Patent Publication Number: US-2012026613-A1

Title: Actuator, drive device, lens unit, image-capturing device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation application of PCT/JP2010/001943 filed on Mar. 18, 2010 which claims priority from Japanese Patent Application No. 2009-072779 filed on Mar. 24, 2009, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an actuator, a drive apparatus, a lens unit, and an image capturing apparatus. 
     2. Related Art 
     An actuator is known that moves a moving element in a rotational direction of a shaft by moving the shaft, which is inserted in the moving element, in the rotational direction by extending and contracting a piezoelectric element bonded to an axial end of the shaft, as shown in, for example, Patent Document 1. In this actuator, friction between the shaft and the moving element occurring when the piezoelectric element extends and contracts causes the shaft and the moving element to move as a single body. Furthermore, by causing the piezoelectric element to contract more quickly than it extends, the inertia of the moving element keeps the moving element moving in the same direction when the shaft moves in a direction opposite the movement direction of the moving element. 
     Patent Document 1: Japanese Patent Application Publication No. 2006-311788 
     In the actuator, the displacement amount of the moving element is the same as the extension/contraction amount of the piezoelectric element, and it is necessary to enlarge the extension/contraction amount of the piezoelectric element in order to enlarge the displacement amount of the moving element, Therefore, it is an object of the present invention to provide an actuator that can efficiently enlarge the displacement amount of the moving element. 
     SUMMARY 
     According to a first aspect of the present invention, provided is an actuator that moves a moving element, comprising a drive element that contacts the moving element; a drive unit that moves the moving element in a movement direction by moving a contact portion of the drive element contacting the moving element in the movement direction and in an opposite direction that is opposite the movement direction, such that movement speed in the opposite direction is greater than movement speed in the movement direction; and a displacement enlarging section that joins the drive unit and the drive element to each other, and transmits enlarged displacement of the drive unit to the drive element. 
     The summary clause does not necessarily describe all necessary features of the embodiments or the present invention. The present invention may also be a sub-combination of the features described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a motor  10  provided with an actuator  100  according to an embodiment of the present invention. 
         FIG. 2  is an exploded perspective view of the motor  10 . 
         FIG. 3  is a cross-sectional side view of the motor  10 . 
         FIG. 4  is a cross-sectional view over the line  4 - 4  shown in  FIG. 3 . 
         FIG. 5  is a perspective view of an actuator  100 . 
         FIG. 6  is a graph showing the waveform of the drive voltage of the first electromechanical transducer  161  and the waveform of the drive voltage of the second electromechanical transducer  162 . 
         FIG. 7  is a side view of the operation of the stator  150 . 
         FIG. 8  is a side view of an actuator  200  according to another embodiment. 
         FIG. 9  is a side view of an actuator  600  according to another embodiment. 
         FIG. 10  is a side view of an actuator  700  according to another embodiment. 
         FIG. 11  is a side view of an actuator  800  according to another embodiment. 
         FIG. 12  is a side view of an actuator  900  according to another embodiment. 
         FIG. 13  is a cross-sectional side view of an image capturing apparatus  1000  including the motor  10 . 
         FIG. 14  is a perspective view of the inside of a lens unit  300  including the actuator  100 . 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, some embodiments of the present invention will be described. The embodiments do not limit the invention according to the claims, and all the combinations of the features described in the embodiments are not necessarily essential to means provided by aspects of the invention. 
       FIG. 1  is a perspective view of a motor  10  provided with an actuator  100  according to an embodiment of the present invention. For ease of explanation, a drive output side in the axial direction of the rotating axle  110  is referred to as the “output side,” and the opposite side is referred to as the “non-output side.” Furthermore, a “planar view” refers to a view of the motor  10  from the axial direction of the rotating axle  110 , sometimes simply referred to as the “rotational axis direction,” and a “side view” refers to a view of the motor  10  from the radial direction of the rotating axle  110 . 
     As shown in  FIG. 1 , the motor  10  includes the rotating axle  110 , along with a nut  210 , an attachment plate  120 , a biasing member  130 , a washer  230 , a rotor  140 , three actuators  100 , a base  190 , and a nut  220  arranged in the stated order along the rotating axle  110  beginning at the output side. The attachment plate  120  is disc-shaped and the rotating axle  110  is inserted through the center thereof. A pair of U-shaped fastening holes  122  are formed in the attachment plate  120  and are symmetrical with respect to the central axis. The attachment plate  120  is fastened to an apparatus that uses the motor  10  as a drive source, by fasteners such as screws inserted into the fastening holes  122 . 
     The rotor  140  is disc-shaped and the rotating axle  110  is inserted through the center thereof. A gear portion  144  is formed on the output side end of the rotor  140 . The biasing member  130 , which is exemplified by a compression spring in  FIG. 1 , has the rotating axle  110  inserted therethrough. The actuators  100  each include a stator  150 , an electromechanical transducer  160 , a pair of flexible print wiring boards  170  and  172 , and a base  180 . 
     The base  180  is a rectangular plate component, and is screwed onto the base  190 . The electromechanical transducer  160  includes a first electromechanical transducer  161  and a second electromechanical transducer  162 . The first electromechanical transducer  161  and the second electromechanical transducer  162  are layered piezoelectric elements formed by layering piezoelectric elements in the rotational axis direction, and extend and contract in the layering direction when a drive voltage is supplied thereto. 
