Patent Publication Number: US-2023144997-A1

Title: Method of controlling piezoelectric driving apparatus, method of controlling robot, and robot

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-181063, filed Nov. 5, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a method of controlling a piezoelectric driving apparatus, a method of controlling a robot, and a robot. 
     2. Related Art 
     For example, JP-A 2008 172853 describes a driving method of an ultrasonic actuator (piezoelectric driving apparatus) that causes a friction contact portion to generate substantially elliptical vibration by generating longitudinal vibration and bending vibration, and that moves a driven body using the friction force of the elliptical vibration as a thrust force. The driving method of the ultrasonic actuator described in the JP-A-2008-172853 is characterized in that the bending vibration is excited after the longitudinal vibration is excited at the time of activation for the purpose of suppressing a drop of the driven body due to the influence of gravity. 
     However, although the drop of the driven body due to the influence of gravity may be suppressed by the driving method of the ultrasonic actuator described in JP-A-2008-172853, there is a problem in that it is difficult to control the minute movement of the driven body depending on the magnitude and direction of external forces applied to the driven body such as gravity. 
     SUMMARY 
     A method of the present disclosure for controlling a piezoelectric driving apparatus including a vibration section that has a piezoelectric element and a transmission section that transmits vibration of the vibration section to a driven body, and, by energization of the piezoelectric element, vibrates the vibration section in a combination of longitudinal vibration and bending vibration to cause the transmission section to perform an elliptical motion and to move the driven body by the elliptical motion, the method of controlling the piezoelectric driving apparatus comprising switching, according to an external force received by the driven body, a drive algorithm of the piezoelectric driving apparatus between a first drive mode in which a separation amplitude, which is an amplitude of the longitudinal vibration, is changed while a feed amplitude, which is an amplitude of the bending vibration, is constant and a second drive mode in which both the feed amplitude and the separation amplitude are changed. 
     A method of the present disclosure for controlling a robot, the robot including a piezoelectric driving apparatus including a vibration section that has a piezoelectric element and a transmission section that transmits vibration of the vibration section to a driven body, and, by energization of the piezoelectric element, vibrates the vibration section in a combination of longitudinal vibration and bending vibration to cause the transmission section to perform an elliptical motion and to move the driven body by the elliptical motion and a movable section driven by the piezoelectric driving apparatus, the method of controlling the robot comprising switching, according to an external force received by the driven body, a drive algorithm of the piezoelectric driving apparatus between a first drive mode in which a separation amplitude, which is an amplitude of the longitudinal vibration, is changed while a feed amplitude, which is an amplitude of the bending vibration, is constant and a second drive mode in which both the feed amplitude and the separation amplitude are changed. 
     A robot of the present disclosure including a piezoelectric driving apparatus including a vibration section that has a piezoelectric element and a transmission section that transmits vibration of the vibration section to a driven body, and, by energization of the piezoelectric element, vibrates the vibration section in a combination of longitudinal vibration and bending vibration to cause the transmission section to perform an elliptical motion and to move the driven body by the elliptical motion, a movable section driven by the piezoelectric driving apparatus, and a controller that controls drive of the piezoelectric driving apparatus, wherein the controller switches, according to an external force received by the driven body, a drive algorithm of the piezoelectric driving apparatus between a first drive mode in which a separation amplitude, which is an amplitude of the longitudinal vibration, is changed while a feed amplitude, which is an amplitude of the bending vibration, is constant and a second drive mode in which both the feed amplitude and the separation amplitude are changed 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram showing a robot according to a first embodiment. 
         FIG.  2    is a diagram showing a piezoelectric driving apparatus. 
         FIG.  3    is a diagram showing a modification of the piezoelectric driving apparatus. 
         FIG.  4    is a diagram showing a drive signal of the piezoelectric actuator. 
         FIG.  5    is a diagram showing a vibration state of the piezoelectric actuator. 
         FIG.  6    is a diagram showing a vibration state of the piezoelectric actuator. 
         FIG.  7    is a block diagram showing a configuration of a controller. 
         FIG.  8    is a diagram showing an example in which the robot is affected by an external force. 
         FIG.  9    is a diagram showing an example in which the robot is affected by an external force. 
         FIG.  10    is a diagram showing an example in which the robot is affected by an external force. 
         FIG.  11    is a diagram showing a first drive mode. 
         FIG.  12    is a diagram showing a second drive mode. 
         FIG.  13    is a flowchart showing a method of controlling the piezoelectric driving apparatus. 
         FIG.  14    is a diagram showing a robot according to a second embodiment. 
         FIG.  15    is a diagram illustrating a robot according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a method of controlling a piezoelectric driving apparatus, a method of controlling a robot, and a robot according to the present disclosure will be described in detail based on embodiments illustrated in the accompanying drawings. 
     First Embodiment 
       FIG.  1    is a diagram showing a robot according to a first embodiment.  FIG.  2    is a diagram showing a piezoelectric driving apparatus.  FIG.  3    is a diagram showing a modification of the piezoelectric driving apparatus.  FIG.  4    is a diagram showing drive signals of the piezoelectric actuator.  FIG.  5    and  FIG.  6    are diagrams showing vibration states of the piezoelectric actuator.  FIG.  7    is a block diagram showing a configuration of a controller.  FIGS.  8  to  10    are diagrams showing examples in which the robot is affected by an external force.  FIG.  11    is a diagram showing a first drive mode.  FIG.  12    is a diagram showing a second drive mode.  FIG.  13    is a flowchart showing a method of controlling the piezoelectric driving apparatus. 
