring of a flexible printed circuit board  14  is connected to the electrodes of the respective phases at the piezoelectric body  13 . Driving signals are supplied to the flexible printed circuit board  14  from amplification sections  104  and  105 , which will be described later (see  FIG. 3 ), and the piezoelectric body  13  expands and contracts in accordance with the driving signals. 
     In the vibrator  11 , the progressive waves are generated at the driving face of the vibrating body  12  by the expansion and contraction of the piezoelectric body  13 . In the present embodiment, four progressive waves are generated. 
     The moving element  15  is formed of a light metal such as aluminum or the like, and is a member which is rotatingly driven by the progressive waves produced at the driving face  12   d  of the vibrating body  12 . The surface of the face of the moving element  15  that touches against the vibrator  11  (the driving face  12   d  of the vibrating body  12 ) is subjected to a surface treatment such as anodization or the like in order to improve abrasion resistance. 
     The output shaft  18  is a substantially cylindrical member. The output shaft  18  is provided with the first end portion touching against the moving element  15 , via a rubber member  23 , so as to rotate integrally with the moving element  15 . 
     The rubber member  23  is a substantially cylindrical member formed of rubber. This rubber member  23  has the function of making the moving element  15  and the output shaft  18  integrally rotatable, with viscoelasticity due to the rubber, and the function of absorbing vibrations, such that vibrations are not transmitted from the moving element  15  to the output shaft  18 , and butyl rubber, silicon rubber, propylene rubber or the like is used. 
     The pressing member  19  is a member which generates a pressure force that pressingly touches the vibrator  11  and the moving element  15  together, and is provided between a gear member  20  and a bearing holding member  21 . In the present embodiment, the pressing member  19  employs a compression coil spring, but this is not a limitation. 
     The gear member  20  is slid on so as to fit onto a D-cut of the output shaft  18 , is fixed by a stopper  22  such as an E-ring or the like, and is provided so as to be integral with the output shaft  18  in the rotation direction and the axial direction. The gear member  20  transmits driving force to the gear  4  (see  FIG. 1 ) by rotating along with rotation of the output shaft  18 . 
     A structure is formed in which the bearing holding member  21  is disposed at the inner diametric side of a bearing  17  and the bearing  17  is disposed at the inner diametric side of the fixing member  16 . 
     The pressing member  19  presses the vibrator  11  toward the moving element  15  in the axial direction of the output shaft  18 . The moving element  15  is pressingly touched against the driving face of the vibrator  11  by this pressing force, and is rotatingly driven. A pressure regulation washer may be provided between the pressing member  19  and the bearing holding member  21 , such that a suitable pressure force for driving of the ultrasonic motor  10  is obtained. 
       FIG. 3  is a block diagram describing the driving device  100  of the ultrasonic motor  10  of the first embodiment. 
     The driving device  100  of the ultrasonic motor  10  includes a vibration section  101 , a control section  102 , a phase shift section  103 , amplification sections  104  and  105 , and a sensing section  106 . 
     The vibration section  101  is a section that generates a driving signal of a required frequency in accordance with instructions from the control section  102   
     The phase shift section  103  is a section that divides the driving signal generated by the vibration section  101  into two driving signals which differ in phase by 90°. 
     The amplification sections  104  and  105  are sections that raise the voltages of the two driving signals which have been divided by the phase shift section  103  to respective required voltages. The driving signals from the amplification sections  104  and  105  are transmitted to the ultrasonic motor  10 . The progressive waves are generated in the vibrator  11  by the application of these driving signals, and drive the moving element  15 . 
     The sensing section  106  is constituted of an optical encoder, a magnetic encoder or the like, and is a section that senses a position and speed of the lens  7  that is driven by the driving of the moving element  15 . In the present embodiment, the position and speed of the lens  7  are sensed by a position and speed of the cam tube  6  being sensed. 