     In the present embodiment, the electromechanical transducer  160  includes the first electromechanical transducer  161  and the second electromechanical transducer  162  as separate components. However, the electromechanical transducer  160  may be formed to include the first electromechanical transducer  161  and the second electromechanical transducer  162  integrally by forming, on a single layered piezoelectric element, a pair of extending/contracting sections that extend and contract in the layering direction when voltage is applied thereto. 
     The first electromechanical transducer  161  and the second electromechanical transducer  162  are arranged in a line in the longitudinal direction of the base  180 . The pair of flexible print wiring boards  170  and  172  are arranged in a line in the longitudinal direction of the base  180 . The flexible print wiring hoard  170  is sandwiched by the base  180  and the first electromechanical transducer  161 , and the flexible print wiring board  172  is sandwiched by the base  180  and the second electromechanical transducer  162 . 
     The stator  150  is formed of an elastic material such as SUS, alumina, silicon carbide, brass, ceramic, or the like. The stator  150  includes a base portion  152  shaped as a rectangular plate and a protrusion  154  that protrudes toward the rotor  140  from the longitudinal center or the base portion  152 . One longitudinal edge of the base portion  152  is engaged with the top end or the first electromechanical transducer  161 , and the other longitudinal edge of the base portion  152  is engaged with the top end of the second electromechanical transducer  162 . The tip of the protrusion  154  is covered in a diamond coating, ceramic coating, or the like to improve abrasion resistance. The protrusion  154  is preferably formed of a functional gradient material. 
     The flexible print wiring board  170  supplies the first electromechanical transducer  161  with a so-called saw-tooth drive voltage, causing the first electromechanical transducer  161  to extend and contract in the rotational axis direction. The flexible print wiring board  172  supplies the second electromechanical transducer  162  with the so-called saw-tooth drive voltage, causing the second electromechanical transducer  162  to extend and contract in the rotational axis direction, In the present embodiment, a positive drive voltage is applied to the first electromechanical transducer  161  and the second electromechanical transducer  162 , but a negative voltage may he applied or an AC voltage that is both positive and negative may be applied instead, 
       FIG. 2  is an exploded perspective view of the motor  10 . As shown in  FIG. 2 , screws  112  that engage respectively with the nuts  210  and  220  are formed at the axial ends of the rotating axle  110 . A disc-shaped flange  114  with an extended diameter is formed between the screws  112 . The nut  210 , the attachment plate  120 , the biasing member  130 , the washer  230 , and the rotor  140  are arranged on the output side of the flange  114 , while the base  190  and the nut  220  are arranged on the non-output side of the flange  114 . The three actuators  100  are arranged between the rotor  140  and the base  190 , in a manner to surround the rotating axle  110 . The rotor  140  is supported in a rotatable manner by the rotating axle  110 , via the bearing  142 . 
       FIG. 3  is a cross-sectional side view of the motor  10 . As shown in  FIG. 3 , the attachment plate  120 , the biasing member  130 , the washer  230 , the rotor  140 , the actuator  100 , and the base  190  are held in the rotational axis direction by the nuts  210  and  220 . The biasing member  130  is elastically compressed in the rotational axis direction, and the rotor  140  is pressed against the actuator  100  via the washer  230 . The direction in which the rotor  140 , the stator  150 , and the electromechanical transducer  160  are arranged is orthogonal to the direction in which the rotor  140  rotates and to the direction in which the protrusion  154 , the rotor  140 , and components contacting the protrusion  154  and the rotor  140  move, as described further below, 
       FIG. 4  is a cross-sectional view over the line  4 - 4  shown in  FIG. 3 . As shown in  FIG. 4 , the three actuators  100  are arranged at intervals of 2π/3 around the rotating axle  110 . The space enclosed by the actuators  100  is triangular in the planar view. The three protrusions  154  are arranged at intervals of 2π/3 around the rotating axle  110 . 
       FIG. 5  is a perspective view of an actuator  100 . As shown in  FIG. 5 , in the actuator  100 , a gap  163  is formed between the first electromechanical transducer  161  and the second electromechanical transducer  162 , such that the first electromechanical transducer  161  and the second electromechanical transducer  162  are separated in a direction orthogonal to the extension and contraction direction, and this direction can be referred to as the “arrangement direction.” 
     A rectangular groove  153  longitudinally dividing the base portion  152  into two portions is formed in the longitudinal center of the base portion  152  of the stator  150 . The groove  153  extends across the entire width of the base portion  152 , and is formed to overlap in the rotational axis direction with the gap  163  between the first electromechanical transducer  161  and the second electromechanical transducer  162 . Therefore, the entirety of one longitudinal end of the base portion  152 , sometimes referred to simply as the “base portion  1521 ,” is joined with the entire end surface of the first electromechanical transducer  161 , and the entirety of the other longitudinal end of the base portion  152 , sometimes referred to simply as the “base portion  1522 ,” is joined with the entire end surface of the second electromechanical transducer  162 . 
     The groove  153  extends to the base end or the protrusion  154  through the base portion  152 . As a result, a pair of leg portions  156  and  157  divided in the longitudinal direction of the base portion  152  by the groove  153  are formed at the base end of the protrusion  154 . The leg portion  156  extends toward the rotor  140  from the edge of the base portion  1521  on the groove  153  side. The leg portion  157  extends toward the rotor  140  from the edge of the base portion  1522  on the groove  153  side. In other words, the protrusion  154  is supported by the base portion  152  on a base end shaped like an inverted rectangular U and including the leg portions  156  and  157 . 
