Abstract:
A motor including a driven unit; an actuator including a vibrating plate having, at an end thereof, a protrusion which is biased toward the driven unit and a piezoelectric body stacked on the vibrating plate; and a biasing unit biasing the actuator toward the driven unit, wherein an axis in a direction in which the biasing unit biases the actuator toward the driven unit intersects with a plane containing a vibrating surface of the vibrating plate.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to motors, robot hands, and robots. 
         [0003]    2. Related Art 
         [0004]    As a motor driving a driven body by the vibration of a piezoelectric element, a motor that drives a driven body by making a protrusion of a reinforcing plate come into contact with the driven body in an actuator formed of the reinforcing plate having the protrusion integrally formed therein, the reinforcing plate on which a rectangular flat plate-like piezoelectric element is stacked, is known (JP-A-2010-233335 (Patent Document 1)). The motor provided with a piezoelectric actuator includes a biasing unit for making the protrusion of the reinforcing plate of the piezoelectric actuator come into contact with the driven body, and a frictional force developed between the protrusion of the reinforcing plate and the driven unit by a biasing force generated by the biasing unit transfers the vibration of the protrusion of the reinforcing plate to the driven unit and drives the driven unit in a predetermined direction. 
         [0005]    However, in Patent Document 1 described above, the direction in which the piezoelectric actuator is biased by the biasing unit toward the driven body is biased along a vibrating surface of planar vibration in the reinforcing plate toward the driving center of the driven body. In such a motor, depending on the deflection of the driven body rotatably secured to an apparatus main body and the amount of backlash of the piezoelectric actuator slidably secured to the apparatus main body, a relative slippage (slip) occurs in a region of contact between the driven body and the protrusion of the piezoelectric actuator in a direction intersecting with the biasing direction. This slippage (slip) greatly reduces the efficiency of transfer of the vibration of the piezoelectric actuator to the driven body. 
       SUMMARY 
       [0006]    An advantage of some aspects of the invention is to provide a motor that prevents a slip between an actuator and a driven body in a region of contact between the driven body and a protrusion of a piezoelectric actuator, the slip caused by a relative slippage in a direction intersecting with a biasing direction, and transfers the vibration of the piezoelectric actuator to the driven body efficiently and a robot hand and a robot that use such a motor. 
       Application Example 1 
       [0007]    This application example is directed to a motor including: a driven unit; an actuator including a vibrating plate having, at an end thereof, a protrusion which is biased toward the driven unit and a piezoelectric body stacked on the vibrating plate; and a biasing unit biasing the actuator toward the driven unit, wherein a direction in which the biasing unit biases the actuator toward the driven unit intersects with a vibrating surface of the vibrating plate. 
         [0008]    According to the application example described above, by disposing the biasing unit biasing the actuator toward the driven unit in such a way that the biasing unit biases the actuator toward the driven unit in a direction intersecting with the vibrating surface of the vibrating plate which is excited by the piezoelectric body included in the actuator, a biasing force biasing the actuator toward the driven unit along the vibrating surface of the vibrating plate and a biasing force biasing the actuator in the direction intersecting with the vibrating surface of the vibrating plate are applied to the actuator. Of these biasing forces, by the biasing force biasing the actuator in the direction intersecting with the vibrating surface of the vibrating plate, the driven unit which makes contact with the actuator is also biased in the direction intersecting with the vibrating surface of the vibrating plate of the actuator. As a result, deflection and backlash due to a clearance between the parts in a driving portion provided to make it possible to drive the driven unit and deflection and backlash due to a clearance between the parts in a sliding portion provided to allow the actuator to slide on a motor base are moved to one side in a predetermined direction by the biasing force biasing the actuator in the direction intersecting with the vibrating surface of the vibrating plate, making it possible to prevent deflection and backlash when the driven unit is driven. This makes it possible to prevent a transfer loss of the vibration of the actuator and obtain a motor that can drive the driven unit efficiently. 
       Application Example 2 
       [0009]    This application example is directed to the motor of the application example described above, wherein an angle θ at which the direction in which the biasing unit biases the actuator toward the driven unit intersects with the vibrating surface may satisfy 0&lt;θ≦30°. 
         [0010]    According to the application example described above, it is possible to obtain an efficient motor with a small transfer loss of the vibration of the actuator, the motor in which a transfer loss of vibration due to frictional resistance in a portion in which the actuator slides on the motor base is reduced, deflection and backlash in the actuator and the driven unit are moved to one side in a predetermined direction by the biasing force biasing the actuator in the direction intersecting with the vibrating surface of the vibrating plate, and deflection and backlash are prevented when the driven unit is driven. 
