Abstract:
Disclosed is an ultrasonic motor whose output is improved by enhancing the exciting force of a vibration caused on a vibrating body having a rectangular portion. The ultrasonic motor includes the vibrating body having a piezoelectric element, and a moving body which contacts the vibrating body. The phases of two difference vibrations caused on the vibrating body are changed to make the moving direction of the moving body or the vibrating body itself variable by selecting whether to apply a drive signal to first electrodes provided at one side of the piezoelectric element or to apply a drive signal to second electrodes provided at a portion whose polarization direction differs from that of the first electrodes.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an ultrasonic motor which frictionally drives a moving body with the vibration of a vibrating body, and an electronic device using the same, and, particularly, to an ultrasonic motor which drives a moving body with a vibration obtained by combining a longitudinal vibration and a bending vibration caused on a rectangular vibrating body. 
   2. Description of the Related Art 
   Recently, with size reduction, functional enhancement and reduction in consumed power of electronic devices, attention has been paid to ultrasonic motors as an actuator to move operational parts, and achievement of the adoption thereof is increasing. Particularly, many linear type ultrasonic motors which can be driven directly are used in electronic devices, such as a precision stage, which need high-accuracy positioning. There is known a typical linear type ultrasonic motor which utilizes a combined vibration of the longitudinal vibration and bending vibration of a rectangular vibrating body. This ultrasonic motor has four electrodes provided at one side of a piezoelectric element to be a vibrating body, which has a rectangular plate shape, and grouped into two sets of electrodes each having two orthogonal electrodes, and a drive signal is applied to one of the two sets of electrodes to provide a vibration necessary to drive the vibrating body (see JP-A-7-184382). The moving direction of the moving body is determined by selecting electrodes to which the drive signal is to be applied. This ultrasonic motor therefore is characterized by simplification of the drive circuit due to a single drive signal used. 
   However, the ultrasonic motor using the vibration of a rectangular plate is disadvantageous in that the exciting force of the vibration (particularly, bending vibration) caused on the rectangular plate to be the vibrating body is weak, so that the ultrasonic motor has a smaller output and lower efficiency. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an ultrasonic motor whose output is improved by enhancing the exciting force of a vibration caused on a vibrating body having a rectangular portion. 
   To achieve the object, according to one aspect of the invention, there is provided an ultrasonic motor including a vibrating body having a piezoelectric element; a moving body which contacts the vibrating body; a first electrode or first electrodes provided at one side of the piezoelectric element, whereby the moving body or the vibrating body itself is driven in a first direction by a vibration caused on the vibrating body by applying a drive signal between the first electrode or first electrodes and a GND electrode provided at an other side of the piezoelectric element; and a second electrode or second electrodes provided at the one side of the piezoelectric element, whereby the moving body or the vibrating body itself is driven in a second direction by a vibration caused on the vibrating body by applying a drive signal between the second electrode or second electrodes and the GND electrode provided at the other side of the piezoelectric element, wherein a polarization direction of a portion of the piezoelectric element where the first electrode or the first electrodes are provided differs from a polarization direction of a portion of the piezoelectric element where the second electrode or the second electrodes are provided. 
   With the configuration, the vibration caused on the vibrating body can be enhanced to increase the drive force of the moving body, thereby improving the output of the ultrasonic motor. 