     The flexible print wiring boards  170  and  172  are connected to a waveform shaper  175  via drivers  171  and  173 , respectively. The driver  171  applies the drive voltage with a waveform shaped by the waveform shaper  175  to the first electromechanical transducer  161 . The driver  173  applies the drive voltage with a waveform shaped by the waveform shaper  175  to the second electromechanical transducer  162 . 
     The following describes the operation of the present embodiment. The graphs of  FIG. 6  show the waveform of the drive voltage of the first electromechanical transducer  161  and the waveform of the drive voltage of the second electromechanical transducer  162 . The upper graph shows the waveform of the voltage applied to the first electromechanical transducer  161 , The lower graph shows the waveform of the voltage applied to the second electromechanical transducer  162 . 
     As shown in the upper graph, from time  0  to time T 1 , the drive voltage applied to the first electromechanical transducer  161  increases from 0 V to V 1 . As shown in the lower graph, from time  0  to time T 1 , the drive voltage applied to the second electromechanical transducer  162  decreases from V 1  to 0 V. 
     At time  0 , the extension amount of the first electromechanical transducer  161  is 0 and the extension amount of the second electromechanical transducer  162  is at the maximum. Therefore, the protrusion  154  is inclined toward the first electromechanical transducer  161  side. On the other hand, at time T 1 , the extension amount of the first electromechanical transducer  161  is at the maximum and the extension amount of the second electromechanical transducer  162  is 0. 
     Therefore, from time  0  to time T 1 , the operation of the first electromechanical transducer  161  and the second electromechanical transducer  162  causes the protrusion  154  to swing from being inclined toward the first electromechanical transducer  161  side to being inclined toward the second electromechanical transducer  162  side. 
     Since the rotor  140  is pressed against the tip of the protrusion  154  by the biasing member  130 , friction occurs between the tip of the moving protrusion  154  and the rotor  140 . The frictional force is set to be greater than the force of the protrusion  154  pressing on the rotor  140 . Therefore, the tip of the protrusion  154  and the rotor  140  become a single body that moves from the first electromechanical transducer  161  side toward the second electromechanical transducer  162  side. 
     As shown in the upper graph, from time T 1  to time T 2 , the drive voltage applied to the first electromechanical transducer  161  decreases from V 1  to 0 V. As shown by the lower graph, from time T 1  to time T 2 , the drive voltage applied to the second electromechanical transducer  162  increases from 0 V to V 1 . 
     At time T 1 , as described above, the protrusion  154  is inclined toward the second electromechanical transducer  162  side. On the other hand, at time T 2 , the extension amount of the first electromechanical transducer  161  is 0 and the extension amount of the second electromechanical transducer  162  is at the maximum. Therefore, the protrusion  154  is inclined toward the first electromechanical transducer  161  side. 
     As a result, from time T 1  to time T 2 , the operation of the first electromechanical transducer  161  and the second electromechanical transducer  162  causes the protrusion  154  to swing from being inclined toward the second electromechanical transducer  162  side to being inclined toward the first electromechanical transducer  161  side. 
     It should be noted that the slope of the drive voltage, i.e. the voltage change per unit time, applied to the first electromechanical transducer  161  and the second electromechanical transducer  162  from time T 1  to time T 2  is greater than the slope of the drive voltage applied to the first electromechanical transducer  161  and the second electromechanical transducer  162  from time  0  to time T 1 . Therefore, the protrusion  154  swings more quickly from time T 1  to time T 2  than from time  0  to time T 1 . 
     From time T 1  to time T 2 , the combined force of the frictional force between the tip of the protrusion  154  and the rotor  140  and the pressing force of the tip of the protrusion  154  against the rotor  140  is set to be less than the inertial force of the rotor  140 . Therefore, the tip of the protrusion  154  slips against the rotor  140 , and so the tip of the protrusion  154  swings from the second electromechanical transducer  162  side to the first electromechanical transducer  161  side while the rotor  140  continues rotating in the same direction. 
     From time T 2  to time T 3 , the drive voltage is applied to the first electromechanical transducer  161  and the second electromechanical transducer  162  in the same manner as from time  0  to time T 1 . From time T 3  to time T 4 , the drive voltage is applied to the first electromechanical transducer  161  and the second electromechanical transducer  162  in the same manner as from time T 2  to time T 2 . From time T 4  onward, the drive voltage is applied to the first electromechanical transducer  161  and the second electromechanical transducer  162  in the same manner as from time  0  to time T 4 . in other words, the drive voltage with the saw-tooth waveform is repeatedly applied to the first electromechanical transducer  161  and the second electromechanical transducer  162 . 
     From time T 2  to time T 3 , the frictional force between the tip of the protrusion  154  and the rotor  140  is greater than the combined force of the momentum of the rotor  140  and the force of the tip of the protrusion  154  pressing on the rotor  140 . Therefore, from time T 2  to time T 3 , the tip of the protrusion  154  and the rotor  140  form a single body that moves from the first electromechanical transducer  161  side toward the second electromechanical transducer  162  side. 
     From time T 3  to time T 4 , the combined force of the frictional force between the tip of the protrusion  154  and the rotor  140  and the pressing force of the tip of the protrusion  154  against the rotor  140  is set to be less than the inertial force of the rotor  140 . Therefore, the tip of the protrusion  154  slips against the rotor  140 , and so the tip of the protrusion  154  swings from the second electromechanical transducer  162  side toward the first electromechanical transducer  161  side while the rotor  140  continues rotating in the same direction. By repeating, from time  14  onward, the operation performed from time T 2  to time T 4 , the rotor  140  continues rotating. 
