Abstract:
An ultrasonic motor includes a fixed member including a surface, a movable member positioned to face the surface of the fixed member, and an actuator to cause at least a portion of the movable member to contact the surface of the fixed member and cause the movable member to move relative to the fixed member.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims benefit from Korean Patent Application No. 10-2008-98397 filed on Oct. 7, 2008 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Apparatuses consistent with the present invention relate to an ultrasonic motor and a conveying apparatus having the same, and more particularly, to an ultrasonic motor, which can obtain high torque efficiency while having a simplified structure, and a conveying apparatus having the same. 
     2. Description of the Related Art 
     Generally, an ultrasonic motor, for example, a traveling wave type hollowed ultrasonic motor, includes a vibrating element to generate a vibration, and a contacting element to rotate due to a friction force generated on a contacting surface thereof being in press contact with the vibrating element when the vibrating element vibrates. To generate the vibration, the vibrating element is provided with an electric field-converting element layer, which generates minute deformations or displacements due to a piezoelectric effect when it is applied with a voltage having a high frequency that is inaudible to the human ear, for example. The vibrating element is fixedly disposed, and acts as a stator. The contacting element is disposed opposite to the vibrating element to rotate while being in friction contact with the vibrating element according to the vibration of the vibrating element caused by the electric field-converting element layer. The contacting element is disposed to be rotatable and acts as a rotor. 
     However, since such a conventional traveling wave type hollowed ultrasonic motor is configured so that the vibrating element is fixed and the contacting element is rotated, there is a need to have a fixing part for fixing the vibrating element and a compressing part for supporting the contacting element to be rotatable while being in friction contact with the vibrating element. In addition, if the contacting element is made up of a pair of contacting elements disposed opposite to upper and lower surfaces of the vibrating element to improve torque, the hollowed ultrasonic motor needs a connecting part for connecting the two contacting elements as a body to connect the two contacting elements without a loss in rotation torque. Accordingly, the hollowed ultrasonic motor comes complicated. 
     Also, since the conventional traveling wave type hollowed ultrasonic motor is configured so that the vibrating element is fixed by the fixing part and the contacting element is rotated by the vibration of the vibrating element generated according to the minute deformations of the electric field-converting element layer, the vibration of the vibrating element generating the rotation torque may be decreased in the process of being transmitted to the contacting element, thereby resulting in a reduction in torque efficiency. 
     Accordingly, it is required to develop a new ultrasonic motor capable of obtaining high torque efficiency while having a simplified structure. 
     SUMMARY 
     Exemplary embodiments of the present invention address at least the above aspects. Accordingly, an aspect of the present invention is to provide an ultrasonic motor capable of obtaining high torque efficiency while having a simplified structure, and a conveying apparatus having the same. 
     Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     According to one aspect of an exemplary embodiment of the present invention, there is provided an ultrasonic motor including a fixed member including a surface, a movable member positioned to face the surface of the fixed member, and an actuator to cause at least a portion of the movable member to contact the surface of the fixed member and cause the movable member to move relative to the fixed member. 
     Here, the movable member may include a plurality of projections facing the surface of the fixed member and the actuator may cause one or more of the projections to contact the surface of the fixed member and cause the movable member to move relative to the fixed member. 
     The projections may be formed on opposite sides of the movable member. In this case, the fixed member may be a first fixed member and the surface of the fixed member is a first surface, and the motor may further include a second fixed member including a second surface. At this time, the movable member may be positioned between the first and second fixed members such that the projections formed on the opposite sides of the movable member face the first and second surfaces. In addition, the actuator may cause one or more of the projections of the movable member to contact the first and second surfaces and cause the movable member to move relative to the first and second fixed members. 
     The movable member and the fixed member may be circular in shape. Alternatively, at least a portion of the movable member and at least a portion of the fixed member may be linear in shape. 
     In an embodiment, the actuator may include an electric field-converting element layer attached on the movable member, to produce a traveling wave when the electric field-converting element layer is supplied with an electric power, the movable member may include at least one vibrating element disposed to be movable, the at least one vibrating element being deformable by the traveling wave, and the fixed member may include at least one contact element fixedly disposed opposite to the at least one vibrating element to come in friction contact with the at least one vibrating element when the at least one vibrating element is deformed by the traveling wave. 