     The control section  102  is a section that, on the basis of driving instructions from an unillustrated CPU provided in the camera body  2 , controls the driving of the ultrasonic motor  10 . The control section  102  receives sensing signals from the sensing section  106 , and on the basis of values thereof, obtains position information and speed information, and controls the driving frequency of the driving signal generated by the vibration section  101  so as to position at a target position. 
     The driving device  100  of the ultrasonic motor  10  operates as follows. 
     First, a target position is transmitted to the control section  102 . A driving signal is generated from the vibration section  101 , and from this signal, two driving signals which differ in phase by 90° are generated by the phase shift section  103 , and are amplified to the required voltages by the amplification sections  104  and  105 . 
     The driving signals are applied to the piezoelectric body  13  of the ultrasonic motor  10 , the piezoelectric body  13  is excited, and fourth-order bending vibrations are generated in the vibrating body  12  by this excitation. The piezoelectric body  13  is divided into the A phase and the B phase, and the driving signals are applied to the A phase and the B phase, respectively. The fourth-order bending vibration generated from the A phase and the fourth-order bending vibration generated from the B phase are offset by a positional phase of a ¼-wavelength, and the A phase driving signal and the B phase driving signal are offset by a 90° phase. Therefore, the two bending vibrations are combined to form four progressive waves. 
     Elliptical movements occur at the wave peaks of the progressive waves. Accordingly, the moving element  15  that is pressingly touched against the driving face of the vibrating body  12  is frictionally driven by these elliptical movements. 
     The sensing section  106 , which is an optical encoder or the like, senses the position and speed of the cam tube  6  that is driven by the driving of the moving element  15 , and transmits them to the control section  102  in the form of electrical pulses. On the basis of these signals, the control section  102  can obtain the current position and current speed of the lens  7 , and the driving frequency generated by the vibration section  101  is controlled on the basis of this position information and speed information and the target position information. 
     The piezoelectric body  13  used in the present embodiment of the ultrasonic motor  10  will be described. 
       FIGS. 4A to 4C  are views showing the piezoelectric body  13  of the first embodiment.  FIG. 4A  is a view in which a piezoelectric body side joining face  13   a , which is joined to the joining face  12   e  of the vibrating body  12 , is viewed from the vibrating body  12  side thereof.  FIG. 4B  is a view in which a face  13   b  (hereinafter referred to as the other face) of the piezoelectric body  13  at an opposite side thereof from the piezoelectric body side joining face  13   a  is viewed from the gear member  20  side thereof.  FIG. 4C  is a magnified view of a cross-section of the piezoelectric body  13  cut along the plane of arrows C 1 -C 2  shown in  FIG. 4A . 
     The piezoelectric body side joining face  13   a  is a face that is joined to the joining face  12   e  of the vibrating body  12  and is substantially parallel to the joining face  12   e . A circumferentially continuous electrode portion D 1  is formed at the piezoelectric body side joining face  13   a.    
     The electrode portions D 2  to D 5  and D 6  to D 9 , at which the electronic signals of the A phase and the B phase are inputted, and an electrode portion D 10 , which is a ground, are formed at the other face  13   b  of the piezoelectric body  13 . The electrode portions D 2  to D 5  and D 6  to D 9  are arranged with polarities thereof alternating. The electrode portion D 10  is formed between the electrode portion D 2  and the electrode portion D 6 , so as to be between the A phase and the B phase. 
     The electrode portions D 1  to D 10  are formed by applying silver paste to the respective surfaces of the piezoelectric body side joining face  13   a  and the other face  13   b , by screen printing. 
     Using the electrode portions, polarization processing is applied to the piezoelectric body  13 . 
     The piezoelectric body side joining face  13   a  and the other face  13   b  of the present embodiment have configurations in which substrate surface of the piezoelectric body  13  are exposed at inner periphery ends and outer periphery ends thereof. 