     In order to rotate the rotor  140  in the opposite direction, the drive voltage with the waveform shown in the lower graph is applied to the first electromechanical transducer  161  and the drive voltage with the waveform shown in the upper graph is applied to the second electromechanical transducer  162 . 
     In the embodiment described above, the electromechanical transducer  160  causes the protrusion  154 , which serves as a drive element arranged between the electromechanical transducer  160  and the rotor  140 , to move back and forth in the rotational direction of the rotor  140 . Furthermore, by causing the extension speed and the contraction speed of the electromechanical transducer  160  to be different, the speed at which the protrusion  154  swings in the opposite direction of the rotational direction is greater than the speed at which the protrusion  154  swings in the rotational direction. As a result, the rotor  140  can continue rotating. 
     The extension and contraction direction of the electromechanical transducer  160  is orthogonal to the rotational direction of the rotor  140 , which is the moving element, and the contacting portion between the rotor  140  and the protrusion  154  protruding from the electromechanical transducer  160  toward the rotor  140  is caused to move in the rotational direction of the rotor  140 . As a result, the electromechanical transducer  160  can be housed between the rotor  140  and the base  190 . Furthermore, the stator  150  side end of the electromechanical transducer  160  in the extension and contraction direction can he fixed to the base  190 . In other words, the electromechanical transducer  160  and the stator  150  serving as the drive element can be housed within the motor  10 , and the electromechanical transducer  160  can be supported with a simple structure. 
     From the above, the actuator  100  according to the present embodiment is suitable for use as a drive source of a rotational motor  10 . Furthermore, the actuator  100  is also suitable for use as a drive source of a linear drive motor, as will be described further below. Accordingly, an actuator can be provided that imposes fewer restriction on the movement direction of the moving element, thereby allowing for more freedom of use 
       FIG. 7  is a side view of the operation of the stator  150 . As shown in  FIG. 7 , the base portion  1521  at one longitudinal end of the base portion  152  is separated from the base portion  1522  at the other longitudinal end of the base portion  152  by the groove  153 . Therefore, as shown by the dashed lines in  FIG. 7 , the base portion  1521  and the base portion  1522  can move independently in the rotational axis direction, thereby having different relative positions in the rotational axis direction. 
     For example, as shown by the dashed lines in  FIG. 7 , the base portion  1521  can move to the rotor  140  side while the base portion  1522  moves to the electromechanical transducer  160  side. In this case, the leg portion  156  formed integrally with the base portion  1521  moves toward the rotor  140  side, while the leg portion  157  formed integrally with the base portion  1522  moves toward the electromechanical transducer  160  side. As a result, the protrusion  154  swings in the direction of the arrow A in  FIG. 7 , to be inclined toward the second electromechanical transducer  162  side while being supported at a central point between the leg portion  156  and the leg portion  157 . 
     When the base portion  1522  moves toward the rotor  140  side and the base portion  1521  moves toward the second electromechanical transducer  162  side, the leg portion  157  moves toward the rotor  140  side and the leg portion  156  moves toward the second electromechanical transducer  162  side. As a result, the protrusion  154  swings in the direction or the arrow  13  shown in  FIG. 7 , to be inclined toward the first electromechanical transducer  161  side while being supported at the central point described above. 
     The distance From the support point of the protrusion  154  to the tip is relatively greater than the distance from the leg portions  156  and  157  to the support point. As a result, the displacement amount of the protrusion  154  along the rotational direction is geometrically greater than the extension/contraction amount of the first electromechanical transducer  161  and the second electromechanical transducer  162 . Furthermore, in the electromechanical transducer  160 , the second electromechanical transducer  162  is contracted when the first electromechanical transducer  161  is extended, and the first electromechanical transducer  161  is contracted when the second electromechanical transducer  162  is extended. As a result, it is possible to enlarge a height difference between the base portion  1521  fixed to the first electromechanical transducer  161  and the base portion  1522  fixed to the second electromechanical transducer  162 . Furthermore, the protrusion  154  elastically deforms with the leg portions  156  and  157  as support points. Accordingly, the relative displacement amount of the protrusion  154  along the rotational direction can be efficiently enlarged with respect to the extension/contraction amount of the first electromechanical transducer  161  and the second electromechanical transducer  162 , thereby efficiently enlarging the output of the actuator  100 . 
     In the actuator  100 , the pair of leg portions  156  and  157  divided by the groove  153  in the rotational direction of the rotor  140  are disposed on the base end of the protrusion  154 , such that the leg portion  156  is supported by the first electromechanical transducer  161  and the leg portion  157  is supported by the second electromechanical transducer  162 . As a result, a displacement amount equal to the extension/contraction amount of the first electromechanical transducer  161  can be applied to the leg portion  156  forming one side of the base end of the protrusion  154  in the rotational direction and a displacement amount equal to the extension/contraction amount of the second electromechanical transducer  162  can be applied to the leg portion  157  forming the other side of the base end of the protrusion  154  in the rotational direction. Accordingly, the relative displacement amount of the protrusion  154  along the rotational direction can he efficiently enlarged with respect to the extension/contraction amount of the first electromechanical transducer  161  and the second electromechanical transducer  162 , thereby efficiently enlarging the output of the actuator  100 . 