       Application Example 3 
       [0011]    This application example is directed to the motor of the application example described above, wherein a regulating unit regulating the actuator in a direction intersecting with the vibrating surface may be provided. 
         [0012]    According to the application example described above, it is possible to prevent the actuator from being excessively moved to one side in a predetermined direction by the biasing force biasing the actuator in the direction intersecting with the vibrating surface of the vibrating plate. This makes it possible to ensure contact between the driven unit and the actuator. 
       Application Example 4 
       [0013]    This application example is directed to a robot hand including the motor of the application example described above. 
         [0014]    The robot hand of this application example can be made compact and lightweight while having a high degree of flexibility and a large number of motors. 
       Application Example 5 
       [0015]    This application example is directed to a robot including the robot hand of the application example described above. 
         [0016]    The robot of this application example is highly versatile and can perform assembly, inspections, etc. of a sophisticated electronic apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
           [0018]      FIG. 1  is an exploded perspective view showing a motor according to a first embodiment. 
           [0019]      FIGS. 2A and 2B  show the motor according to the first embodiment, Fig. A being an assembly plan view and  FIG. 2B  being an assembly side view. 
           [0020]      FIGS. 3A to 3C  are sectional views taken on the line A-A′ shown in  FIG. 2A . 
           [0021]      FIGS. 4A and 4B  are plan views illustrating the operation of an actuator according to the first embodiment. 
           [0022]      FIGS. 5A and 5B  are schematic diagrams illustrating the operation of a biasing unit according to the first embodiment. 
           [0023]      FIG. 6  is an appearance diagram showing a robot hand according to a second embodiment. 
           [0024]      FIG. 7  is an appearance diagram showing a robot according to a third embodiment. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0025]    Hereinafter, embodiments according to the invention will be described with reference to the drawings. 
       First Embodiment 
       [0026]      FIG. 1  and  FIGS. 2A and 2B  show a motor  100  according to an embodiment,  FIG. 1  being an exploded perspective view,  FIG. 2A  being an assembly plan view, and  FIG. 2B  being an assembly side view. As shown in  FIG. 1  and  FIGS. 2A and 2B , the motor  100  includes a driven body  20  rotatably secured to a base  10 , a support  40  slidably secured to the base  10 , a coil spring  60  as a biasing unit that biases the support  40  toward the driven body  20 , and an actuator  30  that is secured to the support  40  to be biased and drives the driven body  20  by vibration. 
         [0027]    Moreover, the actuator  30  is formed of piezoelectric elements  32  and  33 , each being a rectangular piezoelectric body in which an electrode is formed, and a vibrating plate  31 , the piezoelectric elements  32  and  33  bonded together in such a way as to sandwich the vibrating plate  31 . Examples of the piezoelectric elements  32  and  33  are piezoelectric materials such as lead zirconate titanate (PZT:Pb(Zr,Ti)O 3 ), crystal, and lithium niobate (LiNbO 3 ); in particular, PZT is suitably used. Furthermore, the electrode to be formed can be formed by forming a film of conductive metal such as Au, Ti, or Ag by vapor deposition, sputtering, or the like. As the actuator  30 , the vibrating plate  31  has, at an end thereof, a projection  31   a  that is secured to the support  40 , biased by the coil spring  60  toward the driven body  20 , and brought into contact with the driven body  20 . Incidentally, the vibrating plate  31  is formed of stainless steel, nickel, rubber metal, or the like, and stainless steel is suitably used because the stainless steel can be processed easily. The actuator  30  is secured to the support  40  with screws  51  that are placed through holes  31   c  of mounting sections  31   b  formed in the vibrating plate  31  for mounting on the support  40  and are fitted into screw holes  40   b  of fixing sections  40   a  formed in the support  40 . 
         [0028]    The support  40  is slidably secured to the base  10  as a result of securing a fixing pin  70  placed through a guide hole  40   c  of the support  40  to the base  10 . At an end of the support  40  opposite to the driven body  20 , a spring mounting section  40   e  having a biased surface  40   d  on which the coil spring  60  as the biasing unit is placed, the biased surface  40   d  biased by the coil spring  60 , is provided. The coil spring  60  placed in the spring mounting section  40   e  is held, at one end thereof, by a spring holding section  11  of the base  10 , and biases the spring mounting section  40   e , that is, the support  40  toward the driven body  20  by the deflection of the coil spring  60 . 