     Here, the at least one vibrating element may include a hollowed plate having the electric field-converting element layer attached thereon, and a projection part disposed on the hollowed plate and having a plurality of projections formed opposite to the contact element in a spaced-apart relation to one another. 
     At this time, the at least one vibrating element may be disposed to be rotatable or linearly movable. 
     If the at least one vibrating element is disposed to be rotatable, the hollowed plate may be formed in a circular shape, and if to be linearly movable, in an ellipse shape. In addition, if the hollowed plate may be formed in an ellipse shape having linear portions, the projection part may be disposed on at least one of the linear portions of the hollowed plate, so that it comes in friction contact with the contact element and thus linearly moves the hollowed plate when the hollowed plate is deformed by the traveling wave. 
     The electric field-converting element layer may be at least one piezoelectric element layer attached on at least one of a first surface and a second surface of the hollowed plate, and the projection part may be a ring disposed on one of an inner circumferential surface and an outer circumferential surface of the hollowed plate, the ring having a plurality of projections formed on at least one of a first surface and a second surface thereof. At this time, the piezoelectric element layer may be formed of one selected from a group consisting of a PZT (lead zirconate titanate), BaTiO 3 , PbTiO 3 , Pb[Zr x Ti 1-x ]O 3 , KNbO 3 , LiNbO 3 , LiTaO 3 , Na x WO 3 , Ba 2 NaNb 5 O 5 , Pb 2 KNb 5 O 15 , a polymer such as a PVDF (polyvinyldene fluoride), and lead-free piezoceramics such as a KNN (sodium potassium noibate) and BiFeO 3 . 
     If the at least one piezoelectric element layer include first and second piezoelectric element layers attached on the first surface and the second surface of the hollowed plate, respectively, the first and second piezoelectric element layers may be disposed so that polarized pole arrangements thereof coincide, and may be supplied with alternating voltages, which coincide in frequency and size and between which there is no time-phase difference. In this case, each of the first and the second piezoelectric element layers may be divided into a first phase A and a second phase B, each of which positive and negative poles are alternately polarized. The first phase A and the second phase B may be disposed so that respective opposite ends thereof have gaps of λ/4 (here, λ is a length of one wavelength of the traveling wave in a circumferential direction) and 3λ/4 therebetween. 
     Alternatively, the first and second piezoelectric element layers may be disposed so that polarized pole arrangements thereof have a spatial phase difference of λ/4 from each other, and may be supplied with alternating voltages, which coincide in frequency and size and between which there is a time-phase difference of 90 degrees. In this case, each of the first and the second piezoelectric element layers may have a pole arrangement in which 2n polarized surfaces (here, n is the number of wavelengths of the traveling wave produced in a circumferential direction) are alternately polarized as positive and negative poles. 
     If the plurality of projections includes a plurality of first projections and a plurality of second projections formed on the first and the second surfaces of the ring, respectively, the plurality of first and second projections may have the same size, the same number and the same arrangement. 
     The contact element may be fixed through a vibration absorbing body. The vibration absorbing body may include at least one of a vibration absorbing material and an elastic spring. 
     In the embodiment, the at least one vibrating element may include one vibrating element, and the at least one contact element may include two contact elements disposed opposite to a first surface and a second surface of the one vibrating element, respectively. Alternatively, the at least one vibrating element may include one vibrating element, and the at least one contact element may include one contact element disposed opposite to one of a first surface and a second surface of the one vibrating element. In addition, the at least one vibrating element may include two vibrating elements, and the at least one contact element may include three contact elements disposed interposing the two vibrating elements therebetween. In this case, the two vibrating elements may be fixed on individual output shafts. 
     According to another aspect of an exemplary embodiment of the present invention, there is provided a conveying apparatus, including: an ultrasonic motor including a fixed member including a surface, a movable member rotatably positioned to face the surface of the fixed member, and an actuator to cause at least a portion of the movable member to contact the surface of the fixed member and cause the movable member to move relative to the fixed member; and a motion converting unit connected with the ultrasonic motor, to convert a rotation motion of the movable member into a linear motion and transmit the converted linear motion to a subject to be conveyed. 