     The robot  1  shown in  FIG.  1    has a first member  2 , a second member  3  as a movable section, a piezoelectric driving apparatus  5  for pivoting the second member  3  about a pivot axis JO with respect to the first member  2 , and a controller  4  for controlling the drive of the piezoelectric driving apparatus  5 . The first member  2  and the second member  3  can be used as a part of a robotic arm as in a second and a third embodiments to be described later. 
     As shown in  FIG.  2   , the piezoelectric driving apparatus  5  includes a piezoelectric actuator  51 , a rotor  52  as a driven portion that rotates around the pivot axis JO by receiving a driving force from the piezoelectric actuator  51 , a biasing member  53  that presses the piezoelectric actuator  51  against the rotor  52 , and an encoder  54  as a displacement amount detection sensor that detects a displacement amount of the rotor  52 . The piezoelectric actuator  51  is fixed to the first member  2  via the biasing member  53 , and the rotor  52  is fixed to the second member  3 . Therefore, when the piezoelectric actuator  51  is driven, the second member  3  fixed to the rotor  52  rotates around the pivot axis JO with respect to the first member  2 . 
     According to such a piezoelectric driving apparatus  5 , the drive force by the piezoelectric actuator  51  is directly transmitted to the rotor  52 . Therefore, a relay mechanism that relays and transmits the drive force is not needed, and the device can be simplified and miniaturized. In addition, deterioration in movement accuracy due to backlash or insufficient rigidity, which are problems in a relay mechanism such as a reduction gear, is substantially eliminated, and the robot  1  has excellent drive accuracy. In particular, the rotation type (rotary type) piezoelectric driving apparatus  5  is a suitable device for rotationally moving the second member  3 . 
     However, the piezoelectric driving apparatus  5  is not limited to a rotation type, and may be, for example, a linear motion type (linear type) as shown in  FIG.  3   . In the shown piezoelectric driving apparatus  5 , a slider  55  movable along a linear motion axis Jr is used as the driven body, and the slider  55  is fixed to the second member  3 . Therefore, when the piezoelectric actuator  51  is driven, the second member  3  fixed to the slider  55  moves along the linear motion axis Jr with respect to the first member  2 . 
     In this way, the linear motion type (linear type) piezoelectric driving apparatus  5  is a suitable device for linearly moving the second member  3 . 
     The displacement amount detection sensor is not particularly limited as long as it can perform its function, and for example, various inertial sensors such as an acceleration sensor and an angular velocity sensor, a laser displacement meter, an image measuring device, and the like can also be used. 
     As shown in  FIG.  2   , the piezoelectric actuator  51  includes a vibration section  511 , a support section  512  that supports the vibration section  511 , a beam section  513  that connects the vibration section  511  and the support section  512  together, and a protrusion-like transmission section  514  that is disposed at a tip end portion of the vibration section  511  and that transmits the vibration of the vibration section  511  to the rotor  52 . 
     The vibration section  511  has a plate shape, and has a rectangular shape having a length in the vertical direction of the paper surface. The vibration section  511  includes piezoelectric elements  51 A to  51 F for driving and a piezoelectric element  51 G for detecting the vibration of the vibration section  511 . Piezoelectric elements  51 C and  51 D are arranged side by side in the longitudinal direction in a central portion of the vibration section  511 . On one side of the piezoelectric elements  51 C and  51 D, piezoelectric elements  51 A and  51 B are arranged side by side in the longitudinal direction, and on the other side, piezoelectric elements  51 E and  51 F are arranged side by side in the longitudinal direction. Each of the piezoelectric elements  51 A to  51 F expands and contracts in the longitudinal direction of the vibration section  511  when energized. 
     The piezoelectric element  51 G for detection is arranged between the piezoelectric elements  51 C and  51 D. The piezoelectric element  51 G receives external force according to the vibration of the vibration section  511  and outputs a detection signal according to the received external force. Therefore, the piezoelectric driving apparatus  5  can detect the vibration state of the vibration section  511  based on the detection signal output from the piezoelectric elements  51 G. 
     The transmission section  514  is provided at a tip portion of the vibration section  511 , and a tip thereof is in contact with the rotor  52 . Therefore, the vibration of the vibration section  511  is transmitted to the rotor  52  via the transmission section  514 . The support section  512  is a portion that supports the vibration section  511 , and has a U-shape that surrounds both sides and the base end side of the vibration section  511 . In addition, the beam section  513  connects the vibration section  511  and the support section  512  in a state that allows the vibration section  511  to vibrate. 
     The biasing member  53  biases the piezoelectric actuator  51  toward the rotor  52  and presses the transmission section  514  against the rotor  52 . Accordingly, the vibration of the vibration section  511  is efficiently transmitted to the rotor  52  via the transmission section  514 . In addition, when the piezoelectric driving apparatus  5  is not driven, a brake is applied to the rotor  52 , so that it is possible to prevent the rotor  52  from unintentionally rotating. The biasing member  53  includes a holding section  531  that holds the support section  512 , a base section  532  that is fixed to the first member  2 , and a group of springs  533  and  534  that connects the holding section  531  and the base section  532 . The biasing member  53  is fixed in such a state that the group of springs  533  and  534  is deformed, and presses the piezoelectric actuator  51  against the rotor  52  by utilizing the restoring force of the group of springs  533  and  534 . 