     As shown in  FIG. 2  and  FIG. 4C , the piezoelectric body side joining face  13   a  is a substantially flat surface. The thickness of the piezoelectric body  13  (a dimension thereof in the direction orthogonal to the joining face  12   e  of the vibrating body  12  and the piezoelectric body side joining face  13   a ) is formed to be thinner at the inner periphery side and thicker at the outer periphery side. In the present embodiment, the other face  13   b  is formed as an inclined surface; as shown in  FIG. 4C , the thickness of the piezoelectric body  13  gets thinner in a linear manner along the diametric direction, from the outer periphery side to the inner periphery side. 
     Hereinafter, as shown in  FIG. 4C , in the diametric direction of the piezoelectric body  13 , an inner periphery end portion vicinity of the region at which the electrode portions are formed is an inner periphery end portion  13   c  and an outer periphery end portion vicinity of the same is an outer periphery end portion  13   d.    
     In general, if the piezoelectric constant of a piezoelectric body is dt, the thickness of the piezoelectric body is T, a voltage applied to the piezoelectric body by a driving signal is V, and an electric field produced in the piezoelectric body by the driving signal is E, then a piezoelectric strain amount S that is produced in the piezoelectric body by the driving signal is represented by the following expression.
 
 S=dt×E=dt ×( V/T )  (Expression 1)
 
     If the piezoelectric constant dt, the voltage V applied by the driving signal and the thickness T of the piezoelectric body are substantially uniform regardless of diametric direction position in the piezoelectric body, then the piezoelectric strain amount S produced by the driving signal will be substantially constant for any diametric direction position of the piezoelectric body. 
     By contrast, in the present embodiment, although the piezoelectric constant dt and the voltage V applied to the piezoelectric body  13  by the driving signal are constant, a thickness T 1  of the piezoelectric body  13  at an arbitrary point of the inner periphery end portion  13   c  of the piezoelectric body  13  is thinner than a thickness T 2  of an arbitrary point of the outer periphery side end portion  13   d . Therefore, according to the expression 1, an electric field E 1  produced in the inner periphery end portion  13   c  by the driving signal is larger than an electric field E 2  produced in the outer periphery end portion  13   d , and a piezoelectric strain amount S 1  produced in the inner periphery end portion  13   c  of the piezoelectric body  13  by the driving signal is larger than a piezoelectric strain amount S 2  produced in the outer periphery end portion  13   d.    
     Now, if a displacement is a and an arbitrary distance is L, the displacement a can be represented by the following expression.
 
 a=S×L   (Expression 2)
 
     From expression 2, if the distance L is constant, then the vibration amplitude of a progressive wave, which is a displacement a, is proportional to the piezoelectric strain amount S. 
     As described above, the piezoelectric strain amount S 1  produced in the inner periphery end portion  13   c  of the piezoelectric body  13  of the present embodiment is larger than the piezoelectric strain amount S 2  produced in the outer periphery end portion  13   d . Therefore, per unit of distance, a vibration amplitude of a progressive wave generated in a region of the driving face  12   d  that corresponds with the inner periphery end portion  13   c  can be made larger than a vibration amplitude of a progressive wave generated in a region of the driving face  12   d  that corresponds with the outer periphery end portion  13   d.    
     If the thickness of a base portion of a vibrating body is made thinner at the inner periphery side in the diametric direction and the thickness of the base portion at the outer periphery side is made thicker, vibration characteristics such as vibration modes and the like differ between the inner periphery side and the outer periphery side of the vibrating body. In consequence, vibration characteristics of the progressive waves that are produced by driving signals at the inner periphery side of the driving face and the progressive waves that are produced at the outer periphery side are different, a moving element cannot be driven stably, and driving efficiency and the like deteriorate. 
     However, the thickness of the base portion  12   b  of the vibrating body  12  of the present embodiment is constant in the diametric direction, while the thickness of the piezoelectric body  13  is thicker at the outer periphery side and thinner at the inner periphery side. Therefore, a combined thickness of the base portion  12   b  of the vibrating body and the piezoelectric body  13  is thinner at the inner periphery side than the thickness of the same at the outer periphery side. 