     Here, the actuator may include an electric field-converting element layer attached on the movable member, to produce a traveling wave when the electric field-converting element layer is supplied with an electric power, the movable member may include at least one vibrating element disposed to be movable, the at least one vibrating element being deformable by the traveling wave, and the fixed member may include at least one contact element fixedly disposed opposite to the at least one vibrating element to come in friction contact with the at least one vibrating element when the at least one vibrating element is deformed by the traveling wave. 
     The motion converting unit may include a cam barrel coupled with the at least one vibrating element to rotate along with the at least one vibrating element and having a linear motion-guide slot, and a guide projection connected to the subject to be conveyed and inserted in the linear motion-guide slot. 
     The subject to be conveyed may include a focus lens disposed in a lens adaptor of a camera. 
     Another exemplary embodiment of the invention includes an ultrasonic motor including: a fixed member including a surface; and a movable member disposed to face the surface of the fixed member, the movable member including an actuator to cause at least a portion of the movable member to contact the surface of the fixed member and cause the movable member to move relative to the fixed member. 
     In yet another exemplary embodiment of the invention, there is a conveying apparatus including: an ultrasonic motor including a fixed member including a surface, a movable member rotatably positioned to face the surface of the fixed member, and an actuator to cause at least a portion of the movable member to contact the surface of the fixed member and cause the movable member to move relative to the fixed member; and a motion converting unit connected with the ultrasonic motor, which converts a rotational motion of the movable member into a linear motion and transmits the linear motion to convey a device. 
     In another exemplary embodiment of the invention, there is an ultrasonic motor including: a first stator; a second stator, the first and the second stators being substantially fixed; a vibrating rotor disposed between the first and the second stators, the vibrating rotor including: a plurality of projection members disposed at an outer edge of the vibrating rotor and opposingly disposed toward the first and the second stators; a piezoelectric layer disposed between the plurality of projection members and a center of the vibrating rotor; and an output shaft coupled to the vibrating rotor. 
     Other aspects and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above aspects and features of the present invention will be more apparent from the description for exemplary embodiments of the present invention taken with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view exemplifying an ultrasonic motor in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a perspective view exemplifying a vibrating element of the ultrasonic motor exemplified in  FIG. 1 ; 
         FIGS. 3A and 3B  are top plan views exemplifying an example of polarized pole arrangements of first and second piezoelectric element layers of an electric field-converting element layer of the vibrating element of the ultrasonic motor exemplified in  FIG. 1 ; 
         FIGS. 4A and 4B  are top plan views exemplifying another example of the polarized pole arrangements of the first and the second piezoelectric element layers of an electric field-converting element layer of the vibrating element of the ultrasonic motor exemplified in  FIG. 1 ; 
         FIG. 5  is a cross-sectional view exemplifying an modified example of the ultrasonic motor in accordance with an exemplary embodiment of the present invention; 
         FIG. 6  is a cross-sectional view exemplifying another modified example of the ultrasonic motor in accordance with an exemplary embodiment of the present invention; 
         FIG. 7  is a perspective view exemplifying a vibrating element applied to further another modified example of the ultrasonic motor in accordance with an exemplary embodiment of the present invention; 
         FIGS. 8A and 8B  are a perspective view exemplifying a vibrating element applied to also another modified example of the ultrasonic motor in accordance with an exemplary embodiment of the present invention, and a cross-sectional view exemplifying the also another modified example of the ultrasonic motor having the same, respectively; and 
         FIG. 9  is a partial cross-sectional view exemplifying a conveying apparatus having the ultrasonic motor in accordance with an exemplary embodiment of the present invention, when it is cut away by half, based on a center line thereof. 
     
    
    
     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments of the present invention, which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The exemplary embodiments are described below in order to explain the present invention by referring to the figures. Further, the phrase “at least one of,” or “one of,” when preceding a list of elements, modifies the entire list of elements and does not modify each element of the list. 
       FIG. 1  is a cross-sectional view schematically exemplifying an ultrasonic motor  1  in accordance with an exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , the ultrasonic motor  1  in accordance with the exemplary embodiment of the present invention, as a traveling wave type hollowed ultrasonic motor, includes a housing  10 , a vibrating element  20  (see also  FIG. 2 ), and a contact element  30 . 
     The housing  10  may be a cylindrical casing  12 . An opening  14  is formed in the middle of an upper part of the cylindrical casing  12 , and a shaft support boss  16  is formed on an upper surface of the cylindrical casing  12  around the opening  14 . An output shaft  18  in the cylindrical casing  12  extends out through the opening  14  and supported by a support bearing  17  in the shaft supporting boss  16 . 