         [0029]    As shown in  FIG. 2B , the coil spring  60  as the biasing unit is held between the spring holding section  11  and the spring mounting section  40   e  at an angle θ with respect to the direction of an arrow P which is a direction in which the support  40  is biased, that is, the actuator  30  is biased toward the driven body  20 , in such a way as to generate also a force in a direction in which the spring mounting section  40   e  of the support  40  is pressed against the base  10 . It is preferable that the angle θ be 0°&lt;θ≦30° so as not to increase the frictional force in a region of contact between the support  40  and the base  10 . 
         [0030]    Moreover, the base  10  has spring supporting sections  12  to which leaf springs  80  as a regulating unit for the support  40 , which will be described later, are secured, and the leaf springs  80  are secured to the spring supporting sections  12  with screws  52  that are placed through holes  80   a  of the leaf springs  80  and are fitted into screw holes  12   a  of the spring supporting sections  12 . 
         [0031]    The driven body  20  is rotatably secured to the base as a result of attaching a rotating shaft  21  to an unillustrated bearing of the base  10 . The driving (rotation) of the driven body  20  is adjusted to a desired rotation speed or to produce desired output torque via a reduction or speed increasing gear  200  connected to the rotating shaft  21  to drive a driven apparatus. 
         [0032]    A section taken on the line A-A′ shown in  FIG. 2A  is shown in  FIG. 3A . As shown in  FIG. 3A , the leaf springs  80  are secured to the spring supporting sections  12  with the screws  52 , the spring supporting sections  12  secured to the base  10 . In this embodiment, the tips of the leaf springs  80  are fixed in such a way that the tips are close to top sides  40   f  (hereinafter referred to as front sides  40   f ), which are shown in the drawing, of the fixing sections  40   a , and the movement of the support  40  in a direction in which the support  40  moves away from the base  10  is regulated. 
         [0033]    The base  10  has, on a side  10   b  thereof where the actuator  30  is mounted, a rail  10   a  formed as a protrusion for reducing the range of contact between the base  10  and the support  40  to allow the support  40  to slide on the base  10  more smoothly. In this embodiment, as the rail  10   a , two rails  10   a  are formed in the direction in which the coil spring  60  biases the support  40 , but the invention is not limited thereto. There may be one rail  10   a  or three or more rails  10   a . Since the rail  10   a  formed in this manner may allow the support  40  to move toward the base  10 , the support  40  can also be mounted in such a way that the tips of springs  81  are close to sides  40   g  (hereinafter referred to as back sides  40   g ) opposite to the front sides  40   f  as shown in  FIG. 3B . 
         [0034]    Moreover, as shown in  FIG. 3C , it is possible to regulate the movement of the support  40  by leaving a predetermined clearance δ between a regulating surface  91   a  and the front side  40   f  and between a regulating surface  92   a  and the back side  40   g  by using regulating blocks  91  and  92  without using the leaf springs  80  and  81 . In such a case, it is preferable that δ be set at 0.01 to 0.02 mm. If δ is less than 0.01 mm, a collision between the regulating surface  91   a  and the front side  40   f  or between the regulating surface  92   a  and the back side  40   g  increases in number, making it difficult for the support  40  to slide on the base  10  smoothly; if δ exceeds 0.02 mm, an up-and-down movement of the support  40  in the drawing becomes large, which impairs driving efficiency. 
         [0035]    Next, the operation of the actuator  30  will be described by using  FIGS. 4A and 4B .  FIGS. 4A and 4B  are schematic plan views showing vibration movements of the actuator  30 . As shown in  FIG. 4A , by the application of an alternating-current voltage between electrodes  32   c ,  32   b , and  32   d  of electrodes  32   a ,  32   b ,  32   c ,  32   d , and  32   e  formed in the piezoelectric element  32  and electrodes formed on the side opposite to the electrodes  32   c ,  32   b , and  32   d  with an unillustrated piezoelectric body sandwiched between them, longitudinal vibration of the piezoelectric body in regions in which the electrodes  32   c ,  32   b , and  32   d  are formed, the longitudinal vibration in the direction of arrows shown in the drawing, is excited. In the region corresponding to the electrode  32   b , the actuator  30  is longitudinally vibrated in the direction of the arrow shown in the drawing, and, in the regions corresponding to the electrodes  32   c  and  32   d , flexing vibration of the actuator  30 , the flexing vibration indicated with a shape M, is excited. As a result, the projection  31   a  of the vibrating plate  31  vibrates in an elliptic orbit R 1 . 