     The protrusion  154  is supported by the end of the first electromechanical transducer  161  on the second electromechanical transducer  162  side and the end of the second electromechanical transducer  162  on the first electromechanical transducer  161  side. Accordingly, the relative displacement amount of the protrusion  154  along the rotational direction can be more efficiently enlarged with respect to the extension/contraction amount of the first electromechanical transducer  161  and the second electromechanical transducer  162 , thereby more efficiently enlarging the output of the actuator  100 . 
     Furthermore, the operation of the electromechanical transducer  160  enlarges the horizontal amplitude of the protrusion  154 , and therefore it is not necessary to use resonance of the entire motor  10  system. Accordingly, the actuator  100  can provide drive with a frequency that is different from the resonance frequency of the overall motor  10  system. 
     In the present embodiment, by applying a positive drive voltage to one of the first electromechanical transducer  161  and the second electromechanical transducer  162  and causing a drop in the positive drive voltage applied to the other, the one of the first electromechanical transducer  161  and second electromechanical transducer  162  extends and the other returns to its natural length. However, it is only necessary that the one of the first electromechanical transducer  161  and second electromechanical. transducer  162  extends relative to the other, while the other contracts relative to the one. Therefore, the other may be caused to contract while the one returns to its natural length, by causing a drop in the negative voltage applied to the other while the negative voltage is applied to the one. 
       FIG. 8  is a side view of an actuator  200  according to another embodiment, As shown in  FIG. 8 , the actuator  200  includes a base  280  arranged facing the rotor  140  in the rotational axis direction, a protrusion  254  disposed on the base  280 , and an electromechanical transducer  260  supported on the base  280 . 
     The bottom end of the protrusion  254  is formed as a semi-sphere, and a bearing section  285  having a bowl shape into which the bottom end of the protrusion  254  is inserted is formed in the base  280 . The curvature radius of the bearing section  285  is greater than the curvature radius of the protrusion  254 . 
     The electromechanical transducer  260  includes a first electromechanical transducer  261  and a second electromechanical transducer  262  arranged in the rotational direction of the rotor  140 . The first electromechanical transducer  261  is arranged farther upstream in the rotational direction than the protrusion  254 , and the second electromechanical transducer  262  is arranged farther downstream in the rotational direction than the protrusion  254 . The first electromechanical transducer  261  and the second electromechanical transducer  262  are supported by supporting walls  281  and  282  formed on the base  280 . 
     The first electromechanical transducer  261  is arranged between the supporting wall  281  and the protrusion  254 . One end of the first electromechanical transducer  261  is fixed to the supporting wail  281 , and the other end of the first electromechanical transducer  261  is fixed to the base  271 . A semi-spherical convex portion  273  is formed on the surface of the base  271  on the protrusion  254  side. The convex portion  273  contacts the bottom end of the protrusion  254 . The first electromechanical transducer  261  extends and contracts in a direction tangential to the rotational direction of the rotor  140 . 
     The second electromechanical transducer  262  is arranged between the supporting wall  282  and the protrusion  254 . One end of the second electromechanical transducer  262  is fixed to the supporting wall  282 , and the other end of the second electromechanical transducer  262  is fixed to the base  272 . A semi-spherical convex portion  275  is formed on the surface of the base  272  on the protrusion  254  side. The convex portion  275  contacts the bottom end of the protrusion  254 . The second electromechanical transducer  262  extends and contracts in a direction tangential to the rotational direction of the rotor  140 . 
     The first electromechanical transducer  261  and the second electromechanical transducer  262  have different relative positions in the rotating axle direction. Therefore, as shown by the dotted lines in  FIG. 8 , by causing the first electromechanical transducer  261  and the second electromechanical transducer  262  to extend with the same phase, the protrusion  254  can be swung in the direction shown by the arrow A, with the central point P between the convex portion  273  and the convex portion  275  as a support point. Furthermore, by causing the first electromechanical transducer  261  and the second electromechanical transducer  262  to contract with the same phase, the protrusion  254  can be swung in the direction shown by the arrow B, with the central point P as a support point. 
     In the present embodiment, the speed used when contracting the first electromechanical transducer  261  and the second electromechanical transducer  262  with the same phase is set to be greater than the speed used when extending the first electromechanical transducer  261  and the second electromechanical transducer  262  with the same phase. As a result, the rotor  140  can continue to rotate from the first electromechanical transducer  261  side toward the second electromechanical transducer  262  side. 
     In the present embodiment, the distance from the support point P of the protrusion  254  to the tip of the protrusion  254  contacting the rotor  140  is greater than the distance between the support point P of the protrusion  254  and the load center of the protrusion  254 . Therefore, the displacement amount of the protrusion  254  in the rotational direction is geometrically greater than the extension/contraction amount of the first electromechanical transducer  261  and the second electromechanical transducer  262 . 
       FIG. 9  is a side view of an actuator  600  according to another embodiment. As shown in  FIG. 9 , the actuator  600  includes a base  680  arranged facing the rotor  140  in the rotational axis direction, a protrusion  254  disposed on the base  680 , and an electromechanical transducer  660  supported on the base  680 . 
     The bottom end of the protrusion  254  is formed as a semi-sphere, and a bearing section  685  having a recessed shape into which the bottom end of the protrusion  254  is inserted is formed in the base  680 . The width of the bearing section  285  is greater than the width of the bottom end of the protrusion  254 . 