     The vibrating element  20  acts as a movable member or a rotor in accordance with the exemplary embodiment of the present invention. When alternating voltages with a high frequency greater than audio frequency, for example, are applied to first and second piezoelectric element layers  28  and  29  of an electric field-converting layer  27 , which acts as an actuator as described below, the vibrating element  20  generates a vibration while being minutely displaced or deformed, so that the vibrating element  20  rotates while being in friction contact with the contact element  30 . In an exemplary embodiment, the vibrating element  20  is minutely displaced or deformed in an elliptical motion. For this, the vibrating element  20  is provided with a hollowed circular plate  21  and a projection part  24 . 
     To rotate along with the output shaft  18  connected with a subject (not shown) to which a rotating force thereof is transmitted, the hollowed circular plate  21  has a central hole  22  accommodating a fixing sleeve  23  to be fixed thereto. The fixing sleeve  23  is fixed by a key (not shown) on a lower part of the output shaft  18 . The hollowed circular plate  21  may be formed of a stainless steel material or a bronze material. 
     To generate vibration when the alternating voltage with high frequency is applied, the hollowed circular plate  21  has an electric field-converting element layer  27  to produce a traveling wave when it is supplied with the alternating voltage with high frequency. To double the torque efficiency of the ultrasonic motor  1 , the electric field-converting element layer  27  may be made up of first and second piezoelectric element layers  28  and  29  attached on an upper surface and a lower surface of the hollowed circular plate  21 , respectively. Each of the first and second piezoelectric element layers  28  and  29  may be formed of a hollowed disc in which positive and negative poles are alternately polarized, so that when it is supplied with the alternating voltage, it is minutely displaced or deformed due to the piezoelectric effect to generate vibration. The positive and the negative poles may correspond to the shaded and the unshaded portions, or vice versa, as shown in the piezoelectric element layer  28  depicted in  FIG. 2 . The hollowed disc may be formed of one selected from a group consisting of a PZT (lead zirconate titanate), BaTiO 3 , PbTiO 3 , Pb[Zr x Ti 1-x ]O 3 , KNbO 3 , LiNbO 3 , LiTaO 3 , Na x WO 3 , Ba 2 NaNb 5 O 5 , Pb 2 KNb 5 O 15 , a polymer such as a PVDF (polyvinyldene fluoride), and lead-free piezoceramics such as a KNN (sodium potassium noibate) and BiFeO 3 . In addition, the hollowed disc may have a thickness of 0.1 through 1 mm, preferably, but not necessarily, about 0.3 mm. 
     The first and second piezoelectric element layers  28  and  29  constructed as described above may be disposed, so that polarized pole arrangements thereof coincide or have a certain spatial phase difference to each other. 
     As shown in  FIGS. 3A and 3B , if the first and second piezoelectric element layers  28  and  29  are disposed to have coinciding polarized pole arrangements, each of the first and the second piezoelectric element layers  28  and  29  is divided into a first phase A and a second phase B, each having a polarized pole arrangement of which positive and negative poles are alternately polarized. In an exemplary embodiment, the positive poles of the first piezoelectric element layer  28  are disposed directly over the positive poles of the second piezoelectric element layer  29 . The first phase A and the second phase B are supplied with alternating voltages of sine and cosine forms, which coincide in size and frequency, through corresponding electrodes (not shown) formed on the first phase A and the second phase B, so that they generate sine waves, respectively. To form one traveling wave from the two sine waves, the two sine waves should have a spatial phase difference of λ/4 (here, λ is a length of one wavelength of the traveling wave produced in a circumferential direction) to each other. Thus, the first phase A and the second phase B are disposed so that respective opposite ends thereof have gaps of λ/4 and 3λ/4 therebetween. The gaps between the first phase A and the second phase B are not supplied with the alternating voltages, but connected to a sensing unit (not shown) or grounded. 