         [0036]    Moreover, as shown in  FIG. 4B , by the application of an alternating-current voltage between the electrodes  32   a ,  32   b , and  32   e  of the electrodes  32   a ,  32   b ,  32   c ,  32   d , and  32   e  formed in the piezoelectric element  32  and electrodes formed on the side opposite to the electrodes  32   a ,  32   b , and  32   e  with an unillustrated piezoelectric body sandwiched between them, longitudinal vibration of the piezoelectric body in regions in which the electrodes  32   a ,  32   b , and  32   e  are formed, the longitudinal vibration in the direction of arrows shown in the drawing, is excited. In the region corresponding to the electrode  32   b , the actuator  30  is longitudinally vibrated in the direction of the arrow shown in the drawing, and, in the regions corresponding to the electrodes  32   a  and  32   e , flexing vibration of the actuator  30 , the flexing vibration indicated with a shape N, is excited. As a result, the projection  31   a  of the vibrating plate  31  vibrates in an elliptic orbit R 2 . 
         [0037]    The elliptic orbits R 1  and R 2  of the projection  31   a  generated by the above-described vibration of the actuator  30  make contact with the driven body  20  by being biased by the biasing force, and drive the driven body  20  in the directions of arrows r 1  and r 2  shown in the drawings. In the motor  100  which is driven in this manner, to secure the driven body  20  to the base  10  in such a way that the driven body  20  can rotate, a predetermined clearance or the like is created between the unillustrated bearing and the rotating shaft  21 . Moreover, the support  40  which is slidably secured to the base  10  is also secured to the base  10  in such a way that the support  40  can slide on the base  10  by an appropriate clearance created between a mounting section for the support  40 , the mounting section formed of the rail  10   a  provided on the base  10  and the fixing pin  70 , and the support  40 . This induces deflection or backlash behaviors of the driven body  20  and the actuator  30  secured to the support  40 . 
         [0038]    Even when there are factors inducing the deflection or backlash in the driven body  20  and the actuator  30 , by mounting the coil spring  60  which is the biasing unit in the motor  100  at an angle θ as shown in  FIG. 2B , it is possible to prevent deflection or backlash which may occur when the driven body  20  is being driven. 
         [0039]      FIGS. 5A and 5B  are schematic diagrams illustrating how to prevent deflection and backlash by the coil spring  60 .  FIG. 5A  shows a case in which the direction of a biasing force F 1  generated by the coil spring  60  mounted at an angle θ1 is away from a barycenter G 1  by D 1  to the side where the base  10  is located, the barycenter G 1  in a state in which the actuator  30  is secured to the support  40 . At this time, moment of “F 1 ×D 1 ” acts on the support  40  by the biasing force F 1  and rotates the support  40  in the direction of T L  shown in the drawing. As a result, the projection  31   a  is pushed upward in the drawing, and a portion of the driven body  20  with which the projection  31   a  comes into contact, the portion with which the projection  31   a  makes contact, is also pushed upward in the drawing. 
         [0040]    In this state, since the biasing force F 1  is made to act at all times by the coil spring  60 , the driven body  20  is driven in a state in which the projection  31   a  and the portion of the driven body  20  with which the projection  31   a  makes contact are always pushed upward in the drawing. In other words, in this state, the driven body  20  is driven with the state shown in  FIG. 5A  being stably maintained. Therefore, even when the deflection or backlash occurs due to the clearance between the support  40  and the base  10  and the clearance between the driven body  20  and the base  10  as described earlier, by mounting the coil spring  60  as the biasing unit at an angle θ1, it is possible to obtain the motor  100  that drives the actuator  30  and the driven body  20  while always biasing the actuator  30  and the driven body  20  in the same direction. 
         [0041]      FIG. 5B  shows a case in which, unlike  FIG. 5A , the direction of a biasing force F 2  generated by the coil spring  60  mounted at an angle θ2 is away from a barycenter G 2  by D 2  in the direction opposite to the side where the base  10  is located, the barycenter G 2  in a state in which the actuator  30  is secured to the support  40 . Therefore, moment of “F 2 ×D 2 ” rotates the support  40  in the direction of T R  shown in the drawing, the projection  31   a  is pushed downward in the drawing, and a portion of the driven body  20  with which the projection  31   a  comes into contact, the portion with which the projection  31   a  makes contact, is also pushed downward in the drawing. As a result, by mounting the coil spring  60  at an angle θ2, it is possible to obtain the motor  100  that drives the actuator  30  and the driven body  20  while always biasing the actuator  30  and the driven body  20  in the same direction. 