     Accordingly, in the present embodiment, a difference in bending stiffness magnitudes between the inner periphery side and the outer periphery side of a portion including the base portion  12   b  and the piezoelectric body  13  may be made smaller, without characteristics such as vibration modes and the like of the vibrating body  12  being altered. 
     Because, as described above, the thickness T 1  of the inner periphery end portion  13   c  of the piezoelectric body  13  is thinner than the thickness T 2  of the outer periphery end portion  13   d , the following effects are provided. 
     (1) The piezoelectric strain amount S 1  produced in the inner periphery end portion  13   c  of the piezoelectric body  13  is larger than the piezoelectric strain amount S 2  produced in the outer periphery end portion  13   d.    
     (2) In regard to stiffnesses of the portion including piezoelectric body  13  and the base portion  12   b  of the vibrating body  12 , a difference between the inner periphery side and the outer periphery side of the piezoelectric body  13  is smaller. 
     Because of these effects, a difference between the vibration amplitude magnitudes of the progressive waves produced at the driving face  12   d  at the inner periphery side of the vibrator  11  and the vibration amplitude magnitudes at the outer periphery side is smaller. 
     Therefore, according to the present embodiment, differences in vibration amplitude magnitudes of progressive waves with respect to the diametric direction of the driving face  12   d  may be made smaller, the moving element  15  can be driven stably, and driving performance and driving efficiency of the ultrasonic motor  10  may be improved. 
     Moreover, according to the present embodiment, cracking of the piezoelectric body which occurs when the piezoelectric body is joined to the vibrating body may be reduced. 
     Ordinarily, grain boundaries of a piezoelectric body change when polarization is carried out. Consequently, in a piezoelectric body with substantially uniform thickness as is conventional, stiffness with respect to the circumferential direction at the outer periphery side is weaker than the stiffness at the inner periphery side, and substrate surface is deformed to a shape such that the inner periphery side is recessed or protruding relative to the outer periphery side. When a piezoelectric body in which this deformation has occurred is joined to the joining face  12   e  of a vibrating body, which is a substantially flat surface, cracking may occur in the piezoelectric body at the time of joining. 
     In contrast, in the piezoelectric body  13  of the present embodiment, because the thickness of the outer periphery end portion  13   d  is greater than the thickness of the inner periphery end portion  13   c , stiffness in the circumferential direction at the outer periphery side may be made greater. Therefore, according to the present embodiment, the deformation during polarization of the piezoelectric body as described above may be avoided, and cracking of the piezoelectric body in the joining process may be reduced. 
     Furthermore, according to the present embodiment, as described above, the difference between the inner periphery side and the outer periphery side in the vibration amplitudes of the progressive waves produced at the driving face  12   d  can be made smaller. Therefore, even if an ultrasonic motor has a large difference between the external diameter and internal diameter because of miniaturization, stable driving can be performed and excellent driving performance obtained. A particularly remarkable effect may be realized if the present embodiment is applied to, for example, an ultrasonic motor in which the external diameter of the vibrator  11  is not more than 15 mm and which utilizes progressive waves with a wave number of not more than 5. 
     Second Embodiment 
     An ultrasonic motor of the second embodiment has a configuration substantially the same as the ultrasonic motor  10  illustrated in the first embodiment, except in that the form of the piezoelectric body  53  is different. Accordingly, portions that perform the same functions as in the above-described first embodiment are assigned the same reference numerals in the present embodiment, and duplicative descriptions are omitted as appropriate. 
       FIGS. 5A to 5C  are views showing the piezoelectric body  53  of the second embodiment.  FIG. 5A  is a view in which a piezoelectric body side joining face  53   a , which is joined to the joining face  12   e  of the vibrating body  12 , is viewed from the vibrating body  12  side thereof.  FIG. 5B  is a view in which an other face  53   b  is viewed from the gear member  20  side thereof.  FIG. 5C  is a magnified view of a cross-section of the piezoelectric body  53  cut along the plane of arrows C 3 -C 4  shown in  FIG. 5A . 