     The electromechanical transducer  260  includes a first electromechanical transducer  661  and a second electromechanical transducer  662  arranged in the rotational axis direction. The first electromechanical transducer  661  and the second electromechanical transducer  662  are arranged farther downstream in the rotational direction than the protrusion  254 . The first electromechanical transducer  661  and the second electromechanical transducer  662  are supported by a supporting wall  681  formed on the base  680 . 
     The first electromechanical transducer  661  and the second electromechanical transducer  662  are arranged between the supporting wall  681  and the protrusion  254 , One end of each of the first electromechanical transducer  661  and the second electromechanical transducer  662  is fixed to the supporting wall  681 , and the other ends Of the first electromechanical transducer  661  and the second electromechanical transducer  662  are respectively fixed to the bases  271  and  272 . Semi-spherical convex portions  273  are formed on the surfaces of the bases  271  and  272  on the protrusion  254  side. The convex portions  273  contact the bottom end of the protrusion  254 . The first electromechanical transducer  661  and the second electromechanical transducer  662  extend and contract in a direction tangential to the rotational direction of the rotor  140 . 
     A bearing wall  682  is formed on the base  680  further upstream than the protrusion  254  in the rotational direction. The bearing wall  682  faces the supporting wall  681 , and is formed a certain distance from the protrusion  254  to support the protrusion  254  when inclined upstream in the rotational direction. The distance between the bearing wall  682  and the protrusion  254  is set such that the angle of inclination of the protrusion  254  in the rotational direction, as shown by the dashed lines in  FIG. 9 , is equal to the angle of inclination of the protrusion  254  in the direction opposite the rotational direction. 
     Both the first electromechanical transducer  261  and the second electromechanical transducer  262  are positioned downstream from the protrusion  254  in the rotational direction. The first electromechanical transducer  261  is arranged closer to the rotor  140  than the second electromechanical transducer  262 . Therefore, as shown by the dotted lines in  FIG. 9 , by causing the first electromechanical transducer  261  to contract while causing the second electromechanical transducer  262  to extend, the protrusion  254  can be swung in the direction shown by the arrow A, with the central point P between the upper and lower convex portions  273  as a support point. Furthermore, by causing the first electromechanical transducer  261  to extend and causing the second electromechanical transducer  262  to contract, the protrusion  254  can be swung in the direction shown by the arrow B, with the central point P as a support point. 
     In the present embodiment, the speed used when extending the first electromechanical transducer  261  and contracting the second electromechanical transducer  262  is set to be greater than the speed used when contracting the first electromechanical transducer  261  and extending the second electromechanical transducer  262 . As a result, the rotor  140  can continue to rotate from the first electromechanical transducer  661  side toward the second electromechanical transducer  662  side. 
     In the present embodiment, the distance from the support point P of the protrusion  254  to the tip of the protrusion  254  contacting the rotor  140  is greater than the distance between the support point P of the protrusion  254  and the load center of the protrusion  254 . Therefore, the displacement amount of the protrusion  254  in the rotational direction is geometrically greater than the extension/contraction amount of the first electromechanical transducer  661  and the second electromechanical transducer  662 . 
       FIG. 10  is a side view of an actuator  700  according to another embodiment. As shown in  FIG. 10 , the actuator  700  includes a base  780  arranged facing the rotor  140  in the rotational axis; direction, a pillar  790  supported on the base  780 , an electromechanical transducer  760 , an elastic member  770 , a base  752  that is rotatably supported on the top end of the pillar  790 , and a protrusion  754  that is formed on the base  752 . 
     The electromechanical transducer  760 , the pillar  790 , and the elastic member  770  are arranged in the rotational direction in the stated order. The bottom and top ends of the electromechanical transducer  760  are respectively fixed to the base  780  and the base  752 . The bottom end of the pillar  790  is fixed to the base  780 , and the center of the base  752  in the rotational direction is connected to the top end of the pillar  790  in a manner to allow rotation. The base  752  is supported by the top end of the pillar  790  in a manner to allow rotation on an axis that extends along the direction of the rotational radius, with the center of the base  752  in the rotational direction as a support point. 
     The elastic member  770  is a compression spring. The bottom end of the elastic member  770  is fixed to the base  780  and the top end of the elastic member  770  is fixed to the base  752 . The protrusion  754  is arranged on a line extending from the axis of the elastic member  770 , and the tip of the protrusion,  754  contacts the rotor  140 . 
     As shown by the dashed lines in  FIG. 10 , by extending the electromechanical transducer  760 , the side of the base  752  that is upstream in the rotational direction moves toward the rotor  140 , and the side of the base  752  that is upstream in the rotational direction moves against the bias force of the elastic member  770  to move away from the rotor  140 . As a result, the protrusion  754  can be swung downstream in the rotational direction. 
     Furthermore, by contracting the electromechanical transducer  760 , the side of the base  752  that is upstream in the rotational direction moves away from the rotor  140 , and the side of the base  752  that is downstream in the rotational direction uses the bias of the elastic member  770  to move toward the rotor  140 . As a result, the protrusion  254  can he swung upstream in the rotational direction. 
     In the present embodiment, the speed at which the electromechanical transducer  760  contracts is set to be Beater than the speed at which the electromechanical transducer  760  extends. As a result, the rotor  140  can continue to rotate in one direction. 
     In the present embodiment, the distance from the support point of the protrusion  754  to the tip of the protrusion  754  contacting the rotor  140  is greater than the distance from the support point of the protrusion  754  to the rotational center P of the base  752 . Therefore, the displacement amount of the protrusion  254  in the rotational direction is geometrically greater than the extension/contraction amount of the electromechanical transducer  760 . 