   Because the exciting force of the vibration (particularly, bending vibration) caused on the vibrating body can be increased according to the present invention, the acquired output of the moving body becomes greater, thus making the efficiency of the ultrasonic motor higher. This makes it possible to achieve size reduction and reduction in consumed power of an electronic device having the ultrasonic motor of the present invention mounted therein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing the configuration of an ultrasonic motor of the present invention; 
       FIGS. 2A and 2B  are diagrams showing the electrode structure of a vibrating body according to a first embodiment of the invention, and  FIG. 2C  is a side view of the vibrating body shown in  FIG. 2A  showing the polarization directions; 
       FIGS. 3A and 3B  are diagrams showing the vibration modes of the vibrating body according to the first embodiment of the invention; 
       FIGS. 4A and 4B  are diagrams showing the relationship between the frequency-admittance and phase of the vibrating body according to the first embodiment of the invention; 
       FIG. 5  is a diagram showing the relationship between the frequency-admittance and phase of the vibrating body to be compared with the first embodiment of the invention; 
       FIGS. 6A and 6B  are diagrams showing the electrode structure of a vibrating body according to a second embodiment of the invention; 
       FIGS. 7A and 7B  are diagrams showing the relationship between the frequency-admittance and phase of the vibrating body according to the second embodiment of the invention; 
       FIG. 8  is a diagram showing the relationship between the frequency-admittance and phase of the vibrating body to be compared with the second embodiment of the invention; 
       FIGS. 9A and 9B  are diagrams showing the electrode structure of a vibrating body according to a third embodiment of the invention; 
       FIGS. 10A and 10B  are diagrams showing the relationship between the frequency-admittance and phase of the vibrating body according to the third embodiment of the invention; 
       FIG. 11  is a diagram showing the relationship between the frequency-admittance and phase of the vibrating body to be compared with the third embodiment of the invention; 
       FIG. 12  is a perspective view of a vibrating body according to a fourth embodiment of the invention; 
       FIGS. 13A to 13C  are diagrams showing the electrode structure of the vibrating body according to the fourth embodiment of the invention; 
       FIG. 14  is a perspective view of a vibrating body according to a fifth embodiment of the invention; 
       FIGS. 15A and 15B  are diagrams showing the electrode structure of the vibrating body according to the fifth embodiment of the invention; 
       FIG. 16  is a diagram showing the vibration mode of the vibrating body according to the fifth embodiment of the invention; 
       FIGS. 17A and 17B  are diagrams showing the relationship between the frequency-admittance and phase of the vibrating body according to the fifth embodiment of the invention and those to be compared therewith. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 
   First Embodiment 
   An ultrasonic motor according to a first embodiment of the present invention and an electronic device using the same will be described referring to the diagrams. To begin with, the configuration of an ultrasonic motor  100  of the invention using the ultrasonic motor  100  as a stage (electronic device)  100  will be described by way of example referring to  FIG. 1 . 
   The ultrasonic motor  100  of the invention generally includes a vibrating body  50  comprised of a rectangular piezoelectric element  1 , a moving body  3  which is in contact with and is frictionally driven by the vibrating body  50 , and a pressurizing member  2  which generates a contact pressure between the vibrating body  50  and the moving body  3 . 
   A rail  4  provided on a plate-like fixed member  5  is engaged with a guide groove  3   a  provided along the moving direction of the moving body  3 , so that the moving body  3  is guided so as to be movable in the lengthwise direction of the rail  4 . Although the guide structure provided by the rail  4  and the guide groove  3   a  is illustrated, a linear guide commercially available on the market and using rolling of a ball may be used. A center portion of the vibrating body  50  (positioned at the node of a vibration to be discussed later) in the lengthwise direction thereof is fixed by support members  6   a ,  6   b  provided protruding from a support plate  7 . The support plate  7  and the vibrating body  50  are guided so as to be movable in the direction of the moving body  3  by engagement of projections  7   b ,  7   c  protruding from a side face of the support plate  7  with guide grooves  5   a ,  5   b  provided at the fixed member  5 . A friction member  90  of ceramics (alumina or the like) with excellent wear resistance is connected to a lengthwise distal end of the vibrating body  50 . The pressure of the leaf spring (pressurizing member)  2  having one end fixed to the fixed member  5  is applied to a projection  7   a  provided at the support plate  7  to force the friction member  90  provided at the vibrating body  50  to contact the moving body  3  with pressure. A drive signal is applied to the vibrating body  50  from a drive circuit (not shown), so that the vibrating body  50  simultaneously generates two different vibrations. The combined vibration of the two different vibrations causes the friction member  90  to take a motion (basically, elliptical motion) having a displacement component in the moving direction of the moving body  3  and a displacement component in the direction of contact between the vibrating body  50  and the moving body  3 , allowing the moving body  3  to move. In  FIG. 1 , the moving body  3  is a table on which a sample, a workpiece to be worked or the like can be mounted, and the ultrasonic motor  100  itself serves as the stage  100 . 