     Such a piezoelectric driving apparatus  5  is driven as follows. For example, when the drive signal V 1  shown in  FIG.  4    is applied to the piezoelectric elements  51 A and  51 F, the drive signal V 2  is applied to the piezoelectric elements  51 C and  51 D, and the drive signal V 3  is applied to the piezoelectric elements  51 B and  51 E, then, as shown in  FIG.  5   , the vibration section  511  performs bending vibration, in which the vibration section bends in the short-side direction, while performing longitudinal vibration, in which the vibration section expands and contracts in the longitudinal direction, and these vibrations combine so that the tip of the transmission section  514  performs elliptical motion, in which the tip draws an elliptical trajectory counterclockwise as indicated by an arrow A 1 . As a result, the rotor  52  is moved and rotated clockwise as indicated by an arrow B 1 . On the other hand, when the drive signals V 1  and V 3  are switched, that is, when the drive signal V 1  is applied to the piezoelectric elements  51 B and  51 E and the drive signal V 3  is applied to the piezoelectric elements  51 A and  51 F, then, as shown in  FIG.  6   , the tip of the transmission section  514  performs an elliptical motion in which the tip draws an elliptical trajectory clockwise as indicated by the arrow A 2 , and the rotor  52  rotates in the counterclockwise as indicated by the arrow B 2 . 
     Of the longitudinal vibration and the bending vibration of the vibration section  511 , which are the basis of the elliptical motion of the transmission section  514 , the longitudinal vibration is excited by applying the drive signal V 2  to the piezoelectric elements  51 C and  51 D, and the bending vibration is excited by applying the drive signals V 1  and V 3  to the piezoelectric elements  51 A,  51 B,  51 E and  51 F. 
     The controller  4  is constituted by, for example, a computer, and includes a processor that processes information, a memory that is communicably connected to the processor, and an external interface. In addition, the memory stores programs executable by the processor, and the processor reads and executes the programs stored in the memory. The controller  4  receives a command from a host computer (not shown) and controls the drive of the piezoelectric driving apparatus  5  so that the second member  3  moves to a target position based on the command. 
     As shown in  FIG.  7   , the controller  4  includes a drive signal generation section  41 , a drive algorithm selection section  42 , a movement amount detection section  43  that detects a movement amount of the second member  3 , and a movement direction detection section  44  that detects a movement direction of the second member  3 . 
     The movement amount detection section  43  detects the movement amount of the second member  3 , that is, the rotation amount about the pivot axis JO, based on an output signal of the encoder  54 . The movement direction detection section  44  detects a movement direction of the second member  3 , that is, a rotation direction (arrows B 1 /B 2 ) about the pivot axis JO, based on an output signal of the encoder  54 . 
     The drive algorithm selection section  42  selects a drive algorithm for the piezoelectric actuator  51  based on the detection results of the movement amount detection section  43  and the movement direction detection section  44 . The drive algorithm is selected from a first mode Dm 1  and a second drive mode Dm 2  as described below. The drive signal generation section  41  generates the drive signals V 1 , V 2 , and V 3  based on the drive algorithm selected by the drive algorithm selection section  42  and a command from a host computer (not shown), and applies the generated drive signals V 1 , V 2 , and V 3  to the piezoelectric actuator  51 . According to such a method, since the actual rotation amount and rotation direction detected by the encoder  54  are fed back, the movement of the second member  3  can be accurately controlled. 
     The configuration of the robot  1  has been briefly described above. Next, a method of controlling the piezoelectric driving apparatus  5  will be described. In a method of controlling the piezoelectric driving apparatus  5 , the drive algorithm is switched according to the external force F received by the robot  1 . Accordingly, it is possible to reduce the influence of the external force F as much as possible and accurately control minute movement of the robot  1 . The external force F is not particularly limited, and examples thereof include a force F 1  applied to the second member  3  in a direction opposite to the rotation direction, a force F 2  applied in the same direction as the rotation direction, and a force F 3 , which is gravity, applied to the second member  3  in a vertical direction. 
       FIG.  8    shows an example of being affected by forces F 1  and F 2 . In  FIG.  8   , the pivot axis Je extends along the vertical direction. Further, a wiring C for power supply to the second member  3 , communication, and the like is routed from the first member  2  to the second member  3 . Therefore, depending on the posture of the second member  3 , a force F 1  or a force F 2 , which are restoring forces (forces to return to a natural state) of the wiring C, is generated in the second member  3  due to deformation, torsion, or the like of the wiring C, and the forces F 1  and F 2  may affect the rotation of the second member  3 . Specifically, since the force F 1  opposes the drive force of the piezoelectric driving apparatus  5 , the second member  3  may move to the opposite side than the target (force F 1 &gt;drive force), may remain stationary (force F 1 =drive force), or the movement amount may be less than the target (force F 1 &lt;drive force). On the other hand, when the force F 2  is added to the drive force of the piezoelectric driving apparatus  5 , the movement amount of the second member  3  may become larger than the target. As described above, when the force F 1  or F 2  is applied, the rotational characteristic of the second member  3  varies, and it becomes difficult to accurately perform minute movement control of the second member  3 . 
       FIGS.  9  and  10    show an example of being affected by the force F 3 . In  FIGS.  9  and  10   , the lower side of the paper is the lower side in the vertical direction, and the pivot axis JO is along the horizontal direction. Therefore, depending on the posture of the second member  3 , the force F 3  may affect the rotation of the second member  3 . Specifically, in the case shown in  FIG.  9   , since the force F 3  opposes the drive force of the piezoelectric driving apparatus  5 , there are cases where the second member  3  moves to the opposite side than the target direction, remains stationary, or the movement amount becomes smaller than the target. On the other hand, in the case shown in  FIG.  10   , since the force F 3  is added to the drive force of the piezoelectric driving apparatus  5 , the movement amount of the second member  3  may be larger than the target. In this way, by the force F 3  being applied, the rotational characteristics of the second member  3  varies, and it becomes difficult to accurately perform minute movement control of the second member  3 . 