     The first and the second piezoelectric element layers  28  and  29  constructed as described above are attached on the upper surface and the lower surface of the hollowed circular plate  21 , respectively, so that the polarized pole arrangements thereof coincide. The same phases A or B of the first and the second piezoelectric element layers  28  and  29  are supplied with alternating voltages, which coincide in frequency and size and between which there is no time-phase difference. Accordingly, one traveling wave is produced on the first and the second piezoelectric element layers  28  and  29  and thus the first and the second piezoelectric element layers  28  and  29  generate minute displacements and deformations in the form of the traveling wave (i.e., a ripple). 
     As shown in  FIGS. 4A and 4B , if the first and second piezoelectric element layers  28 ′ and  29 ′ are disposed so that the polarized pole arrangements thereof have the certain spatial phase difference, each of the first and the second piezoelectric element layers  28 ′ and  29 ′ is formed to have an polarized pole arrangement in which 2n polarized surface (here, n is the number of wavelengths of the traveling wave produced in the circumferential direction) are alternately polarized as positive and negative poles. 
     The first and the second piezoelectric element layers  28 ′ and  29 ′ constructed as described above are attached on the upper surface and the lower surface of the hollowed circular plate  21 , respectively, so that the polarized pole arrangements thereof have a spatial phase difference of λ/4 from each other. The first and the second piezoelectric element layers  28 ′ and  29 ′ are supplied with alternating voltages, which coincide in frequency and size and between which there is a time-phase difference of 90 degrees, through corresponding electrodes (not shown) formed thereon. Accordingly, one traveling wave is produced on the first and the second piezoelectric element layers  28 ′ and  29 ′ and thus the first and the second piezoelectric element layers  28 ′ and  29 ′ generate minute displacements and deformations in the in the form of the traveling wave (i.e., a ripple). 
     To supply the alternating voltages to the first and the second piezoelectric element layers  28  and  29 , or  28 ′ and  29 ′, a flexible printed circuit board FPCB (not shown) is connected to the electrodes of the first and the second piezoelectric element layers  28  and  29 , or  28 ′ and  29 ′, and thus the alternating voltages are supplied to the first and the second piezoelectric element layers  28  and  29 , or  28 ′ and  29 ′ from an outer power supply. The FPCB does not disturb a motion of the hollowed circular plate  21  or generate a twist when the hollowed circular plate  21  is rotated in a certain rotation angle, for example, an angle of about ±140 degrees, which is required when the ultrasonic motor is mounted on an interchangeable lens of a single lens reflex camera. If the hollowed circular plate  21  should continue to rotate or an amount of rotation of the hollowed circular plate  21  exceeds a permissible range of the FPCB, a power supply having a printed circuit board (PCB) may be used. The PCB includes a circular contact either i) disposed in a vicinity of an inner circumferential surface of the hollowed circular plate  21  (when the first and the second piezoelectric element layers  28  and  29  are employed) or ii) attached on exposed surfaces of the first and the second piezoelectric element layers  28 ′ and  29 ′ and not attached to the hollowed circular plate  21  (when the first and the second piezoelectric element layers  28 ′ and  29 ′ are employed). A brush is disposed to come in contact with the circular contact of the PCB may be used to continue to supply the alternating voltages to the first and the second piezoelectric element layers  28  and  29 , or  28 ′ and  29 ′ from the outer power supply. 
     A projection part  24  increases an amplitude of elliptical motion which is generated on the surface of the vibrating element  20 . The projection part  24  is in friction contact with the contact element  30  when the hollowed circular plate  21  is vibrated by the minute displacements or deformations of the first and the second piezoelectric element layers  28  and  29 , or  28 ′ and  29 ′, and thus generates a rotating force to rotate the hollowed circular plate  21 . For this, the projection part  24  is made up of a circular ring  25  disposed on the hollowed circular plate  21  to face the contact element  30 . The circular ring  25  has a plurality of projections  26 . The circular ring  25  may be disposed on an inner circumferential surface of an outer circumferential surface of the hollowed circular plate  21 . In an exemplary embodiment of the present invention, the circular ring  25  is illustrated as disposed on the outer circumferential surface of the hollowed circular plate  21 . 
     The plurality of projections  26  is made up of a plurality of first projections  26   a  and a plurality of second projections  26   b  formed on an upper surface and a lower surface of the circular ring  25 , respectively. The plurality of first and second projections  26   a  and  26   b  may be formed by forming slits  26   c  in the upper surface and the lower surface of the circular ring  25 , spaced apart from one another and serve to amplify the motion of the circular ring  25 . 