   Next, the structure of the vibrating body  50  which characterizes the ultrasonic motor  100  of the invention will be described in detail referring to  FIGS. 2A-2C . As a matter of convenience for the explanation, the description of the friction member  90  is omitted hereunder. The vibrating body  50  is comprised of the rectangular piezoelectric element  1 . As shown in  FIG. 2A , electrode  8   a ,  8   b ,  9   a ,  9   b  of silver or the like are provided at the top surface (one side) of the piezoelectric element  1  in four areas separated by a line connecting the center portions of two widthwise sides (short sides provided in the moving direction of the moving body  3 ) and a line connecting the center portions of two lengthwise sides (long sides provided in the direction of contact of the vibrating body  50  and the moving body  3 ). Then, an electrode  10  is provided substantially over the entire bottom side (the other side) of the piezoelectric element  1 . With the electrode  10  serving as the GND, a high voltage is applied to the electrodes  8   a ,  8   b ,  9   a ,  9   b , so that the piezoelectric element  1  is polarized in directions of + and − in  FIG. 2A . In  FIG. 2C , which is a side view of the vibrating body  50  shown in  FIG. 2A , the polarization directions are shown by solid arrows. Of the electrodes, two orthogonal electrodes  8   a ,  8   b  constitute first electrodes  8 , and the other two orthogonal electrodes  9   a ,  9   b  constitute second electrodes  9 . 
   The lengthwise length and the widthwise length of the vibrating body  50  are set in such a way that the natural frequency of the longitudinal vibration and the natural frequency of the bending vibration are close to or match with each other, both these vibrations being caused on the vibrating body  50 . The longitudinal vibration and bending vibration are vibrations which cause displacements in a plane including the lengthwise direction and the widthwise direction.  FIGS. 3A and 3B  show displacement distributions of the lengthwise vibration of the vibrating body  50 , namely the amplitude distribution (DL) of the longitudinal vibration and the amplitude distribution (DB) of the bending vibration in the lengthwise direction of the vibrating body  50 , respectively. 
   Next, a drive method for the ultrasonic motor  100  will be described. When the drive signal is applied between the first electrodes  8  provided at the vibrating body  50  and the GND electrode  10 , the vibrating body  50  is excited to have a longitudinal vibration and bending vibration. The combined vibration of those two vibrations causes the moving body  3  to be driven frictionally. When the drive signal is applied between the second electrodes  9  provided at the vibrating body  50  and the GND electrode  10 , the phase relationship between the longitudinal vibration and bending vibration caused by the vibrating body  50  is reversed. Therefore, the direction of the elliptical motion of the friction member  90  caused by the combined vibration of the two vibrations is reversed, thus reversing the moving direction of the moving body  3 . 
   While the vibrating body  50  is fixed and the moving body  3  is moved in the foregoing example, the vibrating body  50  can be driven itself by fixing the moving body  3  and setting the vibrating body  50  operable. 
   Changing the polarization direction for each group of electrodes makes the exciting force of, particularly, the bending vibration (which contributes to feeding of the moving body  3 ), so that the output efficiency of the ultrasonic motor  100  is improved considerably. This will be explained below specifically.  FIG. 4A  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the first electrodes  8  and the GND electrode  10 , and  FIG. 4B  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the second electrodes  9  and the GND electrode  10 . As a comparative example, the relationship between the frequency-admittance and phase when the drive signal is applied between the first electrodes  8  and the GND electrode  10  with all the areas indicated by the electrodes  8   a ,  8   b ,  9   a ,  9   b  of the vibrating body  1  being polarized in the same direction (+) is shown in  FIG. 5 . 
   Those are the examples where by using a finite element method (used software: Piezo Plus (produced by Dynus Co., Ltd.), analysts was conducted on a model with the vibrating body  50  (piezoelectric element  1 ) having a long side of 19 mm, a short side of 5.3 mm and a thickness of 2.0 mm, the individual electrodes having a width of 2.2 mm, and the individual electrodes having a marginal width of 0.3 mm, and a gap of 0.3 mm between the electrodes and the side face. 