     As described above, the influence of the external force F may deteriorate the positional accuracy of the second member  3 . Therefore, as described above, in the present embodiment, by switching the drive algorithm according to the external force F received by the robot  1 , it is possible to reduce the influence of the external force F as much as possible and to accurately control minute movement of the robot  1 . 
     First, a drive algorithm preset in the robot  1  will be described. In the present embodiment, the first drive mode Dm 1  in which, as shown in  FIG.  11   , a separation amplitude W 2 , which is an amplitude of the longitudinal vibration, is increased while a feed amplitude W 1 , which is an amplitude of the bending vibration, is constant and the second drive mode Dm 2  in which, as shown in  FIG.  12   , the separation amplitude W 2  is increased while the feed amplitude W 1  is increased are set as drive algorithms. In the present embodiment, the feed amplitude W 1  is controlled by the voltage value of the drive signals V 3  and V 1 , and the separation amplitude W 2  is controlled by the voltage value of the drive signal V 2 , but the method of controlling the amplitudes W 1  and W 2  is not limited to this, and they may be controlled by, for example, frequencies or phases. 
     As will be understood from the following description, “making the feed amplitude W 1  constant” means a state in which the voltage values of the drive signals V 1  and V 3  that control the bending vibration are made constant, and the actual amplitudes are not necessarily constant. Further, the term “constant” means not only a case where there is no variation with time but also a case where there is a slight variation or the like which may occur due to the configuration of the circuit. 
     In the first drive mode Dm 1  shown in  FIG.  11   , the feed amplitude W 1  is constant and only the separation amplitude W 2  is gradually increased. Therefore, it is easy to generate the minimum necessary drive force. Therefore, a sudden large movement of the rotor  52  is unlikely to occur due to an excessive drive force, and the stopping accuracy is also good. On the other hand, since the drive force is increased little by little in order to generate the minimum necessary drive force, the drive force is easily affected by the external force F at the initial drive start. On the other hand, in the second drive mode Dm 2  shown in  FIG.  12   , both the feed amplitude W 1  and the separation amplitude W 2  are gradually increased. Therefore, it is easily affected by the external force F immediately after the start of driving. However, after that, the drive force is less affected by the external force F than the first drive mode Dm 1  since the increasing rate of the driving force is higher than that of the first driving mode Dm 1 . On the other hand, since the increasing pace of the feed amplitude W 1  is faster than that of the first drive mode Dm 1 , the stopping accuracy may be deteriorated due to excessive drive force depending on the rotational speed of the rotor  52  or the like. By switching the first drive mode Dm 1  and the second drive mode Dm 2 , which in this way have mutually different characteristics, in accordance with the external force F, receiving influence of the external force F is less likely and it is possible to perform highly accurate minute movement control. 
     In addition, as shown in  FIGS.  11  and  12   , in the first drive mode Dm 1  and the second drive mode Dm 2 , the bending vibration is excited in the piezoelectric actuator  51 , and then longitudinal vibration is excited. According to such a method, the first drive mode Dm 1  and the second drive mode Dm 2  are less likely to be affected by the external force F. Specifically, in a state in which the piezoelectric actuator  51  is excited to perform the bending vibration, the transmission section  514  is kept pressed against the rotor  52  by the biasing member  53 . Therefore, the vibration section  511  cannot bend and deform, that is, the bending vibration does not actually occur in the vibrating portion  511 . Using a car as a simile, this state is equivalent to pressing a brake pedal strongly while pressing the accelerator pedal to prevent the car from moving. In this state, when a longitudinal vibration is excited in the piezoelectric actuator  51 , the transmission section  514  is separated from the rotor  52  by the longitudinal vibration, and at the same time, the suppressed bending vibration is released to generate an elliptical motion of the transmission section  514 . In other words, since the time lag between the separation of the transmission section  514  from the rotor  52  and the generation of the drive force is very short (substantially zero), the rotor  52  does not become free and is hardly affected by the external force F. 
     On the other hand, if the longitudinal vibration is excited and then the bending vibration is excited, the transmission section  514  is separated from the rotor  52  before the force that feeds the rotor  52  is generated. In the case of car, this state is equivalent to a state in which the brake pedal is released without pressing the accelerator pedal. Therefore, the rotor  52  becomes free and moves unintentionally due to the influence of the external force F, which makes it difficult to perform minute movement control of the robot  1 . 
     Hereinafter, the method of controlling the piezoelectric driving apparatus  5  will be described based on  FIG.  13   . This control is executed by the controller  4 . In the method of controlling the piezoelectric driving apparatus  5 , first, as step S 1 , the drive algorithm of the piezoelectric actuator  51  is set to the first drive mode Dm 1 , and as step S 2 , the piezoelectric actuator  51  is driven in the set drive mode, here, the first drive mode Dm 1 . The reason why the first drive mode Dm 1  is used first is that, as described above, the minute movement accuracy of the second member  3  in the first drive mode Dm 1  is higher than that in the second drive mode Dm 2 , and if the second member  3  can be driven without any problem in the first drive mode Dm 1 , the first drive mode Dm 1  is better than the second drive mode Dm 2 . 
     Next, as step S 3 , it is determined whether the drive algorithm is the first drive mode Dm 1 . Here, since the drive algorithm is the first drive mode Dm 1 , next, as step S 4 , it is determined based on the output signal of the encoder  54  whether movement amount (rotation amount) in the direction opposite to the movement direction of the second member  3  is equal to or more than a specified value. As a result, it is possible to determine the influence of external force F (such as force F 1  shown in  FIG.  8    and force F 3  shown in  FIG.  9   ) that is in the direction opposite to the movement direction, on drive of the piezoelectric driving apparatus  5 . By making a determination based on the output signal of the encoder  54 , the determination becomes easy and accurate. 