       FIG. 11  is a side view of an actuator  800  according to another embodiment. As shown in  FIG. 11 , the actuator  800  includes a base  880  arranged facing the rotor  140  in the rotational axis direction, a box  890  supported on the base  880 , an electromechanical transducer  860 , base  852  fixed to the top end of the box  890  and the top end of the electromechanical transducer  860 , and a protrusion  854  that is formed on the base  852 . 
     The electromechanical transducer  860  and the box  890  are arranged in the rotational direction in the stated order. The bottom end of the electromechanical transducer  860  is fixed to the base  880 , and the top end or the electromechanical transducer  860  is fixed to the base  852  on the side thereof upstream in the rotational direction. The bottom end of the box  890  is fixed to the base  880 , and the top end of the box  890  is fixed to the base  852  on the side thereof downstream in the rotational direction. The protrusion  854  is arranged on a line extending from the axis of the electromechanical transducer  860 , and the tip of the protrusion  854  contacts the rotor  140 . 
     The region of the base  852  fixed to the box  890  is immobile, but the region of the base  852  further upstream in the rotational direction than the fixed region can be elastically deformed, with a support point P on the upstream end of the fixed region in the rotational direction. As shown by the dashed lines in  FIG. 11 , by extending the electromechanical transducer  860 , the side of the base  852  that is upstream in the rotational direction moves toward the rotor  140 , with the support point P as a support point. As a result, the protrusion  854  can be swung downstream in the rotational direction. 
     By contracting the electromechanical transducer  860 , the side of the base  852  that is upstream in the rotational direction moves away from the rotor  140 , with the support point P as a support point, As a result, the protrusion  854  can be swung upstream in the rotational direction. 
     In the present embodiment, the speed used when contracting the electromechanical transducer  860  is set to be greater than the speed used when extending the electromechanical transducer  860 . As a result, the rotor  140  can continue to rotate in one direction. 
     In the present embodiment, the distance from the support point of the protrusion  854  to the tip of the protrusion  854  contacting the rotor  140  is greater than the distance from the support point of the protrusion  854  to the support point P of the base  752  fixed to the box  890 . Therefore, the displacement amount of the protrusion  854  in the rotational direction is geometrically greater than the extension/contraction amount of the electromechanical transducer  860 , 
       FIG. 12  is a side view of an actuator  900  according to another embodiment. As shown in  FIG. 12 , the actuator  900  is a DC motor, and includes a drive unit  902 , a rotating axle  904 , a rotator  906 , and a drive element  908 . 
     The drive unit  902  rotates the rotating axle  904 . The rotator  906  is a disc fixed to the rotating axle  904 , and the rotating axle  904  is inserted through the center of the rotator  906 . The drive element  908  is provided on the rotator  906 . The drive element  908  is a protrusion that protrudes from the rotator  906  toward the rotor  140  side to contact the rotor  140 , and extends in a radial direction from the rotational center. 
     In the present embodiment, the rotational speed of the rotating axle  904  in the clockwise direction, indicated by the arrow B, is set to be greater than the rotational speed of the rotating axle  904  in the counter-clockwise direction, indicated by the arrow A. As a result, the rotor  140  can continue rotating in one direction. 
     In the present embodiment, the drive element  908  contacting the rotor  140  is arranged on the rotator  906  and extends in the radial direction from the rotational center, and the rotational radius of the work point at which the load from the drive element  908  affects the rotor  140  is greater than the rotational radius of the rotating axle  904 . Therefore, the displacement amount of the drive element  908  in the rotational direction is geometrically greater than the displacement amount of the rotating axle  904  in the rotational direction. 
       FIG. 13  is a cross-sectional side view of an image capturing apparatus  1000  including the motor  10 . The image capturing apparatus  1000  includes an optical component  420 , a lens barrel  430 , the motor  10 , an image capturing section  500 , and a control section  550 . The lens barrel  430  houses the optical component  420 . 
     The motor  10  moves the optical component  420 . The image capturing section  500  captures an image focused by the optical component  420 . The control section  550  controls the motor  10  and the image capturing section  500 . 
     The image capturing apparatus  1000  includes a body  460  and a lens unit  410  containing the optical component  420 , the lens barrel  430 , and the motor  10 . The lens unit  410  is detachably mounted on the body  460 , via a mount  450 . 
     The optical component  420  includes a front lens  422 , a compensator lens  424 , a focusing lens  426 , and a main lens  428  arranged in the stated order from the left side of  FIG. 13 , which is the end at which light enters. An iris unit  440  is arranged between the focusing lens  426  and the main lens  428 . 
     The motor  10  is arranged below the focusing lens  426 , which has a relatively small diameter, in the approximate center of the lens barrel  430  in the direction of the optical axis. As a result, the motor  10  can be housed in the lens barrel  430  without increasing the diameter of the lens barrel  430 . The motor  10  may cause the focusing lens  426  to move forward or backward along a track in the direction of the optical axis, for example. 
     The body  460  houses an optical component that includes a main mirror  540 , a pentaprism  470 , and an eyepiece system  490 . The main mirror  540  moves between a standby position, in which the main mirror  540  is arranged diagonally in the optical path of the light incident through the lens unit  410 , and an image capturing position, shown by the dotted line in  FIG. 13 , in which the main mirror  540  is raised above the optical path of the incident light. 