   In any of the diagrams, the peak of the low-order admittance corresponds to the resonance point of the longitudinal vibration of the vibrating body  1 , while the peak of the high-order resonance corresponds to the resonance point of the bending vibration. 
   The exciting force of the bending vibration is increased by changing the polarization directions of the two groups of electrodes this way (which contributes to feeding of the moving body  3 ). This is because as the polarization directions of those portions of the piezoelectric element  1  where the two groups of electrodes are provided differ from each other, the influence of the counterelectric field generated at the electrode to which the drive signal is not applied at the time of driving the vibrating body  50  on the excitation of the vibration differs. 
   Although the GND electrode  10  is provided over the entire bottom side of the piezoelectric element  1  in the embodiment, the electrodes (a plurality of GND electrodes  10  may be provided) may be provided only at those portions which face the electrodes  8   a ,  8   b ,  9   a ,  9   b . In this case, of the electrodes  8   a ,  8   b ,  9   a ,  9   b , the drive signal is applied between those electrodes to which the drive signal is to be applied and the opposing GND electrodes  10  to drive the vibrating body  50 . 
   Second Embodiment 
   A second embodiment of an ultrasonic motor of the present invention will be described below referring to  FIGS. 6A and 6B . The following description is centered on differences from the illustrated vibrating body  50  of the first embodiment or the electrode structure of the vibrating body  60 . An electrode (third electrode)  14  is provided at the top surface (one side) of a piezoelectric element  11  at a portion located at the center portion of three areas separated by lines connecting points which separates two short sides of the rectangular portion into three portions, electrodes  12   a ,  12   b ,  13   a ,  13   b  are provided at four areas obtained by further separating two end portions of the three areas by a line connecting center points of two long sides of the piezoelectric element  11 , two electrodes  12   a ,  12   b  provided at two orthogonal portions of the four areas constitute first electrodes  12 , and two electrodes  13   a ,  13   b  provided at other two orthogonal portions of the four areas constitute second electrodes  13 . Then, an electrode  15  is provided substantially over the entire bottom side (the other side) of the piezoelectric element  11 . With the electrode  15  serving as the GND, a DC voltage is applied to the electrodes  12   a ,  12   b ,  13   a ,  13   b ,  14  so that the piezoelectric element  11  is polarized in directions of + and − in  FIG. 6A . 
   Next, a drive method for the vibrating body  60  will be described. When the drive signal is applied between the GND electrode  15  and the first electrodes  12  and the third electrode  14 , the moving body  3  is driven with the longitudinal vibration and bending vibration simultaneously excited as per the first embodiment. When the drive signal is applied between the GND electrode  15  and the second electrodes  13  and the third electrode  14 , by way of contrast, the phase relationship between the longitudinal vibration and bending vibration is reversed, so that the moving body  3  is driven in the opposite direction. 
   It is better that the drive signal should substantially be applied between the GND electrode  15  and the first electrodes  12  and the third electrode  14  which have the same polarization directions. The reason will be given below.  FIG. 7A  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the GND electrode  15  and the first electrodes  12  and the third electrode  14 , and  FIG. 7B  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the GND electrode  15  and the second electrodes  13  and the third electrode  14 . As a comparative example, the relationship between the frequency-admittance and phase when the drive signal is applied between the GND electrode  15  and the first electrodes  12  and the third electrode  14  with the polarization directions of the vibrating body  60  shown in  FIGS. 6A and 6B  all being identical (the polarization direction of the area where the second electrodes  13  are positioned is also +) is shown in  FIG. 8 . 
   Those are the examples where by using a finite element method (used software: Piezo Plus (produced by Dynus Co., Ltd.), analysts was conducted on a model with the vibrating body  60  having a long side of 19 mm, a short side of 5.3 mm and a thickness of 2.0 mm, the electrodes constituting the first electrode and the second electrodes having a width of 1.4 mm, the third electrode having a width of 1.3 mm, and the individual electrodes having a marginal width of 0.3 mm, and a gap of 0.3 mm between the electrodes and the side face. 
   In any of the diagrams, the peak of the low-order admittance corresponds to the resonance point of the longitudinal vibration of the vibrating body  60 , while the peak of the high-order resonance corresponds to the resonance point of the bending vibration. (Although the peak of the high-order resonance in  FIG. 7B  is small and difficult to discriminate, it exists at a frequency at which the phase is disturbed). 