     When the movement amount of the second member  3  in the opposite direction is equal to or greater than the specified value, the drive of the piezoelectric driving apparatus  5  is stopped as step S 5 . This is because external forces F (such as forces F 1  or F 3 ) applied to the robot  1  are large and it is difficult to move the second member  3  to the target position by the drive force of the first drive mode Dm 1 . 
     Next, as step S 6 , the drive algorithm is switched from the first drive mode Dm 1  to the second drive mode Dm 2 , and the process returns to step S 2  to drive the piezoelectric actuator  51  in the set drive mode, here, the second drive mode Dm 2 . That is, when the influence of the external force F is larger than the reference value, the drive algorithm is switched to the second drive mode Dm 2  and drive of the piezoelectric actuator  51  is restarted. By this, since a drive force larger than that in the first drive mode Dm 1  can be obtained, the possibility that the second member  3  can be moved to the target position against the external force F is increased. Next, as step S 3 , it is determined whether the drive algorithm is the first drive mode Dm 1 . Here, since the drive algorithm is the second drive mode Dm 2 , next, as step S 7 , it is determined based on the output signal of the encoder  54  whether the second member  3  has reached the target position. 
     Here, returning to step S 4 , if the movement amount of the second member  3  in the reverse direction is less than the specified value, as step S 8 , it is determined based on the output signal of the encoder  54  whether the movement amount (rotation amount) of the second member  3  in the movement direction is equal to or greater than the specified value. Accordingly, it is possible to determine the influence of the external force F (such as the force F 2  shown in  FIG.  8    or the force F 3  shown in  FIG.  10   ) in the movement direction on the drive of the piezoelectric driving apparatus  5 . That is, the influence of the external force F on the driving of the piezoelectric driving apparatus  5  can be determined by step S 4 , S 8 . When the second member  3  moves in the movement direction by the specified value or more, as step S 9 , the drive of the piezoelectric driving apparatus  5  is stopped. This is because the external force F applied to the robot  1  is large and it is difficult to move the second member  3  to the target position in the second drive mode Dm 2 . On the other hand, when the moving amount of the second member  3  in the movement direction is less than the specified value, the process proceeds to step S 7 . 
     In step S 7 , in a case where the second member  3  reaches the target position, the drive of the piezoelectric driving apparatus  5  is stopped as step S 10 . As a result, the movement of the second member  3  to the target position ends normally. On the other hand, when the second member  3  has not reached the target position, it is determined in step S 11  whether both the feed amplitude W 1  and the separation amplitude W 2  have reached the upper limit. If the second member  3  has not reached the target position, it can be considered that, due to the influence of the external force F in the opposite direction, the second member  3  is not moving in the movement direction or the moving speed thereof is reduced. Therefore, when both the feed amplitude W 1  and the separation amplitude W 2  have not reached the upper limit value, the determination in step S 11  is repeated until both the feed amplitude W 1  and the separation amplitude W 2  reach the upper limit value, that is, until the drive force of the piezoelectric driving apparatus  5  becomes maximum. On the other hand, in a case where both the feed amplitude W 1  and the separation amplitude W 2  have reached the upper limits, it is not possible to expect a further increase in the drive force, and thus the process proceeds to step S 9 , and the drive of the piezoelectric driving apparatus  5  is stopped. Then, after drive of the piezoelectric driving apparatus  5  is stopped in step S 9 , an error message is issued in step S 12  to notify the user that the operation has been stopped due to an abnormality. 
     According to such a controlling method, since the piezoelectric driving apparatus  5  is driven in the first drive mode Dm 1  or the second drive mode Dm 2  in which excellent minute movement control is possible, excellent minute movement control can be performed regardless of the presence or absence of external force F, and the second member  3  can be moved to the target position with higher accuracy. Further, when it is determined that it is difficult to move the second member  3  to the target position in the first drive mode Dm 1  due to the influence of external force F, the drive algorithm is immediately switched to the second drive mode Dm 2 , which is capable of exerting a larger drive force than that in the first drive mode Dm 1 , so that the likelihood of receiving influence of the external force F is reduced. Therefore, according to such a controlling method, it is possible to reduce the influence of the external force F as much as possible and also accurately control minute movement of the robot  1 . 
     The method of controlling the piezoelectric driving apparatus  5  has been described above. As described above, the method for controlling the piezoelectric driving apparatus  5 , which includes the vibration section  511  that has the piezoelectric elements  51 A to  51 F and the transmission section  514  that transmits vibration of the vibration section  511  to the rotor  52 , which is a driven body, and, by energization of the piezoelectric elements  51 A to  51 F, vibrates the vibration section  511  in a combination of longitudinal vibration and bending vibration to cause the transmission section  514  to perform an elliptical motion and to move the rotor  52  by the elliptical motion, the method of controlling the piezoelectric driving apparatus  5  including switching, according to an external force received by the rotor  52 , a drive algorithm between the first drive mode Dm 1  in which the separation amplitude W 2 , which is the amplitude of the longitudinal vibration, is changed while the feed amplitude W 1 , which is the amplitude of the bending vibration, is constant and the second drive mode Dm 2  in which both the feed amplitude W 1  and the separation amplitude W 2  are changed. According to such a control method, it is possible to reduce the likelihood of influence from the external force F as much as possible and to accurately control minute movement of the piezoelectric driving apparatus  5 . 