     At the piezoelectric body  53 , similarly to the piezoelectric body  13  illustrated in the first embodiment, the electrode portion D 1  is formed at the piezoelectric body side joining face  53   a , and the electrode portions D 2  to D 5  and D 6  to D 9 , at which the signals of the A phase and the B phase are inputted, and the electrode portion D 10 , which is a ground, are formed at the other face  53   b.    
     As shown in  FIG. 5C , in the diametric direction of the piezoelectric body  53  of the present embodiment, an inner periphery end portion vicinity of the region at which the electrode portions are formed is an inner periphery end portion  53   c  and an outer periphery end portion vicinity of the same is an outer periphery end portion  53   d.    
     The thickness of the piezoelectric body  53  of the second embodiment changes stepwise in the diametric direction, with a thickness T 3  of the inner periphery end portion  53   c  being thinner than a thickness T 4  of the outer periphery end portion  53   d . In the present embodiment, the piezoelectric body side joining face  53   a  is a substantially flat surface while, as shown in  FIG. 5C , the other face  53   b  is formed with a step such that the outer periphery side is thicker. 
     Because the thickness T 3  of the inner periphery end portion  53   c  of the piezoelectric body  53  is thinner than the thickness T 4  of the outer periphery end portion  53   d , a piezoelectric strain amount S 1  produced in the inner periphery end portion  53   c  by a driving signal can be made smaller than a piezoelectric strain amount S 2  produced in the outer periphery end portion  53   d  by the driving signal, and a difference in vibration amplitude magnitudes in the diametric direction of the driving face  12   d  can be made smaller. 
     Moreover, the difference in bending stiffness magnitudes between the inner periphery side and the outer periphery side of the portion including the base portion  12   b  of the vibrating body  12  and the piezoelectric body  13  can be made smaller. 
     From the preceding descriptions, according to the present embodiment, the moving element  15  can be driven stably and improvements in driving efficiency and driving performance of the ultrasonic motor may be achieved. 
     Third Embodiment 
     An ultrasonic motor of the third embodiment has a configuration substantially the same as the ultrasonic motor  10  illustrated in the first embodiment, except in that the form of the piezoelectric body  63  is different. Accordingly, portions that perform the same functions as in the above-described first embodiment are assigned the same reference numerals in the present embodiment, and duplicative descriptions are omitted as appropriate. 
       FIGS. 6A to 6C  are views showing the piezoelectric body  63  of the third embodiment.  FIG. 6A  is a view in which a piezoelectric body side joining face  63   a , which is joined to the joining face  12   e  of the vibrating body  12 , is viewed from the vibrating body  12  side thereof.  FIG. 6B  is a view in which an other face  63   b  is viewed from the gear member  20  side thereof.  FIG. 6C  is a magnified view of a cross-section of the piezoelectric body  63  cut along the plane of arrows C 5 -C 6  shown in  FIG. 6A . 
     Substantially the same as at the other face  13   b  of the piezoelectric body  13  illustrated in the first embodiment, the electrode portions D 2  to D 5  and D 6  to D 9 , at which the electronic signals of the A phase and the B phase are inputted, and the electrode portion D 10 , which is a ground, are formed at the other face  63   b  of the piezoelectric body  63  of the third embodiment. 
     However, at the piezoelectric body side joining face  63   a , an electrode portion D 1 - 1  is formed at the inner periphery side, and an electrode portion D 1 - 2  is formed at the outer periphery side. A slit portion  63   e  is formed between the electrode portion D 1 - 1  and the electrode portion D 1 - 2  so as to expose the substrate surface of the piezoelectric body  63 . In the present embodiment, as shown in  FIG. 6A , the electrode portion D 1 - 1  is formed up to the inner periphery edge of the piezoelectric body side joining face  63   a , and the electrode portion D 1 - 2  is formed up to the outer periphery edge of the piezoelectric body side joining face  63   a.    
     The thickness of the piezoelectric body  63  is substantially uniform in the diametric direction and in the circumferential direction. 