   According to the vibrating body  60 , if the drive signal is applied between the GND electrode  15  and the first electrodes  12  and the third electrode  14 , the bending vibration is excited greater so that the output of the moving body  3  becomes larger as compared with a case where the drive signal is applied between the GND electrode  15  and the second electrodes  13  and third electrode  14 , and further with the comparative example. 
   Third Embodiment 
   A third embodiment of an ultrasonic motor of the present invention will be described below referring to  FIGS. 9A and 9B . The following description is centered on differences from the illustrated vibrating bodies  50  and  60  of the first embodiment and the second embodiment, or the electrode structure of a vibrating body  70 . 
   An electrode  18  is provided at the top surface (one side) of a piezoelectric element  20  at one of two areas separated by a line connecting points which separates two short sides of the piezoelectric element  20  into two portions, and an electrode  16  and an electrode  17  are provided at two areas obtained by further separating the other area by a line connecting center points of two long sides of the piezoelectric element  20 . An electrode  19  is provided substantially over the entire bottom side (the other side) of the piezoelectric element  20 . With the electrode  19  serving as the GND, a high voltage is applied to the electrodes  16 ,  17 ,  18 , so that the piezoelectric element  20  is polarized in directions of + and − in  FIG. 9A . 
   Next, a drive method for the vibrating body  70  will be described. When the drive signal is applied between the GND electrode  19  and the first electrode  16  and third electrode  18 , the moving body  3  is driven with the longitudinal vibration and bending vibration simultaneously excited as per the first embodiment. When the drive signal is applied between the GND electrode  19  and the second electrode  17  and third electrode  18 , by way of contrast, the phase relationship between the longitudinal vibration and bending vibration is reversed, so that the moving body  3  is driven in the opposite direction. 
   It is better that the drive signal should substantially be applied between the GND electrode  19  and the first electrode  16  and the third electrode  18 . The reason will be given below.  FIG. 10A  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the GND electrode  19  and the first electrode  16  and the third electrode  18 , and  FIG. 10B  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the GND electrode  19  and the second electrode  17  and the third electrode  18 . As a comparative example, the relationship between the frequency-admittance and phase when the drive signal is applied between the GND electrode  19  and the first electrode  16  and the third electrode  18  with the polarization directions of the vibrating body  20  shown in  FIGS. 9A and 9B  all being identical (the polarization direction of the area where the first electrode  16  is positioned is also +) is shown in  FIG. 11 . 
   Those are the examples where by using a finite element method (used software: Piezo Plus (produced by Dynus Co., Ltd.), analysts was conducted on a model with the vibrating body  70  having a long side of 19 mm, a short side of 5.3 mm and a thickness of 2.0 mm, the individual electrodes having a width of 2.2 mm, and the individual electrodes having a marginal width of 0.3 mm, and a gap of 0.3 mm between the electrodes and the side face. 
   In any of the diagrams, the peak of the low-order admittance corresponds to the resonance point of the longitudinal vibration of the vibrating body  70 , while the peak of the high-order resonance corresponds to the resonance point of the bending vibration. 
   According to the vibrating body  70 , if the drive signal is applied between the GND electrode  19  and the first electrode  16  and the third electrode  18 , the bending vibration is excited greater so that the output of the moving body  3  becomes larger as compared with a case where the drive signal is applied between the GND electrode  19  and the second electrode  17  and third electrode  18 , and further with the comparative example. 
   Fourth Embodiment 
   A fourth embodiment of the present invention will be described below referring to  FIGS. 12 and 13A  to  13 C. The following describes only differences from the illustrated vibrating body  50  of the first embodiment, or the electrode structure of a vibrating body  80 . The description of the friction member  90  is omitted from the following description. 
     FIG. 12  is a perspective view of the vibrating body  80 , and a broken line  110  in the diagram indicates a jointed surface of two piezoelectric elements  40   a ,  40   b . The vibrating body  80  is one that the illustrated vibrating body  50  of the first embodiment is modified to have a laminated structure. The vibrating body  80  has the piezoelectric elements  40   a ,  40   b  overlaid and coupled integrally. Specifically, after the piezoelectric elements  40   a ,  40   b  in a green sheet state are laminated and pressurized, and baked into a piezoelectric element  40 ; the piezoelectric elements  40   a ,  40   b  may be coupled by an adhesive. 