     When in the standby position, the main mirror  540  guides the majority of the incident light toward the pentaprism  470  arranged thereabove. The pentaprism  470  projects the reflection of the incident light toward the eyepiece system  490 , and so the image on the focusing screen can be seen correctly from the eyepiece system  490 . The remaining incident light is guided to the light measuring unit  480  by the pentaprism  470 . The light measuring unit  480  measures the intensity of this incident light, as well as a distribution or the like of this intensity. 
     A half mirror  492  that superimposes the display image formed by the finder liquid crystal  494  onto the image of the focusing screen is arranged between the pentaprism  470  and the eyepiece system  490 . The display image is displayed superimposed on the image projected from the pentaprism  470 . 
     The main mirror  540  has a sub-mirror  542  formed on the back side of the surface facing the incident light. The sub-mirror  542  guides a portion of the incident light passed through the main mirror  540  to the distance measuring unit  530  arranged therebelow. Therefore, when the main mirror  540  is in the standby position, the distance measuring unit  530  can measure the distance to the subject. When the main mirror  540  moves to the image capturing position, the sub-mirror  542  is also raised above the optical path of the incident light. 
     A shutter  520 , an optical filter  510 , and an image capturing section  500  are arranged to the rear of the main mirror  540  in the stated order. When the shutter  520  is open, the main mirror  540  arranged immediately in front of the shutter  520  moves to the image capturing position, and so the incident light travels to the image capturing section  500 . Therefore, the image formed by the incident light can be converted into an electric signal. As a result, the image capturing section  500  can capture the image formed by the lens unit  410 . 
     In the image capturing apparatus  1000 , the lens unit  410  and the body  460  are electrically connected to each other. Therefore, an autofocus mechanism can be formed by controlling the rotation of the motor  10  while referencing the information concerning the distance to the subject detected by the distance measuring unit  530  in the body  460 , for example. As another example, a focus aid mechanism can be formed by the distance measuring unit  530  referencing the displacement amount of the motor  10 . The motor  10  and the image capturing section  500  are controlled by the control section  550  in the manner described above. 
     In the manner described above, the output torque of the motor  10  can be efficiently increased. Therefore, since the drive force of the autofocus mechanism can be efficiently increased, the autofocus mechanism can receive a large drive force while conserving power. 
     The above describes a case in which the focusing lens  426  is driven by the motor  10 , but the motor  10  may instead drive opening and closing of the iris unit  440 , movement of the variator lens in a zoom lens, or the like. In such a case, by exchanging information with the light measuring unit  480  and the finder liquid crystal  494  in the form of electric signals, the motor  10  can achieve automatic exposure, scene mode execution, bracket image capturing, or the like. 
     The motor  10  can be used in the manner described above to generate Favorable drive in an optical system, such as an image capturing apparatus or binoculars, or in a focusing mechanism, a ?Dom mechanism, or blur correcting mechanism, for example. Furthermore, the motor  10  can be used in precision stages such as an electron beam lithography apparatus, in various detection stages, in a movement mechanism for a cell injector used in biotechnology, or in power sources such as a mobile bed or a nuclear magnetic resonance apparatus, but are not limited to use in these ways. 
       FIG. 14  is a perspective view of the inside of a lens unit  300  including the actuator  100 . The lens unit  300  can be attached to the body  460 . As shown in  FIG. 14 , the lens unit  300  includes the focusing lens  426 , a lens holding frame  302  holding the focusing lens  426 , and a pair of guide bars  304  and  306  that guide the movement of the lens holding frame  302  in the direction of the optical axis. A bearing section  308  is disposed on the left side of the lens holding frame  302 , and a front and back pair of bearing sections  310  and  312  are disposed above and to the right of the lens holding frame  302 . The guide bar  304  is slidably inserted into the bearing section  308 , and the guide bar  306  is slidably inserted into the bearing sections  310  and  312 . 
     The bearing section  310  and the bearing section  312  are joined by a stay  314  that extends in the direction of the optical axis. A moving body  316  shaped as a rectangular plate whose longitude is in the direction of the optical axis is hung from the bottom portion of the stay  314  in a manner to be movable up and down. A flat spring  318  is arranged between the bottom portion of the stay  314  and the moving body  316 . The flat spring  318  biases the moving body  316  downward. 
     The actuator  100  is arranged below the moving body  316 , and the moving body  316  is pressed against the protrusion  154  of the actuator  100  by the flat spring  318 . The actuator  100  is arranged such that the first electromechanical transducer  161  and the second electromechanical transducer  162  are lined up in the direction of the optical axis. Therefore, the operation of the actuator  100  described above causes a thrust force from the protrusion  154  toward the moving body  316  in the direction of the optical axis, thereby causing the lens holding frame  302  and the focusing lens  426  to move in the direction of the optical axis. 
     While the embodiments of the present invention have been described, the technical scope of the invention is not limited to the above described embodiments. It is apparent to persons skilled in the art that various alterations and improvements can be added to the above-described embodiments. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the invention. 
     The operations, procedures, steps, and stages of each process performed by an apparatus, system, program, and method shown in the claims, embodiments, or diagrams can be performed in any order as long as the order is not indicated by “prior to,” “before,” or the like and as long as the output from a previous process is not used in a later process. Even if the process flow is described using phrases such as “first” or “next” in the claims, embodiments, or diagrams, it does not necessarily mean that the process must be performed in this order.