     In the piezoelectric body  63  of the present embodiment, the piezoelectric constant dt 1  of a region at which the electrode portion D 1 - 1  is formed, including the inner periphery end portion  63   c , is different from the piezoelectric constant dt 2  of a region at which the electrode portion D 1 - 2  is formed, including the outer periphery end portion  63   d.    
     As mentioned earlier, a piezoelectric strain amount S that is produced in the piezoelectric body is represented by the following expression.
 
 S=dt×E=dt ×( V/T )  (Expression 1)
 
     Here, dt is the piezoelectric constant, E is the electric field produced in the piezoelectric body by a driving signal, V is the voltage applied to the piezoelectric body by the driving signal, and T is the thickness of the piezoelectric body. 
     If the electromechanical coupling coefficient is K, the permittivity is ε and Young&#39;s modulus is Y, the piezoelectric constant dt is represented by the following expression.
 
 dt=K ×(ε/ Y ) 1/2   (Expression 3)
 
     In general, the permittivity c is proportional to a polarization voltage that is applied during polarization. 
     In the present embodiment, when the piezoelectric body  63  is being polarized, a polarization voltage Vb 1  that is applied to the electrode portion D 1 - 1  at the inner periphery side is larger than a polarization voltage Vb 2  that is applied to the electrode portion D 1 - 2  at the outer periphery side. As a result, the permittivity ε 1  of the region at which the electrode portion D 1 - 1  is formed is larger than the permittivity ε 2  of the region at which the electrode portion D 1 - 2  is formed. 
     The electromechanical coupling coefficient K is constant for the inner periphery end portion  63   c  and the outer periphery end portion  63   d . Therefore, from expression 3, the piezoelectric constant dt 1  of the inner periphery end portion  63   c  is larger than the piezoelectric constant dt 2  of the outer periphery end portion  63   d.    
     Therefore, from expression 1, when a predetermined voltage is applied to the piezoelectric body  63  by a driving signal, a piezoelectric strain amount S 1  that is produced in the inner periphery end portion  63   c  is larger than a piezoelectric strain amount S 2  that is produced in the outer periphery end portion  63   d . Hence, a difference in the diametric direction in the vibration amplitudes of the progressive waves that are produced at the driving face  12   d  of the vibrating body  12  may be made smaller. 
     According to the present embodiment, the piezoelectric body  63  is formed with a substantially uniform thickness. Therefore, previously existing molds may be used when molding the piezoelectric body  63 . 
     The slit portion  63   e  of the present embodiment is provided with the objective of preventing conduction between the region of the piezoelectric body side joining face  63   a  that corresponds with the electrode portion D 1 - 1  and the region that corresponds with the electrode portion D 1 - 2  while polarization is being implemented. In the present embodiment, when the polarization is implemented, polarization is carried out separately for the electrode portion D 1 - 1  and for the electrode portion D 1 - 2 . After the polarization has been implemented, a process that enables conduction between the electrode portion D 1 - 1  and the electrode portion D 1 - 2  is carried out. 
     Fourth Embodiment 
     An ultrasonic motor of the fourth embodiment has a configuration substantially the same as the ultrasonic motor  10  illustrated in the first embodiment, except in that the form of the piezoelectric body  73  is different. Accordingly, portions that perform the same functions as in the above-described first embodiment are assigned the same reference numerals in the present embodiment, and duplicative descriptions are omitted as appropriate. 
       FIGS. 7A to 7C  are views showing the piezoelectric body  73  of the fourth embodiment.  FIG. 7A  is a view in which a piezoelectric body side joining face  73   a , which is joined to the joining face  12   e  of the vibrating body  12 , is viewed from the vibrating body  12  side thereof.  FIG. 7B  is a view in which an other face  73   b  is viewed from the gear member  20  side thereof.  FIG. 7C  is a magnified view of a cross-section of the piezoelectric body  73  cut along the plane of arrows. C 7 -C 8  shown in  FIG. 7A . 