     In addition, as described above, the method of controlling the piezoelectric driving apparatus  5  includes step S 2  of driving the piezoelectric actuator  51  in the first drive mode Dm 1 , and step S 4  of determining the influence of the external force F and, based on the determination result, maintaining the drive algorithm in the first drive mode Dm 1  or switching the drive algorithm to the second drive mode Dm 2 . 
     Accordingly, a preferable drive mode can be selected, and the influence of the external force F can be reduced as much as possible. 
     As described above, when the influence of the external force F is larger than the reference value, the drive algorithm is switched to the second drive mode Dm 2 . By this, since a drive force larger than that in the first drive mode Dm 1  can be obtained, the possibility that the second member  3  can be moved to the target position against the external force F is increased. 
     As described above, the influence of the external force F is determined based on the output signal of the encoder  54  that detects the displacement amount of the rotor  52 . This makes the determination easy and accurate. 
     Further, as described above, in each of the first drive mode Dm 1  and the second drive mode Dm 2 , the bending vibration is excited and then longitudinal vibration is excited. As a result, it becomes more difficult to be affected by the external force F, and more accurate minute movement control becomes possible. 
     As described above, the driven body is the rotor  52  that rotationally moves. This makes it easy to rotational move the second member  3  as the driven body. 
     In addition, as described above, the driven body may be the slider  55  that moves linearly. This makes it easy to linearly move the second member  3 , as the driven body. 
     Further, as described above, the external force F is the force F 1 , F 2  based on the restoring force of the wiring C. Since wiring C is provided in various mechanical devices to which the piezoelectric driving apparatus  5  can be applied, it is highly versatile controlling method. 
     Further, as described above, the external force F is the force F 3  as gravity. Since the force F 3  is normally applied to various mechanical devices to which the piezoelectric driving apparatus  5  can be applied except under a special environment, it is a highly versatile controlling method. 
     As described above, in the method of controlling the robot  1 , the robot includes the piezoelectric driving apparatus  5  including the vibration section  511  that has the piezoelectric elements  51 A to  51 F and the transmission section  514  that transmits the vibration of the vibration section  511  to the rotor  52 , which is the driven body. The piezoelectric driving apparatus  5 , by energization of the piezoelectric elements  51 A to  51 F, vibrates the vibration section  511  in a combination of the longitudinal vibration and the bending vibration to cause the transmission section  514  to perform the elliptical motion, and moves the rotor  52  by the elliptical motion. Further, the robot  1  includes the second member  3  as a movable section driven by the piezoelectric driving apparatus  5 . The controlling method of the robot switches, according to an external force F received by the rotor  52 , the drive algorithm between the first drive mode Dm 1  in which the separation amplitude W 2 , which is the amplitude of the longitudinal vibration, is increased while the feed amplitude W 1 , which is the amplitude of the bending vibration, is constant and the second drive mode Dm 2  in which both the feed amplitude W 1  and the separation amplitude W 2  are changed. According to such a controlling method, it is possible to reduce the influence of the external force F as much as possible and to accurately control minute movement of the robot  1 . 
     In addition, as described above, the robot  1  includes the piezoelectric driving apparatus  5  including the vibration section  511  that has the piezoelectric elements  51 A to  51 F and the transmission section  514  that transmits vibration of the vibration section  511  to the rotor  52  as the driven body, and, by energization of the piezoelectric elements  51 A to  51 F, vibrates the vibration section  511  in a combination of the longitudinal vibration and the bending vibration to cause the transmission section  514  to perform elliptical motion and to move the rotor  52  by the elliptical motion, the second member  3 , which is a movable section, driven by the piezoelectric driving apparatus  5 , and the controller  4  that controls drive of the piezoelectric driving apparatus  5 . Also, the controller  4  switches, according to the external force F received by the rotor  52 , the drive algorithm between the first drive mode Dm 1  in which the separation amplitude W 2 , which is an amplitude of the longitudinal vibration, is changed while the feed amplitude W 1 , which is an amplitude of the bending vibration, is constant, and the second drive mode Dm 2  in which both the feed amplitude W 1  and the separation amplitude W 2  are changed. According to such a controlling method, it is possible to reduce the influence of the external force F as much as possible and to accurately control minute movement of the robot  1 . 
     Second Embodiment 
       FIG.  14    is a diagram showing a robot according to a second embodiment. 
     The robot  6  shown in  FIG.  14    is a horizontal articulated robot (SCARA robot). The use of the robot  6  is not particularly limited, and examples thereof include supplying, removing, transporting, and assembling of objects such as precision devices and components constituting the precision devices. 
     The robot  6  includes a base  60  fixed to a floor or the like, a first arm  61  connected to the base  60 , a second arm  62  connected to the first arm  61 , a third arm  63  connected to the second arm  62 , a fourth arm  64  connected to the third arm  63 , and an end effector  65  connected to the fourth arm  64 . 
     Further, the first arm  61  moves in the direction of a first linear motion axis Jr 1  with respect to the base  60 , and rotates around a first pivot axis Je 1  parallel to the first linear motion axis Jr 1 . The second arm  62  moves with respect to the first arm  61  in a second linear motion axis Jr 2  direction perpendicular to the first linear motion axis Jr 1 , and rotates about an second pivot axis Jθ 2  parallel to the first pivot axis Jθ 1 . The third arm  63  rotates with respect to the second arm  62  about a third pivot axis Jθ 3  perpendicular to the second pivot axis Jθ 2 . The fourth arm  64  rotates with respect to the third arm  63  about a fourth pivot axis Jθ 4  perpendicular to the third pivot axis Jθ 3 . The robot  6  moves the end effector  65  to a target position and posture by a combination of the movement about the four pivot axes Jθ 1 , Jθ 2 , Jθ 3 , and Jθ 4  and the movement in the directions of the two linear motion axes Jr 1  and Jr 2 . 