     The plurality of first and second projections  26   a  and  26   b  may be formed to have the same size, the same number and the same arrangement. However, the present invention is not limited thereto, and the plurality of first and second projections  26   a  and  26   b  may be formed to have different sizes, different numbers and different arrangements. 
     The contact element  30  acts as a fixed member or a stator, and as mentioned above, assists to allow the projection part  24  to generate the rotating force for rotating the hollowed circular plate  21  by being in friction contact with the projection part  24  when the hollowed circular plate  21  vibrates while generating the minute displacements or deformations in the form of the traveling wave by the first and the second piezoelectric element layers  28  and  29 , or  28 ′ and  29 ′. For this, the contact element  30  is fixedly disposed opposite to the vibrating element  20  in the housing  10 , so that it is not rotated. 
     The contact element  30  is made up of first and second contact elements  40  and  50 . Each of the first and the second contact elements  40  and  50  is formed of a hollowed disc having a shape corresponding to the hollowed circular plate  21  of the vibrating element  20 . The first and the second contact elements  40  and  50  are provided with first and second contact rings  41  and  51  disposed at circumferential edges thereof to come in contact with the first and the second projections  26   a  and  26   b,  respectively. 
     To prevent the vibration generated from the vibrating element  20  from being transmitted to the housing  10 , the first and the second contact elements  40  and  50  are fixedly disposed on an inner upper surface and an inner bottom surface of the housing  10  through a vibration absorbing body  60 , respectively. The vibration absorbing body  60  may be made up of a vibration absorbing material  61  and an elastic spring  63 . Although in the exemplary embodiment of the present invention, the vibration absorbing body  60  is illustrated and explained as made up of both the vibration absorbing material  61  and the elastic spring  63 , the vibration absorbing body  60  can be made up of only one of the vibration absorbing material  61  and the elastic spring  63 . In an exemplary embodiment, the vibration absorbing body  60  also has a function of urging the first and the second contact elements  40  and  50  toward the vibrating element  20  in a press contact to ensure consistent contact thereinbetween. 
     Since the first and the second contact elements  40  and  50  are supported and fixed by the vibration absorbing body  60  in the housing  10  as described above, there is no need for the ultrasonic motor  1  to have the connecting unit for connecting the contact elements as in the conventional ultrasonic motor. Accordingly, the ultrasonic motor  1  is simple in construction. 
     Also, since the first and the second contact elements  40  and  50  are fixed and the vibrating element  20  is rotated, the rotational torque transmission loss between the vibrating element and the contacting element, which reduce torque efficiency as in the conventional ultrasonic motor, is prevented. 
     In the above description, although the ultrasonic motor  1  according to the exemplary embodiments of the present invention is illustrated and explained as including one vibrating element  20  having the electric field-converting layer  27  attached on the upper and the lower surfaces thereof and two first and second contact elements  40  and  50  disposed opposite to the vibrating element  20 , it can be embodied in various different forms. As part of the principles of the invention, the vibrating element  20  is movably disposed and the contact element  30  ( 40  and  50 ) is fixedly disposed. 
     For instance, as shown in  FIG. 5 , an ultrasonic motor  1 ′ according to an modified example of an exemplary embodiment of the present invention is configured to include one vibrating element  20 ′ having an electric field converting layer  27 ′ and one contact element  30 ′ disposed opposite to the vibrating element  20 ′. In this case, the electric field-converting layer  27 ′ is formed only on a lower surface of the vibrating element  20 ′. In addition, a press unit  80  is disposed under the vibrating element  20 ′ to bring the vibrating element  20 ′ in press contact with the contact element  30 ′ and thus support the vibrating element  20 ′ to be rotatable while being in friction contact with the contact element  30 ′. The press unit  80  is provided with a press plate  83 , a dish spring  85 , and an elastic member  87 . The press plate  83  is arranged on a bearing  81  supporting an output shaft. The dish spring  85  is located on the press plate  83 , so that it brings the vibrating element  20 ′ in press contact with the contact element  30 ′. The elastic member  87  evenly distributes a pressure by an elastic force of the dish spring  85  over the vibrating element  20 ′. 