         [0042]    To prevent the projection  31   a  of the actuator  30  from being pushed upward excessively in the state shown in  FIG. 5A , the springs  80  regulating the front sides  40   f  of the fixing sections  40   a  of the support  40  shown in  FIG. 3A  regulate the projection  31   a  in a direction p 1  shown in  FIG. 5A . Moreover, to prevent the projection  31   a  of the actuator  30  from being pushed downward excessively in the state shown in  FIG. 5B , the springs  81  regulating the back sides  40   g  of the support  40  shown in  FIG. 3B  regulate the projection  31   a  in a direction p 2  shown in  FIG. 5B . 
         [0043]    As described above, in the motor  100  according to this embodiment, even when a predetermined clearance is created between the driven body  20  which is a movable element and the base  10  and between the support  40  which is a movable element and the base  10  to move the driven body  20  and the support  40  with respect to the base  10  and this clearance causes deflection or backlash, by always biasing the driven body  20  and the support  40  in a given direction by mounting the coil spring  60  as the biasing unit in such a way as to form a predetermined angle θ with respect to the direction in which the actuator  30  is biased, it is possible to prevent a slip in a region of contact between the projection  31   a  of the actuator  30  and the driven body  20 , the region of contact that is irrelevant to the driving, and convert the vibration of the actuator  30  efficiently into the driving force to drive the driven body  20 . 
       Second Embodiment 
       [0044]      FIG. 6  is an appearance diagram showing a robot hand  1000  according to a second embodiment, the robot hand  1000  provided with the motor  100 . The robot hand  1000  includes a base portion  1100  and finger sections  1200  connected to the base portion  1100 . The motor  100  is incorporated into connections  1300  between the base portion  1100  and the finger sections  1200  and joint sections  1400  between the finger sections  1200 . When the motor  100  is driven, the finger sections  1200  bend and can grip an object. By using the motor  100  which is an ultrasmall motor, it is possible to implement a robot hand which is compact but is provided with a large number of motors. 
       Third Embodiment 
       [0045]      FIG. 7  is a diagram showing the structure of a robot  2000  provided with the robot hand  1000 . The robot  2000  is formed of a main body section  2100 , an arm section  2200 , the robot hand  1000 , etc. The main body section  2100  is secured to, for example, a floor, a wall, a ceiling, and a movable carriage. The arm section  2200  is movably provided on the main body section  2100 , and an unillustrated actuator that generates power to rotate the arm section  2200 , a control unit controlling the actuator, and the like are built into the main body section  2100 . 
         [0046]    The arm section  2200  is formed of a first frame  2210 , a second frame  2220 , a third frame  2230 , a fourth frame  2240 , and a fifth frame  2250 . The first frame  2210  is connected to the main body section  2100  by a rotating and bending shaft in such a way as to be able to rotate or bend. The second frame  2220  is connected to the first frame  2210  and the third frame  2230  by rotating and bending shafts. The third frame  2230  is connected to the second frame  2220  and the fourth frame  2240  by rotating and bending shafts. The fourth frame  2240  is connected to the third frame  2230  and the fifth frame  2250  by rotating and bending shafts. The fifth frame  2250  is connected to the fourth frame  2240  by a rotating and bending shaft. The arm section  2200  is controlled by the control unit so that the frames  2210  to  2250  move in a coordinated fashion while rotating or bending about the rotating and bending shafts. 
         [0047]    To an end of the fifth frame  2250  of the arm section  2200 , the end opposite to the end to which the fourth frame  2240  is connected, a robot hand connection  2300  is connected, and the robot hand  1000  is attached to the robot hand connection  2300 . The motor  100  that rotates the robot hand  1000  is built into the robot hand connection  2300 , and the robot hand  1000  can grip an object. By using the compact and lightweight robot hand  1000 , it is possible to provide a robot that is highly versatile and can perform assembly, inspections, etc. of a sophisticated electronic apparatus. 
         [0048]    The entire disclosure of Japanese Patent Application No. 2011-102756, filed May 2, 2011 is expressly incorporated by reference herein.