     The first arm  61  includes a linear motion section  611  that is connected to the base  60  and moves in the direction of the first linear motion axis Jr 1  with respect to the base  60 , and a first rotation section  612  that is connected to the first linear motion section  611  and rotates about the first pivot axis Jθ 1  with respect to the first linear motion section  611 . 
     The second arm  62  includes an elongated second linear motion section  621  that is connected to the first rotation section  612  and that moves with respect to the first rotation section  612  in the direction of the second linear motion axis Jr 2 , and a second rotation section  622  that is connected to the front end portion of the second linear motion section  621  and that rotates with respect to the second linear motion section  621  around the second pivot axis Jθ 2 . The second linear motion axis Jr 2  is orthogonal to the first pivot axis Jθ 1  and rotates about the first pivot axis Jθ 1  in accordance with rotation of the first rotation section  612  about the first pivot axis Jθ 1 . The second pivot axis Jθ 2  is parallel to the first pivot axis Jθ 1 , and a separation distance D from the first pivot axis Jθ 1  changes with the movement of the second linear motion section  621  in the direction of the second linear motion axis Jr 2 . 
     The third arm  63  includes an arm section  631  connected to the second rotation section  622 , and a third rotation section  632  connected to the arm section  631  so as to be rotatable about the third pivot axis Jθ 3 . The arm section  631  has a substantially L-shape bent at a substantially right angle in the middle thereof, the second moving portion  622  is connected to the base end thereof, and the third rotation section  632  is connected to the front end portion thereof. The third pivot axis Jθ 3  is orthogonal to the second pivot axis Jθ 2 , and rotates about the second pivot axis Jθ 2  in accordance with the rotation of the second rotation section  622  about the second pivot axis Jθ 2 . 
     The fourth arm  64  includes an arm section  641  connected to the third rotation section  632 , and a fourth rotation section  642  connected to the arm section  641  so as to be rotatable about the fourth pivot axis Jθ 4 . The arm section  641  has a substantially L-shape bent at a substantially right angle in the middle thereof, the third rotation section  632  is connected to the base end thereof, and the fourth rotation section  642  is connected to the front end portion thereof. The fourth pivot axis Jθ 4  is orthogonal to the third pivot axis Jθ 3 , and rotates about the third pivot axis Jθ 3  in accordance with the rotation of the third rotation section  632  about the third pivot axis Jθ 3 . 
     The end effector  65  is connected to the fourth rotation section  642 . The end effector  65  is a mechanism for causing the robot  6  to perform a predetermined work, and may have any configuration such as a mechanism for holding a workpiece W, a mechanism for sucking a workpiece W, and a mechanism for applying an adhesive or the like to a workpiece W. 
     The robot  6  further includes a piezoelectric driving apparatus  5 A that moves the first linear motion section  611  with respect to the base  60  in the direction of the first linear motion axis Jr 1 , a piezoelectric driving apparatus  5 B that rotates the first rotation section  612  with respect to the first linear motion section  611  about the first pivot axis Jθ 1 , a piezoelectric driving apparatus  5 C that moves the second linear motion section  621  with respect to the first rotation section  612  in the direction of the second linear motion axis Jr 2 , a piezoelectric driving apparatus  5 D that rotates the second rotation section  622  with respect to the second linear motion section  621  about the second pivot axis Jθ 2 , a piezoelectric driving apparatus  5 E that rotates the third rotation section  632  with respect to the second rotation section  622  about the third pivot axis Jθ 3 , a piezoelectric driving apparatus  5 F that rotates the fourth rotation section  642  with respect to the third rotation section  632  about the fourth pivot axis Jθ 4 , and a controller  4  that independently controls each of the piezoelectric driving apparatuses  5 A to  5 F. 
     Among them, the piezoelectric driving apparatuses  5 A and  5 C are composed of the linear motion type piezoelectric driving apparatus shown in  FIG.  3   , and the piezoelectric driving apparatuses  5 B,  5 D,  5 E, and  5 F are composed of the rotation type piezoelectric driving apparatus shown in  FIG.  2   . 
     Although not shown, in the piezoelectric driving apparatus  5 A, the linear motion axis Jr coincides the first linear motion axis Jr 1 , one of the piezoelectric actuator  51  and the slider  55  is fixed to the base  60 , and the other is fixed to the first linear motion section  611 . Therefore, the first arm  61  is moved in the direction of the first linear motion axis Jr 1  with respect to the base  60  by the drive of the piezoelectric driving apparatus  5 A. In the piezoelectric driving apparatus  5 B, the pivot axis Jθ coincides the first pivot axis Jθ 1 , and one of the piezoelectric actuator  51  and the rotor  52  is fixed to the first linear motion section  611  and the other is fixed to the first rotation section  612 . Therefore, the first rotation section  612  rotates about the first pivot axis Jθ 1  with respect to the first linear motion section  611  by the drive of the piezoelectric driving apparatus  5 B. 