     Further, as shown in  FIG. 6 , an ultrasonic motor  1 ″ according to another modified example of an exemplary embodiment of the present invention is configured to include two vibrating elements  20   a  and  20   b  having electric field-converting layers  27  attached on upper and lower surfaces thereof, respectively, and three contact elements  30   a,    30   b  and  30   c  disposed opposite to the electric field converting layer  27  while interposing the two vibrating elements  20   a  and  20   b  therebetween. In this case, the two vibrating elements  20   a  and  20   b  may be fixed on individual output shafts, that is, first and second output shafts  18   a  and  18   b,  so that they transmit rotating forces to corresponding individual subjects (not shown) to which the rotating forces are transmitted. 
     Also, although the ultrasonic motor  1  according to an exemplary embodiment of the present invention is illustrated and explained as applied to a rotary motor in which the vibrating element  20 ,  20 ′, or  20   a  and  20   b  rotates while being in friction contact with the contact element  30 ,  30 ′, or  30   a,    30   b  and  30   c,  it can be applied to other types of motors within the principles of the invention as mentioned above. 
     For instance, as shown in  FIGS. 7 and 8A , there is a vibrating element  20 ″ or  20 ′″ configured to include a hollowed elliptic plate. The hollowed elliptic plate may have a projection part  26 ′ formed on upper surfaces of linear portions  21   a  and  21   b  thereof and an electric field-converting element layer  27 ″ formed on a lower surface thereof ( FIG. 7 ). Alternatively, there may be a hollowed elliptic plate  21 ′ having the electric field-converting element layer  27   a ″ formed on upper and lower surfaces thereof and an elliptic ring  25 ′ having a projection part  26   a ′ formed on upper and lower surfaces of linear portions  21   a ′ and  21   b ′ thereof ( FIG. 8A ). There is a contact element is configured to come in contact with at least one of the linear portions  21   a  and  21   b,  or  21   a ′ and  21   b ′. As a result, a linear motor in which the vibrating element  20 ″ or  20 ′″ moves in a straight line while being in contact with the contact element, can be achieved. 
     That is, as shown in  FIG. 8B , in case that the vibrating element  20 ′″ include the hollowed elliptic plate  21 ′ and the elliptic ring  25 ′, if the vibrating element  20 ′″ is not fixed to be rotatable about a rotating axis, but to be movable in a straight line by a guide part (not shown) and contact elements  30   a ′ and  30   b ′ are fixedly disposed opposite to the projection part  26   a ′ formed on at least one of the linear portions  21   a ′ and  21   b ′, a linear motor in that when the electric field-converting element layer  27   a ″ is supplied with alternating voltage, the vibrating element  20 ′″ is moved in a straight line while being in contact with the contact elements  30   a ′ and  30   b ′ can be embodied. 
     Hereinafter, an operation of the ultrasonic motor  1  in accordance with an exemplary embodiment of the present invention constructed as described above will be described with reference to  FIGS. 4A through 4B . 
     First, as the first and the second piezoelectric layer  28  and  29 , or  28 ′ and  29 ′ of the electric field-converting layer  27  of the vibrating element  20  are respectively applied with alternating voltages between which there is no time-phase difference or between which there is a time-phase difference of 90 degrees, through the electrodes, a traveling wave is produced on the first and the second piezoelectric layer  28  and  29 , or  28 ′ and  29 ′. As a result, the first and the second piezoelectric layer  28  and  29 , or  28 ′ and  29 ′ generate minute displacements or deformations in the form of a ripple by the traveling wave. Accordingly, the hollowed circular plate  21  of the vibrating element  20  having the first and the second piezoelectric layer  28  and  29 , or  28 ′ and  29 ′attached the upper and lower surfaces thereof also vibrates while generating displacements or deformations in the form of the traveling wave, that is, the ripple. 
     As the hollowed circular plate  21  vibrates, the circular ring  25  of the projection part  24  attached on the outer circumferential surface of the hollowed circular plate  21  also vibrates, and thus the plurality of first and second projections  26   a  and  26   b  formed on the upper and the lower surface of the circular ring  25  rotate the hollowed circular plate  21  while being in friction contact with the contact element  30  ( 40  and  50 ). 
     As the hollowed circular plate  21  rotates, the output shaft  18  fixing the hollowed circular plate  21  thereon is rotated, and the subject connected to the output shaft  18  to receive a rotating force thereof is rotated. 