     The piezoelectric body  73  of the fourth embodiment has a configuration in which a first piezoelectric body  73 - 1  and a second piezoelectric body  73 - 2  are stacked. 
     The first piezoelectric body  73 - 1  has a form substantially the same as the piezoelectric body  13  of the first embodiment except in that the thickness is substantially uniform. The first piezoelectric body  73 - 1  is disposed at the vibrating body  12  side of the piezoelectric body  73 , and includes the piezoelectric body side joining face  73   a  that is joined to the joining face  12   e  of the vibrating body  12 . The electrode portion D 1  is formed on the piezoelectric body side joining face  73   a.    
     The electrode portions D 2  to D 10  are formed on the surface at the other face  73   b  side of the first piezoelectric body  73 - 1 . In  FIG. 7B , the inner periphery side of the first piezoelectric body  73 - 1  is stacked with the second piezoelectric body  73 - 2 . Consequently, it is not possible to see the whole of the first piezoelectric body  73 - 1  in  FIG. 7B . 
     The second piezoelectric body  73 - 2  is disposed at the other face  73   b  side of the piezoelectric body  73 , and has an annular form with a substantially uniform thickness. The second piezoelectric body  73 - 2  has substantially the same inner diameter as the first piezoelectric body  73 - 1 , but the outer diameter is smaller than that of the first piezoelectric body  73 - 1 . The second piezoelectric body  73 - 2  is stacked on the face of the first piezoelectric body  73 - 1  at the other face  73   b  side thereof (the opposite side from the piezoelectric body side joining face  73   a ), in a state in which the central axes of the first piezoelectric body  73 - 1  and the second piezoelectric body  73 - 2  coincide. 
     At a region of the first piezoelectric body  73 - 1  side face of the second piezoelectric body  73 - 2  that corresponds with the electrode portions D 2  to D 10  of the first piezoelectric body  73 - 1 , a similar, unillustrated electrode pattern is formed on the second piezoelectric body  73 - 2 . For example, as shown in  FIG. 7C , an electrode portion D 3 - 3  with the same polarization as the electrode portion D 3  of the first piezoelectric body  73 - 1  is formed at the region of the second piezoelectric body  73 - 2  that corresponds with the electrode portion D 3 . 
     The first piezoelectric body  73 - 1  and the second piezoelectric body  73 - 2  are stacked such that the electrode patterns match up, and are joined. 
     A circumferentially continuous electrode portion D 1 - 3  is formed on the face of the second piezoelectric body  73 - 2  that is at the other face  73   b  side of the piezoelectric body  73 . In the present embodiment, similarly to the electrode portion D 1 , the electrode portion D 1 - 3  is formed, using silver paste, in a form such that substrate surface of the second piezoelectric body  73 - 2  is exposed at the outer periphery end and the inner periphery end thereof. 
     As described above, the inner periphery side of the piezoelectric body  73  of the present embodiment is formed as two layers (the first piezoelectric body  73 - 1  and the second piezoelectric body  73 - 2 ), and the outer periphery side is formed as one layer (the first piezoelectric body  73 - 1 ). In the piezoelectric body  73  of the present embodiment, as shown in  FIG. 7C , an inner periphery end portion vicinity of the region at which the electrode portions are formed is an inner periphery end portion  73   c , and an outer periphery end portion vicinity of the region at which the electrode portions are formed on both the first piezoelectric body  73 - 1  and the second piezoelectric body  73 - 2  is an outer periphery end portion  73   d.    
     With this configuration, when a predetermined driving signal is applied to the piezoelectric body  73 , the outer periphery side only produces a piezoelectric strain amount corresponding to a one-layer piezoelectric body, and the inner periphery side produces a piezoelectric strain amount corresponding to a two-layer piezoelectric body. Therefore, a piezoelectric strain amount S 1  produced in the inner periphery end portion  73   c  of the piezoelectric body  73  by the driving signal is larger than a piezoelectric strain amount S 2  produced in the outer periphery end portion  73   d , and a difference between the inner periphery side and the outer periphery side in the vibration amplitudes of the progressive waves produced at the driving face  12   d  of the vibrating body  12  becomes smaller. 