     In the piezoelectric driving apparatus  5 C, the linear motion axis Jr coincides with the second linear motion axis Jr 2 , one of the piezoelectric actuator  51  and the sliders  55  is fixed to the first rotation section  612 , and the other is fixed to the second linear motion section  621 . Therefore, the second linear motion section  621  is moved in the direction of the second linear motion axis Jr 2  with respect to the first rotation section  612  by the drive of the piezoelectric driving apparatus  5 C. In the piezoelectric driving apparatus  5 D, the pivot axis Jθ coincides with the second pivot axis Jθ 2 , and one of the piezoelectric actuator  51  and the rotor  52  is fixed to the second linear motion section  621  and the other is fixed to the second rotation section  622 . Therefore, the second rotation section  622  rotates about the second pivot axis Jθ 2  with respect to the second linear motion section  621  by the drive of the piezoelectric driving apparatus  5 D. 
     In the piezoelectric driving apparatus  5 E, the pivot axis Jθ coincides with the third pivot axis Jθ 3 , and one of the piezoelectric actuator  51  and the rotor  52  is fixed to the arm section  631 , and the other is fixed to the third rotation section  632 . Therefore, the third rotation section  632  rotates around the third pivot axis Jθ 3  with respect to the arm section  631  by the drive of the piezoelectric driving apparatus  5 E. In the piezoelectric driving apparatus  5 F, the pivot axis Jθ coincides with the fourth pivot axis Jθ 4 , one of the piezoelectric actuator  51  and the rotor  52  is fixed to the arm section  641 , and the other is fixed to the fourth rotation section  642 . Therefore, the fourth rotation section  642  rotates about the fourth pivot axis Jθ 4  with respect to the arm section  641  by the drive of the piezoelectric driving apparatus  5 F. 
     The robot  6  has been described above. In such a robot  6 , the controlling method (hereinafter, also referred to as “present control method”) described in the first embodiment described above can be applied to at least one of the piezoelectric driving apparatuses  5 A to  5 F. That is, it is possible to perform control to switch the drive algorithm between the first drive mode Dm 1  and the second drive mode Dm 2  according to the external force F received by the rotor  52  or the slider  55 . As a result, it is possible to reduce the influence of the external force F as much as possible and to accurately control the minute movement of the robot  6 . Which of the piezoelectric driving apparatuses  5 A to  5 F is to use the present control method can be appropriately determined based on, for example, the installation posture, the trajectory of motion, arrangement of wiring, and the like of the robot  6 . 
     According to the second embodiment as described above, the same effects as those of the first embodiment described above can be exhibited. For any joint section where the present control method is not used, a driving device other than the piezoelectric driving apparatus, for example, a combination of an electromagnetic motor and a reduction gear, may be used. 
     Third Embodiment 
       FIG.  15    is a diagram showing a robot according to a third embodiment. 
     The robot  7  shown in  FIG.  15    is a 6-axis robot having six drive axes. The robot  7  includes a base  70  fixed to a floor or the like, a first arm  71  rotatably connected to the base  70 , a second arm  72  rotatably connected to the first arm  71 , a third arm  73  rotatably connected to the second arm  72 , a fourth arm  74  rotatably connected to the third arm  73 , a fifth arm  75  rotatably connected to the fourth arm  74 , a sixth arm  76  rotatably connected to the fifth arm  75 , and an end effector  77  as a stage provided on a tip end side of the sixth arm  76 . In addition, the end effector  77  includes a base section  771  fixed to the sixth arm  76 , and a table section  772  linearly moving with respect to the base section  771 . 
     The robot  7  includes a piezoelectric driving apparatus  5 G that rotates the first arm  71  with respect to the base  70 , a piezoelectric driving apparatus  5 H that rotates the second arm  72  with respect to the first arm  71 , a piezoelectric driving apparatus  5 I that rotates the third arm  73  with respect to the second arm  72 , a piezoelectric driving apparatus  5 J that rotates the fourth arm  74  with respect to the third arm  73 , a piezoelectric driving apparatus  5 K that rotates the fifth arm  75  with respect to the fourth arm  74 , a piezoelectric driving apparatus  5 L that rotates the sixth arm  76  with respect to the fifth arm  75 , a piezoelectric driving apparatus  5 M that linearly moves the table section  772  with respect to the base section  771 , and a controller  4  that independently controls each of the piezoelectric driving apparatuses  5 G to  5 M. 
     Among them, piezoelectric driving apparatuses  5 G to  5 L are constituted by the rotation type piezoelectric driving apparatus  5  shown in  FIG.  2   , and the piezoelectric driving apparatus  5 M is constituted by the linear motion type piezoelectric driving apparatus  5  shown in  FIG.  3   . 
     The robot  7  has been described above. In such a robot  7 , the present controlling method can be applied to at least one of the piezoelectric driving apparatuses  5 G to  5 M. That is, it is possible to control the drive algorithm to be switched between the first drive mode Dm 1  and the second drive mode Dm 2  according to the external force F received by the rotor  52  or the slider  55 . This makes it possible to reduce the influence of the external force F as much as possible and to accurately control the minute movement of the robot  7 . Which of the piezoelectric driving apparatuses  5 G to  5 M is to use the present controlling method can be appropriately determined based on, for example, the installation posture, trajectory of motion, arrangement of wiring, and the like of the robot  7 . 
     According to the third embodiment as described above, the same effects as those of the first embodiment described above can be exhibited. For any joint section where the present control method is not used, a driving device other than the piezoelectric driving apparatus, for example, a combination of an electromagnetic motor and a reduction gear, may be used. 
     Although the method of controlling a piezoelectric driving apparatus, the method of controlling a robot, and the robot according to the present disclosure have been described above based on the illustrated embodiments, the present disclosure is not limited thereto, and the configuration of each section can be replaced with an arbitrary configuration having the same function. In addition, other arbitrary components may be added to the present disclosure. In addition, the method of controlling the piezoelectric driving apparatus may be applied to any device other than the robot.