       FIG. 9  shows half of a cross-sectional view of a conveying apparatus  100  to which the ultrasonic motor  1  in accordance with an exemplary embodiment of the present invention is applied. 
     The conveying apparatus  100  includes an ultrasonic motor  101  and a motion converting unit  120 . 
     The ultrasonic motor  101  is mounted on a bracket  105  installed on subject to be conveyed, for example, an outer circumferential surface of a lens adapter  103  of a camera. The ultrasonic motor  101  has almost the same constructions as those of the ultrasonic motor  1  in accordance with an exemplary embodiment of the present invention explained with reference to  FIGS. 1 through 4B , except that the first and the second contact elements  40  and  50  are fixedly disposed on the bracket  105  by the vibration absorbing body  60  and the hollowed circular plate  21  is not fixed to the output shaft  18 , but connected to the motion converting unit  120 . Accordingly, a detailed description on constructions of the ultrasonic motor  101  will be omitted. 
     The motion converting unit  120 , as a subject to which a rotating force of the ultrasonic motor  101  is transmitted, is connected to the vibrating element  20  of the ultrasonic motor  1 . The motion converting unit  120  converts a rotation motion of the vibrating element  20  into a linear motion and transmits the converted linear motion to a subject to be conveyed, that is, a focus lens  107  disposed to be movable in left and right horizontal directions (of  FIG. 9 ) in the lens adapter  103 . For this, the motion converting unit  120  is provided with a cam barrel  125  and a guide projection  135 . 
     The cam barrel  125  is disposed to be rotatable in the lens adapter  103  and coupled with the hollowed circular plate  21  of the vibrating element  20  through a connecting part  115  to rotate along with the vibrating element  20 . The connecting part  115  at a first cylinder  115   a  thereof is coupled to an inner circumferential surface of the hollowed circular plate  21  by screws, and at a second cylinder  115   b  thereof is coupled to an upper surface of an outer circumferential surface of the cam barrel  125 . A connecting disc  115   c  of the connecting part  115  is disposed penetrating through an opening  103   a  of the lens adapter  103 , and connects between the first cylinder  115   a  and the second cylinder  115   b.    
     A linear motion-guiding slot  128  is formed on the cam barrel  125  to accommodate a guide projection  135 . The linear motion-guiding slot  128  is formed in such a shape that when the cam barrel  125  is rotated by the vibrating element  20 , the guide projection  135  accommodated therein can be moved in a straight line, that is, in left and right directions (of  FIG. 9 ). In an exemplary embodiment, the linear motion-guiding slot  128  may be a helical gear (or another element capable of restricting the motion of the guide projection  135  in a linear direction). When the cam barrel rotates, a key and a key groove may be disposed between the cam barrel  125  and the fixing bracket  136  so that the focus lens  107  can have only a horizontal motion without a rotation motion. Alternatively, other conventional techniques to restriction the motion of the guide projection  135  in the straight line, may be utilized. 
     The guide projection  135  is fixed to a fixing bracket  136  mounted on an outer circumferential surface of the focus lens  107 , so that it is inserted into the linear motion-guiding slot  128 . When the cam barrel  125  is rotated, the guide projection  135  is moved left and right along the linear motion-guiding slot  128  to move the focus lens  107  left and right (in  FIG. 9 ). 
     Hereinafter, an operation of the conveying apparatus  100  constructed as described above will be described. 
     First, to adjust a focus of the focus lens  107 , the ultrasonic motor  101  is turned on through an adjusting switch (not shown) of the camera, and operated as described with reference to  FIGS. 1 through 4B . As the ultrasonic motor  101  operates, the cam barrel  125  connected with the hollowed circular plate  21  of the vibrating element  20  through the connecting part  115  is rotated along with the hollowed circular plate  21 . 
     When the cam barrel  125  rotates, the guide projection  135  inserted in the linear motion-guiding slot  128  is moved left and right along the linear motion-guiding slot  128 , and thus the focus lens  107  fixed to the guide projection  135  is also moved left and right. 
     After the focus lens  107  is moved to adjust the focus, the ultrasonic motor  101  is turned off through the adjusting switch, and the focus adjusting operation of the focus lens  107  is completed. 
     Although exemplary embodiments of the present invention has been shown and described, it will be appreciated by those skilled in the art that changes may be made in the embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.