   The electrode structure of the vibrating body  80  will be described next.  FIG. 13A  is a view from the top surface of the vibrating body  80  (direction of an arrow  200 ),  FIG. 13B  is a view of an electrode  25  at the boundary between the piezoelectric elements  40   a ,  40   b  (broken line  110 ) from the top surface of the piezoelectric element  40   b , and  FIG. 13C  is a view of the vibrating body  80  (piezoelectric element  40   b ) from the bottom surface (arrow  201 ). 
   Electrodes  21 ,  22 ,  23 ,  24  of silver or the like are provided at the top surface of the vibrating body  80  in four areas separated by a line connecting the center portions of two widthwise sides (short sides to be the moving direction of the moving body  3 ) of the vibrating body  80  (piezoelectric element  40   b ) and a line connecting the center portions of two lengthwise sides (long sides provided in the direction of contact of the vibrating body  80  and the moving body  3 ). Then, the electrode  25  is provided substantially over the entire top side of the piezoelectric element  40   b . Electrodes  25 ,  26 ,  27 ,  28  of silver or the like are provided at the bottom surface of the vibrating body  80  in four areas separated by a line connecting the center portions of two widthwise sides (short sides to be the moving direction of the moving body  3 ) of the vibrating body  80  and a line connecting the center portions of two lengthwise sides (long sides provided in the direction of contact of the vibrating body  80  and the moving body  3 ). 
   Side electrodes  29 ,  30 ,  31 ,  32 ,  33  are provided at a side face of the piezoelectric element  40  (side electrodes  32 ,  33  are hidden and not seen in  FIG. 12 ). The side electrode  29  short-circuits an end portion  24   a  of the electrode  24  and an end portion  28   a  of the electrode  28 . The side electrode  31  short-circuits an end portion  25   a  of the electrode  25 . The side electrode  30  short-circuits an end portion  22   a  of the electrode  22  and an end portion  26   a  of the electrode  26 . The side electrode  32  short-circuits an end portion  21   a  of the electrode  21  and the end portion  25   a  of the electrode  25 . The side electrode  33  short-circuits a bulging portion  23   a  of the electrode  23  and a bulging portion  27   a  of the electrode  27 . 
   With the electrode  25  (side electrode  31 ) serving as the GND, a high voltage is applied to the electrodes  21 ,  22 ,  23 ,  24 ,  25 ,  26 ,  27 ,  28  (side electrodes  29 ,  30 ,  32 ,  33 ), so that the vibrating body  80  is polarized in directions of + and − in the diagrams. Of the electrodes, the electrodes  21 ,  22  and the electrodes  25 ,  26  constitute the first electrodes, and the electrodes  23 ,  24  and the electrodes  27 ,  28  constitute the second electrodes. 
   Next, a drive method for the ultrasonic motor  100  will be described. When the drive signal is applied between the side electrodes  30 ,  32  and the side electrode  31 , the vibrating body  80  is excited to have the longitudinal vibration and bending vibration. The combined vibration of those two vibrations causes the moving body  3  to be frictionally driven. When the drive signal is applied between the side electrodes  29 ,  33  and the side electrode  31 , the phase relationship between the longitudinal vibration and bending vibration caused on the vibrating body  80  is reversed. Therefore, the direction of the elliptical motion of the friction member  90  caused by the combining of the two vibrations is reversed, so that the moving direction of the moving body  3  is reversed. 
   Although the foregoing description has been given of the example where two piezoelectric elements  40   a ,  40   b  alone are laminated to constitute the vibrating body  80 , further piezoelectric elements may be laminated. 
   Such laminated structure of the vibrating body  80  can reduce the polarization voltage and permit the use of the lamination process similar to that for a stacked capacitor, so that the fabrication process becomes simpler and a small-sized vibrating body  80  with a high quality can be realized at a low cost. Because the drive voltage can be reduced, the drive circuit can be simplified, ensuring size reduction of an electronic device having the ultrasonic motor of the present invention mounted therein. Since power which is wasted by a boosting circuit can be saved, the consumed power of the electronic device can be reduced. 