     Therefore, according to the present embodiment, stable driving of the moving element  15  can be performed, and improvements in driving performance and driving efficiency of the ultrasonic motor may be achieved. 
     Moreover, the piezoelectric body  73  may be fabricated with ease simply by stacking the first piezoelectric body  73 - 1  and the second piezoelectric body  73 - 2 . 
     Variant Examples 
     The above embodiments are not limiting; numerous modifications and alterations are possible. 
     (1) In the second embodiment, an example is illustrated in which the step formed in the other face  53   b  of the piezoelectric body  53  is a single step. However, this is not limiting. For example, there may be two or more steps. When the thickness of the piezoelectric body is altered stepwise in a plural number of steps, piezoelectric strain amounts produced in the piezoelectric body by driving signals may be altered in more steps in the diametric direction. Thus, the effect of reducing the difference in the diametric direction between the vibration amplitudes of the progressive waves produced at the driving face  12   d  of the vibrating body  12  may be enhanced. 
     (2) In the third embodiment, an example is illustrated in which, during polarization of the piezoelectric body  63 , the polarization voltage applied to the region at which the electrode portion D 1 - 1  is formed (the inner periphery side) is larger than the polarization voltage applied to the region at which the electrode portion D 1 - 2  is formed (the outer periphery side). 
     However, this is not limiting. The piezoelectric body  63  may be divided into a plural number of regions in the diametric direction and the polarization performed by applying polarization voltages that decrease stepwise from the inner periphery side to the outer periphery side. 
     With this mode, the effect of reducing the difference in the diametric direction between the vibration amplitudes of the progressive waves produced at the driving face  12   d  of the vibrating body  12  may be enhanced. Such a case is a mode in which a plural number of the slit portion that is formed on the piezoelectric body side joining face  63   a  are formed between the regions with different polarization voltage magnitudes. 
     (3) In the third embodiment, an example is illustrated in which the polarization voltage applied during polarization of the piezoelectric body  63  is made different for the inner periphery side and the outer periphery side. However, this is not limiting. For example, the inner periphery side and the outer periphery side may be formed using materials with different piezoelectric constants dt. 
     (4) In the fourth embodiment, an example is illustrated in which the piezoelectric body  73  has a configuration in which the first piezoelectric body  73 - 1  and the second piezoelectric body  73 - 2  are stacked. However, this is not limiting. For example, three or more layers of piezoelectric bodies may be stacked. With such a configuration, the piezoelectric strain amounts produced in the piezoelectric body by a driving signal may be altered in more steps in the diametric direction. Thus, the effect of reducing the difference in the diametric direction between the vibration amplitudes of the progressive waves produced at the driving face  12   d  of the vibrating body  12  may be enhanced. 
     (5) In each of the embodiments, descriptions are given taking the ultrasonic motor in which the moving element  15  is rotatingly driven as an example. However, this is not limiting. Application is also possible to a linear-type vibration actuator in which a moving element is driven to describe an arc. 
     (6) In each of the embodiments, descriptions are given taking the ultrasonic motor in which the moving element  15  is rotatingly driven as an example. However, this is not limiting. For example, application is also possible to a vibration actuator that uses vibrations outside the ultrasonic range. 
     (7) In each of the embodiments, an example is illustrated in which the ultrasonic motor is used for driving a lens during focusing operations. However, this is not limiting. For example, it may be an ultrasonic motor that is used for driving a lens during zoom operations. 
     (8) In each of the embodiments, an example is illustrated in which the ultrasonic motor is used in a camera. However, this is not limiting. For example, it may be used in a driving section of a photocopier, a driving section of a steering wheel-tilting device or a headrest in a car, or the like. 
     The respective embodiments and variant examples may be suitably combined and used, but detailed descriptions are not given herein. The present invention is not to be limited by the embodiments described hereabove.