   Such lamination of piezoelectric elements can be adapted to a vibrating body  200  in a fifth embodiment to be described later as well as the vibrating bodies  60 ,  70  in the second and third embodiments. 
   Fifth Embodiment 
   A fifth embodiment of an ultrasonic motor of the present invention will be described below referring to  FIGS. 14 ,  15 A and  15 B,  16  and  17 A and  17 B. The following description is centered on differences from the illustrated vibrating bodies  50 ,  60 ,  70  of the first to third embodiments, or the electrode structure and vibration mode of the vibrating body  200 . 
   The vibrating body  200  comprises a rectangular piezoelectric element  210  and a friction member  90  provided at a center portion of one long side. 
   The electrode structure of the piezoelectric element  210  to be used in the vibrating body  200  will be described referring to  FIGS. 15A and 15B  (the friction member  90  not shown therein). A first electrode  41  and a second electrode  42  are provided at the top surface (one side) of the rectangular piezoelectric element  210  at two areas separated by a line connecting center portions of two long sides of the piezoelectric element  210 . An electrode  43  is provided substantially over the entire bottom side (the other side) of the piezoelectric element  210 . With the electrode  43  serving as the GND, a high voltage is applied to the electrodes  41 ,  42 , so that the piezoelectric element  210  is polarized in directions of + and − in  FIG. 15A . 
   Next, a drive method for the vibrating body  200  will be described. When the drive signal is applied between the electrode  43  to be the GND and the first electrode  41 , the vibration mode as shown in  FIG. 16  is provided (the friction member  90  not shown therein). At this time, the distal end of the friction member  90  is vibrated to have components in two directions (displacement along the long side of the vibrating body  200  and displacement along the short side thereof), the moving body  3  which is in contact with the distal end is driven. When the drive signal is applied between the electrode  43  to be the GND and the third electrode  42 , on the other hand, the phase relationship between the vibrations in the two directions is reversed, so that the moving body  3  is driven in the opposite direction. 
     FIG. 17A  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the electrode  43  to be the GND and the first electrode  41  in the piezoelectric element  210 .  FIG. 17B  shows the relationship between the frequency-admittance and phase when the drive signal is applied between the electrode  43  and the first electrode  41  in a case where the polarization direction of that portion of the piezoelectric element  210  where the second electrode  42  is provided is set the same as the polarization direction of that portion of the piezoelectric element  210  where the first electrode  41  is provided (both directions being + in  FIG. 17B ) as a comparative example. 
   Those are the examples where by using a finite element method (used software: Piezo Plus (produced by Dynus Co., Ltd.), analysts was conducted on a model with the piezoelectric element  210  having a long side of 20 mm, a short side of 10 mm and a thickness of 2.0 mm, the individual electrodes having a marginal width of 0.3 mm, and a gap of 0.3 mm between the electrodes and the side face. 
   According to the vibrating body  200  (piezoelectric element  210 ), as the polarization direction of the area where the first electrode  41  is provided is set different from the polarization direction of the area where the second electrode  42  is provided, the vibration of the vibrating body  200  is made greater, thus increasing the output of the moving body  3 . 
   Although the electrode  43  to be the GND is provided over substantially the entire bottom side (the other side) of the piezoelectric element  210 , the bottom side of the piezoelectric element  210  may be divided by a line connecting the center portions of two long sides of the piezoelectric element  210  in such a way that the electrode  43  faces the first electrode  41  and the second electrode  42 . In this case, the electrode that faces that electrode to which the drive signal is applied (either the first electrode  41  or the second electrode  42 ) is used as the GND electrode. 
   The ultrasonic motor of the present invention can be used to drive a read head and write head in an information recording device, drive lenses in a digital camera, a video camera or the like, drive various drive sections (calendar, hands, etc.) in a wrist watch which demands a smaller and thinner in size and lower consumed power, in addition to a stage which needs precise positioning, and can be adapted as a drive source for various electronic devices.